Validation of a measurement method for diacetyl using sorbent tubes and thermal desorption

Prepared by the Health and Safety Executive

RR1138 Research Report

© Crown copyright 2018

Prepared 2018 First published 2018

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This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

Diacetyl, also known as 2,3-butanedione, and the closely related chemical 2,3-pentanedione, are naturally occurring substances with a characteristic butter-like odour found in foods such as dairy products, beer and fruits. Diacetyl is also added to various food products as artificial butter flavouring and both substances are present in emissions generated by coffee roasting and grinding. Occupational levels of diacetyl exposure has been linked with the lung disease bronchiolitis obliterans which is life threatening and irreversible. In Great Britain, occupational exposure limits to protect workers’ health are based on recommendations from SCOEL (the European Commission Scientific Committee on Occupational Exposure Limits). SCOEL has recommended introducing an 8-hour time weighted average occupational exposure limit for diacetyl of 20 ppb and a short term exposure limit (STEL) of 100 ppb. Existing scientific measurement methods lack the necessary sensitivity to measure these levels of exposure.

This report describes a new sensitive method for measurement of diacetyl based on the use of thermal desorption tubes for sampling and gas chromatography-mass spectrometry for analysis. The samplers may be used in either pumped (active) or diffusive (passive) mode. For measurement of short duration peak concentrations, or determining compliance with the STEL, pumped sampling is most effective. For longer sampling periods, in particular whole shift monitoring, diffusive sampling is preferable. This method is also applicable to 2,3-pentanedione.

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Ian Pengelly Health and Safety Executive Harpur Hill Buxton Derbyshire SK17 9JN

Validation of a measurement method for diacetyl using sorbent tubes and thermal desorption

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KEY MESSAGES

Diacetyl, also known as 2,3-butanedione, and the closely related chemical 2,3-pentanedione are two naturally occurring but potentially harmful chemicals which are used in the flavouring industry and have also been reported in the coffee manufacturing industry and in emissions from flavoured popcorn. Studies have shown a link between exposure to diacetyl and bronchiolitis obliterans, a serious obstructive lung disease. In Great Britain, occupational exposure limits to protect workers’ health are set based on recommendations for SCOEL (the European Commission Scientific Committee on Occupational Exposure Limits). SCOEL has recommended an 8-hour time weighted average occupational exposure limit (TWA-OEL) of 20 ppb (parts per billion) and a short term exposure limit (STEL) of 100 ppb. In the United States, exposure limits are being recommended for both diacetyl and 2,3-pentanedione by National Institute for Occupational Safety & Health (NIOSH).

Existing scientific measurement methods lack the necessary sensitivity to measure the levels of exposures required at the level of these recommended limits. These methods are based on the use of sorbent tubes, solvent desorption and gas chromatography. Health and Safety Executive scientists have therefore developed a more sensitive measurement technique based on the use of sorbent tubes, thermal desorption and gas chromatography-mass spectrometry. This technology has been used by HSE for many years for monitoring volatile organic compounds. The technique is also applicable to diffusive sampling which doesn’t require a sampling pump and is therefore much easier to use and considerably more convenient for personal sampling.

Validation testing of the new method has demonstrated its sensitivity, robustness and fitness for purpose. In particular, the testing has demonstrated that the technique is able to detect both diacetyl and 2,3-pentanedione at airborne concentrations of less than 0.5 ppb, which is less than 1/40th of the proposed 8-hour TWA-OEL. The storage stability of both substances after sampling has been tested and been shown to be fit for purpose. In addition, the method is able to collect and detect substances other than diacetyl and 2,3-pentanedione on the same sample. This is potentially useful in industries where other chemical compounds are likely to be present as studies have indicated that the health effects of diacetyl may be made worse when present as part of a mixture of compounds.

The new TD-based method is therefore suitable for measurement of exposure to diacetyl and 2,3-pentanedione and monitoring compliance with the proposed exposure limits.

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EXECUTIVE SUMMARY

Objective

The objective of this investigation was to undertake a thorough validation of a proposed thermal desorption (TD) based measurement method for workplace monitoring of diacetyl and the structurally similar compound, 2,3-pentanedione, in order to fully demonstrate its robustness and fitness for purpose. The measurement method is aimed at providing the necessary sensitivity to measure potential levels of worker exposures to these substances in line with the recommended exposure limits by SCOEL.

Main Findings

The report details the technical findings of the validation and is aimed at measurement specialists. The main findings are:

• Thermal desorption sampling tubes containing Tenax TA or Chromosorb 106 sorbent are suitable for sampling of diacetyl;

• Diacetyl is stable on Tenax TA for a time period of at least seven months, whereas samples taken on Chromosorb 106 require analysis within a week. Consequently, Tenax TA is the preferred sorbent for sampling of diacetyl;

• Sampling tubes containing Tenax TA are suitable for sampling of 2,3-pentanedione, but require analysis within one month;

• Due to issues with storage stability, the use of sampling tubes containing Chromosorb 106 is not suitable for sampling of 2,3-pentanedione;

• The presence of water and acetic acid does not adversely affect storage stability of either diacetyl or 2,3-pentanedione;

• For pumped (active) samples, Tenax TA has a safe sampling volume of 3-litres for diacetyl. The maximum sampling time for pumped samples at a flow rate of 100 ml.min-1 is therefore 30 minutes. If the flow rate is reduced to 25 ml.min-1 the maximum sampling time is 120 minutes. The safe sampling volume for 2,3-pentanedione on Tenax TA is more than 24-litres;

• Diffusive uptake rates for diacetyl and 2,3-pentanedione have been obtained for Tenax TA over sampling periods of 1 to 8 hours.

• For longer term sampling, in particular personal samples, diffusive (passive) sampling is the preferred option. However, for measurement of peak concentrations or compliance with short term exposure limits (STELs), pumped sampling is the better option, both to retain sensitivity and because diffusive sampling is not recommended for sampling time of less than 15 minutes.

• Analysis using gas chromatography-mass spectrometry (GC-MS) gives better sensitivity and selectivity than gas chromatography with flame ionisation detection (GC-FID), but either may be used;

• In order to retain optimum levels of precision with analysis by GC-MS, it is recommended to use an internal standard; deuterated toluene has been found to be suitable for this purpose.

• Typical limits of detection, as a collected mass, for diacetyl and 2,3-pentanedione collected on Tenax TA and analysed by thermal desorption and GC-MS are 0.2 ng and 0.1 ng respectively.

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• Limits of detection for airborne concentrations are dependent on the sampling mode (pumped or diffusive) and time, but for a full shift (8-hour) diffusive sample these mass-based limits of detection would equate to airborne concentrations of around 0.3 ppb for diacetyl and 0.1 ppb for 2,3-pentanedione (or less than 1/50th of the proposed long-term time weighted average (TWA) personal exposure limits for the two compounds).

• In addition, the TD based method can also be used to identify and, if required, quantify other volatile organic components that may be present in the work environment.

Conclusions

• Based on the findings of this investigation, the measurement method described in this report is suitable for workplace exposure monitoring of diacetyl and 2,3-pentanedione

• The samplers may be used in either pumped (active) or diffusive (passive) mode depending on the likely circumstances of exposure.

• For measurement of short duration peak concentrations, or determining compliance with 15-minute STELs, pumped sampling is most effective.

• For personal sampling of workers, diffusive sampling is preferable, particularly for whole shift (8-hour TWA) monitoring.

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CONTENTS

KEY MESSAGES……………………………………………………………………………………………. 4

EXECUTIVE SUMMARY……………………………………………………………………………….. 5

1 INTRODUCTION ................................................................................................. 8 1.1 Objective ................................................................................................................................. 8

1.2 Background ............................................................................................................................. 8

1.3 Measurement .......................................................................................................................... 9

2 EXPERIMENTAL ................................................................................................ 11 2.1 Equipment ............................................................................................................................. 11

2.2 Storage Stability .................................................................................................................... 12

2.3 Breakthrough Volume ........................................................................................................... 13

2.4 Relative Humidity .................................................................................................................. 13

2.5 Presence of Acetic Acid ......................................................................................................... 13

2.6 Diffusive Uptake rates ........................................................................................................... 14

3 RESULTS .......................................................................................................... 16 3.1 Storage Stability .................................................................................................................... 16

3.2 Breakthrough ........................................................................................................................ 17

3.3 Effect of Relative Humidity ................................................................................................... 17

3.4 Effect of Acetic Acid .............................................................................................................. 18

3.5 Diffusive Uptakes rates ......................................................................................................... 19

4 DISCUSSION ..................................................................................................... 20

5 CONCLUSIONS ................................................................................................. 21

6 REFERENCES .................................................................................................... 22

7 APPENDICES .................................................................................................... 24 7.1 APPENDIX 1 – Storage Stability ............................................................................................. 24

7.2 APPENDIX 2 – Breakthrough ................................................................................................. 26

7.3 APPENDIX 3 – Effect of Relative Humdity ............................................................................. 28

7.4 APPENDIX 4 – Effect of the Presence of Acetic Acid ............................................................. 29

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1 INTRODUCTION

1.1 OBJECTIVE

The objective of this investigation was to undertake a thorough validation of a proposed thermal desorption (TD) based measurement method for workplace monitoring of diacetyl and the structurally similar compound, 2,3-pentanedione, in order to fully demonstrate its robustness and fitness for purpose. The measurement method is aimed at providing the necessary sensitivity to measure potential levels of worker exposures to these substances in line with the recommended exposure limits by SCOEL. This work builds on previous studies on measurement of diacetyl in emissions from cooking products and monitoring of diacetyl in the workplace using a TD based sampling method (Sandys et al., 2014).

1.2 BACKGROUND

Diacetyl (also known as 2,3-butanedione), a yellowish green liquid with a characteristic butter-like odour, is a naturally occurring substance in many foods such as dairy products, beer and fruits. Diacetyl is also synthesized by chemical manufacturers and used in the food industry as an artificial butter flavouring for a variety of food products. It has also been reported that diacetyl, and the structurally similar compound, 2,3-pentanedione, are generated by coffee roasting (NIOSH, 2016).

In 2000, NIOSH (National Institute for Occupational Safety & Health) investigated the occurrence of severe lung disease amongst former workers at a microwave popcorn packaging plant and found a link between exposure to vapours from flavourings used in the production process and decreased lung function. Medical test results for the affected workers were consistent with bronchiolitis obliterans, a severe obstructive lung disease that is life threatening and irreversible. Further studies indicated that the chemical responsible was diacetyl and that the effects were made worse when diacetyl was present as part of a mixture of other flavouring compounds.

In December 2003 NIOSH issued an alert aimed at preventing lung disease in workers who use or make flavourings. This alert describes health effects that may occur due to workplace exposure to some flavourings, gives examples of workplace settings in which illness has occurred and recommends steps that companies and workers should take to prevent hazardous exposures. The release of this alert was discussed at a meeting of WATCH (HSE Working Group on Action to Control Chemicals) in June 2004. At the time the main concern was thought to be from the manufacture of popcorn, however enquiries by HSE found no evidence of the use of diacetyl for this purpose in the UK. Nevertheless, the meeting decided that HSE should continue to investigate the use of diacetyl as a food-flavouring agent in the UK.

In January 2008, the first UK case of bronchiolitis obliterans was reported in a worker involved in mixing and packaging flavours at a flavourings firm. This brought HSE focus to determining the extent of the use of diacetyl in the UK and the potential risks to health.

In 2014, SCOEL (the European Commission Scientific Committee on Occupational Exposure Limits) recommended an 8-hour time weighted average occupational exposure limit (TWA-OEL) of 20 ppb (SCOEL, 2014). They also concluded that a short term exposure limit (STEL) of 100 ppb was needed to prevent adverse health effects, mainly respiratory damage, which might arise due to peaks in exposure not controlled by the TWA limit. In other evaluations, NIOSH have proposed a TWA-OEL for diacetyl of 5 ppb and a 15-minute STEL of 25 ppb and, in addition, a TWA-OEL of 9.3 ppb for 2,3-pentanedione and a 15-minute STEL of 3.1 ppb (NIOSH, 2011).

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In 2015, NIOSH published a best practices document describing workplace interventions including engineering controls, work practices and methods for monitoring occupational exposure to diacetyl and 2,3-pentanedione (NIOSH, 2015).

1.3 MEASUREMENT

The United States Occupational Safety and Health Administration (OSHA) and NIOSH both published partially-evaluated methods for diacetyl in 2003, OSHA issuing a subsequent revision in 2006 (NIOSH 2003, OSHA, 2006). The NIOSH method may be affected by high humidity resulting in an underestimate of diacetyl concentration. The OSHA method, which has a limit of detection (LoD) of 0.3 ppm, is not affected by humidity and relatively stable under standard sample storage conditions.

In 2008 OSHA published two new validated sampling and analytical methods for diacetyl; Method 1012 (OSHA 2008a) and Method 1013 (OSHA 2008b). In 2010, these were supplemented with a third method, Method 1016, for measurement of 2,3-pentanedione (OSHA, 2010). The sampling media for all three methods is two specially dried silica gel tubes sampling in series. In Method 1012, the samples are solvent desorbed, derivatised and analysed by gas chromatography with electron capture detection (GC-ECD). In Methods 1013 and 1016 the samples are solvent desorbed and analysed by GC with flame ionisation detection (GC-FID). The stated reliable quantitation limits (RQLs) for are 1.3 ppb for Method 1012, 12 ppb for Method 1013 and 9.3 ppb for Method 1016. Revised versions of Methods 1013 and 1016, using GC and mass spectrometry (GC-MS), state improved RQLs for both analytes of 1.1 ppb (LeBouf and Simmons, 2017).

Despite the improved limits of detection offered by the use of GC-MS, the OSHA methods still have some limitations, particularly for long term and personal sampling. Firstly, the method is only suitable for active sampling. Secondly, the samplers are not widely available and must be protected from the light during and after sampling with aluminium foil or opaque tape. Thirdly, in the case of Method 1012, the derivatisation reaction can take up to 36 hours to reach completion. Finally, the recommended sampling time for the method is only 180 minutes, so 8-hour samples require the use of multiple samples.

Because of these limitations, some initial method development was carried out at HSL to investigate whether existing automated thermal desorption (ATD) based sampling and analytical procedures, such as those described in HSE Method 104 (HSE, 2016) could be adapted for measurement of diacetyl. Experience with ATD methods at HSL has shown them to combine good levels of sensitivity, particularly in combination with mass spectrometry (MS), with an easy to use sampling device and a simple, rapid analysis. The findings of this initial investigation are described elsewhere (Sandys et al., 2014), but concluded that the use of sorbent tubes, with analysis by ATD and gas chromatography (GC), could be recommended for workplace monitoring of diacetyl.

As the proposed ATD-based measurement method will be used to monitor workplace exposure to diacetyl and, in particular, compliance with proposed occupational exposure limits, it is essential that it is sufficiently validated to ensure that it is both robust and fit for purpose. The following testing was carried out to investigate the robustness of the method and clearly identify any limitations:-

• Sorbent type;

• Storage Stability;

• Breakthrough and safe sampling volumes;

• Effects of relative humidity;

• Effects of the presence of acetic acid;

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In addition, this investigation also included an assessment of the suitability of the method for measurement of 2,3-pentanedione and determination of diffusive uptake rates for both diacetyl and 2,3-pentanedione.

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2 EXPERIMENTAL

2.1 EQUIPMENT

2.1.1 Sampling Tubes

Pre-packed stainless steel ATD tubes, 89 mm (3.5”) long × 6.4 mm (¼”) outside diameter were used in the following tests. The tubes were packed with one of the following three sorbents retained between two steel gauzes:-

• Older ‘low density’ Tenax TA - 200 ± 10 mg; 35/60 Mesh; nominal 4 cm sorbent bed length.

• Newer ‘high density’ Tenax TA - 200 ± 10 mg; 35/60 Mesh, nominal 3 cm sorbent bed length.

• Chromosorb 106 - 300 ± 10 mg; 60/80 Mesh; nominal 6 cm sorbent bed length.

For diffusive sampling, the tubes were fitted with an aluminium axial diffusion cap. For storage, the tubes were sealed with aluminium end-caps fitted with PTFE ferrules.

2.1.2 Analytical Equipment and Conditions

Samples were analysed using a Perkin Elmer ATD-350 and a Perkin Elmer TurboMass GC-MS. The analytical conditions used are shown in Table 1. These conditions give retention times for diacetyl and 2,3-pentanedione of 4.6 and 6.3 minutes respectively.

Table 1: ATD-GC-MS Instrument Conditions

Column Type

Column Dimensions

Carrier Gas

Column Flow

Outlet Split

Inlet Split

Desorb Flow

Desorb Temp. (Tenax)

Desorb Temp. (C-106)

Desorb Time

Valve Temperature

Transfer Line

VOCOL

60 m × 0.25 mm × 1.5 µm

Helium

1.3 ml.min-1

30 ml.min-1

Off

50 ml.min-1

280°C

200°C

10 minutes

225°C

200°C

Trap (low)

Trap (high)

GC Temperature 1

Time at Temperature 1

Temperature Ramp 1

GC Temperature 2

Time at Temperature 2

Temperature Ramp 2

GC Temperature 3

Time at Temperature 3

Total Run Time

Quantitation Ions

-30°C

280°C

100°C

5 minutes

5°C.min-1

150°C

0 minutes

10°C.min-1

200°C

10 minute

30 minutes

43; 57; 86; 100

2.1.3 Standard Atmosphere Equipment

Samples in the following tests were air loaded using the standard atmosphere equipment shown in Figure 1. The test compounds were prepared as a liquid mixture and introduced into the standard atmosphere chamber using a syringe driver. The concentration of the atmosphere was controlled using three high flow rate (0 – 30 l.min-1) mass flow controllers (MFCs). The sample tubes were mounted in the atmosphere chamber, connected to low flow rate (0 – 250 ml.min-1) MFCs and loaded with the components of interest. The typical flow rate for loading was 100 ml.min-1. Using this equipment up to sixty sample tubes can be simultaneously loaded with the test components.

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Figure 1: Standard Atmosphere Equipment used for Tube Loading

2.2 STORAGE STABILITY

The majority of samples will not be analysed immediately and it is therefore essential that the storage of stability of different analytes on the chosen sorbents are known. Previous work with diacetyl at HSL used Chromosorb 106 as the sampling sorbent (Sandys et al., 2014), so the initial storage trial was carried out using this sorbent. However, Tenax TA is generally the sorbent of choice for VOC sampling at HSL so a smaller scale storage trial was carried out at the same time using the older ‘low density’ (LD) variant of this sorbent. In both cases the sample tubes were loaded with a mixture of VOC compounds, including diacetyl and toluene. Toluene, which has been found to be stable for at least 2 years on Tenax TA (Vandendriessche et al., 1991), was used as an internal standard. The other components loaded onto the tubes were ethanol, isopropanol, ethyl acetate, propyl acetate, methyl isobutyl ketone, butyl acetate, α-pinene and limonene. These components were chosen as being broadly representative of compounds which might be encountered, with diacetyl, in the flavouring industry.

In the storage trial with Chromosorb 106, fifty tubes were air loaded with around 115 ng (20 tubes), 160 ng (10 tubes) and 240 ng (20 tubes) of each component using air volumes of around 0.75 to 1.5 litres. In the storage trial with Tenax, ten tubes were air loaded with around 160 ng of each component using an air volume of around 1.1 litres. Batches of two or three tubes were analysed periodically (with a maximum storage period of 239 days). The amount of each component recovered from each tube was determined and normalised against the mass of toluene recovered from the tube.

Initial findings from the two storage trials described above indicate that storage stability of diacetyl on Tenax TA is superior to that on Chromosorb 106. Consequently, a further, larger scale, storage trial with Tenax TA was carried out. Sixty tubes were air loaded with around 75 ng (20 tubes), 150 ng (20 tubes) and 225 ng (20 tubes) of each component using air volumes of around 0.8 to 2.4 litres. Once again, batches of two or three tubes were analysed periodically (with a maximum storage period of 210 days) and the amount of each component recovered from each tube determined and normalised against the recovered mass of toluene.

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2.3 BREAKTHROUGH VOLUME

A standard atmosphere containing the same analyte mix used in the storage tests (see Section 2.1) was prepared with an airborne concentration of around 0.25 – 0.5 ppm for each component and a relative humidity of around 40% RH. Pumped samples were collected from the atmosphere on to sorbent tubes containing LD Tenax TA or Chromosorb 106. The sampling flow rate used was 100 ml.min-1 which, with sampling times of 10, 30, 60, 120 and 240 minutes, equates to sample volumes of between 1 and 24-litres and sample loadings of around 100 to 2500 ng. Back-up tubes were connected in series behind each sample tube in order to detect any breakthrough. Three replicate pairs of each sampler type and sample volume were collected, with the samples being analysed by TD and GC-FID. In addition to the LD Tenax TA tubes used in most of the other tests, some additional samples were taken on a more recently purchased batch of tubes containing ‘high density’ (HD) Tenax TA.

A second breakthrough test was subsequently carried out using the slightly different analyte mix used in the humidity tests (see Section 2.4). A standard atmosphere containing around 0.25 – 0.5 ppm of each component (at 40% RH) was set up and pumped samples were collected onto tubes containing Tenax TA (both LD and HD) and Chromosorb 106. As previously, the sample tubes were connected to back-up tubes filled with the same sorbent. Samples were taken at a flow rate of 100 ml.min-1, over sampling times of 5, 10, 20, 30, 40 and 50 minutes, which equates to sample volumes of between 0.5 and 5-litres and sample loadings of around 50 to 500 ng. Two replicate pairs of each sampler type and sample volume were collected, with the samples being analysed by TD and GC-FID.

2.4 RELATIVE HUMIDITY

Real samples are likely to be collected under a range of relative humidities. The following test was therefore carried out to investigate the effect of relative humidity on samples of diacetyl and 2,3-pentanedione collected onto LD Tenax TA and Chromosorb 106 tubes. Two sets of thirty tubes were loaded with roughly equal amounts (around 150 ng) of a mixture of nine compounds, including diacetyl and 2,3-pentanedione, in the standard atmosphere chamber. The other compounds were ethyl acetate, propyl acetate, butyl acetate, butanol, limonene, toluene and o-xylene. These compounds were chosen as being representative of other flavouring compounds or, in the case of toluene and o-xylene, compounds which are known to be stable on Tenax TA and Chromosorb 106 tubes for many months, or even years. The tubes were loaded at an air temperature of approximately 20°C; one set at a relative humidity of 0% RH and the other at a relative humidity of 50% RH. Each set of tubes comprised fifteen Tenax TA tubes and fifteen Chromosorb 106 tubes. The tubes were loaded over a 9-minute time period at a flow rate of 40 ml.min-1, giving a sample volume of around 0.36 litres.

Batches of twelve tubes, made up of six tubes (three Tenax TA and three Chromosorb 106) loaded at 0% RH and six tubes (three Tenax TA and three Chromosorb 106) loaded at 50% RH were then analysed by ATD-GC-MS after storage for 0, 7, 14, 28 and 90 days. The amount of each component recovered from each tube was determined and normalised against the mass of toluene recovered from the tube.

2.5 PRESENCE OF ACETIC ACID

Acetic acid is a compound that frequently occurs, often at much higher concentrations, in instances where diacetyl may be present. The following tests were therefore carried out to investigate the effect of the presence of acetic acid on samples of diacetyl and 2,3-pentanedione collected onto Tenax and Chromosorb tubes. Four sets of thirty tubes were loaded with roughly equal amounts (around 150 ng) of the same mixture of compounds, including diacetyl and 2,3-pentanedione, as was

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used in the relative humidity tests (see Section 2.4). However, in addition the tubes were also loaded with much higher amounts of acetic acid, two sets with around 750 ng and two with around 7500 ng. The tubes were loaded at an air temperature of approximately 20°C; two sets at a relative humidity of 0% RH and the other two at a relative humidity of around 50% RH. Each set of tubes comprised fifteen LD Tenax TA tubes and fifteen Chromosorb 106 tubes. The tubes were loaded over a 9-minute time period at a flow rate of 40 ml.min-1, giving a sample volume of 0.36 litres.

Batches of twenty-four tubes, made up of twelve tubes (six Tenax TA and six Chromosorb 106) loaded at 0% RH (half at the higher loading of acetic acid and half at the lower) and twelve tubes (six Tenax TA and six Chromosorb 106) loaded at 50% RH (half at the higher loading of acetic acid and half at the lower) were then analysed by ATD-GC-MS after storage for 0, 7, 14, 28 and 90 days. The amount of each component recovered from each tube was determined and normalised against the mass of toluene recovered from the tube.

2.6 DIFFUSIVE UPTAKE RATES

To minimise the possibility of sample breakthrough, for longer term and personal sampling, particularly samples over 1 hour in duration, diffusive (or passive) sampling is preferable to pumped (or active) sampling. In this mode the sorbent tubes are used without a pump, but with a standard diffusive sampling head fitted to one end of the tube (see Figure 2).

Figure 2: TD Tube Fitted with Diffusive Sampling Head

Using diffusive sampling the airborne concentration of the target substance, or substances, in this case diacetyl and 2,3-pentanedione, are calculated using Equation 1.

Equation 1: 𝐶𝐶 (𝑝𝑝𝑝𝑝𝑝𝑝) = 𝑀𝑀 (𝑛𝑛𝑛𝑛)𝑈𝑈𝑅𝑅 (𝑛𝑛𝑛𝑛.𝑝𝑝𝑝𝑝𝑝𝑝−1.𝑝𝑝𝑚𝑚𝑛𝑛−1) ×𝑇𝑇 (min)

where:

C is the airborne concentration, in ppm;

M is the mass of analyte collected, in ng;

UR is the diffusive uptake rate, in ng.ppm-1.min-1;

T is the sampling period, in minutes.

In order to use the sampling tubes diffusively it is therefore necessary to know the diffusive uptake rates for the analytes of interest, which will differ depending on the sorbent. Diffusive uptake rates

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for many VOCs on commonly used sorbents, such as Tenax TA and Chromosorb 106, are readily available (MDHS 104). However, these sources do not contain diffusive uptake rates for diacetyl and 2,3-pentanedione. The following series of experiments were therefore carried out to determine diffusive uptake rates for these two substances over sampling periods of 1, 2, 4 and 8 hours.

A standard atmosphere containing the same mix of compounds used in the humidity tests (see Section 2.4) was set up with a concentration of approximately 0.5 – 1 ppm of each component. Six pumped samples were collected from the atmosphere at a sampling rate of 5 ml.min-1, over a sampling period of 1 hour. Alongside these, eighteen diffusive samples were taken using TD tubes fitted with standard diffusion caps. The diffusive samples comprised twelve tubes containing Tenax TA (six LD and six HD) and six using tubes containing Chromosorb 106. The tests were carried out at an average temperature of around 21°C and a relative humidity of around 40% RH. The pumped and diffusive samplers, and appropriate blank tubes, were analysed by TD and GC-FID and the results used to determine the mean uptake rates of the diffusive samplers.

The experiment was repeated over 2, 4 and 8-hour sampling periods, but with the airborne concentrations for each component reduced to around 0.25 – 0.5 ppm.

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3 RESULTS

3.1 STORAGE STABILITY

The results of the storage trial for diacetyl collected on Chromosorb 106 are shown in Figure A1.1 in Appendix 1 and summarised in Table 2. The data show recoveries of diacetyl of around 80% after a week, falling to around 60% after a month, 40% after two months and around 10% after 8 months. Tubes at the three loadings showed no consistent differences in sample recovery. These results indicate that if diacetyl is collected on Chromosorb 106, the samples require analysis within a week.

Table 2: Storage Stability of Diacetyl on Chromosorb 106 (Mean Recoveries)

Storage Periods (Days) 0 8 14 21 28 56 239

No. of Samples 9 6 6 7 7 7 4

Mean Recovery 100% 79% 76% 68% 63% 39% 9%

The results of the initial storage trial for diacetyl collected on Tenax TA are shown in Figure A1.2 in Appendix 1 and summarised in Table 3. Compared with the Chromosorb results above, the data show significantly improved stability with recoveries generally within 5% of the initial values over a storage period of 2 months which, based on the coefficient of variation (CV) of the results, may be regarded as within experimental variation. Recoveries in excess of 100% were obtained in some instances, but these are within 5% of the expected value. Once again, sample loading does not appear to have any consistent effect on sample recovery. These initial results indicate that if diacetyl is collected on Tenax TA, the samples are stable for a period of at least two months.

Table 3: Storage Stability of Diacetyl on Tenax TA (Initial Trial; Mean Recoveries)

Storage Periods (Days) 0 8 14 21 28 56

No. of Samples 3 2 2 1 1 1

Mean Recovery 100% 99% 94% 92% 98% 103%

The results of the second, larger scale, storage trial for diacetyl collected on Tenax TA are shown in Figure A1.3 in Appendix 1 and summarised in Table 4. The recovery data show slightly greater variation than that in the initial storage trial. However, storage stability is still significantly better than that of Chromosorb, with recoveries generally within 5% of the initial values over a storage period of 7 months. These results indicate that if diacetyl is collected on Tenax TA, the samples are stable for a period of at least seven months.

Table 4: Storage Stability of Diacetyl on Tenax TA (Second Trial; Mean Recoveries)

Storage Period (Days) 0 7 15 27 54 83 126 210

No. of Samples 9 9 9 9 9 6 4 5

Mean Recovery 100% 99% 94% 92% 98% 103% 106% 100%

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3.2 BREAKTHROUGH

The results of the breakthrough tests for diacetyl and 2,3-pentanedione are shown in Figures A2.1 to A2.3 in Appendix 2 and summarised in Tables 5 and 6. The data from Test 1 show 5% breakthrough from a sampling volume of just over 2-litres for the sorbent tubes containing the older Tenax TA and around 1.5-litres for those containing the newer Tenax TA. The Chromosorb 106 tubes showed no significant breakthrough from a sampling volume of 24-litres. Test 2 produced slightly improved results for the two Tenax tubes, with 5% breakthrough resulting from a sampling volume of approximately 4-litres for the old Tenax TA and 2.5-litres for the newer Tenax TA. Once again, no significant breakthrough was observed in the case of the Chromosorb tubes.

HSE Method MDHS 104 defines the safe sampling volume of a sorbent tube for a given analyte as being not more than 70% of the sampling volume required to cause 5% breakthrough of the analyte (HSE, 2016). Based on this definition, the results of Test 2 would indicate a safe sampling volume, for pumped samples, of around 3-litres in the case of tubes containing the older Tenax TA, 2-litres in the case of tubes containing the newer Tenax TA and in excess of 24-litres in the case of tubes containing Chromosorb 106.

Table 5: Breakthrough of Diacetyl on Pumped Samples (Test 1)

Sample Volume (L) 1 3 6 12 24

Old Tenax TA 2% 7% 15% 33% 47%

New Tenax TA 4% 10% 20% 33% 44%

Chromosorb 106 4% 2% 1% 1% 0%

Table 6: Breakthrough of Diacetyl and 2,3-Pentanedione on Pumped Samples (Test 2)

Sample Volume (L) 0.5 1.0 2.0 3.0 4.0 5.0

Old Tenax TA Diacetyl 0% 0% 2% 5% 3% 8%

2,3-Pentanedione 0% 0% 0% 0% 0% 0%

New Tenax TA Diacetyl 0% 2% 2% 8% 14% 15%

2,3-Pentanedione 0% 0% 0% 1% 1% 0%

Chromosorb 106 Diacetyl 0% 2% 0% 0% 0% 0%

2,3-Pentanedione 0% 0% 0% 0% 0% 0%

3.3 EFFECT OF RELATIVE HUMIDITY

The recoveries of diacetyl and 2,3-pentanedione collected at around 0% RH and 50% RH are shown in Figures A3.1 and A3.2 in Appendix 3 and summarised in Table 7.

Under the test conditions, the results in Table 7 show that the effect of relative humidity on storage stability of both diacetyl and 2,3-pentanedione is generally minimal, i.e. samples loaded at 0% RH and at 50% RH gave similar results for both compounds. However, the results also show the storage stability of diacetyl and 2,3-pentanedione at both humidities to be significantly better on Tenax than on Chromosorb. After 90 days storage, average recovery of diacetyl from the Tenax tubes was approximately 90% of that on Day 0, whereas for Chromosorb it was only around 45%. In the case of 2,3-pentanedione, the difference was even greater, with recoveries, after 90 days storage, of

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around 75% for Tenax and only 5% for Chromosorb. In addition, the data obtained from the Tenax tubes tend to show greater precision, i.e. less scatter, than that obtained from the Chromosorb tubes. Recoveries of the remaining components, relative to toluene, were generally consistent on both sorbents.

Table 7: Effect of Relative Humidity on Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on to Tenax TA and Chromosorb 106 (Mean Recoveries)

Storage Period (Days) 0 7 14 28 90

Tenax TA

Diacetyl 0% RH 99% 94% 93% 93% 91%

45% RH 101% 92% 95% 98% 87%

2,3-Pentanedione 0% RH 99% 88% 94% 92% 76%

45% RH 101% 89% 97% 94% 68%

Chromosorb

106

Diacetyl 0% RH 97% 82% 95% 72% 36%

45% RH 103% 85% 92% 79% 49%

2,3-Pentanedione 0% RH 96% 38% 11% 8% 6%

45% RH 104% 50% 53% 18% 3%

3.4 EFFECT OF ACETIC ACID

The recoveries of diacetyl and 2,3-pentanedione from the four sets of samples are shown in Figures A4.1 to A4.4 and summarised in Table 8.

Table 8: Effect of Acetic Acid on Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on to Tenax TA and Chromosorb 106 (Mean Recoveries)

Storage Period (Days) 0 7 14 28 90

Tenax TA

Diacetyl

750 ng AcOH

0% RH 99% 101% 96% 102% 107%

45% RH 101% 103% 99% 104% 107%

7500 ng AcOH

0% RH 99% 99% 93% 98% 112%

45% RH 101% 101% 94% 98% 108%

2,3-Pentane- dione

750 ng AcOH

0% RH 99% 109% 114% 105% 79%

45% RH 101% 111% 116% 108% 84%

7500 ng AcOH

0% RH 98% 128% 134% 125% 101%

45% RH 102% 125% 133% 128% 100%

Chromosorb 106

Diacetyl

750 ng AcOH

0% RH 102% 92% 78% 76% 39%

45% RH 98% 97% 85% 76% 46%

7500 ng AcOH

0% RH 100% 95% 87% 77% 43%

45% RH 100% 97% 86% 80% 48%

2,3-Pentane- dione

750 ng AcOH

0% RH 100% 43% 30% 19% 0%

45% RH 100% 70% 53% 34% 2%

7500 ng AcOH

0% RH 98% 82% 66% 27% 0%

45% RH 102% 106% 79% 50% 3%

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Under the test conditions, the results in Table 8 indicate that, in general, the presence of acetic acid appears to slightly improve storage stability of diacetyl, particularly in those tubes containing the higher loading of acetic acid, although the differences observed are not great, particularly for samples collected on Tenax TA. In the case of 2,3-pentanedione, the recoveries obtained from some of the Tenax tubes were up to a third higher than the expected values, so the presence of acetic acid appears to be causing a positive bias in these samples.

As with samples containing no acetic acid, storage stability of both diacetyl and 2,3-pentanedione is significantly better on Tenax than on Chromosorb. After 90 days storage, the average mass of diacetyl recovered from the Tenax tubes was fairly similar to that on Day 0, whereas for Chromosorb it was only around 45%. In the case of 2,3-pentanedione, the difference was even greater, with recoveries, after 90 days storage, of around 80% for Tenax and less than 3% for Chromosorb.

The presence of acetic acid did not seem to adversely affect the storage stability of the remaining components, most of which showed fairly similar recovery efficiencies, relative to toluene, to those obtained with no acetic acid present.

3.5 DIFFUSIVE UPTAKES RATES

The results of the diffusive uptake rate tests are summarised in Table 9. These data produced 8-hour diffusive uptake rates of around 1.42 ng.ppm-1.min-1 for the old Tenax TA tubes (which were subsequently used for the field trials), 1.40 ng.ppm-1.min-1 for the newer Tenax TA tubes and 1.63 ng.ppm-1.min-1 for the Chromosorb 106 tubes. The equivalent values for 2,3-pentanedione are 1.76, 1.75 and 1.65 ng.ppm-1.min-1 respectively. Shorter sampling times produced higher diffusive uptake rates, which is consistent with diffusion theory. Typically, the relative standard deviations for the diffusive uptake rate values shown in Table 9 were between 3 and 5%, but relative standard deviations of over 10% were observed for some of the Chromosorb 106 data.

Table 9: Diffusive Uptake Rates for Diacetyl and 2,3-Pentanedione (Mean Values)

Sorbent Exposure

Time (hr)

Diffusive Uptake Rate (ng.ppm-1.min-1)

Diacetyl 2,3-Pentanedione

Mean % RSD Mean % RSD

Old Tenax TA

1 2 4 8

1.76 1.74 1.61 1.42

3.9% 3.3% 2.0% 6.9%

1.92 1.90 1.90 1.76

4.2% 4.4% 1.8% 7.8%

New Tenax TA

1 2 4 8

1.66 1.71 1.56 1.40

5.3% 3.4% 2.9% 3.1%

1.80 1.92 1.83 1.75

4.0% 2.6% 3.9% 3.4%

Chromosorb 106

1 2 4 8

1.74 1.73 1.78 1.63

5.6% 17.2% 4.5% 3.4%

1.71 1.81 1.89 1.65

6.3% 14.1% 2.6% 3.4%

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4 DISCUSSION

The storage trails carried out indicate that, if diacetyl is sampled on to Tenax TA, pumped samples are stable, with variations of less than 10%, for a period of at least seven months. If sampled on to Chromosorb 106, samples show losses of diacetyl of 10 – 20% after only a week. Storage stability of 2,3-pentanedione on both sorbents was generally worse than that of diacetyl, although losses on Tenax TA were generally still less than 10% after storage for four weeks. Losses from Chromosorb 106 were significantly worse, with losses of 50 – 60% after a week and 80 – 90% after a month.

These results indicate that, for diacetyl, samples taken on to Tenax TA may be stored for at least seven months prior to analysis, which should be sufficient for most sampling scenarios, whereas samples taken on to Chromosorb 106 require immediate analysis, and certainly within a week. If measurement of 2,3-pentanedione is required, samples taken on to Tenax TA should be analysed within one month, whilst stability on Chromosorb 106 is so poor that it is not recommended for measurement of 2,3-pentanedione.

Recovery of diacetyl and 2,3-pentanedione does not appear to be adversely affected by the presence of moisture or acetic acid in the test atmosphere. The latter is of importance as acetic acid is a commonly used component in the flavouring industry, which may often occur at airborne concentrations well in excess of those of diacetyl or 2,3-pentanedione.

With regard to breakthrough, tubes containing the older LD Tenax TA sorbent gave results suggesting a recommended safe sampling volume for diacetyl of around 3-litres. Interestingly, the suggested safe sampling volume for the newer HD Tenax tubes was somewhat less; about 2-litres. Safe sampling volumes for diacetyl collected on Chromosorb 106 were found to be in excess of 25-litres. Consequently, whilst storage of diacetyl is better using Tenax TA, breakthrough is better using Chromosorb 106. In the case of 2,3-pentanedione, no significant breakthrough was observed in any of the tests with any of the sorbents, which is probably due to its lower volatility.

Diffusive uptake rates were obtained for both diacetyl and 2,3-pentanedione using Tenax TA and Chromosorb 106. In the case of Tenax TA, the 8-hr diffusive uptake rate was 1.42 ng.ppm-1.min-1, whilst the figure for Chromosorb 106 was 1.63 ng.ppm-1.min-1. These uptakes rates are generally consistent with expected values, based on known uptake rates for similar substances such as methyl ethyl ketone (2-butanone). Uptake rates for shorter sampling times of 1, 2 and 4-hours were also obtained. As expected, based on diffusion theory, the diffusive uptake rates over these shorter sampling times are higher than the equivalent 8-hour values.

For longer sampling times, particularly for personal samples, diffusive sampling is the recommended option, as no pumps are required making sampling easier and cheaper, and removing any potential issues with exceeding the safe sampling volume. However, for short term samples of less than 30 minutes pumped sampling is recommended. In order to get the best sensitivity and selectivity it is necessary to use GC-MS rather than GC-FID. However, this requires the use of a suitable internal standard, in this case d8-toluene, in order to retain optimum levels of precision.

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5 CONCLUSIONS

The conclusions of this investigation are as follows:-

• Thermal desorption sampling tubes containing either Tenax TA or Chromosorb 106 sorbent are suitable for sampling of diacetyl;

• Diacetyl is stable on Tenax TA for a time period of at least seven months, whereas samples taken on Chromosorb 106 require analysis within a week. Consequently, Tenax TA is the preferred sorbent for sampling of diacetyl;

• Sampling tubes containing Tenax TA are suitable for sampling of 2,3-pentanedione, but require analysis within one month;

• Due to issues with storage stability, the use of sampling tubes containing Chromosorb 106 is not suitable for sampling of 2,3-pentanedione;

• The presence of water and acetic acid does not adversely affect storage stability of either diacetyl or 2,3-pentanedione;

• For pumped (active) samples, Tenax TA has a safe sampling volume of 3-litres for diacetyl. The maximum sampling time for pumped samples at a flow rate of 100 ml.min-1 is therefore 30 minutes. If the flow rate is reduced to 25 ml.min-1 the maximum sampling time is 120 minutes. The safe sampling volume for 2,3-pentanedione on Tenax TA is more than 24-litres;

• Diffusive uptake rates for diacetyl and 2,3-pentanedione have been obtained for Tenax TA over sampling periods of 1 to 8 hours.

• For longer term sampling, in particular personal samples, diffusive (passive) sampling is the preferred option. However, for measurement of peak concentrations or compliance with short term exposure limits (STELs), pumped sampling is the better option, both to retain sensitivity and because diffusive sampling is not recommended for sampling time of less than 15 minutes (HSE, 2016).

• Analysis using gas chromatography-mass spectrometry (GC-MS) gives better sensitivity and selectivity than gas chromatography with flame ionisation detection (GC-FID), but either may be used;

• In order to retain optimum levels of precision with analysis by GC-MS, it is recommended to use an internal standard; deuterated toluene has been found to be suitable for this purpose.

• Typical limits of detection, as a collected mass, for diacetyl and 2,3-pentanedione collected on Tenax TA and analysed by thermal desorption and GC-MS are 0.2 ng and 0.1 ng respectively.

• Limits of detection for airborne concentrations are dependent on the sampling mode (pumped or diffusive) and time, but for a full shift (8-hour) diffusive sample these mass-based limits of detection would equate to airborne concentrations of around 0.3 ppb for diacetyl and 0.1 ppb for 2,3-pentanedione (or less than 1/50th of the proposed long-term time weighted average (TWA) personal exposure limits for the two compounds).

• In addition, the TD based method can also be used to identify and, if required, quantify other volatile organic components that may be present in the work environment.

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6 REFERENCES

European Commission. Scientific Committee on Occupational Exposure Limits. (2014). Recommendation from the Scientific Committee on Occupational Exposure Limits for Diacetyl. SCOEL/SUM/149. [pdf] Available at http://ec.europa.eu/social/BlobServlet?docId=6511 (Accessed 8 August 2018). Health and Safety Executive. (2016). Volatile Organic Compounds in Air: Laboratory method using sorbent tubes, solvent desorption or thermal desorption and gas chromatography. Methods for the Determination of Hazardous Substances, MDHS 104. [pdf] Available at http://www.hse.gov.uk/pubns/mdhs/pdfs/mdhs104.pdf (Accessed 8 August 2018).

Kreiss, K., Gomaa, A., Kullman, G., Fedan, K., Simoes, E. and Enright, P. (2002). Clinical bronchiolitis obliterans in workers at a microwave-popcorn plant. New England Journal of Medicine, 347(5), pp.330–338.

LeBouf, R. and Simmons, M. (2017) Increased sensitivity of OSHA method analysis of diacetyl and 2,3-pentanedione in air. Journal of Occupational and Environmental Hygiene, 14(5), pp.343-348.

National Institute for Occupational Safety and Health. (2003). Diacetyl. NIOSH Manual of Analytical Methods. 4th ed. Method 2557. [pdf] Available at http://www.cdc.gov/niosh/docs/2003-154/pdfs/2557.pdf (Accessed 8 August 2018).

National Institute for Occupational Safety and Health. (2003). Preventing lung disease in workers who use or make flavorings. NIOSH Alert, DHHS (NIOSH) Publication No. 2004–110. [pdf] Available at https://www.cdc.gov/niosh/docs/2004-110/pdfs/2004-110.pdf?id=10.26616/NIOSHPUB2004110 (Accessed 8 August 2018).

National Institute for Occupational Safety and Health. (2011). Criteria for a recommended standard: occupational exposure to diacetyl and 2,3-pentanedione. (External review draft). [pdf] Available at http://www.cdc.gov/niosh/docket/archive/pdfs/NIOSH-245/0245-081211-draftdocument.pdf (Accessed 8 August 2018). National Institute for Occupational Safety and Health. (2015). Best practices: engineering controls, work practices and exposure monitoring for occupational exposures to diacetyl and 2,3-pentanedione. DHHS (NIOSH) Publication No. 2015-197. [pdf] Available at http://www.cdc.gov/niosh/docs/2015-197/pdfs/2015-197.pdf (Accessed 8 August 2018).

National Institute for Occupational Safety and Health. (2016). Flavorings related lung disease: coffee making facilities. [Online] Available at http://www.cdc.gov/niosh/topics/flavorings/processing.html (Accessed 8 August 2018).

National Institute for Occupational Safety and Health. (2016). Criteria for a recommended standard: occupational exposure to diacetyl and 2,3-pentanedione. DHHS (NIOSH) Publication No. 2016-111. [pdf] Available at http://www.cdc.gov/niosh/docs/2016-111/pdfs/2016-111-all.pdf (Accessed 8 August 2018). Occupational Safety and Health Administration. (2006). Diacetyl. Method PV2118. [Online] Available at http://www.osha.gov/dts/sltc/methods/partial/t-pv2118/t-pv2118.html (Accessed 8 August 2018).

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Occupational Safety and Health Administration. (2007). Diacetyl and food flavoring containing diacetyl. Stakeholder Meeting, Arlington, Virginia, 17 October 2007. Meeting Summary Report. [Online] Available at http://www.osha.gov/dsg/guidance/101707-diacetyl-meeting-notes.html (Accessed 8 August 2018).

Occupational Safety and Health Administration. (2008). Acetoin/Diacetyl [0.05ppm detection limit]. Method 1012. [Online] Available at http://www.osha.gov/dts/sltc/methods/validated/1012/1012.html (Accessed 8 August 2018).

Occupational Safety and Health Administration. (2008). Acetoin/Diacetyl [0.5 ppm detection limit]. Method 1013. [Online] Available at http://www.osha.gov/dts/sltc/methods/validated/1013/1013.html (Accessed 8 August 2018).

Occupational Safety and Health Administration. (2010). 2,3-Pentanedione [0.5 ppm detection limit]. Method 1016. [Online] Available at http://www.osha.gov/dts/sltc/methods/validated/1016/1016.html (Accessed 8 August 2018).

Sandys, V., Smith, G., Shah, P. and Pengelly, I. (2014). The occupational hygiene implications of the use of diacetyl in the food flavouring and fragrance industries. Research Report RR1021. [Online] Health and Safety Executive. Available at http://www.hse.gov.uk/research/rrhtm/rr1021.htm (Accessed 8 August 2018).

Vandendriessche, S., Griepink, B., Hollander, J., Gielen, J., Langelaan, F., Saunders, K. and Brown, R. (1991) Certification of a reference material for aromatic hydrocarbons in Tenax samplers. Analyst, [Online] Volume 116, pp. 437-441. Available at http://pubs.rsc.org/en/Content/ArticleLanding/1991/AN/AN9911600437#!divAbstract (Accessed 8 August 2018).

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7 APPENDICES

7.1 APPENDIX 1 – STORAGE STABILITY

Figure A1.1: Storage Stability of Diacetyl on Chromosorb 106

Figure A1.2: Storage Stability of Diacetyl on Tenax TA (Initial Storage Trial)

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Figure A1.3: Storage Stability of Diacetyl on Tenax TA (Second Storage Trial)

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7.2 APPENDIX 2 – BREAKTHROUGH

Figure A2.1: Breakthrough of Diacetyl on Pumped Sorbent Tubes (Test 1)

Figure A2.2: Breakthrough of Diacetyl on Pumped Sorbent Tubes (Test 2)

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Figure A2.3: Breakthrough of 2,3-Pentanedione on Pumped Sorbent Tubes (Test 2)

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7.3 APPENDIX 3 – EFFECT OF RELATIVE HUMDITY

Figure A3.1: Effect of Relative Humidity on Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on to Tenax TA

Figure A3.2: Effect of Relative Humidity on Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on to Chromosorb 106

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7.4 APPENDIX 4 – EFFECT OF THE PRESENCE OF ACETIC ACID

Figure A4.1: Effect of Acetic Acid (750 ng) on the Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on Tenax TA

Figure A4.2: Effect of Acetic Acid (7500 ng) on the Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on Tenax TA

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Figure A4.3: Effect of Acetic Acid (750 ng) on the Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on Chromosorb 106

Figure A4.4: Effect of Acetic Acid (7500 ng) on the Storage Stability of Diacetyl and 2,3-Pentanedione Sampled on Chromosorb 106

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Published by the Health & Safety Executive 08/18

Validation of a measurement method for diacetyl using sorbent tubes and thermal desorption

RR1138

www.hse.gov.uk

Diacetyl, also known as 2,3-butanedione, and the closely related chemical 2,3-pentanedione, are naturally occurring substances with a characteristic butter-like odour found in foods such as dairy products, beer and fruits. Diacetyl is also added to various food products as artificial butter flavouring and both substances are present in emissions generated by coffee roasting and grinding. Occupational levels of diacetyl exposure has been linked with the lung disease bronchiolitis obliterans which is life threatening and irreversible. In Great Britain, occupational exposure limits to protect workers’ health are based on recommendations from SCOEL (the European Commission Scientific Committee on Occupational Exposure Limits). SCOEL has recommended introducing an 8-hour time weighted average occupational exposure limit for diacetyl of 20 ppb and a short term exposure limit (STEL) of 100 ppb. Existing scientific measurement methods lack the necessary sensitivity to measure these levels of exposure.

This report describes a new sensitive method for measurement of diacetyl based on the use of thermal desorption tubes for sampling and gas chromatography-mass spectrometry for analysis. The samplers may be used in either pumped (active) or diffusive (passive) mode. For measurement of short duration peak concentrations, or determining compliance with the STEL, pumped sampling is most effective. For longer sampling periods, in particular whole shift monitoring, diffusive sampling is preferable. This method is also applicable to 2,3-pentanedione.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.