Since 1989, work by Dr. K. Grob and M. Biedermann (Official Food Control Authority of the Canton of Zürich), has demonstrated the existance of mineral oil contamination in food. The source of contamination is multiple and includes storage and transportation bags, food processing tools and lubricating oil, packaging material including cardboard made from recycled paper

Introduction

The MOSH-MOAH (1) application requires a simple extraction of food stuff or packaging material. Depend-ing on the sample type the extraction is performed within 2 hours or overnight. The resulting extract is directly injected onto a normal phase HPLC system. After separation a fraction is transferred to the GC by large volume on-column in-jection technique (2). A backflush is then performed to remove the FAT and other unwanted compounds. The whole process is controled by a dedicated combination of software and hardware.

Instrumentation

The instrument includes the PAL autosampler (CTC Analytics, Zwingen, Switzerland), the Phoenix 40 LC syringe pump and Trace Ultra GC (Thermo Scientific, Milan, Italy) UV detector (JASCO, Japan) and data system (Brechbühler AG, Schlieren, Switzerland). The Trace GC includes an on-column injector modified for the Y interface as described by M. Biedemann (3). The transfer is controlled by a transfer valve. The LC part (figure 2) includes an injection valve, backflush valve, (optional) switching valve and a trans-fer valve. The LC signal can be controlled by using a UV detector set at 230nm to ensure a correct separation as well as the transfer of the correct fraction.

Figure 1: LC-GC Instrument

The instrument is setup for automated operation.

Figure 2: LC configuration

Mineral oil determinationin food and food packaging

by LC-GC couplingPhilippe Mottay, Urs Hofstetter, Peter Pichler Brechbühler AG Steinwiessen strasse 3, Ch-8952 Schlieren Switzerland

Sample preparation

The sample preparation depends on the sample type. The simplest one is for cardboard. After weighting 1 g of sample, 10ml of a 1:1 Hexane:Ethanol is added to the sample. Then 20µl of internal standard is added. The sample is let to stand for 2 hoursAfter 2 hours, 5ml of the extract are placed into a 15ml centrifuge tube. The tube is then filled with water and centrifuged for 5 min. The upper layer is transfer to the 2ml vial and placed on the autosampler,

Results

Low level in food

The recommended MOSH detection limit is to be 0.6mg/kg (ppm) food (4). This is easilly achieve since the complete fraction is transferred. Also a reconcen-tration step can be performed to boost the sensitivity.The example below show a rice sample at 0.25mg/kg of MOSH. This is far from the detection limit that can be achieved

Conclusion

Brechbühler AG designed the LC-GC according to the specification of Dr. Koni Grob and Maurus Bieder-mann. The direct Y interface coupled with the Trace on column large volume injection allows the injection of the full fraction yielding to sensitivity allowing for the detection limits required by the MOSH MOAH meth-od. The multi transfer feature allows for analyzing both MOSH and MOAH fraction with a single LC analysis preserving the LC column. Because of the FID no lengthy calibration is needed. Brechbühler also invest-ed in understanding both the technique and the method so that we can support our customer on both fronts.

Acknowledgements: The authors wish to thanks Mr. Maurus Biedermann and Dr Koni Grob from the Of-ficial Food Control Authority of the Canton of Zürich for their valuable support. Contacts:Philippe Mottay: philippemottay@brechbuehler.chUrs Hofstetter: urshofstetter@brechbuehler.chPeter Pichler: peterpichler@brechbuehler.ch(1) Aromatic hydrocarbons of mineral oil origin in foods: method for determining the total concentration and first results M. Biedermann, K. Fiselier and K. Grob, J.

Agric. Food Chem. 57 (2009) 8711-8721(2) Konrad Grob Development of the transfer techniques for on-line high perform-ance liquid chromatography-capillary gasChromatography, Journal of Chromatography A, 703 (1995) 265-276 (3) Biedermann, M.; Grob, K. The Y-piece interface for on-line coupled HPLC-GC. J. Chromatogr., A 2009, in press.(4) Maurus Biedermann, Yoko Uematsu and Koni Grob, Mineral Oil Contents in Paper and Board Recycled to Paperboard for Food Packaging; Packag. Technol.

Sci. 2011; 24: 61–73

Figure 3: MOSH and MOAH Results from recycled cardboard. From top to bottom: LC trace with the 2 fractions GC of the MOSH fraction GC of the MOAH Fraction

LC Column: Luna 5u Silica (2) 100A 250x2.0mm Phenomenex P/N 00G-4274-B0GC Column: Zebron ZB-5 15m L x 0.25mm ID x 0.25µm df - 5% Phenyl, 95% Dimethylpolysiloxane Phenomenex P/N 7EG-G002-11

Figure 4: Low level of MOSH (0.24mg/kg) in rice