a versatile robotic arm for static headspace sampling...

1LC•GC Europe - April 2001 coupling matters

IntroductionDynamic and static headspace samplingare complementary techniques. Whencarefully designed to work together, theycan cover a wide range of components,from volatiles to semi-volatiles to highboilers, which is of utmost importance inthe analyses of complex mixtures, such asbiogenic emissions. Biological material,whether plant or animal, under normal,abiotic or biotic stress conditions, emits aspectrum of components that can be usedto characterize it and/or its reactions toenvironmental changes. The emittedcomponents can range from volatiles, suchas ethylene (1), to semi-volatiles, such asesters, alcohols, terpenes (2) andisothiocyanates (3–5), to high boilingsolutes, such as sterols and long-chain fattyacids (2). The wider the range ofcomponents that an analytical method cancover, the more nearly complete is theemission profile that can be established.This information is of vital importance inbiotechnology.

Dynamic headspace sampling based onadsorption or sorption, followed bythermal desorption, has proved to be avery efficient way to collect andconcentrate trace amounts of volatilecomponents emitted by biologicalmaterials (1, 3). The number ofcomponents that can be enriched dependson the (ad)sorbent used. By using asorbent such as polydimethylsiloxane(PDMS), volatiles, semi-volatiles and highboiling components can be enriched by

operating in the breakthrough (6, 7) orequilibrium (8) mode, and analysed.

Solid-phase microextraction (SPME),although less sensitive than dynamicheadspace sampling, has proved to be apowerful static sampling technique for semi-volatile compounds (9). By careful selectionof the type and thickness of the fibre, therange of compounds applicable can beextended to volatiles (PDMS/Carboxen fibre)or high boiling solutes (7 µm PDMS fibre).Systems for automated SPME arecommercially available, such as the FocusRobotic Sample Processor (ATAS

International BV, Veldhoven, TheNetherlands) (Figure 1(a)), the Varian 8200CX AutoSampler (Varian, Palo Alto,California, USA) (Figure 1(b)) and theGerstel Multi Purpose Sampler MPS-3(Gerstel, Mülheim a/d Ruhr, Germany)(Figure 1(c)). These devices, however, canonly employ specifically designed samplingvials. The vials must also be placed in aholder fixed on top of the gaschromatograph (GC). This limitation iscritical in the analysis of biogenicemissions; sampling units have differentsizes and shapes and are sometimes placed

A robotic arm was constructed to automate static headspace sampling using solid-phase microextraction (SPME). Thereason for its construction was to accommodate sampling units with different sizes, irregular shapes and located farfrom the capillary gas chromatograph. Its modular design enables easy modification and extension, and its controlprogram was conveniently compiled using the master IsaGRAF software. Operation of the robotic arm was found tobe very reliable and user-friendly. Several applications illustrate the performance of the robotic arm for static headspace sampling.

H. Pham-Tuan, J. Vercammen and P. Sandra, Department of Organic Chemistry, Ghent University, Belgium.

A Versatile Robotic Arm forStatic Headspace Samplingwith SPME

Figure 1: Several commercially available automatic samplers with SPME option: (a) ATAS FocusRobotic Sample Processor, (b) Varian 8200 CX AutoSampler, (c) Gerstel Multi Purpose SamplerMPS-3, (d) robotic arm constructed in our laboratory.

(b)(a)

(d)(c)

LC•GC Europe - April 20012 coupling matters

far from the GC in order to keep thesamples under controlled conditions. Therobotic arm constructed in our laboratory(Figure 1(d)) successfully addresses theserequirements.

ExperimentalComponents for robotic arm construction: The following componentswere purchased from Festo NV (Brussels,Belgium):• a 1300 mm linear pneumatic drive shaft

for horizontal movement of the SPMEdevice

• a 300 mm linear drive shaft for verticalmovement of the SPME needle

• a 20 mm linear two-directional cylinderfor movement of the fibre

• corresponding adapters, positionsensors, a gas manometer, a filter,tubings and connectors

• a control unit consisting of a FunctionElectronic Controller (FEC) and a multiplepneumatic valve block

• programming software — IsaGRAF (FECWorkbench, Version 3.21 F, CJ Internationalcopyright owner) from Festo NV(Brussels, Belgium) with fiveprogramming languages: SFC(Sequential Function Chart), FBD(Function Block Diagram), LD (LadderDiagram), ST (Structured Text) and IL(Instruction List).The total cost for instruments was

approximately €5000.Gas chromatographic instrumentation:The GC–MSD (mass selective detector)system from Agilent Technologies (Little

Falls, Delaware, USA) consists of an HP 6890GC and an HP 5973 MSD. The GC is alsoequipped with a flame ionization detector(FID). The front inlet is a split/splitlessinjector equipped with a 0.75 mm i.d. linerfor SPME injections. The rear inlet is anautomated thermal desorption system(TDSG) in combination with a programmedtemperature vaporization inlet (PTV 4) fordynamic sampling (Gerstel, Mülheim a/dRuhr, Germany) (1). Two identical 30 m �250 µm i.d. � 0.25 µm df HP-5 MS(Agilent Technologies) were used toconnect the inlets to the MSD and FID,respectively.

A standard SPME unit, that is, an SPMEholder and a set of PDMS and procainamide(PA) fibres, was purchased from Supelco(Bellefonte, Pennsylvania, USA).

Robotic Arm ConstructionThe robotic arm was constructed from theordered parts in a modular design (Figure 2).This “Lego”-type construction provides the

Figure 2: Construction of the robotic arm: (a) overview; (b) schematic, front view; (c) schematic, side view. 1 � horizontal drive shaft, 2 � verticaldrive shaft, 3 � cylinder, 4 � SPME unit attached, 5 � robotic arm leg, 6 � adapter to the GC, 7 � sampling unit, 8 � TDSG dynamic sampling,9 � GC, 10 � clean air supply.

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2 1

(a)

(b)

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“SPME…has provedto be a powerful static sampling technique.”


ability to modify and extend the set-up fordifferent requirements in size, shape andlocation of the sampling units.

Festo provided an adapter for thevertical drive shaft to mount on thehorizontal one, which in turn wasmounted on legs to ensure a stableposition during operation. The entiresystem was further fixed towards the GCwith a simple adapter (Figure 2, partnumber 6), which was made in ourdepartment workshop. This adapterensures that the SPME needle is placedexactly above the split/splitless injector. Afew other parts were made “in-house.”One of these was the adapter for thecylinder (Figure 2, part number 3) tomount on the vertical drive shaft. Thesecond one was the SPME unit holder andneedle guide (Figure 3).

A very important modification to theSPME needle was also made. The flatsquare tip of the needle was brushed to asharp point (Figure 4). This enabled theneedle to pierce the non-prepierced septaeasily. Utmost care should be taken duringbrushing so that no metal scrap is leftinside the needle tip as this could scratchthe fibre during subsequent operation. Theinner edge of the needle tip was,therefore, smoothly brushed using a microreamer. A scratched fibre can be detectedby regular visual inspection and by anexceptionally high signal of thedegradation products from the fibrematerial. With a PDMS fibre this isrepresented by the typical siloxaneoligomer peaks. SPME needles made in this way have been used for over 100injections without any visible damage.

Compiling the Controlling ProgramUsing the master IsaGRAF software, aprogram to operate the robotic arm waseasily compiled. The program was firstdownloaded to the FEC box. From thispoint there are two options, namely runthe program from a PC, which proved tobe very convenient during thedevelopment stage with programmabletime intervals between commands, or runthe downloaded program from a stand-alone FEC. This is designed for routineanalysis, when only sampling time andnumber of runs in a batch can be changedon the FEC timer.

The first step in compiling the program is todefine input and output parameters (Table 1).

The controlling program consists of threelevels as shown in Figure 5. The first, mainlevel takes care of a safety measure byengaging the emergency stop function.When the EMER. STOP button is pressed,

Figure 3: Mounting of the SPME device on the robotic arm: (a) schematic, front view;(b) schematic, side view; (c) overview. 1 � Adapter for the cylinder to mount on the verticaldrive shaft, 2 � cylinder for the SPME fibre movement, 3 � vertical drive shaft, 4 � SPMEdevice, 5 � SPME holder on the vertical drive shaft, 6 � SPME needle guide.

1

2

3

4

5

6

(a) (b) (c)

Figure 4: Modification of the SPME needle: (a) standard needle, (b) sharpened needle. 1 � septum piercing needle, 2 � fibre attachment metal tubing, 3 � coated fused-silica fibre,4 � smoothly reamed inner edge of the needle.

4321

(a)

(b)

Figure 5: Sample pop-up windows of IsaGRAF software for compiling the robotic armcontrolling program.


the run is terminated and the vertical driveshaft lifts the SPME device to the upperposition after withdrawing the fibre intothe needle. The robotic arm cannotoperate again unless the emergency stopbutton is released.

In the second level, a child programguards the stop/pause function of the arm.Whenever the STOP/PAUSE button ispressed the run is temporarily suspended,the SPME device remains at the sameposition and the timer of the FEC stopscounting. The run can be resumed bypressing the START button.

The real operational program is actually a child subprogram placed on thethird level. At this level all the parameters,such as sampling time, injection time,waiting time between movements, gettingthe input signals from the position sensorsand sending corresponding outputcommands, are integrated. Steps can beeasily added to or subtracted from therobotic arm controlling program. Moreover,time parameters can also be readilymodified rendering the operation of therobotic arm highly flexible should it be rundirectly from the computer. The programcan also be downloaded to the FEC from which the arm is operated withoutthe aid of the computer. Now only thesampling time and the number of runs in a batch can be changed on the timer of the FEC.

Compiling the program proved to bequite easy, even for an analytical chemistwith no previous knowledge in computerprogramming languages.

ApplicationsThe goal of the robotic arm was toaccommodate different sampling units, asneeded, for example, when housing thebiological materials for biogenic emissionanalysis. This goal was fulfilled and therobotic arm proved to be highly versatile inthis respect. Different sampling units weresuccessfully incorporated into the set-up asshown in Figure 6. Some applications arepresented.Simultaneous dynamic and staticheadspace analysis of a floweringjasmine plant: The sampling unit used inthis experiment was the “in-flow”chamber shown in Figure 6(a). A floweringjasmine plant was placed into the glassbulb, which was fixed and gas-tightsecured with a glass plate and a clamp. Adetailed arrangement was describedelsewhere (1). A flow of 50 mL/min ofmoisturized N 50 clean air (Air Liquid,Schelle, Belgium) was fed into the bulb.The gas flow was then led to the TDSG

Table 1: Definitions of the Input and Output Parameters of the Robotic Arm Controlling Program.

Name Attribute FALSE TRUE Comment

Xr Input off on I 0.0-horizontal drive right sensor X0

Xl Input off on I 0.1-horizontal drive left sensor X1

Yup Input off on I 0.2-vertical drive sensor for drawn uppositon Y0

Ydown Input off on I 0.3-vertical drive sensor for push downposition Y1

Zup Input off on I 0.4-cylinder upper sensor Z0

Zdown Input off on I 0.5-cylinder lower sensor Z1

Input0_6 Input I 0.6-free

batch Input off on I 0.7-from the batch counter of the timer

start Input standby running I 1.0-start knob

stop Input on off I 1.1-stop knob

emer_stop Input off on I 1.2-emergency stop

timer Input off on I 1.3-from the timer output

Z Output off on O 0.0-cylinder

Y Output off on O 0.1-vertical drive ventil

Xright Output off on O 0.2-horizontal drive to the right

Xleft Output off on O 0.3-horizontal drive to the left

GCstart Output off on O 0.4-remote start the GC

reset Output off on O 0.5-reset input of the timer

signalst Output off on O 0.6-to signal input of timer

batchres Output off on O 0.7-to reset batch counter of the timer

Figure 6: Examples of the sampling units the robotic arm can accommodate: (a) “in-flow”chamber for simultaneous dynamic and static headspace sampling, (b) “regular” vial tray usinga simple fraction collector, (c) glass bottles for aseptic cultured plants, (d) portable greenhouse.

(a) (b)

(c) (d)


dynamic sampling device (1) via the “in-flow” chamber. In this chamber the SPMEsampling takes place.

In order to synchronize the robotic armoperation with the TDSG unit, the task ofgiving a remote start signal to the GC wasleft to the TDSG. The robotic arm wasprogrammed to run continuously with 35 min cycles; that is, 30 min sampling and5 min desorption/injection. The TDSG andGC were also programmed to perform a 35 min cycle, in this instance consisting of10 min TDSG sampling, TDS desorption andGC start. The degree of synchronization canbe further improved by employing theremaining free input (Input0_6) (Table 1)for an external event signal from the GC.The GC can send this signal immediatelyafter its run is started by the TDSG unit.After completing the SPME sampling time,the robotic arm would wait for this signalto start injection. The compounds collectedvia TDSG were detected with the FID.SPME injection was fed to the MSD.Corresponding chromatograms are shownin Figure 7. Table 2 lists the componentsidentified by library search.Automatic SPME injections using a simplefraction collector as the sample vial tray:The robotic arm can also operate as anSPME autosampler. For this function a7000 Ultrorac Fraction Collector (LKB,Bromma, Sweden) was used as the samplevial tray (Figure 6(b)). The 7000 Ultroracwas chosen because it moves the tubingracks instead of the drop head, which iscommon in many other fraction collectors.The 7000 Ultrorac can thus deliver the vials to a fixed sampling point of therobotic SPME autosampler in a timelymanner. In order to synchronize itsoperation with the robotic arm, thestepping time of the fraction collector wasset to coincide with the total cycle time,that is, sampling time plus injection timeand moving time, of the robotic SPMEdevice. The synchronization could alsohave been performed using the remainingfree input signal of the FEC, but for thesake of simplicity, the operation of thefraction collector was left independent.Headspace SPME analysis of several“special” Belgian beers and fruit teas wasperformed using this instrumental set-up.Portions of each beer (2 mL) weretransferred to 8 mL screw-cap vials (AlltechAssociates Inc., Deerfield, Illinois, USA),which were placed into the rack of thefraction collector. A few empty vials werealso placed randomly among the beersample vials to check the blank andcompleteness of the SPME injections. Nocarryover was found on the series of

Figure 7: Simultaneous analyses of a flowering jasmine plant by (a) static (robotic SPME) and(b) dynamic (on-line thermal desorption unit) headspace sampling. (a) Robotic arm SPME, polyacrylate fibre, 30 min sampling; MSD scan 50–550 amu; TIC scale 5 � 106. (b) On-lineTDSG – polydimethylsiloxane (PDMS) tube, 10 min at 20 °C and 50 mL/min; FID signal scale 5 � 105. Components: Table 2.

0 5 10 15

123

4

5 68

7

910

1112

13

14

15

16

17

18

19

20

21 22

(a)

(b)

Time (min)

Table 2: Peak Identification for the Jasmine Plant Analysis Using the RoboticSPME–GCMSD.

Peak Compound Peak Compound

1 3-hexenyl acetate 12 benzyl isocyanide

2 2-hexenyl acetate 13 phenethyl acetate

3 benzyl alcohol 14 2-methylbenzylalcohol

4 benzyl acetaldehyde 15 eugenol

5 methylphenol 16 �-carvone

6 linalool 17 methyl cinnamate

7 benzeneacetonitrile 18 isoeugenol 1

8 benzylacetate 19 trans-caryophyllene

9 cis-3-hexenyl butyrate 20 isoeugenol 2

10 2-methoxy-4-methylphenol 21 3-hexenyl benzoate

11 cis-3-hexenyl-2-methylbutanoate 22 benzophenone

“Compiling the program proved to be quite easy.”


robotic injections. Each beer was analysedthree times. The reproducibility of theanalysis was determined using the peakareas of several characteristic peaks of theprofiles. Relative standard deviations in therange of 5–8%, typical for SPME analysis,were found. Figure 8 shows the headspaceprofiles of the beers analysed in thisexperiment. Identified components arelisted in Table 3.

The “regular” beers, such as Jupiler andGulden Draak, do not exhibit any specialtaste. This corresponds to similarheadspace profiles with ethyl esterhomologues of saturated acids.Alternatively, the taste of “special” beerscould be assigned to monoterpenes andmonoterpenoids (Timmermans ‘Peche’),and sesquiterpenes and sesquiterpenoids(St Bernardus and Mort Subite Framboise)in their headspace profiles. The unique

flavour of these speciality beers originatesfrom plant essential oils.

Teas were made in the normal way and2 mL portions were taken for analysis in amanner similar to that described for thebeer samples. Headspace profiles areshown in Figure 9 and identifiedcomponents are summarized in Table 4.

ConclusionThe robotic arm constructed in-house as anautomation tool for SPME sampling hasshown several features: versatility,reliability, easy set-up and control, easyextension and modification, and low initialand operational costs. The majoradvantage of this robotic arm overcommercially available autosamplers is itsability to accommodate sampling unitswith different sizes, irregular shapes andlocated far from the GC instrument. This

feature is vital in biogenic emissionanalysis. Based on this construction, otherdevices for static sampling techniques canbe mounted and automated. Only slightmodifications are required.

AcknowledgementsWe thank Ghent University for supportingthis work through grant GOA 12.0518.98.Joeri Vercammen thanks the FlemishInstitute for the Promotion of Scientific andTechnological Research in the Industry(IWT), Flanders, Belgium, for a study grant.

Further InformationFor more information about the roboticarm controlling program, please contactthe authors at Dept. of Organic Chemistry,Ghent University, Krijgslaan 281/S4, B-9000 Ghent, Belgium or fax +32 9 264 49 98.

Figure 8: Headspace profiles of Belgian “special” beers analysed by the robotic SPME. (a) Blank, (b) Juliper, (c) St-Bernadus, (d) Gulden draak, (e) Timmermans “Peche”, (f) Mort subite Framboise. Conditions: 100 µm PDMS fibre, 30 min sampling; MSD scan 50–550 amu; TIC time scale0–15 min; the grey vertical lines indicate the change in the TIC abundance scale from 1 to 5 � 106; GC oven: 40 °C (2 min) to 280 °C (5 min) at15 °C/min; splitless time 2 min; He carrier gas at 35 cm/s constant flow.

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References(1) H. Pham-Tuan et al., J. Chromatogr. A, 868,

249–259 (2000).(2) C.S. Charron, D.J. Cantliffe and R.R. Heath,

Hortic. Rev., 17, 43–72 (1995).(3) J. Vercammen et al., in Proc. 23rd Int. Symp.

Capillary Chrom., P. Sandra and A.J. Rackstraw,Eds, (Riva del Garda, Italy, 5–10 June, 2000,CD-ROM, I.O.P.M.S. vzw, Kortrijk, Belgium), J. Chromatogr. A, in print.

(4) K.J. Doughty et al., Phytochemistry, 43(2),

371–374 (1996).(5) L. Tollsten and G. Bergdtröm, Phytochemistry,

27(12), 4013–4018 (1998).(6) J. Vercammen et al., J. High Resolut.

Chromatogr., in print.(7) E. Baltussen et al., J. High Resolut. Chromatogr.,

21, 332–340 (1998).(8) E. Baltussen et al., Anal. Chem., 71, 5193–5199

(1999).(9) J. Pawliszyn, Solid Phase Microextraction: Theory

and Practice (Wiley-VCH Inc., 1997), 247.

Pham-Tuan Hai was a postdoctoralresearcher at Ghent University. Hepresently works for Unilever,Vlaardingen, The Netherlands. JoeriVercammen is a PhD student at GhentUniversity. Pat Sandra is a professor inseparation sciences at both GhentUniversity and the University ofStellenbosch, South Africa.

Figure 9: Headspace profiles of several fruity teas analysed by the robotic SPME. (a) Strawberry, (b) citrus, (c) passion (d) cherry, (e) forest fruits, (f) tropical, (g) peach, (h) melon. Conditions: 100 µm PDMS fibre, 30 min sampling; MSD scan 50–550 amu; TIC time scale 0–15 min; abundancescale 5 � 106; GC oven: 40 °C (2 min) to 280 °C (5 min) at 15 °C/min; splitless time 2 min; He carrier gas at 35 cm/s constant flow.

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(g)

(b)

(d)

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Time (min)

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S PDMS degradationproducts

1 ethyl acetate

2 3-methyl-1-butanol

3 2-methyl-1-butanol

4 ethyl butanoate

5 isoamyl acetate

6 styrene

7 ethyl methylpentanoate

8 �-myrcene

9 ethyl hexanoate

10 hexyl acetate

11 limonene

12 ethyl methylhexanoate

13 ethyl heptanoate

14 phenethyl alcohol

15 octanoic acid

16 ethyl benzoate

17 ethyl octanoate

18 ethyl benzeneacetate

19 2-phenylethyl acetate

20 ethyl nonanoate

21 4-vinyl-2-methoxy-phenol

22 ethyl 9-decenoate

23 ethyl decanoate

24 3-methylbutyl octanoate

25 perolidol

26 ethyl dodecanoate

27 ethyl tetradecanoate

28 phthalate

29 ethyl hexadecanoate

30 isobutyl acetate

31 2-methylbutyl acetate

32 ethyl 2-methyl-2-butenoate

33 heptyl acetate

34 ethyl methylheptanoate

35 octyl acetate

36 isobutyl octanoate

37 decyl acetate

38 caryophyllene

39 �-humulene

40 �-selinene

41 �-selinene

42 �-selinene

43 �-amorphene

44 �-cadinene

45 2-methylethyl butanoate

46 3-methylethyl butanoate

47 2-heptanone

48 benzaldehyde

49 3-hexenyl acetate

50 2-hexenyl acetate

51 p-cymene

52 ocimene

53 �-terpinene

54 �-terpinolene

55 linalool

56 linolyl acetate

57 butanedioic acid,diethylester

58 ethylguaiacol

59 �-imene

60 5-pentyldihydro-2(3H)-furanone

61 dihydro-�-ionone

62 5-hexyldihydro-2(3H)furanone

63 1,1,4,7-tetramethyl-indane

64 menthadiene

65 �-cedrene

66 �-ionone

67 methyl-�-ionone

68 di-t-butyl phenol

69 2-methyl-2, 6-di-t-butylphenol

70 methyl-�-ionone

71 �-isomethylionone

72 �-cedrol

73 aromadendrene

Table 3: Identification of the Components Detected in Beers’ Headspace.

Peak Compound Peak Compound Peak Compound Peak Compound

S PDMS degradationproduct

1 ethyl butanoate

2 ethyl 2-methylbutanoate

3 3-hexenol

4 3-methyl-1-butanol,acetate

5 3-hexenyl acetate

6 hexyl formate

7 ethyl 2,3-dimethyl-butanoate

8 ethyl hexanoate

9 2-hexenyl acetate

10 hexyl acetate

11 isoamyl butyrate

12 2-nonanone

13 isoamyl isovalerate

14 neronine

15 benzyl acetate

16 cis-3-hexenyl butyrate

17 ethyl 2, 4-dimethyl-3-furancarboxylate

18 methyl salicylate

19 cis-3-hexenyl-2methylbutanoate

20 3-hexenyl hexanoate

21 cinnamic acid, methylester

22 5-hexyldihydro-2(3H)-furanone propanoicacid, 2-methyl-1-(1,1

23 -dimethylethyl)-2methyl-1, 3-propanediylester

24 phthalate

25 phthalate

26 �-thujene

27 �-pinene

28 camphene

29 �-pinene

30 �-myrcene

31 phellandrene

32 �-terpinene

33 limonene

34 �-ocimene

35 �-terpinene

36 �-terpinolene

37 linalool

38 4,8-dimethyl nonatricene

39 isomenthone

40 3-phenethyl alcohol

41 decanol

42 Z-citral

43 �-carene

44 E-citral

45 undecanol

46 citronellyl acetate

47 neryl acetate

48 �-copaene

49 �-cubebene

50 cyclododecanol

51 2-(methylamino)-benzoic acid, methylester

52 trans-caryophyllene

53 �-humulene

54 valencene

55 �-lisabonene

56 �-cadinene

57 2-phenylethyl acetate

58 ethyl decanoate

59 ethyl dodecanoate

60 isobutyl acetate

61 isobutyl butyrate

62 benzaldehyde

63 ethyl octanoate

64 citronellyl formate

65 ethyl nonanoate

66 �-ionone

67 4-heptyldihydro-(3H)-furanone

68 3-methylbutyl butanoate

69 dihydro-�-ionone

70 muskolactone

71 butyl acetate

72 selinene

73 2-propenyl hexanoate

74 linalyl isobutyrate

75 hexyl hexanoate

76 cis-caryophyllene

77 octyldihydro-2(3H)-furanone

78 2-heptanone

79 4-methyl-2-isopropyl thiazole

80 dihydrolinalool

81 menthone

82 cis-3-hexenyl isobutyrate

83 cyclopropylpentane

84 trans-anethole

85 geranyl acetate

86 �-damascenone

87 2-methyl-1-butanol,acetate

88 pentyl propanoate

89 linalyl acetate

90 isopeulegyl acetate

91 dihydrocarvyl acetate

92 benzyl benzoate

Table 4: Identification of the Components Detected in Fruity Teas’ Headspace.

Peak Compound Peak Compound Peak Compound Peak Compoun

a versatile robotic arm for static headspace sampling...

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