Sampling Technique for Qualitative Volatile Headspace Outgassing from Solid Matrices

By: Gary Y. Oishi, Jamie L. Brown, Olga I. Shimelis, Kristen L. Schultz, Reporter US Volume 31.3

Introduction

Volatile compounds in solid samples have always presented a challenge for the chromatographer to analyze. The common approach of testing by static headspace is limited by the compound concentration and sample volume. Selective solvent extraction is another common sample preparation technique; however, the compound(s) of interest can be masked by the solvent peak during instrumental analysis and unwanted extractables may be introduced into the gas chromatography system. An alternative to these restrictive approaches is to outgas the volatiles directly from a solid sample and trap them onto an adsorbent tube which is thermally desorbed. The Adsorbent Tube Injector System (ATIS) was used to fingerprint various solid samples and the collected volatile compounds were thermally desorbed and analyzed by GC/MS.

Adsorbent Tube Injector System (ATIS)

Experimental

The ATIS unit, (Cat No. 28520-U, 28521-U) was configured with the optional thermal extraction glassware (Figure 1). Samples were placed in an aluminum boat then loaded into the ATIS unit’s heated zone (Figure 2) set at 60 °C.

Figure 1. Optional Thermal Extraction Glasware; Cat. No. 28523-U (top), Cat. No. 28524-U (bottom)
Figure 2. ATIS, heated zone

Sample sizes and purge times were adjusted to prevent overloading of the thermal desorption unit trap and sampling tube. The resulting offgassing compounds were trapped onto an attached glass Carbotrap® 300 thermal desorption tube (Figure 3, 30141-U) packed with three adsorbent beds (Carbopack™ C, Carbopack B and Carbosieve® SIII). The thermal desorption tubes were preconditioned before sampling. The same adsorbent tube was used for the background check and  method blank before being used for sample analysis.

Figure 3. Carbotrap 300 glass TD Tube; Cat. No. 30141-U

A PerkinElmer® TurboMatrix™ 150 was used for the thermal desorption process. Peak identification was determined by comparison (match quality greater than 90) of mass spectral fragmentation against the NIST® (Ver. 2.0f ) library.

Method
Column: Supelco SPB®-HAP, 60 m x 0.32 mm I.D., 4 µm (25020-U)
Oven: 40 °C (3 min), 12 °C/min to 200 °C (20 min)
Carrier Gas: Helium
Detector: Agilent® 5973 MSD
MSD Interface: 220 °C
Scan Range: m/z 35-225
Adsorbent Tube: Carbotrap 300 (30141-U)

Thermal Desorption Unit: PerkinElmer TurboMatrix 150
Tube Purge: 5 mL/min for 2 min
Tube Desorb: 45 mL/min for 5 min at 330 °C
Transfer Line/Valve Temp.: 180 °C/180 °C
Head Pressure: 16 psi helium
Trap Collection: -20 °C
Trap Desorption Temp: 350 °C with 10 min hold
Trap Packing (custom): Carboxen® 1000/Carbopack B/Carbopack Y

Tube Conditioner: CDS Analytical Model 9600 6 Tube Conditioner
Tube Conditioning: 300 °C for 30 minutes at 50 mL/min

Sample Preparation Unit: ATIS
Temp: 60 °C
Flow Rate: 70 mL/min nitrogen
Sample Purge Time: Sample dependent
Sample Amount: Variable

 

Figure 4. Sample – PVC Pipe Schedule 40
1 g of pipe purged for 1 hour
Cross-sectioned pipe material was cut into smaller pieces

Figure 5. Sample – 1/4 in. Drywall
1 g of drywall purged for 1 hour

Figure 6. Sample – Purple Nitrile Glove
0.5 g of glove material purged for 15 minutes

Figure 7. Sample – New Residential Carpet
0.5 g of carpet purged for 15 minutes

Figure 8. Sample – Black Tea
0.3 g of black tea purged for 20 minutes

Figure 9. Sample – Cumin Powder
0.005 g of cumin powder purged for 2 minutes

Conclusion

The ATIS was originally developed to aid in spiking solvent and thermal desorption tubes, but this unit can also be used to examine volatile compounds off-gassing from solid samples. The ATIS technique allows for fingerprinting of various solid samples using thermal desorption. Sample size, purge time, and purge temperature can be adjusted for variations in the volatile concentration of different samples. Thus, the ATIS device can be helpful in versatile sample preparation for qualitative fingerprinting.

Featured Products  
Description Cat. No.
ATIS System, 110V 28520-U
ATIS System, 220V 28521-U
Purge and Trap Humidifier Module 28522-U
Extraction Glassware w/Ground Joint 28524-U
Extraction Glassware w/Micro Connector 28523-U
Half-hole Septa (6 mm O.D. x 9 mm L), pk/100 20668
Ferrules, 1/4 in., PTFE, white, pk/10 29024-U
Thermal Desorption Tube
Unconditioned Carbotrap 300 Fritted 89 mm Glass TD Tube, pk/10 30141-U
GC Capillary Column
SPB-HAP, 60 m x 0.32 mm I.D., 4 µm 25020-U

Trademarks
Carbotrap, Carbopack, Carbosieve. SPB and Carboxen are trademarks of Sigma-Aldrich Co. LLC
Agilent is a registered trademark of Agilent Technologies Inc.
NIST is a registered trademark of National Institute of Standards and Technology FEDERAL AGENCY UNITED STATES
PerkinElmer is a registered trademark of PerkinElmer. TurboMatrix is a trademark of PerkinElmer

Related Information
For more information, visit sigma-aldrich.com/atis

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