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Note 99: Volatile and Semi-Volatile Profile Comparison of Whole vs. Dry Homogenized Wheat, Rye and Barley Grains by Direct Thermal Extraction GC/MS

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Ronald E. Shomo, II, Christopher Baker, and John J. Manura
Scientific Instrument Services,
1027 Old York Road, Ringoes, NJ 08551
(presented at Pittcon 2015)

Introduction

The ability to profile volatile and semi-volatile components present in grains without the use of solvent extractions has several advantages including improving sample throughput, reducing the chance of a volatile component being “lost” in the extraction process and eliminating the need for solvent disposal. This study utilizes the advantages of direct thermal extraction GC/MS to profile whole grains of wheat, rye & barley as harvested (Figure 1-3) and after being homogenized into a dry powder form. Direct Thermal Extraction GC/MS provides for fast analysis with no carryover problems that can be associated with other GC/MS techniques.

Materials and Methods

A small aliquot (100-200 mg) of grain was inserted into a preconditioned thermal desorption tube. The tubes are preconditioned by baking out at 320C for four hours with a stream of high purity nitrogen passing through at 50 ml/min. The tubes are Silco coated and have a 4 mm ID. The overall dimensions of the tubes are 0.25” x 4.0”.
The Desorption tube was placed on a SIS TD5 thermal desorption system. (Figure 4A & 4B) and a 35 mm preconditioned SS Desorption needle was attached. The TD5 was coupled to an Agilent 6890 GC utilizing a 5973 MSD as a mass detector. The 6890 GC had a SIS Cryotrap installed on the injector that was cooled to -60C with liquid CO2 to cryofocus the sample during the desorption process. The TD5 was programmed to allow for a 30 second dry purge to remove any residual air from the sample. The sample was desorbed at 175C for a duration of 5 minutes. During the desorption process a divert valve is actuated by the desorption software and allows the injection port helium flow to pass through the desorption tube needle and into the injection port. After desorption has concluded the divert valve switches the flow back through the GC inlet in a seamless fashion.
During the desorption the cryotrap remains at -60C, after the 5 minute desorption period the cryotrap is ballistically heated to 200C for 3 minutes and the GC/MS data acquisition is initiated. The MSD is scanning a mass range of 35- 500 with a 1 second scan rate.
The GC column used in this analysis was a J&W DB-5MS (0.25 mm ID x 60M) with a 0.25 μm film and was operated at 40-250C with a ramp rate of 5C/minute. The GC operated in the split mode with a 5:1 split ratio. All desorption parameters were controlled by the TD5 software that is integrated within the Chemstation program. Mass spectral data was compared with the NIST14 AMDIS software for component identification.


The grain samples were cracked using a Next Advance Stomper™ (Figure 5) and homogenized using a Next Advance Bullet Blender Storm™ (Figure 6). Grains used were Rye, Wheat & Barley, (organic and non-organic varieties)

Results & Discussions

Figures 7-9 show the TIC chromatograms of the organic barley seeds.

Figure 7 shows the result of desorbing the intact hull, this yielded 24 unique compounds. Most prevalent was urea, followed by Furfural.

Figure 8 shows the chromatogram after the hull was cracked with the Stomper™, the compounds identified rose to 55. Urea increased two fold and Furfural rose 3 times versus the intact hull. Also released was a series of alcohols, aldehydes, lactones and esters.

Figure 9 shows the results of desorption of the barley hull after cracking and subsequent dry homogenizing with the Bullet Blender Storm™, the chromatogram revealed 73 unique compounds. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran- 4-one was found to have the largest increase in intensity after the homogenizing step, but also found was the triazole fungicide Triadimefon. Triadimefon is a commonly used fungicide for seed treatment of grains, including barley. But somehow managed to find its way into the barley labeled “Organic”.

Table 1 – Shows a list of the most abundant components identified via the NIST14 library software for the Barley TD/GC/MS samples.

Barley Volatile & Semi-Volatile Components
1 Urea 21 Trimethyl amine
2 N-Nitrosodimethyl amine 22 Methyl Formate
3 1,2:3,4 diepoxybutane 23 2-Propanoic acid
4 Furfural 24 Methyl Pyrazine
5 2-Heptanone 25 2-Furanmethanol
6 2,5 Dimethyl Pyrazine 26 4-Cyclopentene-1,3-dione
7 Butyrolactone 27 2(5H)-Furanone
8 Hexanoic acid 28 6-oxa-bicyclo[3.1.0]hexan-3-one
9 2-pentyl furane 29 5-Methyl Furfural
10 N-tert-butylamine 30 5-Methyl-1,3-cyclopentanedione
11 4-Hydroxy-2,5-dimethyl-3(2H)-furanone 31 1-Nitrosopiperidine
12 Maltol 32 Methyl 4-imidazolecarboxylate
13 d-Mannose 33 Diethyl Nitrosoamine
14 5-hydroxymethylfurfural 34 4H-Pyran-4-one,3,5-dihydroxy-2-methyl
15 1,4-benzenediol, 2-methoxy 35 2-methoxy-4-vinyl phenol
16 Triadimefon 36 Guanosine
17 Oleic Acid 37 Hexanoic acid
18 Orcinol 38 Hexanal
19 2,3-Dihydrobenzofuran 39 Allyl glycidyl ether
20 2,3-Dihydro-3,5-dihydroxy-6-methyl-4(H)-pyran-4-one 40 5-Methyl-2-Furancarboxaldehyde

Conclusion

Utilizing Direct Thermal Extraction, the Stomper™ and the Bullet Blender™ homogenizer, enabled a complete volatile and semi-volatile profile comparison of the outside and interior of the Rye, Wheat and Barley grains. This process would historically have been attempted via a Soxhlet extraction. The Direct Thermal Extraction eliminates the need for solvents and the associated expense of disposal as well as reduces the chances of losing components in the solvent evaporation step. Direct Thermal Extraction also reduces contamination risks due to reduced handling steps and no solvent

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