Capillary-column GCMS

Although considerable work had been done in the past with packed columns, they are now rarely utilized in GCMS because of lower chromatographic and transfer efficiencies. Capillary column GCMS, with its simpler interface design and higher chromatographic efficiency, is typically preferred in all areas of analysis and will be exemplified in this discussion. 

Pyrolysis Photoionization GCMS. Details of the instrument have been described earlier (11). Curie point pyrolysis was performed in nitrogen which also served as the carrier gas. Pyrolysis occurred directly in front of the capillary column, which exits in the photoionization chamber of the mass spectrometer. A 50 m fused silica column coated with CP-Sil 5-CB (I.D.=0.32 mm, film thickness 1 micron) was used for the separation. The oven was programmed from 80-260 C after a period at room temperature during pyrolysis of the sample. Argon I resonance photons (11.6 and 11.8 eV) were used for ionization of the GC effluent. Ion source teoqterature was 150°C. Pressure in the ion source was 10 2 Torr and in the vacuum chamber 10" Torr. The quadrupole was scanned at 1 scan/s over 30 to 235 amu. 

GC-MS is conducted with the same types of capillary columns using He carrier gas. Gas chromatographic conditions are usually similar to GC-ECD. There are a range of possible detection modes for POPs by GCMS and the reader is referred to recent texts on the subject (Chapman, 1995, Oehme, 1999). Electron ionization (El) mode is used for... 

Sterane and terpane biomarkers in the saturated hydrocarbon fractions of oil samples were analyzed by MRM-GCMS using a Micromass ProSpec-Q instrument. Compound separation was achieved using a 30-m J W Scientific DB-5 capillary column (0.32 mm ID., 0.25 /rm film thickness). The column was programmed from 75 to 200°C at 5°C/min using helium carrier gas and 5p-cholane as the internal standard. Further details are in Peters and Moldowan (1993). 

GCMS-OP 1100EX column Shimadzu capillary column HiCap-CBP10-W25-100, 0.53 mm i.d. x25m cyanopropyl (thickness 1.0 pm) column temperature 140°C carrier gas helium 20 ml min h ion source temperature 270°C electron energy 20/70 e/V. 

Capillary columns of 0.18 and 0.25 mm i.d. should be used for GCMS systems, because the lower flowrates with these columns will not exceed the limitations of the vacunm system. 

There are numerons reports for the gas chromatographic determination of THC and its metabolites, ll-nor-A-9-tetrahydrocannibinol-9-carboxylic acid (THC-COOH) and ll-hydroxy-A-9-tetrahydrocannibinol (11-OH-THC) in urine and blood. THC is not normally found in urine, so it must be determined in blood at levels around 2-4 ng/mL. The TMS derivative is the most widely used derivati-zation procedure with GCMS for the determination of cannabinoids. In addition to the obvious advantages of derivatizing the THC metabolites, the acidic constituents of cannabis mnst be derivatized because they can easily decarboxylate above 80°C. Almost aU gas chromatographic procedures today use fused-silica capillary columns for this analysis. Determination of THC in blood is routinely done in forensic toxicological samples, and the detection and quantification of the two THC metabolites in mine is a routine procedure for proof of cannabis use in workplace testing. Several of the procedures used for this type of analysis are listed in Table 16.9. 

The extracts were analyzed by GCMS, using a CP-Sil 8 CB low-bleed/ MS fused silica capillary column (60 m x 0.25 mm i.d., 0.25-pm film... 

Clark RR, Zalikowski JA. 1990. Comparison of capillary and packed column analysis for volatile organics by GCMS. In Friedman D, ed. Waste testing and quality assurance. Special technical publication 1062 vol. 2. Philadelphia, PA American Society for Testing and Materials, 333-350. 

All the products were analyzed by GC (HP 5880) using a capillary (cross-linked methylsilicone gum) column and flame ionization detector. The identity of some of the products was confirmed by QC/mass spectroscopy (Shimadzu, Japan, model GCMS-QP 200A). 

Many liquid phases for packed-column purposes were unacceptable for capillary GC. Although they offered selectivity, overriding factors responsible for their disfavor were overall lack of thermal stability and the instability of the stationary phase as a thin film at elevated temperatures and during temperature programming. In the latter processes, it is crucial that the phase remain a thin uniform film otherwise, loss of both inermess and column efficiency result. Today, these problems have been solved and the refinements are reflected in the high performance of commercial columns. The impetus has been driven by the improvements in the sensitivity of mass spectrometers such that the MS detector is now the second most popular detector in GC (the FID is the most widely used detector). This rise in the use of GCMS has also necessitated more thermally stabile columns offering much less column bleed. 

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