GC-MS procedure

One anabohc steroid, the presence of which has proven difficult to analyze, is stanozolol [10418-03-8] C2 H22N20. A metaboUte of the parent dmg, hydroxy stanozolol, detected in equine urine eight hours after ingestion of the parent dmg is actually identified, usually at very low levels. Analysis was done by Ic/ms/ms which had a shortened analysis time advantage over gc/ms procedures because of the elimination of the need for a derivatization step (33). 

In 1994, only 15% of EPA method validations (tolerance method validation and environmental chemistry method validations) that involved GC were carried out using GC/MS. In 2002, this number is reversed in that 85% of the GC methods that were validated by both programs used GC/MS. Many of the compounds investigated in these method trials were polar compounds, and hence these compounds required derivatization in order to be amenable to GC. One common methylating agent is (trimethylsilyl)diazomethane, which is used, for example, to methylate the sulfonamide flumetsulam. As opposed to HPLC/MS, where derivatization is often not necessary, the GC/MS procedure involves an extra step to methylate this compound, under dry conditions, prior to determination by GC/MS. 

The following subsections describe some case studies dealing with GC/MS procedures used to investigate lipid materials in archaeological objects and paintings. 

Figure 9.1a reporting GC-MS results taken on laboratory blank in a GC-MS procedure [87] shows negligible amino acid contamination. Indeed, quantitating a protein as the sum of 14 amino acids, a value of about 200 ng is the minimum required threshold to positively consider the protein identification. Figure 9. lb reports the chromatogram of an amino acid standard solution acquired in the SIM mode and corresponds to the quantitation limit that is a content of about 700 ng in the sample at a confidence level of 95%. This seems amenable when working at the trace level. 

Table 9.4 Recent applications of GC/MS procedures to determine proteins in artworks...

The use of HMDS as a derivatization reagent in the analysis of triterpenoid resins has been less explored. The TMS derivatives of triterpenoids bearing hydroxyl groups [a-amyrine, p-amyrine and hop-22(29)-en-3p-ol] have been identified in the triterpenic fraction of Burseraceae resins, thus demonstrating that HMDS combined with Py-GC/MS is effective in the derivatization of triterpenoid compounds [59]. However, the range of structures that can be fully derivatized and detected must be extended and, in order to get comprehensive results comparable with those coming from the well assessed off-line GC/MS procedures, general improvements in the on-line trimethylsilylation-pyrolysis method are needed. 

It is critical when performing quantitative GC/MS procedures that appropriate internal standards are employed to account for variations in extraction efficiency, derivatization, injection volume, and matrix effects. For isotope dilution (ID) GC/MS analyses, it is crucial to select an appropriate internal standard. Ideally, the internal standard should have the same physical and chemical properties as the analyte of interest, but will be separated by mass. The best internal standards are nonradioactive stable isotopic analogs of the compounds of interest, differing by at least 3, and preferably by 4 or 5, atomic mass units. The only property that distinguishes the analyte from the internal standard in ID is a very small difference in mass, which is readily discerned by the mass spectrometer. Isotopic dilution procedures are among the most accurate and precise quantitative methods available to analytical chemists. It cannot be emphasized too strongly that internal standards of the same basic structure compensate for matrix effects in MS. Therefore, in the ID method, there is an absolute reference (i.e., the response factors of the analyte and the internal standard are considered to be identical Pickup and McPherson, 1976). 

The assay is performed using [13C2]-GA and [2H3]-S-adenosylmethionine as substrates followed by the measurement of [13C2-2H3]Cr by the regular GC-MS procedure, which represents GAMT activity (Table 7.2.6). 

The function of the Cr transporter is assayed using intact fibroblasts, which are cultured for 24 h in a medium that is enriched with either 25 pM or 500 pM Cr [ 18]. The intracellular concentration of Cr in the fibroblasts is determined using the GC-MS procedure described in detail in this chapter (Table 7.2.8). 

GC of midchain dimethylalkane carbon skeleton alkylthiophenes, 475,477/ GC-MS procedure, 449-450 geological setting, 446-447 hydrocarbon biomarkers, 453-457 implications for reconstruction of palaeoenvironments, 478,480 lithology, 448/",452... 

Wolf M, Riess M, Heitmann D, et al. 2000. Application of a purge and trap TDS-GC/MS procedure for the determination of emissions from flame retarded polymers. Chemosphere 41 693-699. 

As mentioned previously, the formation of the methyl derivative is similar to several methods that already have been developed for organotin pesticides. The utilization of this derivative in conventional gas chromatographic residue procedures presents many challenges. Electron capture detection is sensitive enough but requires extensive clean-up while with FID and FPD the sensitivity is lower than desired. The development of a routine GC/MS procedure (single or multiple ion monitoring) was chosen then as the only possible alternative. A SIM (selective ion monitoring) method is specific for retention time and as well as for characteristic ions (m/e). 

In our experience, GC/MS procedures for analysis of alkyl MPAs at the low ppb level lack robustness, possibly due to differences in SPE cartridges, the... 

The GC/MS procedures for methamphetamine are described in Table 4. The papers published in Japanese - have corresponding reports in English. - - Methamphetamine was detected and determined by mass fragmentography in rat hair after administration of the substance. Nine methods also detected the metabolite amphetamine or amphetamine alone. Suzuki et al. determined methamphetamine also in nail, sweat and saliva. The workup (EX after acid or alkaline hydrolysis) and derivatization technique (methanol-trifluoroacetic acid [TEA]) is rather uniform in most procedures. Nakahara et al. ° used methoxyphenamine excretion into beard hair to discuss several washing procedures. Alkaline or methanolic extraction are used with one exception. Derivatization is mainly made by fluorinated anhydrides. A review ° gives details on analytical procedures, incorporation rates of amphetamines from blood to hair, and relationship between drug history and drug distribution in hair. 

As indicated previously, when a GC/MS procedure is applied for the analysis of a pyrolysate, it is difficult to detect the variety of compounds generated during the pyrolysis by using only one chromatographic procedure. Two chromatographic techniques are, however, able to cover a wide range of volatility. The CMC pyrolysate... 

Clarkson ED, Lesser D, Paul BD. Effective GC-MS procedure for detecting iso-LSD in urine after base-catalyzed conversion to LSD. Clin Chem 1998 44 287-92. 

ElSohly MA, Stanford DF, Murphy TP, Lester BM, Wright LL, Smerigiio VL, et al. Immunoassay and GC-MS procedures for the analysis of drugs of abuse in meconium. J Anal Toxicol 1999 23 436-45. 

Table 4.4.1 Comparison of the pharmaceutical compounds detected by the POCIS passive sampler (5-day deployment) and by simultaneous spot sampling (1 L) in the Meuse River. The detection limit for the GC/MS procedure are mentioned in brackets (Togola, 2007)...

Benzene in gasoline can also be measured by infrared spectroscopy (ASTM D-4053). But additional benefits are derived from hyphenated analytical methods such as gas chromatography-mass spectrometry (ASTM D-5769) and gas chromatography-Fourier transform infrared spectroscopy) ASTM D-5986), which also accurately measure benzene in gasoline. The gas chromatography-mass spectrometry method (ASTM D-5769) is based on the Environmental Protection Agency s gas chromatography/mass spectrometry (EPA GC/MS) procedure for aromatics. 

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