Confirmation thin layer chromatography-mass

The laboratory devised a special vacuum pump and filters to take samples from various sections of the garage. The laboratory was able to confirm the presence of heroin, using rigorous isolation techniques combined with fluor-imetry, thin-layer chromatography, and mass spectrometry. The laboratory s work played a major role in the successful prosecution of this case. 

FSIS laboratories also use chemical techniques and instrumentation to identify select antibiotic residues. The tetracyclines of interest are identified by thin layer chromatography. Sulfonamides are detected and quantified by fluorescence thin lay chromatography and confirmed by gas chromatography/mass spectrometry. Amoxicillin and gentamycin are identified and/or quantified by high pressure liquid chromatography. Similar techniques are used to identify ionophores and other antimicrobials of interest. 

The most recent modification of the NBD-Cl method involves a further improvement in its qualitative support (616). It involves the infusion of the extract employed for thin-layer chromatography via an electrospray interface into a mass spectrometer operating in the multiple-stage mass spectrometry mode, thus allowing confirmation of suspect results. The cleanup of the thyroid gland samples was also performed with a selective extraction procedure, based on the specific complex formation of the thiouracil, methylthiouracil, propylthiouracil and phenylthiouracil, tapazole, and mercaptobenzimidazole residues with mercury ions bound in a Dowex 1-X2 affinity column. 

Confirmation of the identity of the gas chromatographic components has been accomplished by thin layer chromatography, relative retention times on different gas chromatographic columns, "p" values, and most recently by mass spectrometry. Dicofol can be separated from its phenone by using a Florisil column (17) or TLC. Dehydrochlorination of dicofol to DBP can be used as a confirmatory test for the parent compound. Gajan and Lisk (23) used cathode ray polarography to analyze vegetables for dicofol residues. 

About 10 g of VLB (vincaleucoblastine or simply vinblastine) sulfate were converted by standard procedures to VLB free base. The free base, obtained as a residue after evaporation of the dried ethereal solvent, was dissolved in about 200 ml of anhydrous methanol. Anhydrous liquid ammonia (300 ml) was added, and the reaction mixture sealed and maintained at about 100°C for 60 hours. The reaction vessel was opened, and the contents removed and evaporated to dryness in vacuo. The resulting residue, containing 4-desacetyI VLB C-3 carboxamide, as shown by thin layer chromatography, were combined and the solvent evaporated therefrom in vacuo, yielding asa residue purified 4-desacetyl VLB C-3 carboxamide free base. The NMR and IR spectra of the solid free base confirmed the structure indicated. The free base showed a band in the infrared at 1,687 cm-1, characteristic of the amide function. The molecular weight of the free base determined by mass spectroscopy was 753 which is in agreement with theoretical value calculated for C43H55N5O7. 

Thompson et al. [113] emphasise that even the use of two dissimilar gas chromatographic columns does not ensure irrefutable compound identification. For example, if the retention characteristics of a given peak obtained from two dissimilar columns suggest the possibility of the presence of a compound which appears wholly out of place in a specific sample, further confirmation is clearly indicated by such techniques as specific detectors, coulometry, p values, or gas chromatography-mass spectrometry or thin layer chromatography. 

About 30 PAH compounds were identified tentatively by co-chroma-tographic methods and several of these identifications were confirmed from mass spectral data. Many components, however, could not be identified conclusively because of incomplete resolution from other components and the fact that isomers are not generally distinguishable by mass spectrometry. Clearly, the next step is to subfractionate the PAH isolate by techniques such as gel permeation or thin layer chromatography in order to facilitate making more positive identifications. 

Chemists now routinely use open-access MS systems in the same way that they previously used thin-layer chromatography (TLC) to monitor reaction mixtures for the desired product and to optimize reaction conditions. In practice, medicinal chemists require only molecular weight data, and are comfortable with a variety of MS ionization methods to obtain this information. However, confidence in the actual method and procedure is a requisite. Today, molecular mass measurement has quickly become a preferred means of structure confirmation over NMR and IR during the early stages of synthetic chemistry activities (i.e., drug discovery), where sample quantities are limited. 

RD Budd, FC Yang, WJ Leung. Mass screening and confirmation of methaqualone and its metabolites in urine by radioimmunoassay-thin-layer chromatography. J Chromatogr 190 129, 1980. 

Mass spectrometry is the technique of choice for confirmation of pesticides. In the case of OPs, the sample extract can be run on different columns. Relative retention times (RRj) of a given peak can be compared with a table of RRi for different columns (FDA, 1994). For CMs, the alkylated CMs can be chn>malograpbed using GC with NPD detector. The retention time of peaks can be compared with the retention lime of the standard compound. If enough of the residue compound is present, then thin-layer chromatography can be used to confirm the presence of the pesticide (FDA, 1982). 

PND was shown to be 10 to 50 times more sensitive than FID (Wink et al. 1982). The other detection method commonly used to obtain further information on the chemical structures was EI-MS. However, even GC-MS data are not always sufficient for the identification of quinolizidine alkaloids, since structural isomers such as tetrahydrorhombifoline and N-methyl-angustifoline were found to have the same retention time and very similar mass spectra but could be distinguished by TLC (thin-layer chromatography) (Balandrin and Kinghorn 1981). From some esters of hydroxylupanine it was not possible to detect the molecular ion (Wink et al. 1982). FD-MS (field desorption) was performed directly on the alkaloid extract to detect the molecular ions of the various bases in the mixture. The identity of the compounds was further confirmed by comparison of their retention indices with the ones of authentic samples. More recently, also CI-MS (isobutane or... 

The extent to which thin-layer chromatography (TLC) is used in forensic investigations varies considerably from laboratory to laboratory and is now very dependent on the alternative analytical techniques to be found within any particular laboratory. Invariably TLC is but one of a number of techniques that could be used for a particular analysis. On many occasions the alternatives are likely to be more precise and/or specific than TLC and, since these criteria are usually of paramount importance, are likely to be used preferentially. For example, the combination of radioimmunoassay, to carry out the rapid screening of samples for the presence of a member of a particular class of drug, and gas chromatography-mass spectrometry (GC-MS) for the identification or confirmation of the presence of a particular drug, is likely to provide a more precise and sensitive analysis than will the use of TLC. 

According to this bottom-up approach, the (somewhat arbitrary) minimum number of IPs that must be obtained for the confirmation of regulated substances is proposed (European Commission 2002) to be three, but for positive identification of banned compounds the number is increased to four in order to decrease the risk of false positives examples of IPs for various combinations are shown in Table 9.3. For banned substances at least some IPs earned by mass spectrometry are mandatory but, since some analytes do not yield a sufficient number of ions, other techniques can be used to contribute a maximum of one IP each, including LC coupled with full scan diode array spectrophotometer (DAD) or with fluorescence detection or immunochemical detection, or two-dimensional thin-layer chromatography (TLC) coupled with spectrometric detection. 

Under routine conditions, enrichment and isolation of single anthocyanins followed by classical structural elucidation (mass spectrometry, elemental analysis, UVA IS absorbance evaluation using shift reagents, NMR, thin layer chromatography of sugars and anthocyanidins) is rarely necessary, hence will not be discussed in detail. Routine analysis focuses on the quantification and the distribution of known anthocyanins to confirm the content and source of anthocyanins. 

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