Thin-layer chromatography drug testing

Ordinary impurities are considered innocuous in that they have no significant undesirable biological activity at or below the specified limits. These impurities arise from the synthesis, formulation, or degradation of the drug. The USP monograph for glycopyrrolate contains a thin-layer chromatography (TLC) test for ordinary impurities for which the limits are 0.5% for individual impurities and 2.0% for the total of all impurities. 

In the search for unknown drugs and/or pharmaceuticals in body fluids, a combined instrumental approach is especially helpful. Table III shows our extraction scheme. For drug analysis, steam distillation is usually omitted. Different extraction steps isolate the strongly acidic, weakly acidic, neutral, basic and amphoteric compounds in separate fractions. All are analyzed by UV-spectro-photometry, in organic solution and (with the exception of the neutral extract) also in water at 3 different pH-values. Thin- layer chromatography, color tests, IR- and fluorescence-spectrophotometry may yield additional information. Fractions of interest are analyzed by GC-MS. 

Table 1 provides the urinalysis test results for the 4,847 arrestees, While PCP was tested for by an EMIT test only, cocaine, opiates and methadone were tested for by both EMIT and thin layer chromatography (TLC). (The EMIT test for opiates is not specific to morphine, the metabolite of heroin, and can detect the recent use of a variety of opiates. A specimen positive for opiates is most likely to indicate the use of heroin in this population, however.) Our analyses will use only the results from the EMIT tests, because we have learned that the TLC general drug screen is less sensitive for detecting recent use of these illicit street drugs (Wish et al. 1983 Wish et al. 1984). 

If the specimen provided is a trace sample, sufficient material should be recovered to allow an instrumental analysis directly. The nature of the sample will often provide a clue as to the drug(s) involved and direct comparison can be made by using gas chromatography-mass spectrometry (GC-MS), for example. If the specimen is a bulk sample, presumptive (colour) tests are undertaken to determine the class or classes of drugs which the sample contains. Thin layer chromatography (TEC) is used to determine which members of the classes are present and it might also be possible to make a semi-quantitative estimate of the amount(s) of drug(s) present. Standard mixes can then be prepared for use in the confirmatory techniques. 

Following the possible identification of the presence of LSD, the next stage in the analysis is the use of thin layer chromatography (TLC). This is employed because although it cannot be used to prove the identity of LSD, it can be used as a rapid, cost-effective method to eliminate those samples which gave a positive colour reaction in the presumptive tests but which do not contain this drug. These will be rarer when blotter acids are suspected, but may be more common where other substrates have been used as the carrier medium for the LSD itself. 

In order to achieve this, a full physical description of the materials should first be carried out. It is sometimes possible, following this process, to feed the information obtained into relevant databases to identify the drug(s) present in the dose form. The identification process then becomes a simple matter of confirmation. If the dose form is not included in the databases, however, a full chemical analysis, including drug extraction from the tabletted material, presumptive testing, thin layer chromatography and a confirmatory technique must be undertaken. 

Characterization in the solid-state and compendial methods has been discussed already. Quantitative tests to characterize drug substance and drug product composition require that significant consideration be given to method development. Methods such as thin layer chromatography, gas chromatography, HPLC, supercritical fluid chromatography, and capillary electrophoresis... 

See alsa Chemometrics and Statistics Multivariate Classification Techniques. Forensic Sciences Drug Screening in Sport Illicit Drugs Thin-Layer Chromatography. Gas Chromatography Overview Mass Spectrometry Forensic Applications. Liquid Chromatography Clinical Applications. Microscopy Applications Forensic. Spot Tests. 

Wood, J.L. and Steiner, R.R. 2011. Purification of pharmaceutical preparations using thin layer chromatography to obtain mass spectra with direct analysis in real time and accurate mass spectrometry. Drug Test. Anal., 3 345-351. 

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