Drug analysis extraction

The progress made in interfacingHPLC instruments with mass spectrometry has been a significant development for laboratory analyses in the pharmaceutical industry. The low concentrations of test drugs in extracts of blood, plasmas, serums, and urine are no problem for this highly sensitive HPLC detector. In addition, the analysis is extremely fast. Lots of samples with very low concentrations of the test drugs can thus be analyzed in a very short time. At the MDS Pharma Services facility in Lincoln, Nebraska, for example, a very busy pharmaceutical laboratory houses over 20 LC-MS units, and they are all in heavy use daily. 

Studies of the metabolism of vincristine and vinblastine have been complicated by chemical alterations of the drugs that occur during processing of samples for analysis. Extraction of these compounds under acidic conditions has been reported to minimize chemical degradation, and HPLC studies of the metabolism of vincristine indicate that microsomal preparations from mouse liver, but not those from human rhabdomyosarcoma tissue, convert vinblastine to 4-deacetyl vinblastine in vitro (38). 

Wahbi reported on the use of second-derivative spectroscopy for the determination of canrenone in spironolactone, and found that the method is stability-indicating for spironolactone [21]. First and second-derivative spectroscopy were also utilized for the simultaneous analysis of spironolactone in combination with either hydrochlorothiazide or frusemide [22], The drugs are extracted with ethanol and analyzed through the use of the zero-crossing method. Nowakowska [23] analyzed mixtures of spironolactone and hydrochlorothiazide in tablets by measuring the absorbance of all species at 239 nm, and that of hydrochlorothiazide at 318 nm. The recoveries for spironolactone were found to be 97.9 to 101.8%, with a coefficient of variation of less than 0.1%. 

T. Hirai, Usability of a normal solid-phase extraction as the sample clean-up procedure for urinary drug analysis by high-performance liquid chromatography, CCAB 97 Mini Review, http //neo.pharm.hiroshima-u.ac.jp/ccab/lst/mini review/mr002 /hirai.html (August 1, 2002). 

Traditionally, the impurities are isolated and purified by off-line HPLC and then characterized by using FT-IR, NMR, MS, and X-ray crystallography, among others. The main limitation associated with this approach is that relatively large sample quantities are needed for analysis, and the process can be very labor-intense. In contrast, LC/MS and LC/MS/MS are highly sensitive techniques requiring typically less than Ipg of material for analysis. In certain cases, if the impurities are found at very low levels in the drug substance, extraction procedures are used to concentrate them to detectable levels. 

LC/MS/MS to support the clinical development [104-108]. The conventional sample preparation procedures require labor-intensive sohd-phase extraction (SPE) sample pretreatment steps and extensive method development time for the LC/MS drug analysis. One of the popular alternatives to SPE is the resurgence of the on-line SPE or column switching techniques [109-111]. More recently, this strategy has been further developed to determine the drug candidates in human plasma by LC/MS/MS analysis [104,109,112]. 

Initially, SPE was based on the use of polymeric sorbents, such as XAD resins (polymeric adsorbents), which were packed in small disposable columns for use on drug analysis. The early environmental applications consisted of both XAD resins and bonded-phase sorbents, such as C-18 (McDonald and Bouvier, 1995). These precolumns were used for sample trace enrichment prior to liquid chromatography and were often done on-line, which means at the same time as liquid chromatography. However, these first, steel, on-line precolumns quickly were replaced with an off-line column made of plastic in order to be both inexpensive and disposable. Eventually, the term solid-phase extraction was coined for these low-pressure extraction columns (Zief et al., 1982). Thus, solid-phase extraction is an analogous term to liquid-liquid extraction, and in fact, solid-phase extraction might also be called liquid-solid extraction. However, it is the term solid-phase extraction or the acronym SPE that has become the common name for this procedure. 

AUTOMATION AND ON-LINE SOLID-PHASE EXTRACTION FOR DRUG ANALYSIS... 

Extraction of Active Compounds from Plant Materials. A variety of natural products present in plant materials, especially high-value-added products, can be processed with supercritical fluids. Because many of these have pharmacological activity, a natural extension of this application is to the field of drug analysis. 

Zeng, M., and Zhao S. (1985) Supercritical fluid extraction and its application in crude drug analysis. (Chinese) Zhongcaoya 16 (5), 209-11 (Chem. Ahstr. 106, 144063c). 

Extraction techniques—in particular, liquid-liquid extraction and solid phase extraction—are used in toxicological analysis and some drug analysis prior to chromatographic analysis. The process of extraction is used to extract organic substances, such as drugs, directly from body fluids and tissues. The two main types of extraction used in these types of analyses are liquid-liquid extraction and solid phase extraction. 

As well as sampling, another important aspect of sample preparation for drug analyses is the homogenisation of a subsequent extraction of the sample. This step is necessary, particularly if we have a powder that is not homogenous. A number of homogenisation techniques are available in drug analysis and these are summarised in Table 11.1. 

This procedure was worked out for the drug probenecid extracted from biological fluids (0.2 ml). To the extract were added 1 ml of 0.5% KjCOj in methanol (10 ml of 5% aqueous K2CO3 diluted to 100 ml with MeOH) and 0.1ml of Me2S04. The mixture was heated at 70 °C for 5 minutes and evaporated to dryness. The residue was mixed with 1 ml of pH 5.6 acetate buffer and 5 ml of chloroform, the chloroform was separated and evaporated to dryness, and the residue was dissolved in 100 y of chloroform for analysis by gas chromatography [83],... 

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