Recovery from biological samples

Significant improvements have been achieved in the separation of isomeric hydroperoxides and other labile oxidation products from complex lipids, and their direct characterization by various advanced MS techniques avoiding sample manipulation, problems of variable recoveries from biological samples and tedious derivatization. However, the direct analyses of lipid oxidation products achieved with many of these advanced MS techniques have not yet produced reliable quantitative information. Although a few synthetic and enzymatically-derived polyunsaturated lipid hydroperoxides have been described in the literature, they have not been generally used as standards for quantitative MS analyses. This chapter is organized in chronological order of method development. 

Supercritical fluid extraction, offers also some desirable advantages including processing at low temperature, recovery of a solvent-free extract, and rapid extraction. However, very limited studies have been published on the use of supercritical fluids for the isolation of corticosteroids from biological samples. A combination of supercritical fluid extraction and liquid chromatography has been employed for the detection of dexamethasone residues in bovine tissues (448). 

Methods for recovery of lead from biological samples have been frequently described and much discussed In the lltera-... 

Regardless of the method chosen for the recovery of retinoids from biological samples, it is extremely important to remember that retinoids vary widely both in their solubility properties and in their stability. For these reasons, when an extraction method is being considered for the isolation of a given retinoid and/or its metabolites, two important points must be taken into account (1) whether the method chosen will result in a complete extraction of the retinoid of interest, and (2) whether it will contribute to the production of artifacts, either through hydrolysis of esters, isomerization, or production of nonphysiological compounds that may be mistaken for metabolites. 

Solid—phase extraction (SPE) is an alternate technique ably suited for the extraction of a wide class of compounds from biological samples [2,3,9—11]. A nonselective recovery is achieved through the use of C8, C18, or polymeric-based sorbents. As the aqueous sample... 

The use of ethyl acetate was suggested by Oszmianski and Lee (1990) to wash out phenolics other than anthocyanins. Finally, a relatively pure anthocyanin extract can be removed from the colnmn with acidified methanol (0.1% HCl). Anthocyanin extracts can be enriched in this way by use of solid phase purification, which is especially helpful for diluted samples such as biological samples. Two factors in the nse of these purification techniques are the stability of anthocyanins to the conditions nsed and the ease of anthocyanin recovery from the column. ... 

An internal standard method gives more reliable results when elaborate sample preparation is required, as in extraction of a drug substance from biological fluids, or extraction of pesticides and herbicides from soil and plant matter. The addition of internal standard (IS) to the sample and standard acts as a marker to give accurate values of the recovery of the desired compound(s). Since the determination of wt% involves the ratio of the detector responses in the two chromatograms, the injection volume is not critical as in an external standard method. 

PCBs in biological samples are usually extracted by a Soxhlet column and with a nonpolar solvent such as hexane. The sample is first mixed with sodium sulfate to remove moisture. The extraction of PCBs from sediments was tested with sonication, with two sonications interspersed at a 24-h quiescent interval, with steam distillation, or with Soxhlet extraction (Dunnivant and Elzerman 1988). Comparison of the recoveries of various PCB mixtures from dry and wet sediments by the four techniques and the extraction efficiency of four solvents showed that the best overall recoveries were obtained by Soxhlet extraction and the two sonication procedures. In comparisons of solvent systems of acetone, acetonitrile, acetone-hexane (1+1), and water-acetone-isooctane (5+1.5+1), recoveries of lower chlorinated congeners (dichloro- to tetrachloro-) were usually higher with acetonitrile and recoveries of higher chlorinated congeners (tetrachloro- to heptachloro-) extracted with acetone were superior (Dunnivant and Elzerman 1988). The completeness of extraction from a sample matrix does not seem to discriminate against specific isomers however, discrimination in the cleanup and fractionation process may occur and must be tested (Duinker et al. 1988b). 

Hexachloroethane can be detected in tissues at levels as low as 0.001 pg/g (Nolan and Karbowski 1978) and recoveries range from 50 to 130%. Prior to analysis, hexachloroethane must be separated from the biological sample matrix and prepared for introduction into the analytical instrument. Separation may be effected by purging with an inert gas (helium), and trapping on an adsorbent cartridge (Tenax GC ), followed by... 

DNB in biological samples (Miller et al. 1991). The method showed good specificity and comparable recovery of 1,3-DNB from blood samples when compared with HPLC/UV and HPLC/radiochemical detection. No information was located that specifically discussed the detection of 1,3,5-TNB and metabolites in blood and urine by any method. 

The LDH+ALT reactor provided a linear response from 0.1 to 50 pmol/L lactate, thereby increasing lactate conversion by 117-183% relative to LDH alone. The intra- and inter-assay CV were both less than 5%, and recoveries ranged from 93 to 106%. Even though roughly 100% of the LDH and ALT added bound to the support under the immobilization conditions used, the activities of the immobilized enzymes were ca. 3% of those of the free enzymes, which is consistent with previous results obtained by the same [67] and other authors [69,70]. Jointly immobilized LDH and ALT preserved ca. 50% of their original activity after 60-90 days of intermittent use. On the other hand, immobilized luciferase was less markedly inhibited than that in the free solution by substances present in the biological samples assayed [71]. 

Biological Samples. There were three types of biological samples obtained from workers at the plant urine, whole blood, and feces. All urine and blood samples were internally "spiked" at the factory with 1 yg/mL of a nitrosopiperidine (NPiP) standard. NPiP was used for spiking because it has a similar stability and recovery characteristic to nitrosomorpholine, and to provide a means of gauging the accuracy of the analytical methods. Due to the inability to perform homogeneous mixing on-site, the feces samples were not spiked until they were thawed upon return to the laboratory. Ethyl acetate extracts of urine samples were examined for the presence of N-nitrosodiethanolamine (NDEIA), a metabolite of NMOR, by HPLC-TEA. All samples were immediately frozen at the plant (-80°C) and kept at this temperature until analysis. 

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