Plasma ECD

Quantification. Gas Chromatography. In plasma or urine fenfluramine and norfenfluramine, detection limits fenfluramine 5 ng/ml and norfenfluramine lOOpg/ml in plasma, ECD— K. K. Midha era/.. Can. J.pharm. ScL, 1979,14,18-21. 

Quantification. Gas Chromatography. In plasma or urine phenformin and other biguanides, detection limit < 1 ng/ml in plasma, ECD—S. B. Matin et al., Analyt. Chem., 1975, 47, 545-548. 

An alternative approach is plasma ECD [86], in which electrons (0.1-15 eV) are collided with pulsed nitrogen gas prior to the trapping of ions in the ICR cell. The induced plasma conditions result in significant increase in ECD efficiency. A single plasma ECD mass spectrum of carbonic anhydrase ca 29 kDa) showed peaks corresponding to cleavage of 183/253 N-Ca bonds c/116/258 by activated ion ECD. 

GC/MS has been employed by Demeter et al. (1978) to quantitatively detect low-ppb levels of a- and P-endosulfan in human serum, urine, and liver. This technique could not separate a- and P-isomers, and limited sensitivity confined its use to toxicological analysis following exposures to high levels of endosulfan. More recently, Le Bel and Williams (1986) and Williams et al. (1988) employed GC/MS to confirm qualitatively the presence of a-endosulfan in adipose tissue previously analyzed quantitatively by GC/ECD. These studies indicate that GC/MS is not as sensitive as GC/ECD. Mariani et al. (1995) have used GC in conjunction with negative ion chemical ionization mass spectrometry to determine alpha- and beta-endosulfan in plasma and brain samples with limits of detection reported to be 5 ppb in each matrix. Details of commonly used analytical methods for several types of biological media are presented in Table 6-1. 

Kashiwazaki67 has fabricated a complementary ECD using plasma-polymerized ytterbium bis(phthalocyanine) (pp—Yb(Pc)2) and PB films on ITO with an aqueous solution of 4M KC1 as electrolyte. Blue-to-green electrochromicity was achieved in a two-electrode cell by complementing the green-to-blue color transition (on reduction) of the pp—Yb(Pc)2 film with the blue (PB)-to-colorless (PW) transition (oxidation) of the PB. A three-color display (blue, green, and red) was fabricated in a three-electrode cell in which a third electrode (ITO) was electrically connected to the PB electrode. A reduction reaction at the third electrode, as an additional counter electrode, provides adequate oxidation of the pp Yb(Pc)2 electrode, resulting in the red coloration of the pp—Yb(Pc)2 film. 

While GC has not been used extensively to analyze polyamines, a review in 2002 comprehensively covers useful methods (Teti et al., 2002) and a review in 2001 includes specific methods for various polyamines that are used to monitor cancer remission (Khuhawar and Qureshi, 2001). Using activated Permutit for cleanup and heptafluorobutyric anhydride for derivatization, sensitivities of 0.02-0.1 pmol were achieved for commonly analyzed polyamines using GC-ECD and human plasma samples (Teti et al., 2002). NPD also has utility because low detection limits are easily attained (Teti et al., 2002). PFB derivatives have shown some utility with GC-ECD (Coutts and Baker, 1982 Clements et al., 2004), and heptafluorobutryic anhydride with GC-ECD has also been used with success for analysis in human blood samples (Fujihara et al., 1983). 

Many antipsychotics show great interindividual variation in plasma levels and so analysis of therapeutic levels can be important clinically as well as in the research laboratory. In addition, nonresponse to the drugs may actually be due to excessive levels of neuroleptics, a paradoxical situation that requires analysis to identify (Rockland, 1986). Several methods using FID were cited in the previous edition of the Handbook of Neurochemistry but ECD and NPD have both shown utility for the typically low therapeutic levels (Cooper, 1988). GC-FID has been used to analyze levels of clozapine in blood, gastric, and urine samples in fatal cases of overdose with this drug (Ferslew et al., 1998), and olanzapine has been measured in blood and urine samples by GC-NPD in overdoses (Stephens et al., 1998). 4-(4-Chlorophenyl)-4-hydroxypiperidine, a metabolite of haloperidol, was analyzed in urine, plasma, brain, and liver from haloperidol-treated rats by GC-ECD, after derivatization with PFBC under aqueous conditions (Fang et al., 1996). 

Plasma Extract denatured sample with petroleum ether- GC-ECD 1.0 g/L 102 (for hexa) Willet et al. 1978... 

Figure 6.1 Bar-graph of MeHg in CRM 580. The results correspond to six replicate determinations as performed by different laboratories using various methods. MEANS indicates the mean of laboratory means with 95% confidence interval. Abbreviations-. CVAAS, cold vapour atomic absorption spectrometry CVAFS, cold vapour atomic fluorescence spectrometry ECD, electron capture detection GC, gas chromatography HPLC, high-performance liquid chromatography ICPMS, inductively coupled plasma mass spectrometry MIP, microwave induced plasma atomic emission spectrometry QFAAS, quartz furnace atomic absorption spectrometry SFE, supercritical fluid extraction.

Giachetti et al. [60] compared the performance of mass selective detector (MSD), electron capture detector (ECD) and nitrogen-phosphorus detector (NPD) of gas chromatography systems in the assay of six nonsteroidal antiinflammatory drugs in the plasma samples. As a practical test, six NSAIDs (mefenamic, flufenamic, meclofenamic and niflumic acids, diclofenac and clonixin) added to plasma samples were detected and quantified. The analyses were carried out after solvent extraction from an acidic medium and subsequent methylation. The linearity of response was tested for all the detection systems in the range of 1-25 ng/mL. Precision and accuracy were detected at 1, 5 and 10 ng/mL. The minimum quantifiable level for the six drugs was about 1 ng/mL with each of the three detection systems. 

The external factors influencing nimodipine concentrations during intravenous administration were studied using GC-electron-capture detection [18]. Nimodipine was extracted from plasma and analyzed using a column (1.8 m x 2 mm) packed with 3% of OV-17 on gas-Chrom Q (50-100 mesh). The column was operated at 255°C with nitrogen as the carrier gas (flow rate of 25 mL/min), and 63 Ni ECD. The calibration graph was linear for upto 1000 ng/mL, and the limit of detection was 0.5 ng/mL. 

Halogenated acyl derivatives of steroids have been applied in order to increase sensitivity of the analysis. It follows from a comparison of the ECD responses of haloacetates of steroids that the highest sensitivity can be obtained with the aid of monochloro-acetates [351]. Brownie et al. [352] applied them in the analysis of testosterone in blood. The method involves the extraction of blood plasma with diethyl ether, purification by TLC and derivatization. GC analysis is performed only after a preliminary separation on a thin layer. Preparation of the derivatives is carried out by treating a dried extract with... 

Peritafluorobenzyloximes also provide high ECD responses and have been applied to the determination of dehydroepiandrosterone in human plasma [377]. As in previous instances, the reaction is carried out in pyridine, as follows. Pentafluorobenzyloxyammo-nium chloride (0.2 mg) is added to a solution of 17-ketosteroids (ca. 1 ng) in pyridine (2 drops) and is heated for 1 h at 60°C. The reaction mixture is diluted with n-hexane (3 ml), washed gradually with water (1 ml), 0.1 N HC1 (1 ml), 0.1 N NaOH solution (1 ml) and water (1 ml) and centrifuged. After evaporation of the solvent, the residue is silylated with HMDS (0.) ml) + TMCS (0.1 ml) in pyridine (5 drops). After 5 min at room temperature, the mixture is analysed directly or the solvent is evaporated, the residue is dissolved in -hexane (1 ml) and 2 /u 1 are analysed. 

Pentafluorophenylhydrazones permit up to 0.1 ng of estrone to be determined with the ECD [381 ]. A hydroxyl group in position 3 is blocked by methylation with dimethyl sulphate and the reaction with pentafluorophenylhydrazine is performed in methanol in the presence of acetic acid. A column packed with 1% of XE-60 on Gas-Chrom Q at 205°C is suitable for the analysis. The determination of free estrone in blood plasma by this procedure provides good results provided that the measurement is corrected for the total recovery. 

For the GC analysis of these substances trimethylsilyl derivatives are mostly prepared. Chloramphenicol is silylated with the aid of BSA [520,521 ]. Some workers [522], however, prefer an HMDS—TMCS mixture in pyridine as it is said to result in a more uniform product. The analysis is performed on silicone stationary phases of the SE-30 and OV-17 types. The related thiamphenicol is converted into the TMS derivative by treatment with BSA [523,524] and the same stationary phases are used for GC. If this method is applied to the determination of these substances in plasma and body fluids, and a selective detector is used (63Ni ECD), a sensitivity of determination of 0.1 jug/ml can be reached. 

Anticholinergics, such as atropine and oxyphenonium bromide, which are esters of carboxylic acids, were analysed in plasma and urine as pentafluorobenzyl esters [541,542], The method involves ion-pair extraction of the material under analysis, hydrolysis of esters and derivatization of the acid moiety. The minimal detectable amount was found to be 0.15 pg with the use of an ECD. 

Propranolol and related substances can be converted into TFA derivatives [558,559], which permit concentrations down to 10 ng/ml in plasma and similar samples to be analysed with the use of an ECD. The application of pentafluoropropionic anhydride [560] leads to a reduction in the time necessary for the analysis (acylation for 1 min at 70°C) and enables higher sensitivity of the determination to be obtained. 

Tolmetin, an anti-inflammatory drug, and its metabolites were chromatographed after esterification of the carboxyl group with diazomethane [564], The extraction was performed with diethyl ether and was followed by purification and analysis on 3% of OV-17. The determination of pethidine in plasma [565] involves extraction, purification of the extract by partition chromatography and derivatization, which is performed by treatment with trichloroethyl formate in the presence of anhydrous sodium carbonate. The detection limit with an ECD was reported to be 5 pg. 

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