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91.
92.
Cyclic voltammetry in a perfluorocarbon emulsion based blood substitute (PEBS) was evaluated. The intent was to determine how PEBS affects the voltammetry of four representative electroactive compounds: potassium ferricyanide, ruthenium(II) trisbipyridine (rutris), hydroquinone, and 2,6‐dichloroindophenol (DCIP). Voltammograms in 0–20% PEBS‐Tris buffer mixtures are affected by PEBS, but reasonably well‐defined voltammograms are obtained in as much as 20% v/v. This report also shows that PEBS has only a small effect on amperometric detection of the reaction between DCIP and nicotinamide adenine dinucleotide (NADH), which has importance in clinical homogeneous immunoassays. Results support continued exploration of voltammetry/amperometry for quantitative analysis in this medium. 相似文献
93.
Summary A method is described for the determination of the enantiomeric purity (enantiomeric excess) of the anticholinergic drug oxyphenonium. The method for this quaternary ammonium compound is based on the direct HPLC analysis with a chiral stationary phase. Two kinds of 1-acid glycoprotein-bonded phases were used.For the detection a post-column extraction with fluorescence detection of the ion-pair counter ion dimethoxyantracene sulphonate was used. 相似文献
94.
Three different types of SCD combustion source have been evaluated for use in the chromatographic analysis of atmospheric sulfur compounds. The conventional FID source and the newer inverted burner source were found to be less sensitive and less stable than the flameless design. Overall, the flameless source was superior for use with HRGC-SCD. 相似文献
95.
Summary A comparison of the official EPA method 515.1 for determination of chlorinated acidic pesticides and a modification of it is illustrated. Extraction of the analytes from water and their determination and quantitation is by gas chromatography-electron capture detection (GC-ECD), liquid chromatography-UV detection and liquid chromatography-particle beam mass spectrometry. Although HPLC-PBMS was found to be less sensitive than the GC-ECD method, it was, nevertheless, more sensitive than HPLC-UV. The modified method is simpler, quicker and allows more accurate determination of pesticides in aqueous samples.Deceased July 31, 1996 相似文献
96.
A method for the determination of trace Cr(III) in aqueous solution by solid-phase microextraction (SPME) coupled with gas chromatography (GC)-flame photometric detection (FPD) was developed. Aqueous Cr(III) was first converted to the volatile chromium trifluoroacetylacetonate (Cr(tfa)3) by derivatization with 1,1,1-trifluoroacetylacetone (Htfa), followed by SPME extraction using a polyimide-coated silica fiber. The distribution constants (K) of derivatized cis- and trans-Cr(tfa)3 between the polyimide phase and aqueous phase were 2012 and 2214, respectively. The two Cr(tfa)3 isomers extracted can be efficiently separated by a DB-210 GC column within 9 min. Selective detection of Cr was performed by a FPD equipped with a 385-nm long-pass filter. Linearity (r> 0.99) over the concentration range 5-300 ng ml(-1) Cr was obtained and the limit of detection was 2 ng ml(-1) Cr. The relative standard deviation was 7% at 10 ng ml(-1) Cr (n = 5). Applicability of this method to water analysis was tested by analyzing the chromium content in a reference standard water sample and an industrial effluent. 相似文献
97.
We report a common HPLC method for the single or simultaneous determination of four calcium channel blockers (CCB), namely diltiazem (DTZ), verapamil (VER), nifedipine (NIF) and nitrendipine (NIT) and their active metabolites demetildiltiazem and deacetildiltiazem (MA and M1), norverapamil (NOR), and dehydronifedipine (DHN). DHN was first synthesised in our laboratory and different pH values of the mobil phase were subsequently prepared and tested for chromatographic separation. The detection system and the environmental light conditions were optimised. The best separations of all analytes were obtained using a C18 column and a mobile phase of methanol, 0.04 M ammonium acetate, acetonitrile and triethylamine (2:2:1:0.04 v/v). Quantitation was performed using imipramine (IMI) as the internal standard. For DTZ and its metabolites (M1 and MA), the wavelength chosen was 237 nm; for VER and its metabolite NOR, it was 210 nm; and, finally for NIF and its metabolite DHN and NIT it was 216 nm. When a simultaneous analysis was carried out the wavelength was of 230 nm. The optimum pH were 7.90 and 7.10 when the separation of NIT and DTZ or VER and NIF were carried out, respectively, and 7.90 when a simultaneous separation was carried out. The detection limit of the assay was less than 8 ng ml−1 for all compounds, with coefficients of variation less than 7% (for inter- and intra-day) over the concentration range of 1–1000 ng ml−1. The retention times were less than 11 min. When NIF or NIT were studied, it was necessary to use a sodium vapour lamp in order to avoid the photodegradation which takes place under daylight conditions. 相似文献
98.
Summary Capillary electrophoresis (CE) has proved to be a fast and convenient method for the determination of the dissociation constants
of non-UV absorbing solutes in the acidic pK
A range (2.0–2.5).
The electroosmotic flow was reversed by washing the capillary with 0.2% polybren aqueous solution. A series of background
electrolytes was prepared with phenylphosphonic acid (pK
A=1.29) and β-alanine (pK
A=3.55) with the same ionic strength and a high buffer capacity in order to improve the repeatability (0.1–0.2 %) of the electrophoretic
mobility and to determine the values of pK
A accurately.
This procedure was applied to the determination of the dissociation constants of several alkyl-alkylphosphonic acids whose
pK
A values have not yet been published in the literature. In this work, their dissociation constants have been found to vary
between 1.91 and 2.34 for alkyl-methylphosphonic acids and between 2.10 and 2.38 for alkyl-ethylphosphonic acids. 相似文献
99.
Thermal lens detection with a 325.0 nm He-Cd excitation laser is used for thermooptical indirect detection in combination with the capillary electrophoretic separation of organic anions. The optimization of indirect thermooptical detection is discussed. With Mordant Yellow 7 (an azo dye) chosen as a probe ion limits of detection for 1-heptane-, 1-pentane-, 1-butane-, 1-propanesulfonic, and acetic acid at a level of n × 10−7 M were achieved with a separation electrolyte containing 50 μM of the probe ion and 5 mM Tris pH 9.90. A further increase in the detection sensitivity (twofold decrease in the limit of detection ) was obtained with a separation electrolyte containing a volume fraction of 20% acetonitrile. 相似文献
100.
Regulations for pesticide residue analysis in food require very low detection limits; thus requiring maximum sensitivity in
the gas chromatographic determination. This is accomplished by an overall method optimisation, which includes optimisation
of injector parameters. Here we study the effect of the inlet liner design on the optimisation by comparing five liner designs
in splitless and pulsed splitless injection modes, using a test mixture of fifteen pesticides analyzed by GC-ECD. Possible
links between the injection parameters and liner types were evaluated, with the result that, accurate choice of inlet liner
and injection parameters can reduce detection limits by up to 300%.
Revised: 25 October 2005 and 9 January 2006 相似文献