Determination of cadmium in indium phosphide by electrothermal atomic absorption spectrometry and ion-selective electrode potentiometry

 Two independent methods for the determination of cadmium in cadmium-doped indium phosphide have been developed. Electrothermal atomic absorption spectrometry (ETAAS) utilized both platform atomization and a chemical modifier composed of magnesium nitrate and orthophosphoric acid. As the matrix mass was found to influence the cadmium sensitivity, matrix matched calibration standards were necessary. The detection limit (3s_B) is 0.20 μg/g for a 100 mg sample. The electrochemical method employed a solid-state cadmium sulfide-silver sulfide electrode as potentiometric sensor. An excess of indium (III) influenced the electrode response. A preliminary chelation-extraction of indium with acetylacetone at pH 5.0 in acetate buffer overcame the interference. The detection limit of the ISE-potentiometric method is 10 μg/g for a 200 mg sample. Two indium phosphide single crystals grown from melts doped with cadmium sulfide or cadmium telluride were analyzed for their cadmium content. Received: 27 August 1996/Revised: 27 January 1997/Accepted: 30 January 1997     

Determination of fluoride in natural waters by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate

The most effective conditions for masking aluminium in the determination of mug/1. levels of fluoride in water by ion-selective electrode potentiometry after co-precipitation with aluminium phosphate have been re-examined. The effectiveness of citrate for masking aluminium increases with pH, and up to 1.5 x 10(-2)M aluminium can be masked quantitatively at pH 8.5. Fluoride (5-100 mug in 500 ml of sample solution) is quantitatively co-precipitated at pH 4.7 with approximately 90 mg of aluminium phosphate. After dissolution of the precipitate and adjustment of the solution to pH 8.5 with TISAB, the fluoride content can be measured with a fluoride ISE. The method is simple and rapid, and is suitable for the determination of trace amounts of fluoride in various water samples.     

Determination of chlorine in silicate rocks by ion-exchange chromatography and direct potentiometry with an ion-selective electrode

The method has been developed for determination of chlorine in silicate rocks by ion-exchange chromatography and an ion-selective electrode.     

A micromethod for the determination of selenium in tissues and biological fluids by single-test-tube fluorimetry

A sensitive single-test-tube procedure for the fluorimetric determination of ng quantities of selenium with diaminonaphthalene, from small samples of animal origin is described. Several parameters related to the nitric/perchloric/sulphuric acid digestion, subsequent reduction and piazselenol formation are studied using blood as the matrix. The detection limit is 0.45 ng Se. The within-series precision for blood and heart tissue is 4.2% and 2.3% and between series is 5.0% and 3.6%, respectively. Recovery of added selenite and selenomethionine to blood, heart tissue and urine ranges from 98–101%. The correlation coefficient between the proposed and an electrothermal atomic absorption spectrometric method for serum samples is 0.997. This procedure is especially suitable for serial operation with a daily (8-h) throughput of 25 samples in duplicate.     

Simplified computations for standard-addition methods in ion-selective potentiometry

A fast iterative procedure is described for calculating the initial concentration or the slope of the calibration plot on the basis of two standard additions. An iterative non-linear least-squares procedure is reported for evaluation of the unknown concentration, slope and standard potential in the Nernst equation and the Basic program has only 56 statements.     

Determination of phosphate in hydroponic nutrient solutions using flow injection potentiometry and a cobalt-wire phosphate ion-selective electrode

The direct flow injection potentiometric (FIP) analysis of phosphate in hydroponic nutrient solution has been carried out using a cobalt-wire ion-selective electrode (ISE). Synthetic hydroponic nutrient solution, commercial hydroponic nutrient solution and working hydroponic farm nutrient solution were analysed for phosphate using the FIP technique. It is shown that FIP results compare favourably to standard methods of analysis such as spectrophotometry and indirect photometric ion-pair chromatography. Reproducible FIP response curves with a slope of −(47.57±0.03) mV per decade and intercept of −(169.7±0.1) mV were obtained for four separate calibrations in the concentration range 5.0×10⁻⁴–1.0×10⁻² M H₂PO₄⁻. Anion corrections for interferences by Cl⁻, NO₃⁻ and SO₄²⁻ were applied to all samples using the selectivity coefficients determined independently using a fixed interference method. Nevertheless, it was found that anion corrections were not necessary, as the deviations fell within the bounds of experimental error for the cobalt-wire ISE technique (i.e.±2–5% R.S.D.). The proposed FIP method enables the direct determination of phosphate in hydroponic nutrient solutions.     

Stopped-flow kinetic determination of aluminum in Chinese tea leaves by fluoride ion-selective electrode potentiometry

A stopped-flow kinetic potentiometric method for the determination of aluminum is described, based on monitoring the reaction between aluminum and fluoride at pH 3.0 using fluoride ion-selective electrode. The initial rate of the reaction is proportional to the concentration of aluminum present in the solution. The method is simple and rapid and has been applied to the determination of aluminum in Chinese tea leaves after microwave digestion.     

Determination of N-acetyl-L-cysteine by flow-injection potentiometry

A multi-purpose tubular flow-through sensor was constructed with an AgI-based membrane. The membrane was prepared by pressing silver salts (AgI, Ag₂S) and powdered Teflon. This membrane was incorporated in the tubular flow-through sensor body. A 2-mm diameter hole was drilled through the center of the tubular sensor and the membrane, thus determining the active sensor volume of about 4 μL. The tubular sensor with reference electrode was placed into a complex flow-injection system and used for the flow-through determination of N-acetyl-L-cysteine, (NAC), in perchloric acid medium, pH = l. Linear dependence was established between the recorded signal height and the concentration of NAC in the injected sample. The recorded change in potential for a decade change in concentration, 62 mV {p (NAC)}^–1, in the concentration range from 1 × 10^–4 to 1 × 10^–1 mol L^–1, was based on the formation mechanism of the sparingly soluble deposit between silver and NAC on the surface of the sensitive part of the membrane. Received: 7 July 1997 / Revised: 22 September 1997 / Accepted: 26 September 1997     

荧光法测定尿中的富马酸比索洛尔

建立了直接测定尿中富马酸比索洛尔的荧光分光光度法。荧光强度与富马酸比索洛尔含量在100－1000ng/mL范围内呈线性关系。检测限20ng/mL。对浓度100ng/mL与500ng/mL的标准溶液进行测定,其回收率分别为95．6％和99．6％,相对标准偏差为5．6％和2．3％,可用于 尿中富马酸比索洛尔含量的测定。     

Determination of histamine in biological fluids by capillary isotachophoresis and fluorescence

Analytical isotachophoresis was used for the determination of histamine in biological fluids. For biological fluids with a very low content of histamine a method was developed that combines the fluorescing condensation product of histamine and o-phthaldialdehyde with the high concentration effect of isotachophoresis. This method permits the determination of histamine in serum and other biological fluids down to less than 3 ng/ml.     

Determination of mercury in biological fluids by potentiometric stripping analysis

A method is described for the determination of mercury by potentiometric stripping analysis. The analyte, Hg²⁺, is employed for oxidizing a fixed amount of cadmium, previously reduced and amalgamated at a thin mercury film preplated on a glassy carbon electrode. The cadmium stripping signal correlates well with the amount of Hg²⁺ added. Correlation coefficients of 0.9971 and 0.9960 were obtained for the two working ranges: (25 ng–2.5 g) and (5.0–50) g Hg²⁺, respectively, in spiked water samples. The method was investigated with respect to precision and accuracy by spiking a natural water sample with 25 g Hg²⁺.Nine replicate determinations gave a mean value of 24.8 g with a standard deviation ±0.31 g. The 95% confidence limit of the mean suggested the absence of systematic errors. Using the highest possible sensitivity, detection limits of 2.0 ng (167 ng/l) and 0.5 ng (4.2 ng/100 ml of whole blood) were obtained in water and blood samples, respectively. The applicability of the method was successfully extended to include the more complex matrices after recording a zero blank from authentic samples spiked with Cd²⁺ (25 g).The described PSA procedure is a simple and rapid method compared with the cold-vapor technique, with a 5.2% and 4.9% RSD, respectively.     

Determination of ciclazindol in biological fluids by differential pulse polarography

A differential pulse polarographic method has been developed for determination of the antidepressant, 10-(m-chlorophenyl)-2,3,4,10-tetrahydropyrimido[1,2a]indol-10-ol hydrochloride in plasma and urine. The method involves solvent extraction of the drug from the plasma or urine, evaporation to dryness and dissolution of the residue in 10% methanolic 0.01 M tetraethylammonium chloride solution followed by differential pulse polarography. The mean recovery of the drug from plasma containing 0.5–5.0 μg ml^-1 is 80%; the coefficient of variation is 5.5% at the 1.0-μg ml^-1 (2.98 × 10^-6 M) level on 2-ml samples. The method is not subject to interference from the chemical degradation products and metabolites. The techniques described have been applied to the analysis of human plasma; the polarographic and gas Chromatographic results showed good agreement.     

Determination of chlorproguanil and metabolites in biological fluids

Summary The retention behaviour of chlorproguanil and its putative metabolites chlorcycloguanil and 3,4-dichlorophenylbiguanide has been studied on a reversed phase chromatographic system incorporating sodium lauryl sulphate as hydrophobic pairing ion. On the basis of data obtained and comparison of standard compounds with components present in urine following the administration of chlorproguanil, the identity of the metabolites have been confirmed chromatographically. A third unidentified metabolite is also observed. The retention study allows selection of a solvent system which, when used with a small volume, 100 × 2 mm, 3μm ODS column, enables chlorproguanil and its two major metabolites to be determined in plasma, whole blood and urine. The analytical characteristics of the method are reported and the usefullness of the method in obtaining pharmacokinetic data on the drug and its metabolites is discussed.     

Determination of drugs and metabolites in biological fluids

The determination of drugs and metabolites in biological fluids (biopharmaceutical analysis) is becoming increasingly important in the pharmaceutical and biomedical sciences. Successful analyses require sensitivities at ppb-level or less, high selectivity, and minimal interferences from artifacts. Modern approaches to biopharmaceutical analysis rely principally on chromatographic and immunochemical methods.     

Determination of trimethoprim in biological fluids by high-performance liquid chromatography

A rapid, sensitive, and specific high-performance liquid chromatographic assay was developed for the determination of trimethoprim in blood, plasma, and urine using normalphase (adsorption) chromatography on a microparticulate silica column and UV monitoring at 280 nm. Trimethoprim is selectively extracted from the biological sample matrix at alkaline pH with chloroform, providng nearly quantitative extraction (greater than 95%) and a sensitivity limit of 0.01 to 0.02 microgram/ml blood or plasma, without interference from sulfonamides.