Spectrophotometric kinetic and determination of quinones and barbiturates.

The kinetics of 1,3-dimethylbarbituric acid with some quinones, namely 1,4-benzoquinone, 1,4-naphthoquinone and p-chloranil in 50% methyl alcohol-water mixture have been investigated spectrophotometrically at 30-50 degrees C. The reaction follows overall second-order kinetics, first order each in reactant. From the dependence of the rate constants on temperature, activation parameters have been calculated. A plot of deltaH# versus deltaS# for the reaction gave a good straight line with an isokinetic temperature of 387.66 K. The rate of reaction increases with increasing dielectric constant of the medium. Based on this reaction, a spectrophotometric determination method of quinones is described. Beer's law was obeyed within the concentration range 2.7-61.5 microg ml(-1) quinone. The method was applied for determination of barbituric, thiobarbituric and 1,3-dimethylbarbituric acids with 1,4-naphthoquinone within a concentration range of 3.2-39.5 microg ml(-1) barbiturate. The reaction mechanism and reactivity have been discussed.     

A.C. polarographic determination of unsaturation

A wide range of olefins can be determined by a.c. polarography of their addition compounds with mercuric acetate. The first step in the reduction of these compounds is a reversible, one-electron process to form the organo-mercury radical and gives a well defined a.c. peak. The optimum conditions for the determination of a representative selection of olefins has been established.     

Isotachophoretic determination of 3-methylhistidine.

A capillary isotachophoretic (cITP) method to determine the concentration of 3-methylhistidine (3-MeHis) in meat and meat products is described. A clear separation of the 3-MeHis from histidine, 1-methylhistidine and other components of acidic sample hydrolyzate was achieved within 20 min. Method characteristics (linearity, accuracy, precision and detection limit) were determined. Low laboriousness, sufficient sensitivity and low running cost are the important attributes of cITP method. The developed method was successfully applied to analyses of real samples and used for the determination of lean meat content in meat and meat products.     

Fluorometric determination of N-nitroso-N-methylurea with nicotinamide and acetophenone.

A fluorometric method for the determination of N-nitroso-N-methylurea (NMU) has been developed. It is based on the N-methylation reaction of nicotinamide with NMU and a subsequent condensation reaction with acetophenone, followed by an acid treatment to form a fluorescent 2,7-naphthyridine derivative. This method enabled the determination of NMU in the range 0.05 - 2 nmol/200 microl with a relative standard deviation of ca. 3%. It was applied to the determination of NMU formed from a precursor N-methylurea (MU) under simulated gastric conditions containing nitrite and thiocyanate ions at pH 3.0 in the presence of fresh orange juice and milk. NMU was extracted by an Extrelut 20 column and then determined. The mean recoveries of NMU added to the simulated gastric juice containing water, orange juice and milk were 86.5, 85.1 and 69.8%, respectively. The amounts of NMU formed from MU were found to decrease to below 25% in the presence of orange juice and milk.     

Stability-indicating method for the determination of clorazepate dipotassium-II. Via N-desmethyldiazepam and determination of its degradation products

A spectrophotometric method for the determination of the intact clorazepate dipotassium in the presence of its degradation products is developed. It depends upon preliminary hydrolysis of clorazepate dipotassium-thus liberating its equivalent of N-desmethyldiazepam which is extracted, with benzene-methylene chloride (9:1). The extract is evaporated, the residue dissolved in methanol and its absorbance measured at about 315 nm. The procedure determines 0.4-1.6 mg of clorazepate dipotassium with an accuracy of 100.2+/-0.7%. The procedure is applied successfully for the determination of clorazepate dipotassium in bulk powder and in capsules; retaining its accuracy in the presence of up to 80% degradation. Determination of the different degradation products is also possible. Thus, N-desmethyl diazepam is determined after preliminary extraction with benzene-methylene chloride mixture, followed by TLC separation, 2-amino-5-chlorobenzophenone by directly applying the first derivative spectrophotometric technique, and glycine in the aqueous layer determined colorimetrically with ninhydrin reagent in the presence of pyridine.     

Spectrofluorimetric determination of tetracycline and anhydrotetracycline in serum and urine.

A spectrofluorimetric method, involving alkaline degradation and formation of a magnesium complex, is described for the determination of tetracycline (TC) and anhydrotetracycline (ATC) in their mixed solution. Tetracycline is degraded and determined in alkaline solution. This treatment of ATC produces almost no fluorescence, but a fluorescent magnesium complex forms at pH 7.5. Several synthetic samples of TC and ATC, with TC:ATC ratios ranging from 50:1 to 1:50, were analysed. The recoveries of TC and ATC are about 71-76 and 61-63% in serum, respectively, and are all about 100% in urine.     

The specific fluorimetric determination of digoxin.

The simultaneous determination of Cd, Cu, Pb and Zn in lead and zinc concentrates by fundamental, second-harmonic and linear-sweep a.c. and pulse polarographic methods is described. Calibration curves are linear over wide concentration ranges, so that both major and minor trace constituents can be determined in the same experiment; thus the polarographic method is highly competitive with atomic absorption spectrometry (a.a.s.). Conventional a.c. polarography and a.a.s. were compared in the first instance with conservative instrumentation. More sophisticated polarographic methods were then utilized; with the phase-selective linear sweep a.c. (fundamental- and second-harmonic) methods the four elements were determined simultaneously from voltammograms obtained in less than 20 s down to the 10^-6-10^-7M concentration range.     

High-performance liquid chromatographic determination of sulphobromophthalein and its conjugates.

A simple, sensitive and selective high-performance liquid chromatographic method for the determination of sulphobromophthalein and its mercaptide conjugates in rat bile was developed. These pigments, which have an absorption maximum at 580 nm in alkaline solution, were separated isocratically on an alkali-resistant ODS column by paired-ion chromatography. Analysis of bile samples obtained after intravenous administration of sulphobromophthalein to rats showed the presence of at least twenty peaks of metabolites, of which thirteen were identified and seven quantified.     

蔬菜、水果中12种限量有机磷农药残留量测定方法

建立了蔬菜、水果中12种限量有机磷农药的提取、净化及毛细管柱气相色谱测定法。目标农药经乙腈萃取,弗罗里硅土柱净化,浓缩后用带火焰光度检测器(FPD)的双塔双柱气相色谱测定,前柱(DB-17)定量,后柱(DB-1)定性。12种农药线性良好,线性相关系数大于0.9990,对蔬菜、水果添加0.01～0.1mg/kg的水平,12种有机磷的平均回收率在70.9%～119.9%之间,相对标准偏差0.12%～12%,本方法的最低检测限0.005～0.05mg/kg。     

Enrichment and determination of zinc by high-speed countercurrent chromatography.

The capability of high-speed countercurrent chromatography (HSCCC) has been investigated for enrichment and determination of metal ions at trace levels. Separation of selected divalent metal ions was performed using a small coiled column. A hexane solution of 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (EHPA) was employed as the stationary phase. Loaded divalent metal ions such as Ni, Co, Cu, and Zn were chromatographically eluted in the order of increasing extractability by passing a mobile phase buffered at a desired pH. Individual metal ions showed good linearity between concentrations and chromatographic peak areas of the absorbance, as detected by postcolumn reaction with 4-(2-pyridylazo)resorcinol (PAR). Metal ions enriched into the stationary phase from a sample solution were separated into individual metal ions. The trace quantity of zinc in natural mineral water was determined by enrichment separation through an HSCCC column.