Sensitive flotation-spectrophotometric method for the determination of vanadium (IV) with 3,5-dinitrosalicylic acid and rhodamine B

Vanadium(IV) is determined by reaction with 3,5-dinitrosalicylic acid and rhodamine B in weakly acidic medium. The flotation of the ternary ion-association complex is carried out with cyclohexane followed by dissolution in acetone for subsequent spectrophotometric determination. The molar absorptivity is 5.91×10⁵ l mole^–1 cm^–1 at 555 nm. Beer's law is obeyed in the range 0.05–1.5 g vanadium(IV) in 25 ml. The method is selective for vanadium(IV) in the presence of sodium fluoride and has been applied to standard reference materials.     

Continuous-flow potentiometric determination of creatinine in urine with a picrate ion-selective electrode

A completely automated potentiometric method for the determination of creatinine in urine is described. Creatinine reacts with picrate in alkaline media (Jaffé reaction) in a flow system, and the decrease in picrate activity is continuously monitored with a picrateselective flow-through electrode. Creatinine in urine, in the range 0.5–3 g/liter, was determined in a sample volume of 0.15 ml, with a relative standard deviation of about 1%. Forty samples per hour can be analyzed without previous dilution or pretreatment. Recovery of creatinine added to urine samples ranged from 90 to 111% with an average of 96.7%. The method compares favorably with a photometric method. The proposed automated method is suitable for routine clinical measurements and screening tests.     

Differential pulse polarographic determination of sulfuric acid

Acetonitrile is used as a solvent for the determination of micromolar amounts of sulfuric acid by differential pulse polarography. Contaminants in the supporting electrolyte and solvent present the biggest problems to the accurate determination of sulfuric acid. The detection limit is 2 × 10^-7 M. Nitric acid. bromide, soluble sulfates, and ammonium hydrogensulfate interfere under certain conditions.     

乙醛酸的微分脉冲极谱法定量分析

建立了乙醛酸的微分脉冲极谱定量分析方法, 乙醛酸在100 g/L KOH底液中, 于-1.35 V (vs. Ag/AgCl)处出现一良好的微分脉冲极谱峰, 并能排除主要杂质草酸的干扰. 乙醛酸浓度与其电流峰幅值呈显著的线性关系, 当标准加入的极谱电流峰高和样品极谱电流峰基本一致时, 测量误差小于0.5%.     

Spectroscopic studies on intra- and inter-molecular hydrogen bonding in 2,4-dinitrophenol and 3,5-dinitrosalicylic acid

Effect of solvent on the electronic spectral behaviour of 2,4-dinitrophenol (I) and 3,5-dinitrosalicylic acid (II) is examined and discussed. It is deduced that in case of (I) the intramolecular hydrogen bond to nitro breaks to form an intermolecular hydrogen bond depending upon the nature of solvent used whereas (II) remains intramolecularly hydrogen bonded to carbonyl group in solvents as strongly basic as DMF.     

Determination of the second ionization constant of 3,5-dinitrosalicylic acid (DNSH2) and the instability constant of [DNSFe]+ and titrimetric determination of thiourea with a 3,5-dinitrosalicylate-selective electrode

Measurements made with a combination of glass and 3,5-dinitrosalicylate-selective membrane electrode in DNSHNa solutions varying in pH and ionic strength have been used to determine the second ionization constant of 3,5-dinitrosalicylic acid. Also the instability constant of the complex [DNSFe]⁺ has been determined by titrating known amounts of iron(III) with standard DNSHNa solution. A method has been developed for the semiautomatic potentiometric titration of thiourea with silver nitrate in the presence of 3,5-dinitrosalicylate ions, using the aforementioned selective electrode. Thiourea in the range 1.5–15 mg was determined with average relative error and relative standard deviation of about 1%.     

The polarographic determination of microgram quantities of oxalic acid

A brief critical summary of possible methods for the determination of micro quantities of oxalic acid in solution is presented, and details are given of a satisfactory polarographic procedure for the determination of this material down to a level of 10 microg per ml in the final solution. This method involves the adjustment of the pH of the sample solution, followed by precipitation of the oxalic acid as europium oxalate. The excess europium is then determined polarographically. The method is applicable in the presence of 1M ammonium nitrate and in the presence of ammonium salts of other common acids. Iron and chromium interfere and must be absent.     

Differential pulse polarographic determination of citric acid with a soluble enzyme preparation

Summary An electrochemical method for the specific determination of citric acid in sports drink and plaster using citrate lyase and oxaloacetate decarboxylase has been studied. The technique is reasonably rapid and simple to perform. Results from recovery experiments are excellent, i.e. recovery is 99.7±3.0% at a confidence limit of 95% (n=3), and reproducibility (R.S.D.) at 20 mol/l citric acid is 1.46% (n=3). The method can possibly be used for monitoring citric acid in clinical and food-processing samples.

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Differentialpuls-polarographische Bestimmung von Citronensäure mit Hilfe eines löslichen Enzympräparats

     

3,5-二硝基水杨酸比色法在烷基多苷体系中的应用研究

将3,5-二硝基水杨酸比色定糖法(DNS法)引入烷基多苷体系中,研究了丁苷化过程中葡萄糖含量随时间的变化,表征了丁苷化反应产率,测定了烷基多苷产品中残留的葡萄糖含量,并将测定结果与传统方法进行了比较,结果表明该法是一种简便快速、准确度高的方法。     

Dissociation of 5-fluoro- and 3,5-dinitrosalicylic acids in water-methanol mixtures at 25 degrees

The association constants and molar conductivities, extrapolated to zero concentration, have been determined for 3,5-dinitrosalicylic and 5-fluorosalicylic acids in water-methanol mixtures at 25 degrees .     

Binding studies on substituted benzoic acids: Part I. 3,5-dinitrosalicylic acid—acid dissociation and complexation with nickel(II) and cobalt(II)

The values of pK₁ and pK₂ for 3,5-dinitrosalicylic acid (DNSA, H₂L) have been determined at 25.0°C and 0.1 M ionic strength (sodium perchlorate) as 0.25 and 7.20. respectively. The binding of nickel(II) and cobalt(II) has been investigated over the pH range 1.0–7.0 at the same temperature and ionic strength. Values of log K_ML for the formation of the unprotonated complexes are 4.05±01 and 3.82±01 for nickel(II) and coball(ll) respectively. Values for log K_MHL are close to 11 mol^-1 for both metals; it seems probable that these species are not inner-sphere complexes, and possible reasons for this are suggested. The stability constants obtained are compared with others in the literature, and the possibility of using DNSA as a metal-ion indicator is discussed briefly.     

Differential-pulse polarographic determination of isonicotinic acid hydrazide,and analogous hydrazides in admixture

The differential pulse polarographic behaviour of isonicotinic, nicotinic and picolinic acid hydrazides in Britton-Robinson buffers of pH 2–11 is described. The isonicotinic compound (isoniazid) is best determined at pH 5–6 at a peak potential at ca. ?1.0 V (vs. Ag/AgCl). This method was applied to analysis of tablets. At pH 9, the peak potentials are ?1.22, ?1.34 and ?1.6 V, respectively, for the three hydrazides mentioned. Calibration graphs are linear in the range 10^?6?5×10^?4 M with relative standard deviations of 1.4–2.5%.     

New analyser for the determination of urinary vanillylmandelic acid, homovanillic acid and creatinine

We have developed a novel analyser for the determination of vanillylmandelic acid, homovanillic acid and creatinine in urine by high-performance liquid chromatography using three different types of column, cation-exchange, anion-exchange and reversed-phase and the column-switching technique. In this procedure, 10 microliters of intact urine were directly injected into the cation-exchange column, and the pass-through fraction, containing vanillylmandelic acid and homovanillic acid was transferred to the anion-exchange column by column switching. The fraction partially purified from endogenous urinary impurities on the anion-exchange column was transferred to the reversed-phase column. Vanillylmandelic acid and homovanillic acid, separated by the solvent-switching technique, were detected fluorimetrically (excitation at 280 nm, emission at 320 nm). Then, creatinine eluted from the cation-exchange column is spectrophotometrically detected (254 nm). Therefore the successive simultaneous analysis of the three could be performed in a 15-min cycle; the within-assay coefficients of variation for normal and patients' urines were less than 1.9%, less than 3.3% and less than 3.0% for vanillylmandelic acid, homovanillic acid and creatinine, respectively; the recoveries averaged 100, 103 and 100%, respectively, for supplemented urines.