吖啶红动力学荧光法测定痕量甲醛

在H2SO4介质中，以KCIO3-吖啶红为指示反应，建立了测定甲醛的动力学荧光分析法。方法的线性范围为40～600μg／L，检出限为27μg／L。方法用于树脂整理特殊织物和动物标本室内空气中甲醛的测定，与标准方法乙酰丙酮分光光度法进行对照，所测结果经t-检验无显著性差异。     

动力学光度法测定痕量甲醛

在稀硫酸溶液中,甲醛对KClO3氧化罗丹明6G褪色反应有催化作用,研究了其动力学条件,建立了测定痕量甲醛的动力学光度分析方法,线性范围为0.02～1.8μg/mL,检出限为1.5×10-8g/mL。该法用于湖水、饮料和漆料中痕量甲醛的测定,标准加入回收率为93.8%～108.5%,RSD为2.6%～3.4%。     

Kinetic potentiometric determination of citric acid with a perbromate-selective electrode

Citric acid is determined in the 96–960-μg range with relative errors of about 1% by means of its iron(II)-induced reaction with perbromate. Each analysis takes about 8 min. Tartaric and lactic acids interfere.     

Kinetic identification and determination of certain carbohydrates with a periodate-sensitive perchlorate-selective electrode

The reactions between periodate and carbohydrates are easily monitored with a perchlorate-selective electrode as a periodate sensor. The relative reaction rate constant of each carbohydrate compared to glucose is introduced as a new characteristic constant, the “periodate index”, which could be related to the molecular configuration. Since appreciable differences are observed between the “periodate index” values of various carbohydrates, this constant can be used for the identification of 20-mg amounts of single pure compounds. An automatic potentiometric reaction rate method is described and shown to be simple, rapid and accurate for the determination of glucose. Amounts of glucose in the range 7–54 mg were determined in 20–140 s with precision and relative errors of about 0.4 and 0.8 %, respectively.     

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

A new kinetic method for the potentiometric determination of creatinine in urine based on the creatinine-picrate reaction in alkaline medium (Jaffé reaction) is described. The reaction is monitored with a picrate-selective electrode, and the increase in electrode potential within a fixed period of time (90 sec) is measured and related directly to the creatinine concentration. Analytical recovery of creatinine added to urine was 86–101% (average, 95.5%). Comparison with a spectrophotometric method gave a correlation coefficient of 0.992 over a concentration range of 0.6–2.6 g/liter.     

Effect of metal ions on the response of a cyanide-selective electrode

An extended model and its experimental verification are presented for the response of a cyanide-selective electrode in the presence of metal ions. The model takes into account the effect of metal-hydroxide complexes ar high pH values. The electrode responds to the total cyanide concentration even in the presence of an excess of zinc and cadmium ions. When copper(I) is present, the cyanide complexes must be decomposed before the total cyanide concentration can be measured. The results show the importance of considering both metal-cyanide and the metal-hydroxide complexation.     

Kinetic determination of l-alanine and l-alanine dehydrogenase with an ammonia gas-sensing electrode

The ammonia gas-sensing electrode is used to assay l-alanine and l-alanine dehydrogenase. Alanine is de-aminated by bacterial alanine dehydrogenase in the presence of β-NAD⁺. The initial rate of ammonia release is proportional to alanine concentration or the enzyme activity. Optimal conditions for the assays are specified. Alanine (1.0 × 10^?4-1.0 × 10^?3 M in a 1-ml sample) and enzyme (0.181-0.181 U in a 0.1-ml sample) can eb determined. Application to the determination of alanine in human serum gave results that compared well with values obtained by the Yoshida method.     

Differential-pulse voltammetric determination of trace formaldehyde using magnetic microspheres and magnetic electrode

A new type of magnetic polymer microsphere containing acylhydrazine groups on the surface was synthesized. They can be reacted with formaldehyde to produce an electroactive adduct. Reduction of these derivatives following aggregation on a magnetic electrode is possible and is effective in the indirect determination of formaldehyde. The experimental conditions and electrode structure are discussed. Under the optimum conditions, it was found that the peak potential (Ep) of formaldehyde is -1.01 V (vs. Ag/AgCl). Formaldehyde in the range 1-1000 micrograms l-1 can be determined. The detection limit for formaldehyde is 0.3 microgram l-1 and the relative standard deviation for the determination of 100 micrograms l-1 formaldehyde was 2.26%. The method was applied to the determination of formaldehyde in environmental samples with satisfactory results.     

Kinetic spectrophotometric method for rapid determination of trace formaldehyde in foods

A simple and sensitive kinetic-spectrophotometric method was developed for the determination of ultra trace amount of formaldehyde in food samples. The method was based on the oxidation of rhodamine B (RhB) by potassium bromate in sulfuric acid medium (formaldehyde as catalyst). The reaction was monitored by measuring the decrease in absorbance of the dye at 515 nm after 6 min. The developed method allowed the determination of formaldehyde in the range of 10–100 μg L⁻¹ with good precision, accuracy and the detection limit was down to 2.90 μg L⁻¹. The relative standard deviations for the determination of 10 and 60 μg L⁻¹ of formaldehyde were 3.0% and 1.9% (n = 10), respectively. The method was found to be sensitive, selective and was applied to the determination of formaldehyde in foods with satisfactory results.     

Kinetic determination of glycerol in soaps and of alkaline phosphate activity in serum with a periodate-selective electrode

The reaction of glycerol (0.56–24 μmol in 2-ml samples) with periodate at pH 4.5 is monitored with an improved periodate-selective electrode; the rate of potential increase is measured. The average error is 1.2%; measurement times are < 2 min. Alkaline phosphatase activity is determined indirectly by hydrolysis of β-glycerophosphate.     

Kinetic study of N-bromosuccinimide reactions and kinetic determination of pyridoxine using a bromide-selective electrode

The bromide released by the alkaline hydrolysis of N-bromosuccinimide and its reactions with bromide, pyridoxine and thiamine have been studied potentiometrically using a solid-state bromide-selective electrode to monitor the consumed or produced bromide ion. Potential-time indications are obtained using a microcomputer-controlled potentiometric system. The overall rate constants and the activation energies have been calculated. A kinetic-potentiometric procedure for the determination of pyridoxine in the presence of thiamine in pharmaceutical preparations, based on its reaction with N-bromosuccinimide, is presented.     

煌焦油蓝-溴酸钠体系催化动力学光度法测定痕量甲醛

基于H2SO4介质中甲醛催化NaBrO3氧化煌焦油蓝的褪色反应,建立了测定痕量甲醛的催化动力学分析方法。探讨了该方法的反应机理,对其反应条件进行了研究。测定线性范围为0．16～2．00μg／mL,检出限为8ng／mL。方法已应用于海产品水发液中痕量甲醛的测定。     

乙基橙-溴酸钾体系动力学光度法测定痕量甲醛

研究了在稀H2SO4介质中,痕量甲醛催化KBrO3氧化乙基橙褪色反应的适宜条件和影响因素,建立了测定痕量甲醛的动力学光度法。方法采用固定时间法于507 nm波长处测量体系的吸光度,在适宜条件下,ΔA与甲醛质量浓度具有良好的线性关系,方法的线性范围为0~0.24 mg/L,检出限为0.004 mg/L。该方法用于饮料、废水和废气中痕量甲醛的测定,测定结果的相对标准偏差RSD≤3%(n=6),回收率为102%。     

Multi-electron oxidation of formaldehyde on a platinum electrode

The time evolution of a self-sustained potential oscillation under constant current oxidation of formaldehyde was observed on the rotating ring disk electrode assemble. Under the condition when the potential was controlled, the laser deflection voltammogram as well as the conventional cyclic voltammogram were measured. The mechanism of the multi-electron oxidationof formaldhyde on a platinum electode is discussed.     

Potentiometric and spectrophotometric determination of the protonation constant of hexamethylenetetramine

The protonation constant of hexamethylenetetramine (urotropine) was determined by a potentiometric and a spectrophotometric method. The calculations gave log K_HL (concentration constants): 4·89 at μ = 0·1 and 5·05 at μ = 0·5. The temperature was 25° and potassium chloride was used to adjust the ionic strength.     

铊(I)离子选择电极动力学分析法测定超痕量铁

Fe(II) induces the reaction between Tl3+ and H2O2. The rate of reaction is linearly proportional to the concentration of Fe2+ in the range 2.5 ?10-9-2.5 ?10-8 mol dm-3 (20? and 5 ?10-9-5 ?10-8 mol dm-3 (15?. The standard deviation is less than 0.071 ?10-8. A 1000-fold excess of Zn2+, Cd2+, Mg2+, Ni2+, Pb2+, Ba2+, Ca2+, Li+, Na+, Ag+, NO3-, SO42-, AcO-, HPO42-, 500-fold excess of Al3+, Fe3+, Co2+, Hg2+ and 100-fold excess of Ti4+, Cr3+, Cu2+, Br-, Cl- can be tolerated, but reducing agents such as (NH2)2SO4, NH2OH.HCl interfered. This kinetic method was applied to determine Fe(II) in standard zinc sample and fountain water, with satisfactory results.     

Ampeometric determination of formate with a nickel electrode

Comparison of the amperometric response of platinum and nickel electrodes for formate showed that the sensitivity of the Pt electrode changed with time while that for Ni did not. The nickel electrode was used in a flow-injection system to monitor formate and other single-carbon species and to study the kinetics of selected reactions that produce formate. The detection limit for formate in a 30 μl sample was 0.02 mM with linear response to 7.0 mM. Rate constants for hydrolysis and hydration of chloroform, carbon monoxide, and dimethylformamide in 0.10 M NaOH solution were found to be 2.30 ± 0.05 × 10^?4, 8.5 ? 0.05 × 10^?4, and s^?1, respectively, at 25°C. Advantages of this technique are direct detection of reaction product, low detection limits, fast measurements, reduced exposure to air, and low sample volumes.     

Catalytic determination of selenium with a picrate-selective electrode

A method is described for the determination of selenium, based on its catalytic effect on the picrate—sulfide reaction. The determination involves a variable-time kinetic procedure using potentiometric monitoring with a picrate-selective electrode and automatic measurement of the time required for the potential to change by a preselected amount (5.0 mV). Selenium in the range 3–30 μg was determined with an average error of about 4% and relative standard deviations of about 2%. The reaction can also be followed spectrophotometrically.     

Flow-injection determination of iodide with a silver electrode

A procedure is developed for the flow-injection determination of iodide using a modified silver electrode; it extends the analytical range of iodide by an order of magnitude as compared to potentiometric determination using an iodide-selective electrode with a polycrystalline membrane. The detection limit is 7 μg/L. The procedure was used to determine iodide in natural mineral waters and model solutions. The throughput was 20–25 samples/h.