痕量亚硝酸根的测定及其反应动力学研究

基于盐酸介质中亚硝酸根对过硫酸钾氧化甲基红的褪色反应具有明显的催化作用，提出了测定痕量亚硝酸根的“NO-₂-S₂O2-₈-MR”新体系。结合单因素实验和正交实验建立了该新体系测定痕量亚硝酸根的最佳条件，分析了最佳实验条件下痕量亚硝酸根测定的标准曲线、检出限、精密度和抗离子干扰性能，并讨论了其反应动力学原理及参数，推导了测定痕量亚硝酸根的定量依据。研究表明，该痕量亚硝酸根测定方法的最佳实验条件为：1.0 mL 0.3 mol·L-1盐酸，1.0 mL 0.01 mol·L-1过硫酸钾，0.6 mL 0.2 g·L-1甲基红，在80 ℃水浴加热9 min;定量依据为：在最佳条件下，甲基红最大吸收波长518 nm处的浓度变化ln(A₀/A)与亚硝酸根浓度呈良好线性关系，其线性范围为0.01～0.80 mg·L-1，检出限为0.007 mg·L-1;动力学特征为：亚硝酸根是一级反应，该体系符合准一级反应特征，表观活化能为85.04 kJ·mol-1，80 ℃时表观速率常数为0.021 4 min-1，半衰期为32.39 min;动力学原理为：甲基红浓度变化ln(A₀/A)与亚硝酸根浓度符合以下正比关系ln(A₀/A)=kｃ_NO-2;该痕量亚硝酸根测定方法尚未见报道，精密度、准确度高，选择性好，多数常见离子不干扰亚硝酸根测定，且该方法操作方便，所用试剂廉价无毒，直接用于实测食品及水样中痕量亚硝酸根含量，结果满意。

Determination of Trace Amounts of Nitrite and Its Chemical Reaction Kinetics

A catalytic kinetic spectrophotometric method for the determination of nitrite, NO₂--S₂O2-₈-MR, was developed. It is based on the fading reaction of methyl red (MR) oxidized by potassium persulfate which can be catalyzed by NO-₂ in the medium of dilute HCl. The optimum experimental conditions were gained by combining single factor experiments with orthogonal experiments. Calibration curve, detection limit, precision, and anti-interference under the optimum experimental conditions were researched. Its kinetics principles and parameters were discussed. Its quantitative principle was investigated. The results show that the optimum experimental conditions of this method should be as follows: 1.0 mL 0.3 mol·L-1 HCl，1.0 mL 0.01 mol·L-1 K₂S₂O₈，0.6 mL 0.2 g·L-1 MR，reaction temperature 80 ℃ and reaction time 9 min. The principles for the quantitative determination of trace nitrite is that variation of MR concentration at the maximum absorption wavelength of 518 nm, ln(A₀/A), shows a good linear relationship with the concentration of NO-₂ under the optimum experimental conditions. Its determination range is 0.01～0.80 mg·L-1 and its detection limit is 0.007 mg·L-1. The kinetic characteristics are that the reaction order in NO-₂ is 1 and the fading reaction is a pseudo first order reaction. Its apparent activation energy is 85.04 kJ·mol-1. Its apparent rate constant is 0.021 4 min-1, and the half-life is 32.39 min at 80 ℃. The kinetic principle is that the variation of MR concentration is directly proportional to the concentration of NO-₂, ln(A₀/A)=kｃ_NO-2. This new method for the determination of trace nitrite has never previously been reported in the published literature so far. It is highly sensitive and selective. Most of the common ions don’t interfere with the determination of nitrite. This method has the advantages of convenient operation and the regents used are cheap and nontoxic. It was applied to the determination of trace nitrite in food and water samples with satisfactory results.