示波极谱滴定法测定显影液中米吐尔和对苯二酚含量

用１．５ｍｏｌ／Ｌ乙酸铵－氨（ｐＨ８．２）－无水乙醇（２：１，Ｖ／Ｖ）混合溶液为极谱底液，以Ｋ２ＣｒＯ４与米吐尔和对苯二酚的氧化还原反应为基础，用Ｋ２ＣｒＯ４作为滴定剂，以示波极谱图上ＣｒＯ４＾２－切口出现指示终点，测定显影液中米吐尔和对苯二酚的含量。本法简便易行，灵敏准确，终点直观，应用于Ｄ－７２和Ｄ－７６显影液中米吐尔和对苯二酚的测定，获得满意结果。     

Determination of pentoxifylline in pharmaceutical formulations using iodine as oxidizing agent

Simple, selective and sensitive spectrophotometric methods are described for the determination of pentoxifylline, based on the haloform reaction with a known and excess of standard iodine solution under alkaline conditions. The excess of iodine is determined at pH 3.0 with metol–isoniazid (λ_max=620 nm; method A) or wool fast blue BL (λ_max=540 nm, method B). All the variables have been optimised and the reaction mechanisms presented. Regression analysis of Beer's law plots showed good correlation in the concentration ranges 4.0–24.0 and 0.4–2.4 mg ml⁻¹ for methods A and B respectively. No interferences were observed from excipients and the validity of the methods was tested by analysing pharmaceutical formulations. Recoveries were 99.0–100.0%. The concentration measurements were reproducible within a relative standard deviation of 1.0%.     

Electrochemical behaviors of metol on ionic-liquid-modified carbon paste electrode and its analytical application

The electrochemical behaviors of metol on an ionic liquid N-butylpyridinium hexafluorophosphate modified carbon paste electrode (IL-CPE) were studied in this paper. The results indicated that a pair of well-defined quasi-reversible redox peaks of metol appeared with the decrease of overpotential and the increase of redox peak current, which was the characteristics of electrocatalytic oxidation. The electrocatalytic mechanism was discussed and the electrochemical parameters were calculated with results of the charge-transfer coefficient (α) as 0.45, the electrode reaction rate constant (k _s) as 4.02 × 10⁻³ s⁻¹, and the diffusion coefficient (D) as 6.35 × 10⁻⁵ cm²/s. Under the optimal conditions, the anodic peak current was linear with the metol concentration in the range of 5.0 × 10⁻⁶ ∼ 1.0 × 10⁻³ mol/L (n = 11, γ = 0.994) and the detection limit was estimated as 2.33 × 10⁻⁶ mol/L (3σ). The proposed method was successfully applied to determination of metol content in synthetic samples and photographic solutions.