适于微量芝麻样品酸价测定的铜皂比色法的建立与评价

Establishment and Evaluation of Copper Soap Colorimetric Method for Acid Value Determination of Slight Amount of Sesame Sample

为快捷、准确地测定微量芝麻样品的酸价,选用13份芝麻油脂和20份芝麻籽粒样品,开展了铜皂染色液配方改良及铜皂反应显色强度分析,首次建立了适于微量芝麻样品酸价测定的铜皂比色方法。结果显示,建立的铜皂比色法测定芝麻样品酸价的最佳测定波长为710 nm;单次样品测定芝麻油脂最低用量为60 mg,芝麻籽粒样品平均用量为0.11 g。在0.1~10 mg/mL油酸下,铜皂比色法标准工作曲线方程为y=0.199x+0.0172(R2=0.9997);铜皂比色法可检测芝麻样品的酸价为0.18~17.50 mg/g。测定结果显示,室温久置的13份芝麻油脂样品以及20份芝麻籽粒样品酸价分别为1.36~6.32 mg/g和1.02~5.03 mg/g。铜皂比色法测定方法相比于标准酸碱滴定法,精密度和准确度均较高,二者结果差异不显著,因此可用铜皂比色法代替酸碱滴定法进行芝麻籽粒和芝麻油脂酸价测定。另外,检测发现,测定时间对样品酸价测定值也有一定的影响,配制好铜皂络合物后应尽快用于检测。

In order to quickly and accurately determine the acid value of trace sesame samples,13 sesame oil samples and seeds of 20 sesame varieties were selected to improve the formula of copper soap staining solution and analyze the color development intensity of copper soap reaction,and then a colorimetric method of copper soap for determining acid value of slight amount of sesame sample was established for the first time.Results showed that the optimum wavelength for determining sesame oleic acid samples was 710 nm.The minimum amount of sesame oil for single sample determination was 60 mg,and the average dosage of sesame seed sample was 0.11 g.Among the range of 0.1-10 mg/mL oleic acid,the standard working curve equation of copper soap colorimetric method was y=0.199x+0.0172(R^(2)=0.9997)and the acid value of sesame samples was 0.18-17.50 mg/g by the method.Determination results showed that the acid value of 13 sesame oil samples and 20 sesame seed samples were 1.36-6.32 mg/g and 1.02-5.03 mg/g,respectively.Compared with the standard acid‑base titration,copper soap colorimetric method had higher precision and accuracy,and the difference between the two results was not significant.Therefore,the copper soap colorimetric method can be used instead of the standard acid‑base titration method to determine the acid value of sesame seeds and sesame oil.Moreover,the copper soap complex should be used for determination as soon as possible after preparation as the assay time also had influence on the acid value of sesame samples.