Determination of 1,2-Glycol in Epoxy Resins by Potentiometric Titration and Its Reliability

Abstract

This report is a validation for an iodometry potentiometric titration analysis for determining the 1,2-glycol content in epoxy resins. An analytical method, JIS K 7146, exists for the analysis of 1,2-glycol in epoxy resins. This method is based on manual titration with a color-change end point. However, the manual titration method sometimes has problems when it is used for the analysis of some solid-type epoxy resins (SERs), which are initially colored when a sample is dissolved during the procedure. This is because the resin color makes it difficult to detect the solutions' color change at the end point. This problem contributes to poor test precision and increased variability in results determined by different analysts. In this study, improvements in the method were achieved by implementing potentiometric titration. This uses an automatic titrator, which is equipped with a data processor, and disposable mayonnaise bottles as the titration vessel. This method is applicable to the analysis of 1,2-glycol in epoxy resins over the range of 0.05% to 7% (wt/wt). The precision was determined by pooling results from thirteen (13) analyses of two different solid epoxy resins. This corresponds to 11 (pooled) degrees of freedom ; [t(n−1) = 2.201]. The pooled relative standard deviations (RSDpooled) was calculated as the square root of the pooled relative variance for the two samples : RSDpooled = √Relative variancepooled ; RSDpooled = 0.45%. The relative prediction interval at the 95% confidence level [±t(n−1)× RSDpooled] is ±0.99%. This relates to future final results determined on similar solid epoxy resin samples. The distribution of the results is assumed to be normal. The validity of this assumption was verified using the Shapiro-Wilk test for normality. The test confirmed that the results could originate from a normal distribution. A recovery study, using 1,2-butanediol (reagent grade) and two epoxy resins (E and F), was carried out, and satisfactory results were obtained : 98.7, 97.4 and 97.3%, respectively. A LOQ (limit of quantitation) study was also carried out. The result indicated that it is possible to measure approximately 0.05% (wt/wt) or less 1,2-glycol in an epoxy resin sample.