Spectrophotometric (ASTM E2313) and DNPH-Derivatized UV-HPLC method comparison to quantify Aldehydes in Glycols

Commercial surfactants often consist of impure mixtures, as high purity is not always necessary for their function. However, certain impurities can significantly impact their suitability for use.

The carbonyl content in polyethoxylated surfactants, such as ethylene oxide/propylene oxide copolymers, is typically measured despite their nominal structure lacking a carbonyl group. The presence of carbonyl compounds in polyethers suggests degradation or insufficient removal of lower molecular weight aldehydes.

Analysis of aldehydes in glycols has been run by ASTM E2313-22, an accepted spectrophotometric method. This test method describes the spectrophotometric determination of total aldehyde content in mono-, di-, and triethylene glycol (MEG, DEG, and TEG). Alkoxyalcohols (hemiacetals), if present, are co-determined, whereas dialkoxyalkanes (acetals), if present, are not. The results provide a measure of the purity of the sample with respect to total aldehyde content. However, the spectrophotometric method is not selective and cannot provide a specific amount of each aldehyde component. Instead, high-sensitivity Liquid Chromatography allows individual and simultaneous quantification of formaldehyde, acetaldehyde, propionaldehyde, and carbonyl components, through analysis of their 2,4-dinitrophenylhydrazine (DNPH) derivatives performed at 360 nm UV detection.

This study is intended to compare spectrophotometric and Liquid Chromatographic approaches, exhibiting the most relevant differences between both methods, experimental values, statistical results, and advantages and disadvantages of each technique.