Flow injection determination of diesters as ferric hydroxamate complexes

Diesters such as succinylcholine chloride (SCC) and dioctylsulfosuccinate (DOSS) can be converted to hydroxamic acids which are found to react with Fe³⁺ in methanol to form a purple chelate complex having an useful absorption band at 520 nm with a molar absorptivity of about 171 L/mole*cm, and a detection limit of 1.5 × 10^–4 M. To adapt this method for flow injection, a methanol-water solvent and acidification of the sample were required to reduce the large blank peak. The reproducibility of the flow injection method was a factor of two better than standard spectrophotometry but the detection limit of the former method was two times higher. This colorimetric method can permit analysis of pharmaceutical products containing either SCC or DOSS. Phosphatidylcholine (lecithin) can also be determined using this method.