A multicomponent mobile phase for ion chromatography applied to the separation of anions from the residue of low explosives

A multicomponent mobile phase utilizing ion-exchange, ion-exclusion, and io n-pairing principles for the rapid isocratic separation of anions in low ex plosives residue by ion chromatography (IC) has been developed. The notable feature of this system is that an ion-pairing reagent and an ion-exclusion reagent are combined in the same mobile phase. Contrary to expectation, th ese reagents act independently of each other in solution. The stock mobile- phase composition consisted of boric acid, D-gluconic acid, Lithium hydroxi de, and glycerol. Tetrapropylammonium hydroxide, an ion-interaction reagent was used to achieve pH 8.5. Acetonitrile (ACN) was added to enhance resolu tion and octanesulfonic acid, an ion-exclusion reagent, was added to adjust the retention time of perchlorate, Separation of a mixture of anions commo n to low explosives residue was achieved in less than 16 min using a Waters IC-Pak Anion HR column, Optimization studies were performed by changing th e concentration of the ACN and by altering the pH or the type of ion-intera ction or -exclusion agents. Simulated case studies were performed using pos tblast residues from pipe bombs. The results show this method to be a valid and reproducible procedure for forensic casework analysis. The practical s ignificance of this system is that a reduction in the analysis time and an improvement in efficiency of late-eluting peaks can be achieved without res orting to gradient elution techniques. For the analysis of anions detected in explosives residue, the Waters IC-Pak Anion HR column has proven to be a suitable replacement for the Vydac 300IC405 column, which has been discont inued by the manufacturer.