Determination of nonnitrogenous organic acids and inorganic anions in sugarcane molasses and molasses alcohol waste by ion chromatography with solid-phase extraction

A method was established for the determination of main nonnitrogenous organic acids (including acetic, lactic, succinic, maleic, tartaric, oxalic, fumaric, citric, and aconitic acids) and three inorganic anions (Cl-, SO(4)(2- )and PO43-) in sugarcane molasses and molasses alcohol waste by ion chromatography with solid-phase extraction. The diluted sample solution was purified by strong anion exchange (SAX) solid-phase extraction (SPE) in a small packed column to remove most of sugar, pigment and other interfering matrices. The eluate obtained from the column was rinsed with diluted KOH solution and filtered through a 0.45 mu m inorganic membrane, finally separated on an anion column of IonPac AS15 with the gradient elution of KOH solution and determined with a suppressed conductivity detector. The pretreatment and procedures of SPE for separating organic acids and inorganic anions from their matrix were investigated. The detection limits were less than 0.20 mg/L. The relative standard derivations were less than 6.7%. The organic acids and inorganic anions in three real samples (two sugarcane molasses samples and an alcohol waste sample) were determined, the recovery ranges were from 94% to 109%. The method shows good precision and linearity.