On line pre-concentration for simultaneous determination of low molecular weight organic acids and inorganic anions in Amazonian river water samples employing ion chromatography with conductivity detection

Abstract

An ion chromatography procedure, employing an IonPac AC15 concentrator column was used to investigate on line preconcentration for the simultaneous determination of inorganic anions and organic acids in river water. Twelve organic acids and nine inorganic anions were separated without any interference from other compounds and carry-over problems between samples. The injection loop was replaced by a Dionex AC15 concentrator column. The proposed procedure employed an auto-sampler that injected 1.5 ml of sample into a KOH mobile phase, generated by an Eluent Generator, at 1.5 mL min -1 , which carried the sample to the chromatographic columns (one guard column, model AG-15, and one analytical column, model AS15, with 250 x 4mm i.d.). The gradient elution concentrations consisted of a 10.0 mmol l -1 KOH solution from 0 to 6.5 min, gradually increased to 45.0 mmol l -1 KOH at 21 min., and immediatelly returned and maintained at the initial concentrations until 24 min. of total run. The compounds were eluted and transported to an electro-conductivity detection cell that was attached to an electrochemical detector. The advantage of using concentrator column was the capability of performing routine simultaneous determinations for ions from 0.01 to 1.0 mg l -1 organic acids (acetate, propionic acid, formic acid, butyric acid, glycolic acid, pyruvate, tartaric acid, phthalic acid, methanesulfonic acid, valeric acid, maleic acid, oxalic acid, chlorate and citric acid) and 0.01 to 5.0 mg l -1 inorganic anions (fluoride, chloride, nitrite, nitrate, bromide, sulfate and phosphate), without extensive sample pretreatment and with an analysis time of only 24 minutes. KEY WORDS: On-line pre-concentration, inorganic anions, organic anions, ion chromatography, river waters Pré-concentração em linha para a determinação simultânea de ácidos carboxílicos de baixo peso molecular e ânions inorgânicos em amostras de rios da Amazônia empregando cromatografia de íons com detecção por condutividade elétrica RESUMO A metodologia analítica foi desenvolvida empregando coluna pré-concentradora AC15 em linha na cromatografia iônica na determinação simultânea de ânions orgânicos e inorgânicos, com uso de coluna de guarda AG15 e analítica AS15, 250 x 4 mm i.d. (Dionex Corp.). O gradiente de concentração do eluente foi fixo em 10,0 mmol.l -1 KOH nos tempos de retenção de 0 até 6,5 min, seguido do aumento da concentração até 45,0 mmol.l -1 KOH a 21 min, imediatamente retornando e mantendo a concentração inicial até o tempo total de análise de 24 min. Os compostos foram separados com boa resolução e deslocados para uma cela de detecção de condutividade elétrica acoplada a um detector eletroquímico. O emprego da coluna pré-concentradora em linha apresentou vantagens analíticas na determinação de rotina dos íons na faixa linear de 0,01 até 1,0 mg l -1 (r=0,9989) de ácidos orgânicos (acético, propiônico, fórmico, butírico, glicólico, pirúvico, tartárico, ftálico, metanossulfônico, valérico, maleico, oxálico e cítrico) e 0,01 até 5,0 mg.l -1 (r=0...