Simultaneous determination of borate, chloride and molybdate in pyrohydrolysis distillates of plant and soil samples by ion chromatography

Determination of concentrations of micronutrients in plant samples is important in order to assess the growth and quality of plants. An ion chromatography (IC) method was developed for the simultaneous determination of B, Cl and Mo (micronutrients present in their anionic form in aqueous samples) using a gradient elution with D-mannitol and NaOH. Despite their different chemical nature, these elements could be separated from the matrix by employing pyrohydrolysis. IC was employed for their sequential determination from single aliquot injection into the IC column. It was observed that the optimised procedures developed earlier in our laboratory for the separation of B and halogens using D-Mannitol-NaOH or bicarbonate eluents could not be extended to B-Mo-CI separation. The concentration levels of D-mannitol in the eluent required for separation of boron impeded the conductivity detection of Mo and the peak sensitivity was seen to be critically dependent on D-mannitol concentration in the eluent. In addition, D-mannitol in NaOH eluent altered the retention times of analytes (B, F-, Cl-, NO3-, SO42- and MoO42-) which were not observed in the case of bicarbonate eluent. The current study deals with the investigation on the influence of D-mannitol on the molybdate as well as its role on the retention time. Formation of Mo-mannitol complex at different pH conditions and de-protonation of mannitol were correlated to the observed effects. Based on the observations, a gradient elution method was proposed for the simultaneous separation and determination of B, CI and Mo in the pyrohydrolysis distillates of plant samples. The method was calibrated for B (0.05-1 mg/L), Cl (0.1-10 mg/L) and Mo (0.5-10 mg/L) and the linear regression coefficients obtained were 0.9992, 0.9998 and 0.997 respectively. The limit of detection (LOD) for B, Cl and Mo was calculated to be 19, 23 and 96 mu g/L, respectively. The developed IC method after pyrohydrolytic separation of B, Cl and Mo was successfully applied for the analysis of real samples. (C) 2017 Elsevier B.V. All rights reserved.