A capillary electrophoresis method for the simultaneous analysis of ammonium and metals in animal wastes used in biogas production

Abstract

Capillary electrophoresis (CE) was studied for the simultaneous analysis of ammonium and metals from animal wastes used in biogas production. The feedstock materials for fermentation consisted of dairy manure and a mixture of dairy manure and fish offal waste. An imidazole background electrolyte containing 18-crown-6-ether and 30% methanol was capable of the efficient separation of ammonium, sodium, potassium, magnesium and calcium in the samples. CE results for the analysis of metals (K⁺, Ca²⁺, and Mg²⁺) in animal wastes were comparable to the results obtained with ICP-MS/OES analysis. Furthermore, the CE results of the analysis of ammonium in dairy manure samples were well comparable with the titrimetric/distillation method. Interestingly, the analysis of ammonium in fish waste samples by the titrimetric/distillation or the spectrophotometric method used was not reliable, likely due to matrix interferences. In contrast, the CE analysis of all analytes and matrices was reproducible and matrix interferences were not found. The reproducibility of the CE method calculated as the relative standard deviation was ≤10% both for the intra-day (n ≥ 7) analysis and during a three month inter-day (n = 45) study. The only sample pre-treatment needed was the dilution of water extract prior to the CE analysis. In addition, the separation time in CE analysis was only six minutes. Therefore, capillary electrophoresis can be considered to be a very competitive alternative method for rapid and reliable simultaneous analysis of ammonium and metals in fermentation samples containing animal wastes.