Simultaneous determination of TOC and TNb in surface and wastewater by optimised high temperature catalytic combustion

Total nutrition parameters as e.g. total organic carbon (TOC) and total bound nitrogen (TNb) are indispensable to water quality and elemental nutrient balances. The recommended and most often applied wet chemical digestion for TNb measurement, however, is discouragingly labour intensive. Therefore, high temperature (690°) catalytic (Pt/Al2O3) combustion (HTC) was investigated for simultaneous determination of TOC and TNb. Using commercially available instruments a fast and simple procedure was established by coupling a TOC-analyzer to a chemiluminescence detector (CLD) for determination of NOx gases in the combustion exhaust. Dissolved compounds as well as particulate matter were used to test carrier gases, hot zone fillings and injection volumes influencing N-recovery rates. Injecting dissolved wastewater components (e.g. ammonium, urea, antipyrine) direct onto the catalyst yielded low N-recovery rates (40–90%) depending on concentration. Instead of increasing the oven temperature the evaporation of injected sample solution was improved which resulted in quantitative recovery rates for all investigated compounds except hydrazine. A representative number of TNb values from river and domestic wastewater obtained by HTC-CLD were compared to wet chemical digestion. No significant differences between the two methods were found.