Overestimation of nitrate and nitrite concentrations in water samples due to the presence of nitroglycerin or hexahydro-1,3,5-trinitro-1,3,5-triazine

A large number of laboratory studies have reported nitrite (NO2−) and nitrate (NO3−) to be among the most common degradation products of the high explosives nitroglycerin (NG) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX). Additionally, several field studies have reported the presence of RDX or NG along with NO3− in groundwater near production plants. Most studies, however, did not specify whether their NO2− and NO3− analyses were performed on samples which also contained RDX or NG. Inconsistent NO2−/NO3− results obtained in our laboratory suggested that the presence of RDX or NG in water samples caused an overestimation of NO2− and NO3− concentrations when using two of the most common analytical methods, namely ionic chromatography and automated colorimetry. This could have important implications for mass balance calculations and for environmental decisions. This paper focused on quantifying the overestimation of NO2−/NO3− due to the presence of RDX and NG, and finding a method for extracting RDX and NG from water samples without affecting NO2−/NO3−. Results showed that the overestimation can be predicted using regression coefficients; however the margin of error at the 95% confidence level was between 5 and 15%. Alternatively, a cartridge was found which retains both RDX and NG without affecting NO2−/NO3−. The cartridge can be used for concentrating the RDX or NG in dilute environmental samples, while removing RDX/NG from solution to allow the interference-free analysis of NO2−/NO3−. Additionally, if recovery of RDX/NG from the cartridges is not desired, the cartridges could be used for the extraction of more than one sample, thus reducing the costs.

► The interference of RDX/NG with nitrate/nitrite (NO2−/NO3−) analysis was evaluated.
► The presence of RDX/NG leads to an overestimation of NO2−/NO3− concentrations.
► NO2−/NO3− values can be corrected after analysis, with an error range of 5–15%.
► Solid-phase extraction (SPE) of RDX/NG prior to NO2−/NO3− analysis is preferable.
► A SPE cartridge was selected to remove RDX or NG without affecting NO2−/NO3−.