Vs and are best described by a second order polynomial equation with a Pearson coeff. r of 0.998. The measured δ 15 N values of 50 mg L -1 N-NaNO3 was -0.4 ± 0.2 ‰. The lowest injected nitrate concentration of 10 mg L -1 N shows a noticeable increase in measurement uncertainty and the largest shift of δ 15 N values. However, δ 15 N values were stable once a concentration of 100 mg L -1 N-NaNO3 was reached and peak areas showed a linear increase from 50 mg L -1 onwards. These concentrations are about 10 to 50 times higher than what is usually observed in water samples from areas affected by substantial agricultural activities, which results in nitrate concentrations between 10 and 50 mg/L -1 N-NO3 -. Especially, nitrate concentration in groundwaters or areas with limited agricultural activities were below the currently expected detection limits of the modified interface. As mentioned earlier, increasing the injection volume is a potential way of achieving the necessary analyte amount on the column if chromatographic separation is assured and the column is not overloaded. However, in our current set-up, sample enrichment prior to injection was necessary. Such an enrichment could be achieved by evaporation under vacuum (see next section) or by the use of anion exchange columns to preconcentrate nitrate, as described by the ion-exchange method. an individual background detection algorithm with a 5 second history. The increase in peak area over the concentration range is best described by a second polynomial equation with R-Square of 0.998.