Determination of amines in the presence of excess ammonia by ion chromatography-mass spectrometry

Abstract

A new method for the simultaneous determination of several amines in the presence of an excess of ammonia by ion chromatography-mass spectrometry detection was developed. Current methods using ion chromatography with suppressed conductivity detection are not selective enough to determine small amines at the required level of 10 μg/L or preferably lower in the presence of a large excess of ammonia (̃1 mg/L) without resorting to time-consuming sample pre-treatment techniques. By using mass spectrometric detection, which is capable of resolving eluting compounds on their m/z values, an additional dimension of confirmation is added to the analysis. Detection based on the analytes m/z value overcomes problems such as co-elution or background interferences that complicate the quantification when using conductivity detection. The optimal conditions for mass spectrometry detection of amines in the presence of an excess of ammonia were investigated by a four-factor central composite design. The four factors investigated were scan time, cone voltage, probe temperature, and needle voltage. Evaluation of the obtained experimental data showed that detection limits were up to a factor of 100 lower when using mass spectrometry as the detection technique instead of the conventional suppressed conductivity detection. Detection limits of 1 μg/L and lower can be achieved for the six amines investigated in the presence of a large excess of ammonia (̃1 mg/L).