Dynamic reaction cell inductively couple plasma-mass spectrometry optimization for seawater analysis

A direct method for dynamic reaction cell inductively coupled plasma- mass spectrometry (DRC-ICP-MS) trace mineral elements determination in seawater was optimized by Experimental Statistical Design. Five instrumental parameters, such as radiofrequency, sample, nebulizer and reaction gas flows, rejection parameter q and axial field voltage were studied. A Plackett-Burman design was used for screening the most important parameters and the most significant ones were optimized with a Central composite design. Fifteen elements and different isotopes for some of these were considered through the study. The optimization was achieved by using three different reaction gases (NH3, CH4 and O2). The optimized method was used for the quantification of trace minerals in a certified seawater sample. The standard mode was adequate for the quantification of those elements that have a reduced number of interferences like 111Cd and 238U. However, the best results were obtained employing ICP-MS in NH3-DRC mode which allowed the simultaneous determination of elements like 51V, 55Mn, 58Ni, 68Zn and 238U, which can be determined in the reference sample with an accuracy error lower than 10% and 95Mo determined with an accuracy error of 15%. The use of CH4-DRC was restricted to quantify 111Cd with an error of 16%. The use of O2-DRC was suitable for determining 55Mn, 66Zn with errors lower than 3% and 51V, when monitored it in oxide form 67VO, with an accuracy error of 2%. O2-DRC is the single DRC mode that allowed a satisfactory quantification of 75As, with an error of 33% for a very low concentration, compared to other analysis mode in the direct analysis of seawater. Additionally Pb can be quantitatively recovered from spiked samples using NH3 and O2-DRC modes.