Inductively coupled plasma mass spectrometry coupled to cation exchange chromatography for the determination of trace nickel in alkaline electrolyte†
Direct analysis of alkaline solutions poses a challenge for inductively coupled plasma mass spectrometry (ICPMS) due to two main problems. Firstly, the caustic environment rapidly degrades instrument performance and lifetime by reacting with the glass and quartz components. Secondly, the high concentration of alkalis (Na, K, etc.) causes a large analyte signal suppression. To overcome these problems without a lengthy sample preparation, an on-line separation of Ni from the interfering matrix components was performed using a Dionex IonPac CS-10 cation exchange column. This also enabled the use of the regular glass/quartz components for the ICPMS sample introduction system. Samples of Ni in both NaOH and KOH were injected onto the cation exchange column and eluted isocratically using 0.6 M HNO3, which provided a compromise between the maximum sensitivity and the separation of the Ni peak from the valley caused by elution of the alkalis, which largely suppressed the background signal. The valley feature had elution times of approximately 115 s in the case of K+ and 125 s for Na+. To remove this feature from the chromatogram, an in-line 6-port valve was added to divert the column effluent during the elution of the alkalis. This resulted in a more optimized method, which allowed for sample analysis within approximately 260 s.