Precise Measurement of Ion Ratios in Solid Samples Using Laser Ablation With a Twin Quadrupole Inductively Coupled Plasma Mass Spectrometer

Abstract

Laser ablation (LA) is used with steel samples to assess the ability of a twin quadrupole inductively coupled plasma mass spectrometer to eliminate flicker noise. Isotopic and internal standard ratios are measured in the first part of this work. Results indicate that flicker noise cancels and significant improvements in precision are possible. The isotope ratio ⁵² Cr ⁺ : ⁵³ Cr ⁺ can be measured with a relative standard deviation (RSD) of 0.06–0.1%, depending on the dwell time and averaging method used. The level of noise above the shot noise limit is greater in internal standard measurements than when doing isotope ratio measurements. Nevertheless, RSDs improve from 1.9% in the Cr ⁺ signal to 0.12% for the ratio of ⁵¹ V ⁺ to ⁵² Cr ⁺ in a steel standard reference material (SRM). In the second part of this work, one mass spectrometer is scanned while the second channel measures an individual m / z value. When the ratio of these two signals is calculated, the peak shapes in the mass spectrum are improved significantly for a wide range of elements. This technique corrects for flicker noise from the LA process while scanning a mass spectrum for multi-element determinations.