Gas-Screen Slotted Quartz Tube Atomic Absorption Spectrometry: A Remedy for Reducing Interference Effects of Calcium and Chromium

Abstract

A simple device for the reduction of nonspectral interferences in flame atomic absorption spectrometry is proposed. It has been reported that the use of a gas screen (GS) system together with a slotted quartz tube (SQT) enhances the residence time of analyte atoms in measurement zone even more than the SQT alone. This combination causes enhancement of sensitivity and improves the reproducibility of absorbance measurements. In addition, it protects the optical windows of the atomic absorption spectrometer. The operational mechanism of gas screen is simply applying two argon gas walls at both ends of SQT to provide an environment that is partly protected from air. This action enhances the sensitivity of measurement.

In this study, interference effects of excess amounts of calcium and chromium on the measurements of Cd, Co, Cu, Pb, Mn, Ni, Se, and Zn were studied using flame AAS. The presence of both Ca and Cr cause higher absorbance values; it is suggested that this is due to formation of oxide species of Ca and Cr and as a result analyte oxide production is suppressed. Therefore, analyte free atom population and sensitivity are enhanced. This enhancement results in a positive error in measurements. For instance, presence of solely 8.0 mg L⁻¹ of Cr or Ca for Pb as the analyte enhances the signals by 75% and 56%, respectively. When SQT or GS-SQT is used, this effect is significantly reduced.

Keywords:

• Flame atomic absorption spectrometry
• Gas screen slotted quartz tube
• Nonspectral interference

Notes

Note. Parameters which are same for all the analytes are, 5.0 cm for flame path length, 1.5 mm for thickness of quartz tube used for SQT, 12.0 cm for length of SQT, and 7.0 cm for length of lower slot of SQT (Gholami et al. 2011).

^a For FAAS, FAAS-SQT, and FAAS-GS-SQT.

^b For FAAS-SQT and FAAS-GS-SQT.

^c For FAAS-GS-SQT.

^a Interferant concentration was 2.0 mg L⁻¹ for for Cd and Zn, 8.0 mg L⁻¹ for other analytes.

^b Relative enhancement (RE) in calibration sensitivity, slope, L mg⁻¹, in presence of interferant.

RE = (Slope in the presence of interferant)/(Slope in the absence of interferant).

Note. The critical value for t is 3.18 for the 95% confidence level and 3 degrees of freedom.