Determination of phosphorus by molecular absorption of phosphorus monoxide using a high-resolution continuum source absorption spectrometer and an air–acetylene flame

Abstract

PO molecular absorption bands, produced between 200 nm and 350 nm in an ordinary air–acetylene flame, were investigated using a high-resolution continuum source absorption spectrometer. The bands comprise sharp structures with half-widths similar to those of common atomic lines. Four PO band heads, located at 246.40 nm, 247.78 nm, 324.62 nm and 327.04 nm, were selected and systematically evaluated with regard to the determination of phosphorus. Nitric, sulfuric, hydrochloric and hydrofluoric acids, with concentrations of up to 5% (v/v), and up to 2000 mg L⁻¹ solutions of Al, Co, Cr, Cu, Fe, K, Mn, Na, and Ni, were examined for possible matrix or spectral interferences. The only serious spectral interference found was the disturbance of the PO band head at 324.62 nm by the 324.754 nm Cu resonance line at high concentrations. Apart from this, a suppression effect on the PO absorption caused by the presence of Ca and Mg was observed and will be discussed in a separate paper in this journal. The determination of phosphorus via molecular PO absorption proved to be a rapid and reliable method. Performance was verified by analyses of standard reference materials, where good precision and accuracy were achieved. The limit of detection for phosphorus was found to be 1.3 mg L⁻¹ for a measurement time of 25 s, using the PO band head at 324.62 nm. The linear dynamic range covers more than three orders of magnitude.