Optimal accuracy, precision and sensitivity of inductively coupled plasma optical emission spectrometry: bioanalysis of aluminium

Abstract

The accurate and precise analysis of trace elements in biological samples by inductively coupled plasma optical emission spectrometry (ICP-OES) has not been established, particularly for elements such as Al, Ni and Pb, for which the literature is contradictory and methodology and sample preparations are poorly reported. We outline important features for the successful analysis of aluminium by ICP-OES. Three analytical lines for aluminium were considered; 167.020 nm is the most sensitive, but an unresolvable iron interference (≈ 1 : 500, Fe : Al) means that this line cannot easily be used for some biological samples, particularly blood. The line at 308.215 nm is least sensitive. The line at 396.152 nm is the most suitable, but requires baseline correction for a broad hydroxy peak at 397.000 nm and a calcium peak at 396.847 nm. There is also potential interference from a previously unreported iron peak at 396.121 nm (≈ 1 : 2500, Fe : Al). Sheath gas, height of the plasma viewing zone, and sample diluent were most critical for optimum analytical conditions, and these parameters may be inter-dependent. For a sheath gas flow of 1.05 l min^–1, urine diluted 1 + 4 with a 100 g l^–1 potassium chloride solution yielded a significantly enhanced net aluminium signal compared with urine diluted 1 + 4 with water, whereas reducing the sheath gas flow to 0.41 min^–1 gave a relatively greater signal for the sample diluted with water. An analytical profile with a window size of 0.1 nm, containing 54 wavelength increments, each of 5 s integration time, further maximized sensitivity and precision. Spectra required dynamic background correction and deconvolution. Thus, sub µg l^–1 detection of aluminium is possible, with 0.9 µg l^–1 achievable in diluted clinical samples. These approaches are widely applicable for other elements by ICP-OES.