Effect of acids, modifiers and chloride on the atomization of aluminium in electrothermal atomic absorption spectrometry

Abstract

The effect of HNO₃, HCl and H₂SO₄, as well as various modifiers, Mg(NO₃)₂, Pd(NO₃)₂, Ca(NO₃)₂ and NH₄H₂PO₄, on the atomization of aluminium from a L'vov platform in electrothermal atomic absorption spectrometry was investigated. No interference was observed on the integrated absorbance of Al from any acid studied. The m₀ observed for 10 µg l^–1(200 pg) Al aqueous solution, prepared by diluting a commercial Al stock solution with doubly de-ionized water, was much poorer than expected, owing to a failure to transfer Al to the furnace, it could be corrected by adding as little as 0.25% v/v of a mineral acid. The expected m₀ for Al was unaffected by modifiers such as Mg(NO₃)₂, Pd(NO₃)₂, Ca(NO₃)₂ and NH₄H₂PO₄. Addition of either calcium, magnesium, or palladium nitrates produced a sharper absorbance peak, and Al was delayed in appearance. Either Ca(NO₃)₂ or Mg(NO₃)₂ can stabilize Al during pyrolysis, allowing a very high (> 1700 °C) thermal pretreatment temperature to be used. However, multiple atomization peaks were observed when using Mg(NO₃)₂. The multiple peaks became more troublesome as the tube aged. Calcium nitrate is recommended as a better modifier for those samples (e.g., bone) in which Ca is a large component of the matrix. A serious interference from chloride salts varied with chloride concentration, pH and pyrolysis temperature. This ‘suppressive’ interference from chloride was overcome by using Ca(NO₃)₂ as a modifier in HNO₃, and a pyrolysis temperature in excess of 1400 °C.