The most appropriate technique to determine levels of the Pb$^{2+}$ ion in blood is A - VCE - SSCE Chemistry - Question 1 - 2009 - Paper 1

The most appropriate technique for determining levels of the Pb$^{2+}$ ion in blood is atomic absorption spectroscopy (C). This method is widely used for analyzing metal ions in biological samples due to its high sensitivity and specificity.

Atomic absorption spectroscopy works by measuring the concentration of gas-phase atoms. In this case, lead (Pb) atoms in the blood sample are vaporized and measured as they absorb light at specific wavelengths. Compared to other techniques mentioned, such as mass spectrometry or infrared spectroscopy, atomic absorption spectroscopy provides a more direct and effective means for measuring trace levels of metals, particularly in complex matrices like blood.