Determination of iron(III) and aluminum in solution with a piezoelectric quartz crystal coated with silicone oil

The frequency of the crystal connected to an integrated circuit oscillator changed on absorption of iron(III) or aluminum ar pH 3.8–5.8 and 5.0–6.0, respectively. Absorption of iron(III) at pH ≥ 5.0 was prevented by addition of excess of sulfate. Iron(III) was determined at pH 4.7; 5–100 μM solutions of both species may be determined with a r.s.d, of ≤3%.