Coopman V., Van Moortel T., Cordonnier J.

Laboratory of Analytical Toxicology, Chemiphar NV, Lieven Bauwensstraat 4, Bruges, Belgium

In horse racing practice, arsenic has been used as a respiratory stimulant. The International Threshold Value has been set on 0.3 µg/ml of total arsenic in urine.
To determine arsenic in post-racing horse urine, we needed a rapid and accurate method. Therefore we developed a microwave digestion method and used it in combination with Inductive Coupled Plasma Atomic Emission Spectrometry (ICP-AES).
Methods. The digestion took place in a MDS-2000 Microwave Sample Preparation System (CEM Cooperation) with temperature and pressure control: to an aliquot of horse urine a mixture of hydrochloric and nitric acid was added. The digestion program was completed within 30 min, resulting in clear, pale yellow digests. When cool, the digested samples were transferred quantitatively into 50 ml calibrated flasks and made up to volume with distilled de-ionised water.
The determination of arsenic was achieved with ICP-AES (Liberty 150AX Turbo, Varian)
Results. Using a 5 ml sample, the detection limit of the method was 0.1 µg/ml (n=10, CV=0.01 µg/ml). This limit was determined by measuring ten calibration curves in matrix blank and was defined as three times the residual standard deviation from the intercept, divided by the slope, and.this value was multiplied by the dilution factor. Spike recoveries at the Threshold Value were: 102.1% (n=18, CV= 0.01 µg/ml). The precision of the method obtained by calculation of the relative standard deviation for ten replicate measurements was 2.8%. The reproducibility of the digestion method was determined by analysing ten digests by ICP-AES over a 3 weeks period and was 9.5%.
Conclusions. The use of the automated microwave system made it possible to have a rapid destruction method which requires a minimum operator attention. The sample preparation method provides good spike recoveries, requires small volumes of samples and strong acidic reagents and is free from reagent and matrix blank problems when measured with ICP-AES. The detection limit is 0.1 µg/ml. Therefore the method can be successfully applied for routine determination of total arsenic in post-racing horse urine.