This paper concerns quality assurance of arsenic determination in urine using the graphite furnace AAS method after toluene extraction. Obtained analytical results are used for validation and quality assurance purposes. The investigated urine samples were acquired from the workers of a large coal-fired Slovak power plant. In the proposed analytical method the following metrological characteristics were calculated: trueness, precision, recovery, the limit of detection and the limit of quantification. The method was satisfactorily used in the intercomparison test. The proposed method is suggested for utilisation in the assessment of occupational or environmental exposure to inorganic arsenic.