Interference-free determination of arsenic in urine by atomic absorption using two-stage probe atomization in a graphite furnace

Highlights: • Two-stage probe atomization provides direct determination of As in urine. • W-probe and Pd-modifier eliminate the interferences. • HR-CS GFAAS was used for spectra observation. • A detection limit of 1.5 μg L⁻¹ of As in urine of adult has been obtained. Inductively coupled plasma mass spectrometry, hydride generation atomic absorption spectrometry and graphite furnace atomic absorption spectrometry are presently used to determine total arsenic in urine, but after labor consuming sample pretreatment. Therefore, we proposed a new approach to solve this problem using two-stage probe atomization. High-resolution continuum source graphite furnace atomic absorption spectrometer was equipped with the probe accessory for that. The sample consisting of 15 μL urine and 20 μg Pd-modifier was dried on the furnace bottom at smooth heating up to 120 ^оС and atomized at 2300 ^оС with internal Ar flow. The resulting vapors of As condensed on a tungsten probe installed above the dosing hole. At the same time, Ar flow removed an essential part of the matrix components without condensation. At the second atomization stage at 2300 ^оС and interrupted internal gas flow, the probe was lowered into the furnace and heated by electric current to accelerate condensate evaporation. This procedure fully separates the analytical signal from the finely structured molecular background. Matrix interference disappears due to significantly different rates of As and urinary phosphates binding with Pd at temperature of 120 °C and distillation on the probe. The limit of As detection in urine is 1.5 μg L⁻¹ and quantification range is 50–1000 μg L⁻¹ that almost covers the entire patients' urine concentration range of interest for environmentalists and physicians.