Directly suspended droplet microextraction combined with energy-dispersive X-ray fluorescence spectrometry to determine nano levels of phosphate in surface water

Abstract

Directly suspended droplet microextraction (DSDME) for determination of phosphate by energy-dispersive X-ray fluorescence spectrometry (EDXRF) is proposed. The method is based on the determination of phosphate, through molybdenum in the phosphomolybdenum blue complex. Because phosphorus is determined indirectly via molybdenum fluorescent radiation the difficulties of low fluorescent yield and low energy of phosphorus radiation are successfully overcome. A good ratio of phosphorus to molybdenum (1 to 37) and a sensitive K_α line of molybdenum give the possibility to determine a low concentration of phosphorus. Under the optimized conditions, good linearity, up to 20 μg of phosphorus (r = 0.9995), and the detection limit (2.8 ng mL⁻¹) for the sample of 1.5 mL were achieved. The total RSD for the EDXRF determination of phosphorus followed by DSDME was 2.6% and taking into account all steps preceding the determination and the uncertainty of EDXRF measurements, the proposed method can be recognized as highly precise. The enrichment factor was equal to 56.8. The developed method was used to determine the total phosphorus content in surface waters. The accuracy and repeatability of the proposed procedure were checked by the standard addition method. The recovery in the range 93.5–97% was satisfactory and indicated the usefulness of the developed procedure.