Solid phase microextraction and determination of dichromate in aqueous solution based on pine needle powder-modified carbon paste electrode by potentiometry

Abstract

Pine needle is a low-cost natural biopolymer, and Cr 2 O 7 2-is a poisonous anions in the environment. In the present paper, pine needle powder was used as a solid phase microextractant in the modification of carbon paste electrode for extraction and determination of Cr 2 O 7 2-anions. The extraction process was monitored by an open circuit potential method, and an apparent first-order rate constant of 0.06474 s -1 was obtained from a Richard model. The extraction isothermal curve follows a logarithm adsorption model with a adsorption equilibrium constant of 5.95. Under the optimal conditions, the concentration of K 2 Cr 2 O 7 in river water of Shenyang Normal University campus was determined by the potentiometric method in the concentration range of 1.0 9 10 -6 -1.0 9 10 -2 M with a detection limit of 1.0 9 10 -7 M (the signal to noise Ratio was 3:1), relative standard deviation of 3.44 %, and standard addition recovery in the range of 94.70-103.5 %. The large amounts of common existing ions such as Cr 3? , Cu 2? , and SO 4 2-showed no interference with the molar ratio up to 100:1, but CrO 4 2-, Pb 2? ions showed a great interference in the detection of Cr 2 O 7 2-due to the transformation from CrO 4 2-to Cr 2 O 7 2-and precipitations of PbCrO 4 and PbCr 2 O 7 , respectively.