Spectrophotometric Determination of Ultra trace Tri & Hexavalent Chromium by Using on-line Flow Injection Analysis with Dual Pre-concentration Column

Abstract

An on-line flow injection analysis with dual pre-concentration method was developed to determine the ultra trace tri and hexavalent chromium in water. In this system, the cation and anion pre-concentration columns were combined with a 10-port injection valve and then used to separate and concentrate Cr (III) and Cr (VI) selectively. The two species of concentrated chromium were sequentially eluted and determined by using HClKCl buffer of pH 1.8 as an eluent. Cr (III) was oxidized by hydrogen peroxide to Cr (VI). It was detected spectrophotometrically at 548 nm by complexation with DPC (diphenylcarbazide). Several factors such as concentration of H 2 O 2 , DPC and coil length in reaction condition were optimized. The linear range for Cr (III) and Cr (VI) was 0.1-50 µg/L. The limit of detections (3σ) of Cr (III) and Cr (VI) were 52 ng/L and 44 ng/L under the optimized FIA system, and their recoveries 98% and 103%, respectively. This method was applied to analyze contamination level of chromium species in tap water, groundwater and bottled water.

Matrix isolation with an ion transfer device for interference-free simultaneous spectrophotometric determinations of hexavalent and trivalent chromium in a flow-based system

“…This is because after acidification with the DPC reagent some Cr(VI) can be lost by H 2 O 2 acting as a reductant and this loss is dependent on the residual H 2 O 2 concentration. While others have suggested a carbonate buffer [16] as the medium for the H 2 O 2 oxidation of Cr(III), this is incompatible with the present system because of formation of CO 2 bubbles after addition of the acidic DPC solution.…”

“…Because Cr(III) and Cr(VI) are oppositely charged, solid phase extraction (SPE) with ion exchangers that selectively sorb Cr(III) or Cr(VI) can be exploited to selectively measure either or both; DPC chemistry can still be used if the Cr(III) is oxidized to Cr(VI) after elution [16]. Similar strategies are possible with atomic spectrometric techniques as the measurement method; the general area of Cr speciation with SPE has been reviewed [17,18].…”

“…As Cr(III) does not react with DPC, an oxidation procedure is required. We considered the three different oxidants that have mainly been used for this purpose: Ce(IV) [11], deep-UV radiation [13,14], and H 2 O 2 [12,16]. Oxidation with Ce(IV) requires acidic conditions, under these conditions, Cr(VI) formed also functions as an oxidant and can be lost by reaction with slowly oxidized material such as organic acids [11] that may be present in a soil extract.…”