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

Abstract

Chromium speciation by spectrophotometric determination of hexavalent chromium (Cr(VI)) with diphenylcarbazide (DPC) has several problems. These include: (1) the inability to directly detect trivalent chromium (Cr(III)) with DPC, (2) positive interference in Cr(VI) determination by other metal cations and (3) negative interference by any reducing agent present in the sample. These are addressed with an ion transfer device (ITD) in a flow injection analysis system. We previously developed the ITD for electrodialytic separations. Here we separate oppositely charged Cr(III) and Cr(VI) species by the ITD into two different acceptor solutions within ~5 s. The acceptor solutions consist of buffered HO to oxidize the Cr(III) to Cr(VI). Then DPC is added to either acceptor to measure Cr(III) and Cr(VI) spectrophotometrically. The system was optimized to provide the same response for Cr(VI) and Cr(III) with limits of detection (LODs, S/N=3) of 0.5 μg L for each and a throughput rate of 30 samples h. The ITD separation was also effective for matrix isolation and reduction of interferences. Potential cationic interferences were not transferred into the anionic Cr(VI) acceptor stream. Much of the organic compounds in soil extracts were also eliminated as evidenced from standard addition and recovery studies.

A smartphone-based device for simultaneous measurement of ratiometric fluorescence and absorbance demonstrated by the determination of hypochlorous acid

“…34 The spectrophotometry using DPC as the chromogenic agent for Cr(VI) determination is approved as a standard analytical method in many countries, and it has been used for more than one century due to its high sensitivity and selectivity. 35,36 As shown in Fig. S2, (ESI †) the reaction mixture of DPC and Cr(VI) has a strong absorption peak at the wavelength of 540 nm.…”

“…Because the ratiometric brightness signal is insensitive to the variations in light source intensity and shooting parameters of the camera, the portable dual-mode device offers good baseline stability for absorbance and ratiometric fluorescence measurements. The availability of the ratiometric fluorescence and absorbance modes was tested by using rhodamine 6G (R6G) and 1,5-diphenylcarbazide (DPC)-Cr(VI) system 31,32 as the models, respectively. The application of the dual-mode portable device was demonstrated by the determination of hypochlorous acid by using a heptamethine cyanine-based fluorescent and colorimetric probe (Cy-ANP).…”

Semi-continuous Monitoring of Cr(VI) and Cr(III) during a Soil Extraction Process by Means of an Ion Transfer Device and Graphite Furnace Atomic Absorption Spectroscopy

“…The electrodialytic ion transfer device (ITD) used in this study is as same as previously reported. 7,8 The ITD consists of five thin solution channels, which are separated by ion-permeable membranes (dialysis or ion exchange membranes). The sample solution was pumped through the center channel at 0.1 mL min -1 with a peristaltic pump (Minipuls 3, www.gilson.com).…”

Flow-based System: A Highly Efficient Tool Speeds Up Data Production and Improves Analytical Performance

“…In addition, we found the combination of a flow injection and flow-batch system and SIA for Cr(VI). 133,134 Moreover, lab-in-syringe and SIA systems were proposed for speciation analysis 135 and lab-on-valve sequential injection ELISA for the determination of carbamazepine. 136 The microfluidic platform still becoming important for developing new methods for environmental applications.…”