Automated syringe-pump-based flow-batch analysis for spectrophotometric determination of trace hexavalent chromium in water samples

Abstract

In this work, we established an automated spectrophotometric method for determining hexavalent chromium in water samples using an integrated syringe pump-based environmental water analyzer (iSEA) based on the classic 1,5‑diphenylcarbazide chemistry. The device was computer-controlled with programs written by LabVIEW. The effects of reagent concentration, sample salinity and foreign ion interferences were investigated. Standard solutions (GBW(E)081584-1) were used to test the accuracy of the method. When equipped with a 5 cm Z-shaped flow cell, the detection limit was 0.024 μM with sample throughput of >30 h−1. In order to meet the requirements for trace Cr(VI) determination, the system was modified with a 2.5 m liquid waveguide capillary cell (internal diameter of 0.55 mm). The sample consumption was <2.1 mL. The detection limit was 0.54 nM with sample throughput of 20 h−1 and good linearity with R2 = 0.9985 (n = 110, obtained over 14 days). The two methods were successfully applied to determine Cr(VI) level in different water samples including tap water, river water, industrial wastewater and 37 brands of bottled water with spiked recovery in the range of 89.5%–117%.