Development of a microfluidic membraneless vaporization flow system for trace analysis of arsenic.

A new design of a membraneless vaporization (MBL-VP) unit coupled with a specific flow system is presented for the determination of arsenic at trace levels using a hydride generation process. The MBL-VP unit contains two concentric conical reservoirs, with the outer cone selected as the donor reservoir. The volume of the outer donor reservoir is thereby greater than the acceptor volume, necessary for holding sufficient sample and reagents for the generation of arsine gas by reaction between As(iii) and sodium borohydride under acidic conditions. The arsine gas diffuses into the narrow headspace and is absorbed by an aliquot of 150 µL of mercuric chloride acceptor solution. The resulting reaction produces hydronium ions which is monitored by the absorbance change at 530 nm of the methyl orange indicator added in the acceptor solution. To decrease the detection limit, the aspiration and removal of the donor plug, comprising the sample, borohydride and acid, into and out of the donor cone are repeated several times, while the acceptor solution is kept unchanged. As a result, analysis of arsenic was achieved in the range of 10 to 100 µg L-1 with a detection limit of 8 µg L-1. Application to surface water was investigated. Percent recoveries of spiked surface water samples were in the range of 94-110%. For comparison of total arsenic (As(iii) and As(v)), the results obtained from the developed method are not statistically different from the ICP-OES method.