Optical emission spectrometric determination of arsenic and antimony by continuous flow chemical hydride generation and a miniaturized microwave microstrip argon plasma operated inside a capillary channel in a sapphire wafer

摘要

Continuous flow chemical hydride generation coupled directly to a 40 W, atmospheric pressure, 2,45 GHz microwave microstrip Ar plasma operated inside a capillary channel in a sapphire wafer has been optimized for the emission spectrometric determination of As and Sb. The effect of the NaBH4 concentration, the concentration of HCl, HNO3 and H2SO4 used for sample acidification, the Ar flow rate, the reagent flow rates, the liquid volume in the separator as well as the presence of interfering metals such as Fe, Cu, Ni, Co, Zn, Cd, Mn, Pb and Cr, was investigated in detail. A considerable influence of Fe(III) (enhancement of up to 50 %) for As(V) and of Fe(III), Cu(II) and Cr(III) (suppression of up to 75%) as well as of Cd(II) and Mn(II) (suppression by up to 25%) for Sb(III) was found to occur, which did not change by more than a factor of 2 in the concentration range of 2-20 mu g ml~(-1). The microstrip plasma tolerated the introduction of 4.2 ml min~(-1) of H2 in the Ar working gas, which corresponded to an H2/Ar ratio of 28%. Under these conditions, the excitation temperature as measured with Ar atom lines and the electron number density as determined from the Stark broadening of the H_(beta) line was of the order of 5500 K and 1.50 centre dot 10~(14) cm~3, respectively. Detection limits (sigma) of 18 ng ml~1 for As and 31 ng ml~(-1) for Sb were found and the calibration curves were linear over 2 orders of magnitude. With the procedure developed As and Sb could be determined at the 45 and 6.4 mu g ml~(-1) level in a galvanic bath solution containing 2.5% of NiSO4. Additionally, As was determined in a coal fly ash reference material (NIST SRM 1633a) with a certified concentration of As of 145 ±15 mu g g~(-1) and a value of 144±4 mu g g~(-1) was found.