This communication presents a novel approach to perform sequential extraction of elements in solid samples by using a sequential injection (SI) system incorporating a specially designed extraction microcolumn. Based on the operation of the syringe pump, different modes of extraction are potentially feasible, uni-directional and bi-directional flow schemes being used herein. A three-step sequential extraction scheme, using conventionally adopted extractants, was used to evaluate the system by determining Ca, Fe, Mn, Cu, Zn in a soil certified reference material (NIST, SRM 2710). It is demonstrated that the system entails many advantages such as being fully automated, and besides being characterised by rapidity, ease of operation and robustness, it is less prone to risks of contamination and personal errors as encountered in traditional batch systems. Moreover, improvement of the precision and accuracy of the chemical fractionation of metal in solids as compared with previous reports are obtained. The system ensures that extraction is performed at designated pH values. Variation of sample weight to column volume ratios do not affect the amounts of extractable metals, nor do extraction flow rates ranging from 50 to 100 mul sec-1 show any effect on the extractability of the metals studied. With uni-directional and bi-directional flows the extractable amounts of metals are, with the exception of Mn, not different from those obtained in conventional procedures, but the saving in operation time is drastic (a few hours as compared to days).
Analytica Chimica Acta, 2004, Vol 526, Issue 2, p. 177-184
Sequential extraction; Sequential injection (SI); Soil; Metal determination; Microcolumn