Octadecyl immobilized surface was, for the first time, proved to be a superb precipitate-collecting medium. Surface charge effect was assumed to dominate the adsorption of cadmium hydroxide precipitate, facilitated by electrostatic interaction between the negatively charged C18 bead surface and positively charged cadmium hydroxide clusters. Residual silanol groups on the C18-immobilized silica surface did not contribute to precipitate adsorption. A novel procedure for ultratrace cadmium preconcentration was proposed by incorporating a renewable microcolumn in a lab-on-valve system. Cd (OH) 2 precipitate was adsorbed onto the C18 surface, which was afterward eluted with 20μL of nitric acid (1%) and quantified with detection by electrothermal atomic absorption spectrometry. An enrichment factor of 28 and a limit of detection of 1.7ng L-1, along with a sampling frequency of 13 h-1 were obtained with a sample consumption of 600μL within the concentration range of 0.01-0.2μg L-1, achieving a precision of 2.1% RSD at the 0.05μg L-1 level. The enrichment factor was further enhanced to 44 by increasing the sample volume to 1200μL. The procedure was validated by analyzing cadmium in three certified reference materials, that is, river sediment (CRM 320), sea lettuce (CRM 279), and frozen cattle blood (GBW 09140). Good agreement between the obtained results and the certified values was achieved.

A sequential injection (SI) on-line lab-on-valve separation/preconcentration system incorporating a renewable ion-exchange micro-column interfaced with inductively coupled plasma mass spectrometry (ICP-MS) via a home-made direct injection high efficiency nebulizer (DIHEN) is described. Aimed at eliminating spectroscopic and non-spectroscopic interferences, the renewable micro-column is first loaded by aspirating 15ml of a SP Sephadex C-25 cation-exchanger bead suspension and then exposed to a defined volume of sample solution. Residuals of matrix components are pre-eluted with carrier solution (nitric acid,1: 80v/v), and the measurands are subsequently eluted with a defined volume of nitric acid (1: 16v/v). The leading volume of eluate (ca. 30ml) is collected and introduced into the plasma via the DIHEN. The eluted beads are then discarded and a new column is aspirated for the next operation. Data acquisition is performed in parallel with the ensuing preconcentration process. With 2.0ml sample loading, the enrichment factors are 35.2 (0.05-2.4mg l21) for Ni, and 9.1 (0.04-1.6mg l21) and 28.4 (1.6-3.2mg l21) for Bi. The detection limits (3s) are 15 ng l21 (Ni) and 4 ng l21 (Bi), while the sampling frequency is 12 per hour. The precisions are 2.9% (0.8mg l21 Ni) and 1.7% (0.8mg l21 Bi). The procedure is validated by determination of nickel and bismuth in a certified reference material (CRM 320, River Sediment), and the recoveries are measured by spiking two human urine samples.

% for the procedure in which the loaded beads are transported directly to the graphite furnace for pyrolysis and atomization, and even improved in comparison to the traditional unidirectional and bidirectional repetitive elution procedures which under comparable conditions yield R.S.D.-values of 5.8 and 4.9%, respectively. The tolerance limits for cations such as Pb (II), Zn (II), Co (II) and Mn (II) were improved up to 10-50-folds, and the linear calibration range extended to comprise 0.02-1.20g l−1. Because of lower operating temperature, the life time of the graphite tube is extended. An enrichment factor of 71.1 and a detection limit of 10.2ng l−1 along with a sampling frequency of 12 h−1 were obtained, which are at the same levels as those for the previously described procedure without elution. The present approach was validated by determination of the nickel contents in two certified reference materials, an industrial waste water sample and a human urine sample.

An automated sequential injection (SI) on-line solvent extraction-back extraction eparation/preconcentration procedure is described. Demonstrated for the assay of cadmium by electrothermal atomic absorption spectrometry (ETAAS), the analyte is initially complexed with ammonium pyrrolidinedithiocarbamate (APDC) in citrate buffer and the chelate is extracted into isobutyl methyl ketone (IBMK), which is separated from the aqueous phase by means of a newly designed dual-conical gravitational phase separator. A metered amount of the organic eluate is aspirated and stored in the PTFE holding coil (HC) of the SI-system. Afterwards, it is dispensed and mixed with an aqueous back extractant of dilute nitric acid containing Hg(II) ions as stripping agent, thereby facilitating a rapid metal-exchange reaction with the APDC ligand and transfer of the Cd into the aqueous phase. The aqueous phase is separated in a second dual-conical gravitational phase separator, and 30 l of it is entrapped and metered in a sample loop (SL) and subsequently introduced via air segmentation into the graphite tube for analyte quantification. The ETAAS determination is performed in parallel with the separation/preconcentration process of the ensuing sample. An enrichment factor of 21.4, a detection limit of 2.7ng l−1, along with a sampling frequency of 13h−1 were obtained at a sample flow rate of 6.0ml min−1. The precision (R. S. D.) at the 0.4g l−1 level was 1.8% as compared to 3.2% when quantifying the organic extractant directly. The applicability of the procedure is demonstrated for the determination of trace levels of cadmium in three certified reference materials.

A novel way of exploiting flow injection/sequential injection (FIA/SIA) on-line ion-exchange preconcentration with detection by electrothermal atomic absorption spectrometry (ETAAS) is described and demonstrated for the determination of trace-levels of nickel. Based on the use of a renewable microcolumn incorporated within an integrated micro FI-system, the column is loaded with a defined volume of small beads of an SP Sephadex C-25 cation-exchange resin and subsequently exposed to a metered amount of sample solution. However, instead of eluting the retained analyte from the organic ion-exchange resin, the beads are along with 30ml of carrier (buffer) solution transported via air segmentation directly into the graphite tube, where they are ashed during the pyrolysis and atomization process. The ETAAS determination is performed in parallel with the preconcentration process of the ensuing sample. An enrichment factor of 72.1, a detection limit of 9ng l−1, along with a sampling frequency of 12h−1 were obtained with 150 s of sample loading time at a sample flow rate of 12ml s−1 (corresponding to 0.72ml min−1). The relative standard deviations were 3.4%. The procedure was validated by determination of the nickel contents in two certified reference materials and in a human urine sample.