An automated sequential injection on-line preconcentration procedure for trace metals by using a PTFE bead-packed microcolumn coupled to ICP-MS is described, and used for simultaneous analyses of cadmium and lead. In dilute nitric acid (0.5%, v/v), neutral complexes between the analytes and chelating reagent, diethyldithiophosphate (DDPA), are formed and adsorbed onto the surface of the PTFE beads. The adsorbed complexes are afterwards eluted with 20% nitric acid and the leading part of the eluate (40ml) is stored in a sample loop (SL), the contents of which are subsequently transported, via a direct injection high efficiency nebulizer (DIHEN), into the ICP-MS for quantification. The packed column (PC) generates considerably lower hydrodynamic impedance than other commonly used sorbent columns, while its preconcentration efficiencies, in terms of retention efficiency and enrichment factor, are significantly improved as compared to a knotted reactor (KR). Inherently, the column approach results in low blank values and consequently in low limits of detection (LODs). With a 40s sample loading time at 4.5ml min21, along with a sampling frequency of 18h21, the retention efficiencies/enrichment factors for cadmium and lead were 96%/72 and 104%/81, respectively, versus 45%/34 and 54%/41 for a knotted reactor with similar internal surface area. In addition, the limits of detection (LODs) and precisions were at the same levels, i.e., the LODs were 2.9ng l21 Cd (PC), 3.5ng l21 Cd (KR), 6.0ng l21 Pb (PC) and 4.7ng 121 Pb (KR), while the RSDs were 1.9% (Cd, PC), 2.7% (Cd, KR), 2.2% (Pb, PC) and 2.5% (Pb, KR). The procedure was validated by determination of trace cadmium and lead in certified reference materials and urine samples.

An automated sequential injection on-line preconcentration procedure for determination of trace levels of copper and lead via solvent extraction/back extraction coupled to ICP-MS is described. In citrate buffer of pH 3, neutral complexes between the analytes and the chelating reagent, ammonium pyrrolidinedithiocarbamate (APDC), are extracted into isobutyl methyl ketone (IBMK). The organic phase is separated from the aqueous one by means of a dual-conical gravitational phase separator, and stored in a PTFE holding coil. Afterwards, the organic phase is propelled and mixed with an aqueous back extractant of nitric acid containing Pd (II) ions as stripping agent, thereby facilitating a rapid metal exchange reaction with the APDC ligand and transfer of the analytes back into the aqueous phase. The aqueous phase is separated in a second dual-conical gravitational phase separator, and 30 ml is entrapped in a sample loop, the content of which is subsequently introduced into the ICP-MS, via a direct injection high efficiency nebulizer (DIHEN), for quantification. nrichment factors of 29.6 (Cu) and 23.3 (Pb), detection limits of 17 ng l21 (Cu) and 11ng l21 (Pb), along with a sampling frequency of 13 h21 were obtained at a sample flow rate of 6.0ml min21. The precisions (RSD) at the 0.2mg 121 level were 4.4%(Cu) and 4.8%(Pb), respectively. The applicability of the procedure is demonstrated for the determination of copper and lead in three certified reference materials and a urine sample.

An automated sequential injection hydride generation (HG) atomic fluorescence spectrometric (AFS) method was developed, with the aim of screening blood lead levels for Chinese citizens, especially for children. Lead hydride was generated from acid solution, with potassium ferricyanide as an oxidizing agent, by reaction with alkaline tetrahydroborate solution. The hydride was separated from the reaction medium in a gas–liquid separator (GLS1) and swept directly into the atomizer. A thorough scrutiny was made of the various factors, including the modification of the AFS instrument and related parameters, the various wet digestion protocols, the variables of the flow system and the reaction conditions. Under the optimized conditions the blank signal was satisfactorily minimized, giving rise to a limit of detection of 0.014μgl-1, defined as 3 times the blank standard deviation divided by the slope of calibration graph, and a RSD value of 0.7%(at the 2.0μgl-1 level, n=11), along with a sampling frequency of 120h-1. The sensitivity of the procedure was found to be significantly superior to those obtained by HG-atomic emission spectrometry (AES), direct sampling electrothermal atomic absorption spectrometry (ETAAS), tungsten filament atomizer ETAAS, and quartz tube atomizer HG-AAS; it was even lower than those by in-atomizer-trapping HG-ETAAS and comparable to ICPMS-based methods. The accuracy and practical applicability of the procedure were validated by analysing certified reference materials of frozen cattle blood GBW 09139 and GBW 09140, and further demonstrated by spiking recoveries of lead in human whole blood samples.

Flow injection (FI) analysis, the first generation of this technique, became in the 1990s supplemented by its second generation, sequential injection (SI), and most recently by the third generation (i. e., Lab-on-Valve). The dominant role played by FI in automatic, on-line, sample pretreatments in recent decades is amply demonstrated by the large number of publications to which it has given rise. Among these, its hyphenation with electrothermal atomic absorption spectrometry (ETAAS) is one of the most attractive sub-branches because of the high sensitivity of ETAAS instruments for metal species. After a decade of development, it is apparent from the literature that coupling FI sample pretreatment with ETAAS remains most dynamic in the new millenium; meanwhile, it is exciting to note that some novel trends associated with this subject have also emerged. The aim of this mini-review is thus to illustrate the state-of-the-art progress in implementing miniaturized FI/SI systems for on-line separation and preconcentration of trace metals with detection by ETAAS since 2000. We also discuss future perspectives in this field.

Within the last decade, the first generation of flow injection (FI) has been supplemented by sequential injection (SI), also termed the second generation, and, recently, by the third generation, i.e., SI-Lab-on-Valve (SILOV). As apparent from the literature, FI and/or SI have become dominant as substitutes for labor-intensive, manual, sample-pre-treatment and/or solution-handling procedures prior to analyte detection by inductively coupled plasma mass spectrometry (ICP-MS). The present review presents and discusses the progress of the state of the art in implementing miniaturized FI/SI systems for on-line matrix separation and pre-concentration of trace levels of metals with detection by ICP-MS. It highlights some of the frequently applied on-line, sample-pre-treatment schemes, including solid phase extraction (SPE), on-wall molecular sorption and precipitate/(co)-precipitate retention using a polytetrafluoroethylene (PTFE) knotted reactor (KR), solvent extraction-back extraction and hydride/vapor generation. It also addresses a novel, robust approach, whereby the protocol of SI-LOV-bead injection (BI) on-line separation and pre-concentration of ultra-trace levels of metals by a renewable microcolumn is interfaced to ICP-MS, as conducted in the present authors' group. It discusses the future outlook in this field.

A micro-sequential injection spectrophotometric procedure for DNA assay was developed based on the employment of a lab-on-valve (LOV) meso-fluidic analytical system. A small amount of crystal violet solution (10μl) was de-colored inside the flow cell of the LOV at the presence of 5μl λ-DNA/HindIII within a certain pH range, and the absorbance decrease of crystal violet solution at 591 nm was measured via optical fibers and was employed as the basis of quantification. A uni-variant approach was adopted for the optimization of experimental parameters, including buffer pH, concentration and volume of crystal violet solution, reaction time and sample/reagent loading flow rates. A linear calibration graph was obtained within 0.2-6.0μgml−1, along with a detection limit of 0.07μgml−1. The procedure was applied for the determination of λ-DNA/HindIII in synthetic samples in comparison with a documented procedure.

Termed the third generation of flow-injection analysis, sequential injection (SI)-lab-on-valve (LOV) has specific advantages and allows novel, unique applications-not least as a versatile front end to a variety of detection techniques. This review presents and discusses progress to date of the SI-LOV approach as well as its applications in the automation and the micro-miniaturization of on-line sample pre-treatment. Special emphasis is placed on using SI-LOV in conjunction with bead injection (BI) for on-line separation and pre-concentration of ultra-trace levels of metals by exploiting the renewable micro-column approach. With detection by ETAAS and ICP-MS, it is shown, as illustrated by recent results in the authors' laboratory, that this methodology eliminates the problems encountered in conventional on-line column pre-concentration systems, improves the overall operational efficiency and yields the robustness necessary for routine assays. Also discussed is the future potential of the SI-LOV approach as a front end to various analytical protocols.

A sequential injection (SI) on-line matrix removal and trace metal preconcentration procedure by using a novel microcolumn packed with PTFE beads is described, and demonstrated for trace cadmium analysis with detection by electrothermal atomic absorption spectrometry (ETAAS). The analyte is initially complexed with diethyldithiophosphate (DDPA) and adsorbed onto the column, which is afterwards eluted with 50ml of ethanol and subsequently introduced via air segmentation into the graphite tube for quantification. The ETAAS determination is synchronized with sample pre-treatment in the SI system. No flow resistance is encountered at a flow rate of 9.0ml min21 through the column. The preconcentration efficiency was improved significantly by using the packed column as compared with a knotted reactor. With a 40 s sample loading time at 4.5ml min21 along with a sampling frequency of 16 h21, quantitative adsorption of cadmium (99% retention efficiency) and an enrichment factor of 59.4 were obtained, as compared with only 46.7% and 28.0 by using a knotted reactor of similar internal surface area as the packed column. The detection limits and precision (RSD, 0.1mg l21 Cd) are at the same levels, i.e., 1.3ng l21 (LOD), 1.3% (RSD) for the packed column, and 1.2ng l21 (LOD), 1.5% (RSD) for the knotted reactor. The practical applicability of the procedure is demonstrated by the determination of trace levels of cadmium in three certified reference materials.

An automatic protocol for in-situ assay of dsDNA is presented by employing a micro-sequential injection lab-on-valve meso-fluidic system, which facilitates precise fluidic handling at the 0.1-10ml level. Sub-nano-liter to a few micro-liters of DNA sample and ethidium bromide (EB) solutions were introduced into the meso-fluidic system, where EB binding onto DNA takes place and an intercalated DNA-EB adduct was formed, which was afterwards excited in the flow cell of the LOV by a 473nm laser beam, and the emitted fluorescence was monitored in-situ via optical fibers. The experimental variables, i.e., pH of the buffer solution, the concentration and volume of EB solution, the reaction time and the fluid flow rates, were investigated. By loading 600nl sample and 1.0ml EB solution, a linear calibration graph was obtained within 0.03-3.0mg ml21 (dsDNA), and a detection limit (3s) of 0.009mg ml21 was achieved, along with a sampling frequency of 60h21 and a precision of 1.9% at the 1.0mg ml21 level. The detection limit was further improved to 0.006mg ml21 by increasing the sample volume to 2.0ml. Plasmid DNA in E. Coli extraction and l-DNA/Hind III in four synthetic samples were assayed by using this procedure. For the plasmid DNA, a good agreement with the documented UV method was obtained, while spiking recoveries for the synthetic samples were 95.6-103.4%.

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.