Flow Injection On-line Separation Research Articles

MultiSimplex optimization of on-line sorbent proconcentration and determination of iron by FI-AAS and microcolumn of immobilized ferron

A simple flow injection on-line separation and proconcentration system for determination of iron in milk and water samples were developed. Ferron was physically immobilized on alumina particles in the pH range of 2.5–6 and was used as sorbent in microcolumn preparation. Deposition of iron was effected by processing a standard or solution of analyte at pH range of 3–6 on the microcolumn. Injection of 300 μl of HNO 3 (5 mol l −1) served to elute the retained species to FAAS. Different factors affecting the performance of the system were optimized by MultiSimplex and univariable methods. MultiSimplex program based on the simplex algorithm allowed the simultaneous study of the variables affecting immobilization, sorption or elution process. The capacity of the sorbent under working condition was found to be 989.0 μg irons per gram of packing material. A sample volume of 20 and 40 ml resulted in preconcentration factors of 65 and 129, respectively. Precision ( n = 6) at 125 and 50 μg l −1 were 2.0 and 2.9%, respectively. With 20 ml sampling volume a detection limit of 1.06 μg l −1 was determined. The method was applied to determination of iron in tap water, river water, rain water, spring water, infant dry formula milk, human and cow milk. The accuracy was assessed through recovery experiments, independent analysis by furnace atomic absorption, and analysis of certified reference alloy.

A Simple and Sensitive Flow-Injection On-line Preconcentration Coupled with Hydride Generation Atomic Fluorescence Spectrometry for the Determination of Ultra-trace Lead in Water, Wine, and Rice

A simple and sensitive flow-injection on-line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for ultra-trace lead determination in water, wine, and rice samples, with the salient advantages of its minimization of transition-metal interferences and tolerance to an ethanol matrix. A lead hydroxide precipitate was achieved by the on-line merging of a sample and an ammonium buffer solution and collected onto the inner walls of a knotted reactor (KR). Removal of the residual solution from KR was achieved by air flow, and dissolution of the precipitate was carried out by using 0.2 mol l(-1) HCl. With a sample consumption of 11.7 ml, an enhancement factor of 16 was obtained at a sample throughput of 30 h(-1). The limit of detection (3s) was 16 ng l(-1) and the precision (RSD) for 1.0 microg l(-1) Pb was 3.4%.

Online Separation and Preconcentration of Gold and Palladium on Amidinothiourea Immobilized Glass Bead for Interference-Free Flame Atom Absorption Spectrometry Determination

Amidinothiourea immobilized glass bead (AGB) was applied as the microcolumn packing for the flow-injection online separation and preconcentration of Au(III) and Pd(II) coupled with FAAS determination. The peak-area absorbance (A) and the peak-height absorbance (H) were all used as the evaluating modes. Au(III) and Pd(II) in 0.50 M HCl solution were absorbed onto AGB completely and then eluted into AAS with thiourea solution. Base metal ions with a concentration of 2.0 mg/mL and anions with a concentration of 20.0 mg/mL caused no interference in the determination of Au(III) and Pd(II). The LODs of Au(III) and Pd(II) for a preconcentration time of 60 s with a sampling flow rate of 5.0 mL/min for 0.20 µg/mL of Au(III) and 0.30 µg/mL of Pd(II) were 2.7 and 6.5 ng/mL with the H mode and 4.6 and 10.2 ng/mL with the A mode, respectively. The RSD of seven replicate determinations of 0.20 µg/mL of Au(III) and 0.30 µg/mL of Pd(II) were 0.018 and 0.024 for the H mode and 0.013 and 0.018 for the A mode, respectively. The method was successfully applied to the determination of Au and Pd in real samples.

Flame atomic absorption determination of trace cobalt in steel samples using a flow-injection on-line separation system

Flame atomic absorption determination of trace cobalt in steel samples using a flow-injection on-line separation system

Monitoring, sampling, and automated analysis

Monitoring, sampling, and automated analysis

Differential determination of chromium(VI) and total chromium in natural waters using flow injection on-line separation and preconcentration electrothermal atomic absorption spectrometry.

A rapid, sensitive and selective method for the differential determination of CrIII and CrVI in natural waters is described. Chromium(vi) can be determined directly by flow injection on-line sorbent extraction preconcentration coupled with electrothermal atomic absorption spectrometry using sodium diethyldithiocarbamate as the complexing agent and C18 bonded silica reversed-phase sorbent as the column material. Total Cr can be determined after oxidation of CrIII to CrVI by potassium peroxydisulfate. Chromium(III) can be calculated by difference. The optimum conditions for sorbent extraction of CrVI and oxidation of CrIII to CrVI are evaluated. A 12-fold enhancement in sensitivity compared with direct introduction of 40 microliters samples was achieved after preconcentration for 60 s, giving detection limits of 16 ng l-1 for CrVI and 18 ng l-1 for total Cr (based on 3 sigma). Results obtained for sea-water and river water reference materials were all within the certified range for total Cr with a precision of better than 10% relative standard deviation in the range 100-200 ng l-1. The selectivity of the determination of CrVI was evaluated by analysing spiked reference materials in the presence of CrIII, resulting in quantitative recovery of CrVI.

Flow injection on-line separation and preconcentration for electrothermal atomic absorption spectrometry. Part 1. Determination of ultratrace amounts of cadmium, copper, lead and nickel in water samples

Combining a micro-scale flow injection preconcentration system on-line with electrothermal atomic absorption spectrometry results in a powerful integrated system. The most outstanding advantages are improved detection limits achieved by preconcentration and matrix separation, and low contamination because of the totally closed system. The discontinuous process of preconcentration is suitably accommodated in the measuring cycle of a graphite furnace, even enhancing the cycle time for complex matrices, because the lengthy programmes that are needed in order to separate the analyte from excess of matrix compounds are avoided. The integrated system permits fully automated operation, avoiding time-consuming manual work and enhancing the reproducibility and precision. Results obtained for the determination of ultratrace amounts of some elements in sea-water demonstrate the high sensitivity, good accuracy and precision of this technique. Using a time based technique equivalent to only 3 ml of sample, the sensitivity of the graphite furnace technique was enhanced about 20-fold compared with a 40 µl injection volume. Detection limits achieved were 0.8, 6.5, 17 and 36 ng l–1(3σ) for Cd, Pb, Cu and Ni, respectively.

Differential determination of arsenic(III) and total arsenic using flow injection on-line separation and preconcentration for graphite furnace atomic absorption spectrometry

Arsenic(III) can be quantitatively extracted using sodium diethyldithiocarbamate (NaDDTC) as the complexing agent and C18 reversed phase packing as the column material for solid phase extraction. Arsenic(V) must be reduced to its trivalent oxidation state prior to extraction. A mixture of sodium sulphite, hydrochloric acid, sodium thiosulphate and potassium iodide was found to be optimum for on-line reduction. When the sorbent extraction is carried out without and with the addition of the reduction mixture, arsenic(III) and total arsenic can be determined sequentially by graphite furnace atomic absorption spectrometry with detection limits (3 σ) of 0.32 ng for As(III) and 0.43 ng for total arsenic. A 7.6-fold enhancement in peak area compared to direct injection of 40 μl samples was obtained after 60 s preconcentration. Results obtained for sea water standard reference materials, using aqueous standards for calibration, agree well with certified values. A precision of 5.5% RSD was obtained for total arsenic in a sea water sample (1.65 solμg l As). Results obtained for synthetic mixtures of trivalent and pentavalent arsenic agreed well with expected values.

Flow injection on-line separation and preconcentration for electrothermal atomic absorption spectrometry. Part 2. Determination of ultra-trace amounts of cobalt in water

Ultra-trace amounts of cobalt in sea-water were determined by flow injection on-line sorbent extraction–preconcentration coupled with electrothermal atomic absorption spectrometry. With sodium diethyldithiocarbamate as the complexing agent and C18-bonded silica reversed-phase sorbent as the column material, a 42-fold enhancement of peak area, compared with that for direct 40 µl sample introduction, was obtained with a 120 s preconcentration and 5.6 ml of sample. The atomization signal was directly proportional to the preconcentration time. An enhancement factor of 210 and a detection limit of 1.7 ng l–1 could be achieved with a 10 min sample loading time (28 ml). Hence, the extremely low cobalt concentration of 4.0 ng l–1 in National Research Council of Canada certified reference material NASS-1 Open Ocean Seawater could be determined within 12 min. Results obtained for sea-water and estuarine water certified reference materials agreed with the certified values with a relative standard deviation of 5.0%.