Flow Injection On-line Preconcentration Research Articles

PAN-Doped SiO2 as a New Packing Material for the Online Preconcentration and Determination of Trace Lead (II) in Biological and Environmental Samples Using Flame Atomic Absorption

ABSTRACT A flow injection online preconcentration and separation–FAAS method was developed for determination of trace lead in biological and environmental samples. Effects of chemicals and flow variables were studied. Under the optimal conditions, the enhancement factor can reach 101 with a sample consumption of 6.5 mL and throughput of 45 hr−1. The detection limit (3σ) was 0.24 µg L−1. At the level of 20 µg L−1 and 40 µg L−1 of Pb (II), the precisions (RSD, n = 11) were found to be 2.2% and 1.2%, respectively. The spike recoveries of real samples were in the range of 97–103%.

Determination of copper by Flame Atomic Absorption Spectrometry using Flow Injection On-line Preconcentration with Double Micro-columns

Determination of copper by Flame Atomic Absorption Spectrometry using Flow Injection On-line Preconcentration with Double Micro-columns

Determination of Cu, Zn, Mn, and Pb by microcolumn packed with multiwalled carbon nanotubes on-line coupled with flame atomic absorption spectrometry

Modified multiwalled carbon nanotubes (MWCNTs) were used as a packing material for flow injection on-line microcolumn preconcentration of trace amounts of the metal ions of Cu, Zn, Mn and Pb, and subsequent flame atomic absorption spectrometry (FAAS) in one run after desorbing the ions with hydrochloric acid and injecting them into the nebulizer of an FAAS. Parameters such as loading time, flow rate, pH, eluent concentration, and flow rate were optimized. Enrichment factors are 20.3, 14.2, 20.6 and 15.4 respectively, and the sample through- put is 25 h �1 . The limits of detection (three times the standard deviation of the blank) are 0.59, 0.62, 0.28 and 1.00 µg L �1 , respectively, and standard deviations range from 2.6 to 4.6% (n=7). The method was applied to the analysis of these ions in vegetables, and accuracy assessed via recovery experiments.

Determination of Trace Inorganic Mercury in Mineral Water by Flow Injection On-line Sorption Preconcentration-Cold Vapor Atomic Fluorescence Spectrometry

Abstract Flow injection on-line sorption preconcentration and separation in a knotted reactor (KR) was coupled to cold vapor atomic fluorescence spectrometry for the determination of trace mercury in mineral water. Mercury was preconcentrated by on-line formation of mercury diethyldithiocarbamate complex (Hg-DDTC) and absorption of the resulting neutral complex on the inner walls of a knotted reactor. A 20% (v/v) HNO 3 solution heated by Electromagnetic induction heating technique was used as eluent to remove the absorbed Hg-DDTC from the KR, and then the vapor mercury generated by mixing the resulting solution and KBH 4 was determined on-line by cold vapor atomic fluorescence spectrometry. The 20% HNO 3 was used as both the efficient eluent and the required acidic medium for subsequent mercury vapor generation. Using 20% HNO 3 instead of conventional organic solvent as eluent, the proposed method is simple, easy operational and environmental friendly. Under the optimal experimental conditions, the sample throughput was approximately 30 per hour with the enhancement factor of 35. The detection limit of mercury was 2.0 ng l −1 . The precision (RSD, n = 11) was 2.2% at the 0.1 μg l −1 Hg 2+ level.

Determination of arsenic in foods by flow injection on-line sorption pre-concentration with hydride generation atomic fluorescence spectrometry

A method was developed for the determination of total arsenic in foods using flow injection on-line sorption coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) using a cigarette filter as the sorbent material. After reducing As(V) to As(III) by using L-cysteine, the determination of total arsenic was achieved through on-line formation and retention of the pyrrolidine dithiocarbamate arsenic complex (As(III)–PDC) on the cigarette filter, which was packed in the pre-concentration column and total arsenic was determined by HG-AFS. The analytes were eluted with 1.68 mol l−1 HCl from the sorbent material. With consumption of 22 ml of the sample solution, an enrichment factor of 25.6 was obtained at a sample throughput of 11.6 h−1. The detection limits (3 standard deviations) and the precision (relative standard deviation) in foods ranged from 2.5 to 9.9 ng g−1 and from 1.1 to 2.2%, respectively. The method was used to determine arsenic in carrot, mushroom, chicken tissue, cod fish, rice, common carp and shrimp.

Simple micro-column with multi-walled carbon nanotubes for on-line preconcentration and determination of lead in natural water by hydride generation atomic fluorescence spectrometry

A flow injection on-line preconcentration system was developed for the determination of lead by hydride generation atomic fluorescence spectrometry (HG-AFS). It is based on a simple micro-column filled with multiwalled carbon nanotubes (MWCNTs). The preconcentration of lead on the MWCNTs was carried out based on the adsorptive retention of analyte via on-line introducing the sample into the micro-column system. A 0.3 mol L−1 HNO3 was introduced to elute the retained analyte and merged with KBH4 solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 26 was obtained with a sample consumption of 14.4 mL. The limit of detection was 2.8 ng L−1 and the precision (RSD) of 11 replicate measurements of 0.2 μg L−1 Pb was 4.4%. The method was validated by analyzing three certified reference materials, and was successfully applied to the determination of trace lead in natural water samples.

Simultaneous determination of palladium and rhodium using on-line column enrichment and electrothermal atomic absorption spectrometric detection

Flow injection on-line micro-column pre-concentration was coupled with electrothermal atomic absorption spectrometry (ETAAS) for the simultaneous determination of Rh and Pd in environmental samples. The micro-column contained 1,5-Bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydrazide (PSTH) immobilised on an anion-exchange resin (Dowex 1 × 8–200). The sorbent was tested in a micro-column, placed in the auto-sampler arm, at the flow rate 3.1 mL/min. Elution was performed with 2 M HNO3 and the system was optimised with a 60 s pre-concentration time.

Flow injection on-line displacement/solid phase extraction system coupled with flame atomic absorption spectrometry for selective trace silver determination in water samples

A novel flow injection (FI) on-line displacement solid phase extraction preconcentration and/or separation method coupled with FAAS in order to minimize interference from other metals was developed for trace silver determination. The proposed method involved the on-line formation and subsequently pre-sorption of lead diethyldithiocarbamate (Pb-DDTC) into a column packed with PTFE-turnings. The preconcentration and/or separation of the Ag(I) took place through a displacement reaction between Ag(I) and Pb(II) of the pre-sorbed Pb-DDTC. Finally, the retained analyte was eluted with isobutyl methyl ketone (IBMK) and delivered directly to nebulizer for measuring. Interference from co-existing ions with lower DDTC complex stability in comparison with Pb-DDTC, was eliminated without need for any masking reagent. With 120 s of preconcentration time at a sample flow rate of 7.6 mL min−1, an enhancement factor of 110 and a detection limit (3 s) of 0.2 μg L−1 were obtained. The precision (RSD, n = 10) was 3.1% at the 10 μg L−1 level. The developed method was successfully applied to trace silver determination in a variety of environmental water samples and certified reference material.

Application of a wool column for flow injection online preconcentration of inorganic mercury(II) and methyl mercury species prior to atomic fluorescence measurement

The use of an unmodified native sheep wool packed minicolumn for the online preconcentration of Hg(II) and methyl mercury species prior to the determination of mercury by atomic fluorescence spectrometry was investigated. Experimental conditions, such as pH, desorbing agents, volume of solution were optimized. 0.5 M thioglycolic acid was found to be a successful eluting agent for both mercury species. Breakthrough and total capacities were determined. The method is simple and rapidly applicable for the determination of Hg(II) and methyl mercury in tap water. The accuracy of the method was examined by the analysis of a peach leaves standard reference material. Recoveries of spiked mercury species in tap water were 105.8% for Hg(II) and 98.8% for methyl mercury.

Flow injection on-line preconcentration with an ion-exchange resin coupled with microwave plasma torch-atomic emission spectrometry for the determination of trace rare earth elements

A sensitive and rapid on-line method has been developed for the determination of trace amounts rare earth elements (REEs), lanthanum, cerium, neodymium and yttrium, by microwave plasma torch-atomic emission spectrometry (MPT-AES) combined with micro-column separation/preconcentration. A strong basic cinnamene anion exchange resin is used for matrix elimination and enrichment of the analytes. The adsorbed metal ions are subsequently eluted from the column and transferred into the detector with nitric acid solution for simultaneous multi-element determination. Various factors influencing the separation/preconcentration, sample flow rate, loading time, acidity and eluent flow rate, concentration, have been studied in detail. Under the optimized conditions, the detection limits for lanthanum, cerium, neodymium and yttrium based on three times of standard deviations of blank by 7 replicates are 0.89, 2.02, 1.56 and 0.78 μg·L − 1, and the relative standard deviations are determined as 1.54, 4.29, 4.95 and 3.90%, respectively. The proposed method has been applied to the analysis of the four REEs in high purity Sm 2O 3, Eu 2O 3, Gd 2O 3, Tb 2O 3, Dy 2O 3, Yb 2O 3, and Lu 2O 3 samples with a recovery range of 95.1–104.8%.

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%.

Flow injection on-line preconcentration coupled to hydride generation atomic fluorescence spectrometry for ultra-trace amounts of cadmium determination in seawater

A simple flow injection on line separation and preconcentration system coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) was developed for ultra-trace cadmium determination in seawater. With the sample pH kept at 3.0, the preconcentration of cadmium on the inner walls of the knotted reactor was carried out based on the retention of cadmium complex with 1-phenyl-3-methyl-4-benzoylpyrazol-5-one. A 0.2 mol L−1 HCl was introduced to elute the retained analyte complex and merge with KBH4 solution for HG-AFS detection. Under the optimal experimental conditions, an enhancement factor of 12 was obtained with a sample consumption of 12.0 mL. The limit of detection was 3.2 ng L−1 with a sample frequency of 24 h−1. The developed method was validated by the analysis of cadmium in certified reference materials, and was applied to the determination of cadmium in four seawater samples with R.S.D. of around 10%.

Application of chitosan functionalized with 3,4-dihydroxy benzoic acid moiety for on-line preconcentration and determination of trace elements in water samples

Chitosan resin functionalized with 3,4-dihydroxy benzoic acid (CCTS-DHBA resin) was used as a packing material for flow injection (FI) on-line mini-column preconcentration in combination with inductively coupled plasma-atomic emission spectrometry (ICP-AES) for the determination of trace elements such as silver, bismuth, copper, gallium, indium, molybdenum, nickel, uranium, and vanadium in environmental waters. A 5-mL aliquot of sample (pH 5.5) was introduced to the minicolumn for the adsorption/preconcentration of the metal ions, and the collected analytes on the mini-column were eluted with 2 M HNO3, and the eluates was subsequently transported via direct injection to the nebulizer of ICP-AES for quantification. The parameters affecting on the sensitivity, such as sample pH, sample flow rate, eluent concentration, and eluent flow rate, were carefully examined. Alkali and alkaline earth metal ions commonly existing in river water and seawater did not affect the analysis of metals. Under the optimum conditions, the method allowed the determination of metal ions with detection limits of 0.08 ng mL−1 (Ag), 0.9 ng mL−1 (Bi), 0.07 ng mL−1 (Cu), 0.9 ng mL−1 (Ga), 0.9 ng mL−1 (In), 0.08 ng mL−1 (Mo), 0.09 ng mL−1 (Ni), 0.9 ng mL−1 (U), and 0.08 ng mL−1 (V). By using 5 mL of sample solution, the enrichment factor and collection efficiency were 8–12 fold and 96–102%, respectively, whereas the sample throughput was 7 samples/hour. The method was validated by determining metal ions in certified reference material of river water (SLRS-4) and nearshore seawater (CASS-4), and its applicability was further demonstrated to river water and seawater samples.

Preconcentration of inorganic antimony(III) in environmental samples by PSTH-Dowex microcolumn and determination by FI-ETAAS

A flow injection on-line sorption preconcentration system has been synchronously coupled to an electrothermal atomic absorption spectrometry (ETAAS) system for the selective determination of trace amounts of Sb(III) in water, soil and plant. The determination was achieved by selective complexation and sorption of Sb(III) with [1,5-bis(2-pyridyl)-3-sulphophenyl methylene thiocarbonohydarzide (PSTH) immobilized on an anion-exchange resin (Dowex 1× 8-200)] at a wide range of pH, quantitative elution with 50 μl of 2 M HNO 3 and subsequent ETAAS detection. ETAAS determination of the analyte was performed in parallel with the preconcentration of the next sample. Using a preconcentration time of 60 s and a sample loading flow rate of 2.8 ml min −1, an enhancement factor of 12 was obtained in comparison with direct injection of 50 μl aqueous solution, resulting in a sampling frequency of 31 samples h −1. The detection limit (3 s) was 2 μg l −1 and the precision was 3.1% (R.S.D.) for 11 replicate determinations at 10 μg l −1. The accuracy of the proposed method was demonstrated by analyzing one certified sample and different spiked samples.

Online separation and preconcentration of trace heavy metals with 2,6-dihydroxyphenyl-diazoaminoazobenzene impregnated amberlite XAD-4

A rapid and sensitive flow injection online preconcentration method was developed for determination of Cd, Co, Cu, and Zn in natural water samples by flame atomic absorption spectrometry. The procedure is based on the retention of analytes in the form of 2,6-dihydroxyphenyl-diazoaminoazobenzene (DHDAA) complexes on a microcolumn packed with XAD-4-DHDAA resin. Cd, Co, Cu, and Zn can be eluted from the microcolumn with 0.5 mol L−1 HCl and pumped directly to the nebulizer-burner system of the flame atomic absorption spectrometer (FAAS). The enrichment factors are 42 (Cd), 33 (Co), 28 (Cu), and 31 (Zn), for a sample volume of 6.0 mL and 1 min preconcentration time relative to direct introduction of aqueous solutions into an atomic absorption spectrometer. The sampling frequency was 30 h−1 with a 1 min loading. The proposed method allowed the determination of Cd, Co, Cu, and Zn with detection limits of 0.1, 0.5, 0.3, and 0.2 µg L−1, respectively. The selectivity of the XAD-4-DHDAA resin for Cd, Co, Cu, and Zn over several electrolytes was also investigated. The method was validated by analysis of a standard reference material (GBW 08301) with the results agreement with those quoted by manufactures. The developed method was applied to the determination of trace Cd, Co, Cu, and Zn in tap water, ground water and river water samples with satisfactory results.

Simultaneous on-line preconcentration and determination of trace metals in environmental samples using a modified nanometer-sized alumina packed micro-column by flow injection combined with ICP-OES

A novel organic reagent 3-(8-quinolinylazo)-4-hydroxybenzoic acid (QAHBA) was synthesized for chemically modified nanometer-sized alumina, and it was characterized with infrared spectrum and 1H NMR spectra. By using modified nanometer-sized alumina as micro-column packing material, a new method of flow injection (FI) on-line preconcentration coupled to ICP-OES was developed for simultaneous determination of trace metals (Ag, Pd, Au, Ga, In and Nb) in geological and environmental samples. The effects of pH, sample flow rate, sample volume, elution and interfering ions on the recovery of the analytes have been investigated. Under the optimized operating conditions, the adsorption capacity of the modified nanometer-sized alumina for Ag, Pd, Au, Ga, In and Nb were found to be 5.1, 7.6, 17.7, 15.6, 8.1 and 12.3 mg g −1, respectively. With 4 min preconcentration time and 24 s elution time, the enrichment factor was 10 and the sample frequency was 10 h −1. The detection limits of this method for Ag, Pd, Au, Ga, In and Nb were 0.12, 0.44, 0.27, 0.19, 0.54 and 0.18 μg l −1, respectively, while the R.S.D.s were 1.6, 2.3, 4.5, 1.6, 1.9 and 1.7% ( n = 7, c = 50 ng ml −1), respectively. The proposed method has been applied to the determination of these trace metals in geological-certified reference materials and natural water samples with satisfactory results.

Non-chromatographic speciation analysis of mercury by flow injection on-line preconcentration in combination with chemical vapor generation atomic fluorescence spectrometry

A novel non-chromatographic approach for direct speciation of mercury, based on the selective retention inorganic mercury and methylmercury on the inner wall of a knotted reactor by using ammonium diethyl dithiophosphate and dithizone as complexing agents respectively, was developed for flow injection on-line sorption preconcentration coupled with chemical vapor generation non-dispersive atomic fluorescence spectrometry. With the sample pH kept at 2.0, the preconcentration of inorganic mercury on the inner walls of the knotted reactor was carried out based on the exclusive retention of Hg–DDP complex in the presence of methylmercury via on-line merging the sample solution with ammonium diethyl dithiophosphate solution, and selective preconcentration methylmercury was achieved with dithizone instead of ammonium diethyl dithiophosphate. A 15% (v/v) HCl was introduced to elute the retained mercury species and merge with KBH 4 solution for atomic fluorescence spectrometry detection. Under the optimal experimental conditions, the sample throughputs of inorganic mercury and methylmercury were 30 and 20 h − 1 with the enhancement factors of 13 and 24. The detection limits were found to be 3.6 ng l − 1 for Hg 2+ and 2.0 ng l − 1 for CH 3Hg +. The precisions (RSD) for the 11 replicate measurements of each 0.2 μg l − 1 of Hg 2+ and CH 3Hg + were 2.2% and 2.8%, respectively. The developed method was validated by the analysis of certified reference materials (simulated natural water, rice flour and pork) and by recovery measurements on spiked samples, and was applied to the determination of inorganic mercury and methylmercury in biological and environmental water samples.

Evaluation of polychlorotrifluoroethylene as sorbent material for on-line solid phase extraction systems: Determination of copper and lead by flame atomic absorption spectrometry in water samples

Polychlorotrifluoroethylene (PCTFE) in the form of beads was applied, as packing material for flow injection on-line column preconcentration and separation systems coupled with flame atomic absorption spectrometry (FAAS). Its performance characteristics were evaluated for trace copper determination in environmental samples. The on-line formed complex of metal with diethyldithiophosphate (DDPA) was sorbed on the PCTFE surface. Isobutyl methyl ketone (IBMK) at a flow rate of 2.8 mL min −1 was used to elute the analyte complex directly into the nebulizer–burner system of spectrophotometer. The proposed sorbent material reveal, excellent chemical and mechanical resistance, fast adsorption kinetics permitting the use of high sample flow rates up to 15 mL min −1 without loss of retention efficiency. For copper determination, with 90 s preconcentration time the sample frequency was 30 h −1, the enhancement factor was 250, which could be further improved by increasing the loading (preconcentration) time. The detection limit (3 s) was c L = 0.07 μg L −1, and the precision (R.S.D.) was 1.8%, at the 2.0 μg L −1 Cu(II) level. For lead determination, the detection limit was c L = 2.7 μg L −1, and the precision (R.S.D.) 2.2%, at the 40.0 μg L −1 Pb(II) level. The accuracy of the developed method was evaluated by analyzing certified reference materials and by recovery measurements on spiked natural water samples.

Online Flow Injection Preconcentration and Flame Atomic Absorption Spectrometric Determination of Palladium(II) Using Inorganic and Inorganic‐Organic Hybrid Materials–Packed Microcolumns

Various inorganic and inorganic‐organic hybrid materials–packed columns, including commercially available C18 bonded silica gel and alumina columns, were tested for the on‐line preconcentration of palladium(II) and subsequent determination by flame atomic absorption spectrometry (AAS). Several thioligands were investigated for complexing palladium(II) and subsequent sorption, elution, and determination by flame atomic absorption spectrometer. Among them, diethyl ammonium dithiocarbamate was found to give the highest enrichment factor for a given concentration of palladium(II) under optimized conditions. After testing the accuracy of the developed method by analyzing certified reference material (SARM 7), it was applied for the analysis of street and domestic fan blade dust samples.

Flow injection on-line solid phase extractive preconcentration of palladium(II) in dust and rock samples using exfoliated graphite packed microcolumns and determination by flame atomic absorption spectrometry

A sensitive and efficient flow injection preconcentration and matrix-separation technique using exfoliated graphite (EG) as column material was developed prior to flame atomic absorption spectrometry (FAAS) determination of palladium(II) in street/fan blade dust and rock samples. The method is based on the sorption of palladium(II)—diethylammonium dithiocarbamate chelate (which was found to be better among various thioligands) complex on to EG material and its subsequent elution with acidified methanol (0.01 M HCl in methanol). Using 8 ml of the sample, the detection limit achieved was 1.0 μg l −1. The accuracy of the method developed was checked by analysing certified reference material SARM-7. The precision obtained for five successive determination of 100 μg l −1 of palladium(II) was 2.4%. The performance of EG material was compared with allotropes of carbon in terms of pH, chelate concentration, weight of column material, sensitivity enhancement (w.r.t. conventional FAAS), detection limit, calibration range, selectivity and precision. Furthermore, performance of the EG material packed column was compared with commercially available C 18 bonded silica gel/alumina columns for on-line FIA-FAAS determination of palladium(II).