Flow Injection On-line Microcolumn Research Articles

Unmodified Multi-Walled Carbon Nanotubes as Sorbent Material in Flow Injection on-Line Sorbent Extraction Preconcentration System for Cadmium Determination by Flame Atomic Absorption Spectrometry

Unmodified multi-walled carbon nanotubes (MWCNTs) were demonstrated as hydrophobic sorbent material for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for cadmium determination in natural water samples. The method was based on on-line chelate complex formation between the analyte with sodium diethyldithiocarbamate and retention onto the surface of MWCNTs. Quantitative elution of the analyte was achieved with methanol which was whereupon delivered to the FAAS nebulizer for atomization and measurement. The microcolumn was packed with a mixture of MWCNTs and silica beads in order to minimize the generated back-pressure in the flow system which arises from the nano dimensions of MWCNTs. All factors affecting the performance of the proposed method were studied thoroughly. For a 180 s preconcentration time the enhancement factor was 54, the detection limit (3s) was 0.24 µg L−1, and the precision as relative standard deviation at a 5.0 µg L−1 Cd(II) concentration level was 3.2%. The method was applied to the analysis of environmental water samples and the accuracy evaluated via certified reference material and recovery experiments.

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.

Simultaneous speciation of inorganic arsenic and antimony in natural waters by dimercaptosuccinic acid modified mesoporous titanium dioxide micro-column on-line separation and inductively coupled plasma optical emission spectrometry determination

A novel absorbent was prepared by dimercaptosuccinic acid chemically modifying mesoporous titanium dioxide and was employed as the micro-column packing material for simultaneous separation/preconcentration of inorganic arsenic and antimony species. It was found that both trivalent and pentavalent of inorganic As and Sb species could be adsorbed quantitatively on dimercaptosuccinic acid modified TiO 2 within a pH range of 4–7, and only As(III) and Sb(III) could be quantitatively retained on the micro-column within a pH range of 10–11 while As(V) and Sb(V) were passed through the micro-column without the retention. Based on this fact, a new method of flow injection on-line micro-column separation/preconcentration coupled to inductively coupled plasma optical emission spectrometry was developed for simultaneous speciation of trace inorganic arsenic and antimony in natural waters. Under the optimized conditions, an enrichment factor of 10 and sampling frequency of 10 h − 1 were obtained with on-line mode. The detection limits of As(III), As(V), Sb(III), and Sb(V) are 0.53, 0.49, 0.77 and 0.71 ng mL − 1 for on-line mode and as low as 0.11, 0.10, 0.15 and 0.13 ng mL − 1 for off-line mode due to its higher enrichment factor (50), respectively. The relative standard deviations of two modes are less than 6.7% (C = 20 ng mL − 1 , n = 7). The concentration ratio of lower oxidation states/higher oxidation states changing from 1:10 to 10:1 has no obvious effect on the recoveries of As(III) and Sb(III). In order to validate the developed method, two certified reference materials of GSBZ5004-88 and GBW(E)080545 water sample were analyzed and the determined values are in good agreement with the certified values. The proposed method was successfully applied to the simultaneous speciation of inorganic arsenic and antimony in natural waters.

Acrylic acid grafted polytetrafluoroethylene fiber as new packing for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for determination of lead and cadmium in environmental and biological samples

In this work, acrylic acid grafted PTFE fibers were prepared as a new packing material for flow injection (FI) on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace lead and cadmium in environmental and biological samples. Effective preconcentration of trace cadmium and lead was achieved in a pH range of 3.5–6.5 on a microcolumn packed with the developed new packing material. The retained lead and cadmium were efficiently eluted, respectively, with 1.0 mol/l HNO3 and 0.5 mol/l HCl for on-line FAAS determination. The developed sorbent exhibited fairly fast kinetics for the adsorption of Pb(II) and Cd(II), permitting the use of high sample flow rates up to at least 10.8 ml/min for the FI on-line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 45 s at a sample loading flow rate of 10 ml/min, the enhancement factor was found to be 49 for Pb and 73 for Cd at a sample throughput of 55 h−1. The detection limits (3σ) was 0.26 and 0.10 μg/l for Pb and Cd, respectively. The precision (RSD) for 11 replicate measurements was 1.9% at the 25 μg/l Pb level, and 0.9% at the 10 μg/l Cd level. The developed method was successfully applied to the determination of trace Pb and Cd in a variety of environmental and biological samples.

Acrylic acid grafted polytetrafluoroethylene fiber as new packing for flow injection on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry for determination of lead and cadmium in environmental and biological samples

In this work, acrylic acid grafted PTFE fibers were prepared as a new packing material for flow injection (FI) on-line microcolumn preconcentration coupled with flame atomic absorption spectrometry (FAAS) for determination of trace lead and cadmium in environmental and biological samples. Effective preconcentration of trace cadmium and lead was achieved in a pH range of 3.5–6.5 on a microcolumn packed with the developed new packing material. The retained lead and cadmium were efficiently eluted, respectively, with 1.0 mol/l HNO 3 and 0.5 mol/l HCl for on-line FAAS determination. The developed sorbent exhibited fairly fast kinetics for the adsorption of Pb(II) and Cd(II), permitting the use of high sample flow rates up to at least 10.8 ml/min for the FI on-line microcolumn preconcentration system without loss of the retention efficiency. With a preconcentration time of 45 s at a sample loading flow rate of 10 ml/min, the enhancement factor was found to be 49 for Pb and 73 for Cd at a sample throughput of 55 h −1. The detection limits (3 σ) was 0.26 and 0.10 μg/l for Pb and Cd, respectively. The precision (RSD) for 11 replicate measurements was 1.9% at the 25 μg/l Pb level, and 0.9% at the 10 μg/l Cd level. The developed method was successfully applied to the determination of trace Pb and Cd in a variety of environmental and biological samples.

Interference-Free Determination of Trace Levels of Gold and Palladium in Geological and Metallurgical Samples by Flame Atomic Absorption Spectrometry Coupled with a Flow Injection On-Line Microcolumn Preconcentration and Separation System

A simple and highly selective method was developed for the routine determination of trace or ultratrace amounts of gold and palladium in geological and metallurgical samples. The method uses flow injection on-line preconcentration and separation with determination by flame atomic absorption spectrometry. Au and Pd in the sample are adsorbed on a 2-mercaptopyrimidine chemically modified silica gel (MPMSG) packed microcolumn in a 0.50M HCl medium and then eluted with 0.5 or 1.0% thiourea solution. The eluates are introduced into the flame atomic absorption spectrometer directly. With the use of a 0.85 mL microcolumn (about 0.14 g MPMSG packed), the present system tolerated concentrations of common base metal ions up to 25.0 mg/mL and concentrations of anions up to 100.0 mg/mL when Au(III) at 0.100 microg/mL and Pd(II) at 0.200 microg/mL were preconcentrated for 60 s with a sample flow rate of 5.0 mL/min. The limits of detection were 3.1 ng/mL for Au(III) and 6.1 ng/mL for Pd(II) with relative standard deviations of < or = 2.5%. The analytical results obtained by the proposed method for geological and metallurgical samples were in good agreement with the certified values.

Selective measurement of ultratrace methylmercury in fish by flow injection on-line microcolumn displacement sorption preconcentration and separation coupled with electrothermal atomic absorption spectrometry.

A novel nonchromatographic speciation technique for ultratrace methylmercury in biological materials was developed by flow injection microcolumn displacement sorption preconcentration and separation coupled on-line with electrothermal atomic absorption spectrometry (ETAAS). In the developed technique, Cu(II) was first on-line complexed with diethyldithiocarbamate (DDTC), and the resultant Cu-DDTC was presorbed onto a microcolumn packed with the sorbent from a cigarette filter. Selective preconcentration of methylmercury (MeHg) in the presence of Hg(II), ethylmercury (EtHg), and phenylmercury (PhHg) was achieved at pH 6.8 through loading the sample solution onto the microcolumn due to a displacement reaction between MeHg and the presorbed Cu-DDTC. The retained MeHg was subsequently eluted with 50 microL of ethanol and on-line determined by ETAAS. Interferences from coexisting heavy metal ions with lower stability of their DDTC complexes relative to Cu-DDTC were minimized without the need of any masking reagents. No interferences from 5.5 mg L(-1) Cu(II), 4.5 mg L(-1) Cd(II), 2.5 mg L(-1) Cr(III), 3 mg L(-1) Fe(III), 10 mg L(-1) Ni(II), 10 mg L(-1) Pb(II), and at least 25 mg L(-1) Zn(II) were observed for the determination of MeHg at the 50 ng L(-1) level (as Hg). With the consumption of only 3.4 mL of sample solution, an enhancement factor of 75, a detection limit of 6.8 ng L(-1) (as Hg) in the digest (corresponding to 3.4 ng g(-1) in original solid sample for a final 50 mL of digest of 0.1 g of solid material), and a precision (RSD, n = 13) of 2.3% for the determination of methylmercury at the 50 ng L(-1) (as Hg) level were achieved at a sample throughput of 30 samples h(-1). The recoveries of methylmercury spike in real fish samples ranged from 97 to 108%. The developed technique was validated by determination of methylmercury in a certified reference material (DORM-2, dogfish muscle), and was shown to be useful for the determination of methylmercury in real fish samples.

Application of isodiphenylthiourea immobilized silica gel to flow injection on-line microcolumn preconcentration and separation coupled with flame atomic absorption spectrometry for interference-free determination of trace silver, gold, palladium and platinum in geological and metallurgical samples

A simple and highly selective flow injection on-line preconcentration and separation–flame atomic absorption spectrometric method was developed for the routine analysis of trace amounts of silver, gold, palladium and platinum in geological and metallurgical samples. The selective preconcentration of the noble metals was achieved in a wide range of sample acidities (0.5–3.0 M HNO3 or HCl for Ag, Au and Pd) on a microcolumn packed with an isodiphenylthiourea immobilized silica gel (DPTSG). The noble metals retained on the microcolumn were effectively eluted with thiourea solution. With the use of a 0.85 mL microcolumn (about 0.14 g of DPTSG) the present system tolerated up to 25.0 mg mL−1 of common base metal ions and 100.0 mg mL−1 of anion when 0.040 µg mL−1 of AgI, 0.200 µg mL−1 of AuIII, 0.200 µg mL−1 of PdII and 1.00 µg mL−1 of PtIV were preconcentrated for 60 s with a sample flow rate of 5.0 mL min−1. The limits of detection were 0.33 ng mL−1 for AgI, 3.2 ng mL−1 for AuIII, 4.7 ng mL−1 for PdII and 69 ng mL−1 for PtIV, respectively, with the relative standard deviation being not more than 3.0%. The analytical results obtained by the proposed method for geological and metallurgical samples were in good agreement with the certified values.

Application of a macrocycle immobilized silica gel sorbent to flow injection on-line microcolumn preconcentration and separation coupled with flame atomic absorption spectrometry for interference-free determination of trace lead in biological and environmental samples.

A simple and highly selective flow injection on-line pre-concentration and separation-flame atomic absorption spectrometric method was developed for routine analysis of trace amounts of lead in biological and environmental samples. The selective preconcentration of lead was achieved in a wide range of sample acidity (0.075 to > or = 3 mol L(-1)HNO3) on a microcolumn (145 microL) packed with a macrocycle immobilized on silica gel. The lead retained on the column was effectively eluted with an EDTA solution (0.03 mol L(-1), pH 10.5). Three kinds of potential interferences, i.e., preconcentration inferences from metal ions with an ionic radius similar to that of Pb(II) due to their competition for the cavity of the macrocyle, elution kinetic interferences from ions which form stable complexes with EDTA due to their competition for EDTA, and interferences in the atomizer from residual matrix, were evaluated and compared in view of the read-out mode of the analyte response (peak area vs peak height), column wash step (with vs without), column capacity (50 vs 145 microL), and column shape (conical vs cylindrical). The results showed that a combination of increase in column capacity, quantitation based on peak area, and use of dilute nitric acid for column wash before elution efficiently avoid the above-mentioned potential interferences. With the use of a 145 microL column the present system tolerated up to 0.1 g L(-1) Ba(II), 1 g L(-1) Sr(II), and at least 10 g L(-1) Fe(III), Cu(II), Ni(II), Zn(II), Cd(II), Al(III), K(I), Na(I), CaII), and Mg(II) in the sample digest. Further improvement of the interference tolerance can be achieved by increasing column capacity if more complicated samples need to be analyzed. At a sample loading rate of 3.9 mL min(-1) with 30-s preconcentration, an enrichment factor of 52, a detection limit (3s) of 5 micrograms L(-1) Pb in the digest and a sampling frequency of 63 h(-1) were obtained. The precision (RSD, n = 11) at the 200 micrograms L(-1) level was 1.9%. The enrichment factor and the detection limit can be further improved by increasing sample loading rate without degradation in the efficiency due to the favorable kinetics and low hydrodynamic impedance of the present system. The analytical results obtained by the proposed method for a number of biological and environmental standard reference materials were in good agreement with the certified and recommended values.

Electrothermal atomic absorption spectrometric determination of lead in high-purity reagents with flow-injection on-line microcolumn preconcentration and separation using a macrocycle immobilized silica gel sorbent

A fully automated procedure for the determination of ng l −1 amounts of lead has been developed using flow injection (FI) online column preconcentration coupled with electrothermal atomic absorption spectrometry (ETAAS). The proposed FI manifold and its operation make possible the introduction of the total eluate volume into the graphite atomizer, avoiding the necessity for optimization of subsampling the eluate. The interference of other heavy metal ions due to competition for active sites of the sorbent is overcome using a highly selective macrocycle immobilized on silica gel (Pb-02). Lead is adsorbed on a microcolumn (50 μl) packed with Pb-02, and after washing the column with dilute nitric acid, air is introduced to remove all solution from the column and connecting tubing. The sorbed analyte is then eluted quantitatively into the graphite tube atomizer, preheated to 100°C, with 36 μl of ETDA solution (0.035 mol l −1, pH 10.5), propelled by air in order to minimize dispersion. The collection efficiency was 77% and with a sample loading flow rate of 3 ml min −1 and a 60 s preconcentration time, the enhancement factor was 77 and the throughput was 17 samples per hour. The relative standard deviation ( n = 10) at the 300 ng l −1 level was 2.7%, and the detection limit (3σ) was 0.4 ng l −1. No interference from heavy metals was observed, but ions of Ba 2+, Sr 2+ and K + were found to interfere when the concentration ratios of interferent to lead exceeded values of 2000, 20 000 and 200 000, respectively. Quantitative recovery of lead was achieved from sodium, magnesium, aluminum, lanthanum and heavy metal salt solutions. The high selectivity and sensitivity, combined with extremely low blank values, make the proposed technique particularly attractive for the analysis of high-purity reagents, semiconductors and other high-purity materials. Results are presented for the determination of lead in some high-purity reagents.

Optimization of Flow Injection On-Line Microcolumn Preconcentration of Ultratrace Elements in Environmental Samples prior to Their Spectrochemical Determination

The preconcentration of some elements such as Cd, Co, Ni, and V(IV) was modeled in the presence of complexing agents such as citrate and oxalate at high Ca, Mg, and sulfate concentrations on iminodiacetic acid/ethyl cellulose (IDAEC), a chelating cellulose. The effect of the species present in the solution was studied after construction of the species distribution curves using critical, estimated, and measured stability constants. The stability constants of the IDAEC chelates were determined potentiometrically. The constants were calculated or estimated using computer programs. The diagrams calculated in homogeneous media were used for optimization of the flow injection on-line preconcentration for analysis of ultratrace metals in the highly mineralized water “Hunyadi.”

On-line preconcentration and separation of palladium, platinum and iridium using α-amino pyridine resin with flame atomic absorption spectrometry

A flow injection on-line microcolumn method has been studied for the separation and preconcentration of noble metals, Pd, Pt and Ir, followed by flame AAS determination. An α-amino pyridine resin was used as preconcentration reagent. Non-noble metals studied could be eliminated by 2 M HCl solution in the rinsing stage. A group-eluent for all Pd, Pt and Ir was studied. Separation of individual noble metals could also be accomplished using selective eluents. This approach can be used both for the separation and determination of Pd, Pt and Ir in samples. The sensitivities and the sample frequency have been improved. The method has been applied to certified samples.