Knotted Reactor Research Articles

Flow on-line sorption preconcentration in a knotted reactor coupled with electrothermal atomic absorption spectrometry for selective As(iii) determination in sea-water samples

Download options Please wait... Article information DOI https://doi.org/10.1039/B416772D Article type Technical Note Submitted 03 Nov 2004 Accepted 10 May 2005 First published 23 May 2005 Download Citation J. Anal. At. Spectrom., 2005,20, 662-664 BibTex EndNote MEDLINE ProCite ReferenceManager RefWorks RIS Permissions Request permissions Flow on-line sorption preconcentration in a knotted reactor coupled with electrothermal atomic absorption spectrometry for selective As(III) determination in sea-water samples P. Herbello-Hermelo, M. C. Barciela-Alonso, A. Bermejo-Barrera and P. Bermejo-Barrera, J. Anal. At. Spectrom., 2005, 20, 662 DOI: 10.1039/B416772D To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page. If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given. If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page. Read more about how to correctly acknowledge RSC content. Social activity Tweet Share Search articles by author Paloma Herbello-Hermelo M. Carmen Barciela-Alonso Adela Bermejo-Barrera Pilar Bermejo-Barrera

Use of lanthanum hydroxide as a trapping agent to determine of hydrides by HG-ICP-OES

The level of arsenic and antimony was determined in sea-water by axial ICP-OES with continuous hydride generation after performing pre-reduction with thiourea and carrying out a pre-concentration by co-precipitation with lanthanum in a PTFE knotted reactor (KR). Optimisation of the whole system was performed using experimental design and with on-line pre-concentration and ultimate hydride generation. Using a pre-concentration time of two minutes and consuming 16 mL of sample, the LOD and LOQ were 0.17 and 0.56 μg L−1, respectively, for As, and 0.27 and 0.88 μg L−1 for Sb. Pre-concentration was carried out off-line in the KR in order to decrease the LOD and LOQ to 0.031 and 0.10 μg L−1 (As 188.979 nm) and 0.043 and 0.15 μg L−1 (Sb 217.582 nm) (sample volume 83 mL). The method was precise, with RSDs (n = 11) of 5.7% for As and 9.4% for Sb. The method was accurate, with a recovery of 108.5% for As and 106.0% for Sb. Moreover, values of 3.0 ± 0.5 μg As L−1 and 14.7 ± 1.5 μg Sb L−1 were obtained for a reference material with certified content of 2.7 ± 1.0 μg As L−1 and 13.7 ± 8.5 μg Sb L−1. The method can be applied to element determination in unpolluted sea-water samples.

Development of an ambient temperature post-column oxidation system for high-performance liquid chromatography on-line coupled with cold vapor atomic fluorescence spectrometry for mercury speciation in seafood

An efficient ambient temperature post-column oxidation system was developed for high-performance liquid chromatography online coupled with cold vapor atomic fluorescence spectrometry for mercury speciation analysis in seafood. The developed system does not require an external heat source, such as a hot water bath, microwave heating or UV irradiation, to decompose organomercury compounds into inorganic mercury ion (Hg(II)). Methylmercury (MeHg), ethylmercury (EtHg), phenylmercury (PhHg) and Hg(II) were baseline separated on an RP-C18 column with a mixture of methanol, acetonitrile and water (75 ∶ 5 ∶ 20) containing 0.01% m/v ammonium pyrrolidine dithiocarbamate (APDC) (pH 3.5) as the mobile phase. Online ambient temperature post-column oxidation of organomercury species eluted from the HPLC column was achieved by mixing the effluent with a 3% m/v K2S2O8 in 10% v/v HCl solution in a knotted reactor made of a 0.5 mm id × 200 cm long PTFE tube. The developed oxidation approach enhanced sensitivity for organomercury by a factor of 4 for MeHg, 3 for EtHg and 6 for PhHg, compared with that obtained without post-column oxidation. The detection limits for 100 μl injection were 0.19–0.27 μg l−1 (as Hg) in extract, corresponding to 4.75–6.75 μg kg−1 (as Hg) in fish tissue for a 50 ml final extract of 2 g tissue. The precision (RSD, n = 5) ranged from 1.8 to 2.8% for peak area, and from 1.7% to 2.9% for peak height at the 1 μg l−1 (as Hg) level. The method was validated by determination of methylmercury in a certified reference material (DORM-2, dogfish muscle) and applied to the speciation analysis of mercury in local seafood samples.

Multi-element analysis of saline matrices by inductively coupled plasma mass spectrometry following on-line preconcentration using a knotted reactor.

A versatile preconcentration system for trace element determination by ICPMS was developed. It is composed of a commercial flow injection analysis system (FIAS) retrofitted with a home-made control unit containing three solenoid valves and working concomitantly with the FIAS, permitting selection and segmentation of sample, reagent, washing solution and elution flow. The knotted reactor used had a length of 200 cm and was made from 0.05 cm i.d. PTFE tubing. The method applies ammonium 1-pyrrolidinedithiocarbamate (APDC) as complexant, allowing the preconcentration and quantitative multi-element determination of Cu, Ni, V, Co, Nb, Mo, In, Sb and Bi. Ethanol and 4-methyl-2-pentanone were tested as eluents. Recovery tests using complex matrices and spike concentrations of 200 ng L(-1) showed typical values in the range of 90% to 110%. Relative standard deviations were < 7% for elution with ethanol and < 5% with methyl isobutyl ketone. For simulated freshwater samples using 4-methyl-2-pentanone as an eluent, a sample loading rate of 5.0 ml min(-1), and a preconcentration time of 60 s, detection limits (ng L(-1)) were in the range of 0.02 (Bi) to 30 (Cu). Under these conditions, analytical frequency was about 15 samples per hour. The feasibility of the method was demonstrated by the succesful analysis of wastewater and seawater certified reference materials.

Optimization of the preconcentration system of cadmium with 1(2-thiazolylazo)- p-cresol using a knotted reactor and flame atomic absorption spectrometric detection

The present paper proposes an on-line preconcentration procedure for cadmium determination in drinking water samples. It is based on the precipitation of cadmium(II) ions on a knotted reactor (KR) using 1(2-thiazolylazo)- p-cresol (TAC) as complexing reagent. The optimization step was performed using a full factorial design involving the variables: pH, eluent concentration (nitric acid) and TAC concentration. The results of this experiment demonstrated that these variables at chosen levels are not statistically significant. Under optimized experimental established conditions, analytical parameters for the preconcentration method were: a detection limit of 40.0 ng/l, precision as relative standard deviation (RSD) of 1.2 and 1.0%, for cadmium concentration of 2.5 and 20.0 μg/l, respectively. The preconcentration factor considering the slopes of the analytical curves with and without preconcentration is 23 for a sample volume of 10 ml. This system shows a sampling frequency of 25 h −1. In order to check the accuracy, the standard reference material, NIST SRM 1643d trace elements in water was analyzed. A comparison, using t-test demonstrates that there is not significant difference among the achieved results with proposed method and the certified values. The addition/recovery experiments in the samples analyzed demonstrated the accuracy and applicability of the system developed for cadmium determination in water samples.

Further study on a flow injection on-line multiplexed sorption preconcentration coupled with flame atomic absorption spectrometry for trace element determination

A further study on a newly developed flow injection (FI) on-line multiplexed sorption preconcentration (MSP) using a knotted reactor coupled with flame atomic absorption spectrometry (FAAS) was carried out to demonstrate its applicability and limitation for trace element determination. For this purpose, Cr(VI), Cu(II), Ni(II) and Co(II) were selected as the analytes, and detailed comparison was made between the MSP–FAAS and conventional FI on-line sorption preconcentration FAAS in respect to retention efficiency and linear ranges of absorbance versus sample loading flow rate and total preconcentration time. Introduction of an air-flow for removal of the residual solution in the KR after each sub-injection in the MSP procedure played a decisive role in the improvement of retention efficiency. The linearity of absorbance versus sample loading flow rate or total preconcentration time was extended to a more degree for the metal ions with less stability of their PDC (pyrrolidine dithiocarbamate) complexes than those with more stable PDC complexes. It seems that the MSP procedure behaves advantages beyond the inflection points in the diagrams of absorbance versus total preconcentration time and sample loading flow rate obtained by conventional (a single continuous) preconcentration procedure. With a sample loading flow rate of 6.0mlmin−1 and a total preconcentration time of 180s, the retention efficiencies were increased from 25, 46, 41 and 63% with a single continuous sorption preconcentration to 44, 78, 65 and 75% with a six sub-injection preconcentration procedure for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The detection limits were 0.40, 0.33, 0.31 and 0.26μgl−1 for Cr(VI), Co(II), Ni(II), and Cu(II), respectively. The precision (R.S.D.) for eleven replicate determination of 2μgl−1 Cr(VI), Co(II) and Ni(II), and 1μgl−1 Cu(II), was 2.1, 4.1, 2.6 and 1.7%, respectively.

Flow injection on-line preconcentration of palladium by ion-pair adsorption in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection (FI) method for the preconcentration/separation of palladium, coupled with electrothermal atomic absorption spectrometry (ETAAS), is presented. The preconcentration was performed by on-line formation of an ion-pair between the positively charged potassium complex of 1,4,7,10,13,16-hexaoxacyclooctadecane (K+18-crown-6) and the palladium thiocyanate anion (Pd(SCN)42−) and its sorption on the inner walls of a PTFE knotted reactor (KR). The elution was achieved by methanol acidified with 1% (v/v) HNO3. An enhancement factor of 29 and a sampling frequency of 14 h−1 were obtained for a preconcentration time of 90 s and a sampling flow rate of 4.4 ml min−1. The detection limit (3σ) is 16 ng l−1 and precision (RSD) for 0.4 µg l−1 Pd is 2.3%. The method was validated by recovery measurements on spiked blood and road dust samples.

Flow injection on-line sorption preconcentration coupled with hydride generation atomic fluorescence spectrometry using a polytetrafluoroethylene fiber-packed microcolumn for determination of Se(IV) in natural water

Polytetrafluoroethylene (PTFE) fiber was demonstrated as a new sorbent for flow injection on-line sorption preconcentration of trace elements. The on-line PTFE fiber packed microcolumn preconcentration system was coupled with hydride generation atomic fluorescence spectrometry (HG-AFS) for the determination of (ultra)trace selenite (Se(IV)) in natural water. Selective determination of Se(IV) in aqueous solution was achieved by on-line formation of Se(IV)–pyrrolidinedithiocarbamate (PDC) complex over a wide sample acidity range of 0.01–50% v/v HCl, its sorption onto the surface of the PTFE fiber in the microcolumn, elution with 3% m/v KBH4 in 0.5% m/v KOH, hydride generation with 15% v/v HCl solution and determination with atomic fluorescence spectrometry. The alkaline KBH4 solution was employed not only as an efficient eluent but also as the reductant to produce selenide anion for subsequent hydride generation. With a consumption of 12.4 ml of sample solution, a detection limit (3σ) of 4 ng l−1 was achieved at a sample throughput of 26 samples h−1. The retention efficiency was 67%, being five times that obtained with a PTFE knotted reactor (KR). The linear ranges of the diagrams of signal intensity against sample loading flow rate, and sample loading time, were much wider than those achieved with a KR, offering more potential for obtaining high sensitivity by increasing sample loading rates and/or sample loading time. The precision for 11 replicate measurements of 0.5 µg l−1 Se(IV) was 1.5% (RSD). The recoveries of Se(IV) from natural water samples varied from 96 to 108%. The concentration of Se(IV) in a certified reference material (NASS-5, sea-water) determined by the present method with a simple aqueous standard curve calibration was in good agreement with the certified value. The developed method was also successfully applied to the detection of Se(IV) in local river water, lake water and sea-water samples.

On-line sample-pre-treatment schemes for trace-level determinations of metals by coupling flow injection or sequential injection with ICP-MS

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 (SI-LOV). 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 Coupled Flow Injection‐Capillary Electrophoresis System for Kinetic Study of Aspirin Hydrolysis in Aqueous Solution

A coupled flow injection‐capillary electrophoresis (FI‐CE) system was developed for automated determination of rate constants of chemical reactions. The system consists of a probe for sampling, a knotted reactor for on‐line quenching reaction, an injection valve in combination with a split‐flow interface for on‐line electrokinetic injection, and a CE unit for separation and detection. Aspirin was used as a model compound to validate the performance of the coupled system. Under the optimized conditions, the coupled system achieved a sampling rate of 20 per hour, and a RSD of 1.1% for 25 consecutive determinations in 75 min. These features of the coupled FI‐CE system allowed it to monitor reactions with half‐reaction time being no less than 15 min. Several rate constants of aspirin hydrolysis in slightly alkaline media were determined with the developed system.

Determination of trace cadmium in rice by flow injection on-line filterless precipitation-dissolution preconcentration coupled with flame atomic absorption spectrometry.

A simple, environmentally friendly, cost-effective, and sensitive method was developed for the determination of trace cadmium in rice by flow injection (FI) on-line precipitation preconcentration coupled with flame atomic absorption spectrometry (FAAS). The precipitation preconcentration of trace cadmium was achieved by on-line merging of the sample and ammonia solutions. The resultant precipitates were on-line collected by a knotted reactor (KR) without filtration. A solution of 1 mol L(-1) HNO(3) was employed to dissolve the collected precipitates and to deliver the analyte into the FAAS system for on-line detection. Preconcentration at a sample loading flow rate of 3.8 mL min(-1) for 35 s gave an enhancement factor of 44 and a detection limit (3sigma) of 0.002 microg g(-1) for the solid sample with a sample throughput of 72 h(-1). The precision (RSD, n = 11) was 2.0% at the 4.0 microg L(-1) level. The concentration of cadmium in a certified reference material (GBW 08511, rice flour) by the developed method using simple aqueous standards for calibration was in good agreement with the certified value. The proposed method was also successfully applied to the determination of trace cadmium in locally collected rice samples.

Determination of scandium in river water by ICP-OES with flow-injection on-line preconcentration using knotted reactor and ultrasonic nebulization

An on-line scandium preconcentration and determination system implemented with inductively coupled plasma optical emission spectrometry (ICP-OES) associated with flow injection (FI) with an ultrasonic nebulization system (USN) was studied. The scandium was retained as the scandium-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol, Sc-(5-Br-PADAP), complex, at pH 9.5. The 5-Br-PADAP solution concentration was 1 × 10−4 mol l−1 and it was dissolved in a 17% (v/v) ethanol–water solution. The scandium complex was removed from the knotted reactor (KR) with 30% (v/v) nitric acid. A total enhancement factor of 1120 was obtained with respect to ICP-OES using pneumatic nebulization –Meinhard, Pneumatic Nebulizer– (25 for USN and 45 for KR) with a preconcentration time of 300 s. The value of the detection limit for the preconcentration of 30 ml of sample solution was 0.45 ng l−1. The precision for 10 replicate determinations at 10 ng l−1 Sc level was 3.5% relative standard deviation (RSD), calculated from the peak heights obtained. The calibration graph using the preconcentration system for scandium was linear with a correlation coefficient of 0.9996 at levels near the detection limits up to at least 50 µg l−1. The method was successfully applied to the determination of scandium in river water samples.

Simultaneous on-line preconcentration and determination of Pt, Rh and Pd in urine, serum and road dust by flow injection combined with inductively coupled plasma time-of-flight mass spectrometry

In this work, ICP-time of flight (TOF)-MS with ultrasonic nebulisation (USN) was combined on-line with a flow injection (FI) system for the determination of Pt, Rh and Pd in biological fluids (urine and blood serum) and road dust. Simultaneous and selective preconcentration of the 3 analytes was performed by sorption of their complexes formed on-line with diethylthiourea (DET) on the inner walls of a PTFE knotted reactor (KR), in a wide range of sample acidity (0.1–0.5 M HNO3 for Pd and Rh and 0.05–0.2 M HNO3 for Pt). A quantitative elution was achieved using 500 µl methanol acidified with 1% HNO3. The detection limits obtained were 0.54, 2.12 and 0.36 ng l−1 for Pt, Rh and Pd, respectively, and the relative standard deviation RSD (for 50 ng l−1 of Pt, Rh and 25 ng l−1 of Pd, n = 6) was ≤ 3%. Using a preconcentration time of 120 s and a sample flow rate of 5 ml min−1, enrichment factors of 55, 5 and 2 for Pd, Pt and Rh, respectively, were obtained in comparison with direct determination by ICP-MS without preconcentration. Special attention was paid to the study of the adverse effects of potentially interfering species present in the matrix (Cd, Cu, Pb, Sr, Fe, Y, Zn, Ni, Rb, Mn and Mo) on the preconcentration and the mass-spectrometric determination of the analytes. The accuracy of the method was demonstrated by the analysis of urine, blood serum and road dust certified reference materials. The method was applied to urine and serum samples of healthy subjects. The concentrations of Pt, Rh and Pd determined in these samples were comparable to reported values.

Filterless pre-concentration by co-precipitation by formation of crystalline precipitate in the analysis of barium by FIA-FAES

A novel method based on flow injection analysis (FIA) and flame atomic emission spectrometry (FAES) is presented. It was developed for direct determination of barium in drinking water, in natural water, in digested samples of bone and liver, in saline water and in a standard reference material (NIST SRM 1640). It was found that digestion of bone by an incineration procedure was required, in order to extract most of the barium. In the FIA manifold, barium was pre-concentrated by co-precipitation with lead chromate leading to a crystalline deposit that adhered well to the inner walls of a nylon knotted reactor (KR). The method documents a novel example of formation of a crystalline compound during the pre-concentration step. The method comprises filterless pre-concentration by co-precipitation that proceeds successfully in a FIA system. An enrichment factor (EF) of 24 was achieved under normal working conditions at a sampling frequency of 50 h−1. The detection limit (LOD, 3σ) was determined as 0.8 µg L−1 and species of iron(II) and iron(III) constituted the main species of interference.

On-Line Preconcentration and Determination of Cadmium in Honey Using Knotted Reactor Coupled to Flow Injection-Flame Atomic Absorption Spectrometry

An on-line cadmium preconcentration and determination system implemented with flame atomic absorption spectrometry (FAAS) associated with flow injection was studied. Cadmium was retained as Cd-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol Cd-(5-Br-PADAP) complex, pH 9.3. The Cd complex was removed from the knotted reactor (KR) with ethanol. A total enhancement factor of 140 was obtained with respect to FAAS (40 for KR and 3.5 due to the use of ethanol) with preconcentration time of 120 s. The detection limit value for preconcentration of 1 g sample was 0.5 ng/g. The repeatability for 10 replicate determinations at 5.0 ng/g Cd level was 3.5% relative standard deviation, calculated from peak heights obtained. The calibration graph using the preconcentration system for Cd was linear with a correlation coefficient of 0.9990 at levels near the detection limits to at least 2000 ng/g. The method was successfully applied to determination of total Cd in honey samples.

Determination of trace mercury in environmental and foods samples by online coupling of flow injection displacement sorption preconcentration to electrothermal atomic absorption spectrometry.

The toxic effects of mercury are well-known. To establish sources of mercury contamination and to evaluate levels of mercury pollution, sensitive, selective, and accurate analytical methods with excellent reproducibility are required. We have developed a novel methodology for the determination of trace mercury in environmental and foods samples by online coupling of flow injection (FI) displacement sorption preconcentration in a knotted reactor (KR) to electrothermal atomic absorption spectrometry (ETAAS). The developed methodology involved the online formation of copper pyrrolidine dithiocarbamate (Cu-PDC), presorption of the resulting Cu-PDC onto the inner walls of the KR, and selective retention of the analyte Hg(ll) onto the inner walls of the KR through online displacement reaction between Hg(ll) and the presorbed Cu-PDC. The retained analyte was subsequently eluted by 50 microL of ethanol and online detected by ETAAS. Interferences from coexisting heavy metal ions with lower stability of their APDC complexes relative to Cu- PDC were minimized without the need of any masking reagents. The tolerable concentrations of Cu(II), Cd(II), Fe(III), Ni(III), and Zn(II) were up to 12, 20, 16, 20, and 60 mg L(-1), respectively. No additional chemical modifiers for the stabilization of mercury were required in the present system owing to the stability of Hg-PDC at the drying stage, and no pyrolysis stage was necessary due to the effective removal of the matrices. With consumption of 2.5 mL of sample solution, an enhancement factor of 91 was obtained in comparison with direct injection of 50 microL of aqueous solution. The relative detection limit (3s) was 6.2 ng L(-1), corresponding to an absolute detection limit of 15.5 pg. The precision (RSD, n = 13) was 1.1% at the 2 microg L(-1) level. The method was successfully applied to the determination of mercury in several certified environmental and foods reference materials and locally collected water samples.

A comparison of enrichment factor of knotted and serpentine reactors using flow injection sorption and preconcentration for the off-line determination of some trace elements by inductively coupled plasma mass spectrometry

The preconcentration efficiency expressed as an enrichment factor (EF) in knotted and serpentine reactors (SR) for FI sorption and preconcentration for the off-line determination of Cd(II), Ni(II), Co(II),Cu(II), Pb(II), Zn(II), Mo(VI), Cr(VI) and W(VI) with ICP-MS was investigated. The preconcentration was carried out by the formation of metal–pyrrolidine dithiocarbamate complex in an acidic solution and sorbed onto the inner wall of the PTFE reactors. The EFs were determined as the ratio between the analyte intensities after preconcentration using the reactors and that obtained without using the reactors. Comparing the two procedures for the equal reactor length (150 cm), the higher EFs obtained by using knotted reactor (KR) were observed for all elements. With the preconcentration time of 120 s and a sample flow rate of 1.2 ml min −1, the EFs of 4–36 and 3–12 were gained using knotted and SRs, respectively. The results obtained indicate that the KR is preferable to use for flow injection sorption preconcentration system over the SR.

Coupling sequential injection on-line preconcentration using a PTFE beads packed column to direct injection nebulization inductively coupled plasma mass spectrometry

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 (40 µl) 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 40 s sample loading time at 4.5 ml min−1, along with a sampling frequency of 18 h−1, 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 2.9 ng l−1 Cd (PC), 3.5 ng l−1 Cd (KR), 6.0 ng l−1 Pb (PC) and 4.7 ng l−1 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 on-line flow-injection microwave-assisted mineralization and a precipitation/dissolution system for the determination of molybdenum in blood serum and whole blood by electrothermal atomic absorption spectrometry

An on-line flow injection (FI) precipitation–dissolution system with microwave-assisted sample digestion has been developed for the electrothermal atomic absorption spectrometry (ETAAS) determination of trace or ultratrace amounts of molybdenum in human blood serum and whole blood samples. After the exposure of the sample to microwave radiation, the on-line precipitation of molybdenum was achieved by the merging-zone of a 0.5-ml plug of sample with a plug of potassium ferrocyanide, which were carried downstream with a solution of 0.5 mol l −1 of HNO 3. The interfering effects of iron and copper were minimized by the introduction of a flow of a 5% (w/v) sodium potassium tartrate (for iron) and 2% (w/v) of thiourea (for copper and zinc) in a 5% (v/v) ammonia and 2% (v/v) ammonium chloride solution previous to the precipitation reaction. The reddish-brown precipitate of molybdenyl ferrocyanide was collected on the walls of a knotted reactor. The precipitate was dissolved with the introduction of 1 ml of a 3.0 mol l −1 NaOH solution and the best performance in terms of detection limit and precision was achieved when a sub-sample of 140 μl was collected in a capillary of a sampling arm assembly, to introduce 20 μl volumes into the atomizer by means of positive displacement with air through a time-based injector. A detection limit (3 σ) of 0.1 μg Mo l −1 using an aqueous standard solution was obtained. The method is quantitative and is applied over the range 0.2–20.0 μg Mo l −1. The precision of the method evaluated by ten replicate analyses of aqueous standard solutions containing 0.5 and 1.0 μg Mo l −1 was 2.8 and 3.1% (relative standard deviation, RSD) (for n=5), respectively. Whereas, the precision evaluated by five replicate analysis of a serum and a whole blood sample were 3.3 and 3.8% RSD. An enrichment factor of ca. 3.5 was achieved with the introduction of 0.5 ml aqueous standard solutions at a sample flow rate of 1.0 ml min −1. Recoveries of spiked molybdenum in blood serum and whole blood were in the ranges 96–102 and 94–98%, respectively. The results obtained for two human whole blood certified reference materials were in good agreement with the indicative values.

Flow injection on-line preconcentration of low levels of Cr(VI) with detection by ETAAS: Comparison of using an open tubular PTFE knotted reactor and a column reactor packed with PTFE beads

A flow injection (FI) on-line sorption preconcentration procedure utilizing a packed column reactor and combined with electrothermal atomic absorption spectrometry (ETAAS) is proposed for the determination of low levels of Cr(VI) in water samples. Polytetrafluoroethylene (PTFE) beads packed in a mini-column is used as sorbent material. The complex formed between Cr(VI) and ammonium pyrrolidine dithiocarbamate (APDC) is sorbed on the PTFE beads, and is subsequently eluted by an air-monosegmented discrete zone of absolute ethanol (35 μl), the analyte being quantified by ETAAS. The preconcentration procedure using the proposed column significantly enhances the preconcentration efficiency as compared with the preconcentration approach incorporating an open tubular PTFE knotted reactor (KR). Comparing the two procedure for equal surface sorption area, the advantages of using a packed column are observed in terms of limit of detection, enrichment factor and retention efficiency. With a preconcentration time of 60 s, and a sample flow rate of 5.0 ml l −1, the enrichment factor (30.1) and the retention efficiency (24.1%) were doubled, yielding a detection limit (3 σ) as low as 8.8 ng l −1. The sample frequency was 16.7 h −1. The concentration efficiency was 8.38 and the precision was 1.05% at 0.5 μg l −1 of Cr(VI). The proposed column has been applied successfully to the analysis of natural water and synthetic seawater. Its performance was verified by the analysis of two certified Cr(VI)-reference materials and by recovery measurements on spiked samples.