Knotted Reactor Research Articles

Post-administration labeling with Palladium(II) ions enables ICP-MS-based determination of the biodistribution of carbonized nanogels

Carbonized nanogels (CNGs) are carbon-based nanomaterials possessing excellent antibacterial and antiviral activities for treating infectious diseases. Thus, investigations of the biodistribution of CNGs are crucial in ensuring their biosafety for in vivo applications. In this study, we combined a labeling scheme, employing tetrachloropalladate (PdCl42−) ions to selectively label the administered CNGs in solubilized tissue samples, and an automatic sample pretreatment scheme, using a knotted reactor to effectively separate the PdCl42–-labeled CNGs from the free PdCl42− ions and the tissue matrices, to enable reliable and interference-free quantification of CNGs through measuring the signal intensities of Pd using inductively coupled plasma mass spectrometry (ICP-MS). After optimizing the labeling conditions and the separation scheme, we observed that the PdCl42− ions bound strongly to the CNGs (dissociation constant: 23.0 nM), with the method's detection limits reaching 1.6 fg L−1 and 0.9 μg L−1 within working ranges from 10−4 to 1 μg L−1 and from 1 to 1000 μg L−1, respectively. We verified the reliability and applicability of this analytical method through spike analyses of solubilized rat liver, spleen, kidney, lung, brain, and blood samples (recoveries ranging from 96 to 102%) and through analyses of these rat organ and tissue samples after giving rats an intravenous dose of CNGs (2.5 mg kg−1 body weight). The biodistribution data indicated that these administered CNGs deposited mainly in the liver, lung, and spleen at 10 min and 1 h post-administration. Our study revealed that this post-administration labeling scheme coupled with ICP-MS allows accurate determination of the biodistribution of carbonized nanomaterials.

Combination of knotted reactor with portable tungsten coil electrothermal atomic absorption spectrometer for on-line determination of trace cadmium

In this work, flow injection (FI) on-line precipitation–dissolution in a knotted reactor (KR) was established and combined with a portable tungsten coil electrothermal atomic absorption spectrometer (W-coil ET-AAS) firstly for preconcentration and determination of ultra-trace cadmium. As a new instrument, the application of the portable W-coil spectrometer was expanded to carry out on-line preconcentration and detection through the coupling with a KR system. A self-assembled FI system was employed to hyphenate the KR system with W-coil ET-AAS. The instrumental conditions and influencing factors relevant to KR efficiency, such as concentration of ammonia, pH, conditions of sampling and elution were studied systematically. The coupling improved the analytical performance of the portable spectrometer considerably. Under the optimal conditions, the limit of detection (LOD) for cadmium was 0.006μg/L, with sensitivity enhancement factor (EF) of 41. The established method could be expanded and used for on-line preconcentration and detection of some other trace metal ions.

Activated carbon-modified knotted reactor coupled to electrothermal atomic absorption spectrometry for sensitive determination of arsenic species in medicinal herbs and tea infusions

A flow injection system based on a modified polytetrafluoroethylene (PTFE) knotted reactor (KR) was developed for arsenite [As(III)] and arsenate [As(V)] species preconcentration and determination by electrothermal atomic absorption spectrometry (ETAAS). Activated carbon (AC) was immobilized on the inner walls of a PTFE KR by a thermal treatment. A significant increase in analyte retention was obtained with the AC-modified KR (100%) as compared to the regular PTFE KR (25%). The preconcentration method involved the on-line formation of As(III)-ammonium pyrrolidinedithiocarbamate (As-APDC) complex, followed by its adsorption onto the inner walls of the AC-modified KR. After analyte retention, the complex was eluted with acetone directly into the graphite furnace of ETAAS. The parameters affecting the flow injection system were evaluated with a full central composite face centered design with three center points. Under optimum conditions, a preconcentration factor of 200 was obtained with 10ml of sample. The detection limit was 4ngL−1 and the relative standard deviation (RSD) for six replicate measurements at 0.2μgL−1 of As were 4.3% and 4.7% for As(III) and As(V), respectively. The developed methodology was highly selective towards As(III), while As(V), monomethylarsonic acid [MMA(V)] and dimethylarsinic [DMA(V)] were not retained in the AC-modified KR. The proposed method was successfully applied for As speciation analysis in infusions originated from medicinal herbs and tea.

Quantitatively profiling the dissolution and redistribution of silver nanoparticles in living rats using a knotted reactor-based differentiation scheme.

Whether silver nanoparticles (AgNPs) degrade and release silver ions (Ag(+)) in vivo has remained an unresolved issue. To evaluate the biodistribution and dissolution behavior of intravenously administered AgNPs in living rats, we employed a knotted reactor (KR) device to construct a differentiation scheme for quantitative assessment of residual AgNPs and their released Ag(+) ions in complicated animal tissues; to do so, we adjusted the operating parameters of the KR, namely, the presence/absence of a rinse solution and the sample acidity. After optimization, our proposed differentiation system was confirmed to be tolerant to rat tissue and organ matrix and provide superior reliability of differentiating AgNPs/Ag(+) than the conventional centrifugal filtration method. We then applied this differentiation strategy to investigate the biodistribution and dissolution of AgNPs in rats 1, 3, and 5 days postadministration, and it was found that the administered AgNPs accumulated predominantly in the liver and spleen, then dissolved and released Ag(+) ions that were gradually excreted, resulting in almost all of the Ag(+) ions becoming deposited in the kidney, lung, and brain. Histopathological data also indicated that toxic responses were specifically located in the AgNP-rich liver, not in the Ag(+)-dominated tissues and organs. Thus, the full-scale chemical fate of AgNPs in vivo should be integrated into future assessments of the environmental health effects and utilization of AgNP-containing products.

Displacement solid-phase extraction on mercapto-functionalized magnetite microspheres for inductively coupled plasma mass spectrometric determination of trace noble metals

A flow injection online displacement solid-phase extraction (DSPE) via magnetic immobilization of mercapto-functionalized magnetite microspheres onto the inner walls of a knotted reactor (KR) coupled with inductively coupled plasma mass spectrometry was developed for selective preconcentration and determination of trace noble metals (Ru, Rh, Pd, Pt, Ir and Au) in complex matrices. Online DSPE of 2.7 mL aqueous solution gave the enhancement factors of 32–46 for the six noble metals in comparison with direct nebulization of aqueous sample solution, and the detection limits (3 s) of 2.1 ng L −1 for Ru, 1.9 ng L −1 for Rh, 2.5 ng L −1 for Pd, 1.8 ng L −1 for Ir, 1.9 ng L −1 for Pt and 1.7 ng L −1 for Au. The sample throughput of the developed method was about 20 samples h −1, and the relative standard deviation for eleven replicate determinations of the noble metals at the 30 ng L −1 level ranged from 1.2% to 2.1%. The recoveries of Ru, Rh, Pd, Pt, Ir and Au still maintained 90% even after successive 140 cycles of DSPE. The developed method was successfully applied to selective determination of trace Ru, Rh, Pd, Pt, Ir and Au in complex matrices.

Magnetic immobilization of amine-functionalized magnetite microspheres in a knotted reactor for on-line solid-phase extraction coupled with ICP-MS for speciation analysis of trace chromium

The use of magnetic microspheres and nanoparticles for sample extraction in analytical chemistry has received increasing interest. However, previous magnetic particle-based solid-phase extraction (SPE) is usually performed in a batch mode. In this work, we report magnetic immobilization of amine-functionalized magnetite (Fe3O4) microspheres (AF-MMPs) onto the inner walls of a knotted reactor (KR) for on-line SPE coupled with ICP-MS for speciation analysis of trace chromium. A tubular magnet is sufficient to immobilize AF-MMPs onto the inner walls of a KR without the need for any frits or plugs. Sensitive speciation analysis of trace CrIII and CrVI in water was achieved based on selective on-line SPE of either CrIII and CrVI under controlled pH conditions on an AF-MMPs magnetically immobilized KR integrated into a flow injection system with on-line ICP-MS detection without the need for extra oxidation/reduction. On-line SPE of 2.4 mL aqueous solution gave an enhancement factor of 96 for CrIII and 47 for CrVI, a detection limit of 1.5 ng L−1 for CrIII and 2.1 ng L−1 for CrVI at a sample throughput of 23 h−1. The precision (RSD) for eleven replicate measurements of 100 ng L−1 CrIII and CrVI was 1.9% and 4.5%, respectively. The batch-to-batch reproducibility (RSD) for three parallel prepared AF-MMPs packed KRs for the SPE of CrIII and CrVI at 100 ng L−1 was less than 5.5%. One AF-MMPs packed KRs can be used for at least 75 cycles of preconcentration without significant loss of extraction efficiency. The developed method was successfully applied to the speciation analysis of trace CrIII and CrVI in drinking water samples.

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.

On-line precipitation–dissolution in knotted reactor for thermospray flame furnace AAS for determination of ultratrace cadmium

A simple, environmentally friendly, cost-effective and sensitive method was developed for the determination of trace cadmium in rice and water by using flow injection (FI) on-line precipitation–dissolution in a knotted reactor (KR) as a preconcentration scheme for thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS). The preconcentration was achieved by online merging the sample solution and the precipitating reagent in a KR and subsequently eluting the resultant precipitate of cadmium hydroxide with 1 mol/L HNO 3. The eluant was then introduced into TS-FF-AAS for the determination. A self-assembled FI system was employed to hyphenate the KR system with TS-FF-AAS. Under optimal chemical and instrumental conditions, a limit of detection of 0.04 μg/L and a sensitivity enrichment factor of 34 for cadmium was obtained with a total initial sample volume of 4 mL. The proposed method was applied to the determination of cadmium in certified reference rice and water samples with analytical results in good agreement with their certified values. Real rice samples and real water samples were also determined by the proposed method, with analytical results confirmed by inductively coupled plasma mass spectroscopy (ICP-MS).

Cloud point extraction for cobalt preconcentration with on-line phase separation in a knotted reactor followed by ETAAS determination in drinking waters

A novel method for cobalt preconcentration by cloud point extraction with on-line phase separation in a PTFE knotted reactor and further determination by electrothermal atomic absorption spectrometry (ETAAS) is proposed. The cloud point system was formed in the presence of non-ionic micelles of polyethyleneglycolmono- p-nonylphenylether (PONPE 7.5) and it was retained on the inner walls of a knotted reactor (KR). The surfactant rich-phase was removed from the knotted reactor with 75 μL of methanol acidified with 0.8 mol L −1 nitric acid, directly into the dosing hole of the L’Vov graphite tube. An enrichment factor of 15 was obtained with a preconcentration time of 60 s, with respect to the direct determination of cobalt by ETAAS in aqueous solutions. The value of the detection limit for the preconcentration of 5 mL of sample solution was 10 ng L −1. The precision, expressed as the relative standard deviation (R.S.D.), for 10 replicate determinations at 0.5 μg L −1 Co level was 4.5%. Verification of the accuracy was carried out by analysis of a standard reference material (NIST SRM 1640e “Trace elements in natural water”). The method was successfully applied to the determination of cobalt in drinking water samples.

On‐Line Preconcentration and Analysis of Zinc in Water by Flow Injection‐Knotted Reactor: Application to Geological and Environmental Exploration

A preconcentration on‐line system composed of flow injection (FI) and a knotted reactor (KR), associated with inductively coupled plasma atomic emission spectrometry (ICP‐AES) has been used to determine Zn concentrations in river water. The zinc was retained as Zn‐2(5‐bromo‐2‐pyridilazo)5‐diethylaminofenol precipitated complex on the knotted reactor (KR). The limit of detection (0.09 µg L−1 of Zn) of this method makes it particularly suitable for hydrochemical exploration in geological and environmental projects. This application has been validated in the volcanogenic gold (copper, zinc, lead) deposit of La Carolina in the province of San Luis, Argentina. The Carolina Stream and the Grande River have been sampled for water downstream this deposit. The regional background in river water is 2 µg L−1. Six times this concentration has been observed at more than 6.5 km from the source, La Carolina mine.

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%.

Indirect Determination of Sulfide at Ultratrace Levels in Natural Waters by Flow Injection On-Line Sorption in a Knotted Reactor Coupled with Hydride Generation Atomic Fluorescence Spectrometry

A simple and sensitive nonchromatographic approach for indirect determination of sulfide at ultratrace levels in natural waters based on its selective precipitation with Hg2+ on the inner wall of a knotted reactor (KR) was developed for flow injection on-line sorption coupled with hydride generation atomic fluorescence spectrometry (HG-AFS). With the Hg2+ pH kept at 2.0, the HgS precipitation was formed in the KR after a reaction time of 120 s. A 10% (v/v) HCl was introduced to elute the remnant inorganic mercury and to merge with the KBH4 solution (0.05% m/v) for HG-AFS detection. Under the optimal experimental conditions, the sample throughputs were 20 h(-1). The detection limit was found to be 0.05 microg L(-1), and the relative standard deviation (RSD, n = 11) for determination of 2.0 microg L(-1) sulfide was 3.3%. The developed method was successfully applied to the determination of sulfide in a variety of natural water samples and wastewater samples with the gas-phase separation and sorption apparatus.

Method performance study of on-line internal standard addition in inductively coupled plasma mass spectrometry

The approach of adding an internal standard to all solutions at a constant level, by on-line merging of the internal standard (steady state) and the sample solution streams, was studied for multi element determinations using inductively coupled plasma mass spectrometry. An internal standard introduction system was developed using a knotted reactor, a mixing T-piece and two peristaltic pump channels. The tube length of the knotted reactor and the wash out time were optimized for achieving the best mixing efficiency. The performance of the optimized system was compared to the traditional method of internal standard addition (batch) and checked by analysis of the NIST 8415 SRM (egg powder). The uncertainty components of the internal standard addition were also evaluated and its contribution to the combined measurement uncertainty estimated. No significant difference was found in terms of accuracy and precision between the two methods. However, the new technique was proved to be very practical, robust and less time consuming than the traditional approach.

On-line organoselenium interference removal for inorganic selenium species by flow injection coprecipitation preconcentration coupled with hydride generation atomic fluorescence spectrometry

The existence of dimethylselenium (DMSe) and dimethyldiselenium (DMDSe) in some environmental samples can cause serious interference on Se(IV) determination by hydride generation atomic fluorescence spectrometry (HG-AFS) due to their contribution on HG-response. A flow injection separation and preconcentration system coupled to HG-AFS was therefore developed by on-line coprecipitation in a knotted reactor (KR) for eliminating interference subjected from organoselenium. The sample, spiked with lanthanum nitrate, was merged with an ammonium buffer solution (pH 8.8), which promoted coprecipitation of Se(IV) and quantitative collection by 150 cm PTFE KR. DMSe and DMDSe, however, were unretained and expelled from the KR. An air flow was introduced to remove the residual solution from the KR, then a 1.2 mol l −1 HCl was pumped to dissolve the precipitates and merge with KBH 4 solution for HG-AFS detection. The interference of DMSe and DMDSe on the Se(IV) determination by conventional HG-AFS and its elimination by the developed separation and preconcentration system were evaluated. With optimal experimental conditions and with a sample consumption of 12.0 ml, an enhancement factor of 18 was obtained at a sample frequency of 24 h −1. The limit of detection was 0.014 μg l −1 and the precision (R.S.D.) for 11 replicate measurements of 1.0 μg l −1 Se(IV) was 2.5%. The developed method was successfully applied to the determination of inorganic selenium species in a variety of natural water samples.

Automatic on-line pre-concentration system using a knotted reactor for the FAAS determination of lead in drinking water

An automatic on-line pre-concentration system is proposed for lead determination in drinking water using flame atomic absorption spectrometry (FAAS). Lead(II) ions are retained as the 1-(2-pyridylazo)-2-naphthol (PAN) complex in the walls of a knotted reactor, followed by an elution step using 0.50 mol L −1 hydrochloric acid solution. Optimisation involving the sampling flow rate, pH and buffer concentration factors was performed using a Box–Behnken design. Other factors were established considering results of previous experiments. The procedure allows the determination of lead with a 0.43 μg L −1 detection limit (3 σ/ S) and precisions (expressed as relative standard deviation) of 4.84% ( N = 7) and 2.9% ( N = 7) for lead concentrations of 5 and 25 μg L −1, respectively. The accuracy was confirmed by the determination of lead in the NIST SRM 1643d trace elements in natural water standard reference material. The pre-concentration factor obtained is 26.5 and the sampling frequency is 48 h −1. The recovery achieved for lead determination in the presence of several ions demonstrated that this procedure could be applied to the analysis of drinking water samples. The method was applied for lead determination in drinking water samples collected in Jequié City, Brazil. The lead concentration found in 25 samples were always lower than the permissible maximum levels stipulated by World Health Organization.

Inductively Coupled Plasma Optical Emission Spectrometric Determination of Gadolinium in Urine Using Flow Injection On‐Line Sorption Preconcentration in a Knotted Reactor

An on‐line gadolinium preconcentration and determination system, implemented with ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry (ICP‐OES), associated with flow injection (FI) was studied. Gadolinium was retained as Gd‐2‐(5‐bromo‐2‐pyridilazo)‐5‐diethylaminophenol complex (Gd‐5‐Br‐PADAP) at pH 9.0, on the inner walls of the knotted reactor (KR). The collected analyte complexes were quantitatively eluted from the 200 cm KR with 30% (v/v) nitric acid. An enhancement factor of 255‐fold was obtained (17 for KR and 15 for USN). The detection limit (DL) value for the preconcentration of 15 mL of sample was 4.0 ng L−1. The relative standard deviation (RSD) was 3.5%, calculated from the peak heights obtained. The calibration graph using the preconcentration system for gadolinium was linear, with a correlation coefficient of 0.9996 at levels near the detection limit up to at least 200 µg L−1. The method was successfully applied to the determination of gadolinium in urine samples.

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.

Determination of trace elements in natural waters by inductively coupled plasma time of flight mass spectrometry after flow injection preconcentration in a knotted reactor

A flow injection on-line sorption system was developed for the separation and preconcentration of traces of Ag, Cd, Co, Ni, Pb, U and Y from natural water samples with subsequent detection by ICP TOF MS. Simultaneous preconcentration of the analytes was achieved by complexation with the chelating reagent 1-phenyl-3-methyl-4-benzoylpyrazol-5-one immobilized on the inner walls of a (200 cm × 0.5 mm) PTFE knotted reactor. The analytes were eluted and transported to an axial ICP TOF MS system with 1% (v/v) HNO 3 containing 0.3 μg l −1 of Rh as an internal standard using ultrasonic nebulization. The detection limits (3 σ) varied from 0.3 ng l −1 for Y to 15.2 ng l −1 for Ni and the precision (R.S.D.) was better than 4%. Using a loading time of 90 s and a sample flow rate of 4.5 ml min −1, enhancement factors of 3–14 were obtained for the different analytes in comparison with their direct determination by ICP TOF MS with ultrasonic nebulization without preconcentration. The accuracy of the method was demonstrated by analysis of water based certified reference materials.

Arsenic and antimony distribution in the Ría de Arousa: before and after the Prestige oil tanker sinking

The behaviour of arsenic and antimony in the Ría de Arousa (Galicia, north west of Spain) and the influence of the Prestige accident in the estuary is evaluated. As and Sb were simultaneously determined by HG-ICPOES in seawater samples after a preconcentration with La in a knotted reactor. The highest As concentration is in the inner and middle parts of the ría where the current is weaker and next to the main ports of the area. The largest Sb concentrations were found in the bay of the ría. Linear variation of concentration vs. salinity for As and As/Sb ratios indicated that there was no pollution in the waters of Arousa. The Prestige oil spillage had no serious influence and the values of arsenic (most of them <1.5 microg L(-1)) are similar to the average oceanic concentration, whereas concentrations for antimony (most of them <0.15 microg L(-1)) are less than the oceanic ones.

Application of Box–Behnken design in the optimisation of an on-line pre-concentration system using knotted reactor for cadmium determination by flame atomic absorption spectrometry

The present paper proposes an on-line pre-concentration system for cadmium determination in drinking water using flame atomic absorption spectrometry (FAAS). Cadmium(II) ions are retained as 1-(2-pyridylazo)-2-naphthol (PAN) complex at the walls of a knotted reactor, followed of elution using hydrochloric acid solution. The optimization was performed in two steps using factorial design for preliminary evaluation and a Box–Behnken design for determination of the critical experimental conditions. The variables involved were: sampling flow-rate, reagent concentration, pH and buffer concentration, and as response the analytical signal (absorbance). The validation process was performed considering the parameters: linearity and other characteristics of the calibration curve, analytical features of on-line pre-concentration system, precision, effect of other ions in the pre-concentration system and accuracy. Using the optimized experimental conditions, the procedure allows cadmium determination with a detection limit (3 σ / S) of 0.10 μg L − 1 , a quantification limit (10 σ / S) of 0.33 μg L −1, and a precision, calculated as relative standard deviation (RSD) of 2.7% ( n = 7) and 2.4% ( n = 7) for cadmium concentrations of 5 and 25 μg L − 1 , respectively. A pre-concentration factor of 18 and a sampling frequency of 48 h −1 were obtained. The recovery for cadmium in the presence of several ions demonstrated that this procedure could be applied for the analysis of water samples. The method was applied for cadmium determination in drinking water samples collected in Salvador City, Brazil. The cadmium concentrations found in five samples were lower than the maximum permissible levels established by the World Health Organization.