Min Preconcentration Time Research Articles

Dynamic thin-film microextraction method using cellulose platforms modified with silver nanoparticles for preconcentration of volatile hydride-forming elements prior to inductively-coupled plasma mass spectrometry determination

In this work, a novel preconcentration method was developed for As, Sb and Bi following trapping of their volatile hydride derivatives onto cellulose-based platforms modified with Ag nanoparticles for ultrasensitive determination by inductively-coupled plasma mass spectrometry (ICP-MS). A continuous flow hydride generation system was coupled to a gas-liquid separation unit integrated with the preconcentration platform. AsH3, SbH3 and BiH3 were retained onto the silver nanoparticles (AgNPs) modified cellulose substrate upon catalytic decomposition. After a 10 min preconcentration time, enrichment factors of 16, 9 and 26 for As, Sb and Bi were obtained, respectively. These values can be increased when needed by a factor of three applying a preconcentration time of 30 min. Elution of analytes trapped onto AgNPs with 0.1 M HNO3 (As, Sb) or 1 M HNO3 (Bi) was performed and metal content in the eluates was measured by ICP-MS. Detection limits of 15, 2 and 1 ng/L for As, Sb and Bi were obtained, respectively. Repeatability values expressed as relative standard deviation (%) was in the range of 1.2–2.7%. Other hydrides tried (i.e. SeH2 and TeH2) did not provide suitable performance owing to inefficient desorption from the cellulose substrate. Simulated water matrices mimicking the major composition of freshwater, seawater, wastewater and groundwater were analyzed, recoveries being in the range of 80–106%.

Comprehensive analysis of synthetic cannabinoids and metabolites in oral fluid by online solid-phase extraction coupled to liquid chromatography-triple quadrupole-mass spectrometry.

The class of novel psychoactive substances known as synthetic cannabinoids (SC) includes illicit compounds that are sprayed on plant material and smoked or sold as liquids to be vaporized in e-cigarettes. In toxicological analysis of SC, fast analytical methods are needed for the detection and confirmation of parent drugs and metabolites at very low levels. While various analytical methods have been developed for SC in blood and urine, few are available for alternative matrices such as oral fluid (OF). There are numerous advantages to using OF as a sample matrix for SC analysis, including non-invasive collection, lesser risk of adulteration, and presence of both parent drug and metabolites. Here we report a validated online solid-phase extraction (online SPE) method coupled to LC-QqQ-MS for rapid confirmation and quantitation of 72 structurally diverse SC parent drugs and metabolites in OF with 2.5min of preconcentration time and a total elution time of < 10min. The use of online SPE for sample pretreatment facilitates rapid and consistent processing and greatly increases sample throughput. The method was fully validated according to relevant guidelines (ANSI/ASB Standard 036). Bias and precision values were within ± 20% for all compounds in human OF matrix. Method detection and quantitation limits ranged from 0.4 to 3.8ng/mL and from 1.1 to 11.6ng/mL, respectively. Recovery, matrix effects, process efficiency, carryover, and stability were also within acceptable limits for the majority of compounds. Successful application of the method was demonstrated using blank human OF fortified with SC in addition to a set of authentic OF specimens previously tested by another laboratory. Graphical abstract.

2D bismuthene/graphene modified electrodes for the ultra-sensitive stripping voltammetric determination of lead and cadmium

Bismuth-based electrodes have been proved the most reliable replacement of highly toxic mercury for the anodic stripping (AS) and cathodic voltammetric determination of metal ions and organic compounds, respectively. Herein, we report for the first time on the implementation of two-dimensional (2D) bismuth, called “bismuthene”, for the AS voltammetric determination of Pb(II) and Cd(II) ions. Bulk bismuth was exfoliated by a facile and fast shear-force liquid phase exfoliation method. Exfoliated bismuthene layers were characterized by means of SEM, EDX, Raman, FT-IR, electrochemical impedance spectroscopy and cyclic voltammetry. Bismuthene colloids were mixed with dispersions of few-layer graphene, which was used as supporting material in order to achieve the desired adherence of bismuthene films onto the surface of glassy carbon electrode (GCE) as well as an effective electrical communication between them and with the electrode surface. The optimum loading of bismuthene in the bismuthene/graphene composite (2D-Bi/Gra) was investigated, while other parameters such as the deposition time and deposition potential were also examined. Under selected conditions and for a 3 min preconcentration time, the limit of detection (S/N 3) of each target ion was 0.3 μg L−1. 2D-Bi/Gra/GCEs were successfully applied to the determination of Pb and Cd in tap water samples in the presence of potassium hexacyanoferrate(II) for the alleviation of copper interference. Results suggest that 2D bismuthene/graphene modified electrodes offer great promise for the determination of sub-microgram per liter Pb and Cd and could contribute greatly in heavy metal ions and other organic compounds sensing applications.

The development and evaluation of a microstill with conductance detection for low level ammonia monitoring in chloraminated water

Monitoring low levels of ammonia in chloraminated water can be challenging but is important for effectively managing potable water disinfection. The lower the concentration of free ammonia that can be determined, the tighter the control at the disinfection point, which supports better maintenance of chloramine residuals in the distribution system. In this study a micro-distillation technique was used to selectively separate ammonia into a boric acid solution allowing determination by conductance (i.e., micro-distillation and conductance measurement instrument - Micro-DCMI). The optimised technique had a linear calibration range of 0.01–60 mg NH3 L−1 with a limit of detection (LOD) of 0.014 mg L−1 and limit of quantification (LOQ) of 0.045 mg L−1. With the optimum operational parameters of 80 °C distillation temperature, 0.3 L min−1 air flow rate, 0.1 mol L−1 boric acid concentration and 8 min pre-concentration time, a sample throughput of 7 samples per hour was achieved. A laboratory comparison between Micro-DCMI and the standard ammonia selective electrode method was conducted on water samples obtained from a chloraminated drinking water distribution system. The results showed that the ratios of the free ammonia values determined by Micro-DCMI and an ammonia selective electrode were between 0.82 and 1.2 for 11 water samples. A custom-built automated analytical system was evaluated at a water treatment plant in Australia and the results compared favourably with the in plant online ammonia ion selective analyser. This study indicated that the Micro-DCMI method was a simple, robust and low cost online monitoring system suitable for determining low concentration ammonia to manage chloramination.

Electrochemical determination of trace mercury in water sample using EDTA-CPE modified electrode

The analytical performance of the EDTA-CPE sensor that is designed for the detection of metals was studied. EDTA plays an important role in the complexation of metal ions because of their good and high response to these ions. The modified electrode EDTA-CPE was used for the voltammetric determination of mercury ions (square wave voltammetry). Sodium chloride solution 0.3mol−1 was used as the support electrolyte. Using optimal parameters, calibration graph is linear (varying from 5 to 35∗10−4mol/l) for 5min of pre-concentration time with the detection limit of 16, 6×10−9molL−1. These results indicate that the developed method is simple, with high stability and sensitivity for the determination of low concentration of Hg (II).

Determination of Cd and Zn with “green” screen-printed electrodes modified with instantly prepared sparked tin nanoparticles

Graphite screen-printed electrodes (GSPEs) modified with tin nanoparticles (SnNPs) through a “green”, fast and extremely facile sparking process were used for the anodic stripping voltammetric determination of trace Cd and Zn. The effect of the magnitude of the energy dissipated during sparking events as well as other sparking parameters on the amount of the deposited tin, the morphology of the sparked surfaces and the electroanalytical properties of SnNP/GSPEs were investigated. Experiments were performed in the presence of bromide ions, which were used to enable well-resolved stripping peaks for cadmium. Other experimental variables, such as the pH of the supporting electrolyte, the square wave voltammetry parameters, the concentration of bromide ions, the deposition potential and the deposition time were also examined. Copper interference on Cd and Zn detection was effectively alleviated by the addition of ferrocyanide and gallium ions, respectively. Under selected conditions, the limits of detection, for a 2 min preconcentration time, were 0.5 μg L−1 Cd and 0.3 μg L−1 Zn. SnNP/GSPEs were successfully applied to the determination of Cd and Zn in tap and bottled water samples. Results suggest that sparked SnNP/GSPEs represent a new promising type of environmentally friendly sensors for the determination of Cd and Zn in the sub-microgram-per-liter level that surpass those previously given in the literature in terms of simplicity, cost, time, labor effort, waste loadings of the modification procedure, and low cost of the final sensor.

Bioinspired materials based on glutathione-functionalized SBA-15 for electrochemical Cd(II) detection

In this work, glutathione was grafted on mesoporous silica materials by silanization with (3-mercaptopropyl)trimethoxysilane, subsequent reaction with 2,2′-dipyridyldisulphide and a final treatment with glutathione. The obtained glutathione-functionalized materials have been characterized by powder X-ray diffraction, FT-IR, scanning electron microscopy, transmission electron microscopy, nitrogen gas sorption and X-ray fluorescence. In addition, the hybrid materials were used in the preparation of modified carbon paste electrodes MCPE by mixing quantities of glutathione-containing materials with paraffin oil and graphite for Cd(II) detection in aqueous media by square wave adsorptive stripping voltammetry. Two materials were used for the preparation of MCPE, (A) the first material was obtained by the grafting of glutathione on the pyridyldisulphide pending ligand of the mesoporous material, (B) the second one, was obtained by grafting a cadmium-glutathione complex on the pyridyldisulphide pending ligand of the mesoporous material. For the latter, elimination of cadmium ions was carried out by treatment with HCl 2 M for 2 h and wash with MilliQ water before preparing the MCPE. To achieve the most accurate and sensitive Cd(II) electrochemical measurements, optimization of the operating parameters in pre concentration and detection steps was performed. The responses are pH dependent, being the optimal conditions 120 s of electrolysis time in buffer solution (pH 6.4). The voltammetric responses increase linearly with the pre concentration time and with metal ion concentrations ranging from 1 to 100 ppb. The metal detection limits were 2 and 4 ppb for materials (A) and (B), respectively, after 5 min pre concentration time.

Highly Sensitive Aluminium(III) Ion Sensor Based on a Self-assembled Monolayer on a Gold Nanoparticles Modified Screen-printed Carbon Electrode.

A new approach for the development of a highly sensitive aluminium(III) ion sensor via the preconcentration of aluminium(III) ion with a self-assembled monolayer on a gold nanoparticles modified screen-printed carbon electrode and current mediation by potassium ferricyanide redox behavior during aluminium(III) ion binding has been attempted. A monolayer of mercaptosuccinic acid served as an effective complexation ligand for the preconcentration of trace aluminium; this led to an enhancement of aluminium(III) ion capture and thus improved the sensitivity of the sensor with a detection limit of down to the ppb level. Under the optimum experimental conditions, the sensor exhibited a wide linear dynamic range from 0.041 to 12.4 μM. The lower detection limit of the developed sensor was 0.037 μM (8.90 ppb) using a 10 min preconcentration time. The sensor showed excellent selectivity towards aluminium(III) ion over other interference ions.

A simple electroanalytical procedure for the determination of calcium in biodiesel

An alternative method is proposed for the determination of calcium in biodiesel samples using square-wave voltammetry and a glassy carbon electrode in a solution containing EDTA. A microwave assisted acid digestion of the biodiesel samples was carried out before analysis. Experimental parameters such as deposition potential, deposition time, frequency, amplitude, step potential, were optimized for the purpose of determination of trace calcium ion in 1×104μmolL−1 ammonium buffer solution (pH9.4) in the presence of 400μmolL−1 of EDTA. Under optimal conditions, the limit of detection was 1.6×10−3μmolL−1 for Ca2+ with a 2min preconcentration time. In addition, the EDTA/GCE displayed good reproducibility (CV maximum of 0.70%) and accuracy (recovery around 102%) making it suitable for the determination of Ca2+ in real biodiesel sample.

Electrochemical determination of trace copper(II) with enhanced sensitivity and selectivity by gold nanoparticle/single-wall carbon nanotube hybrids containing three-dimensional l-cysteine molecular adapters

This paper described how a inorganic–organic hybrids electrochemical sensor, a three-dimensional l-cysteine self-assembled monolayers (SAM) functionalized gold nanoparticles/single-walled carbon nanotubes/glassy carbon electrode (l-cys/AuNPs/SWCNTs/GCE), was applied to improve the performance of detecting trace Cu(II) in stripping voltammetry. The AuNPs/SWCNTs nanohybrid has a three-dimensional porous nanostructure with large active surface area, and the l-cysteine adapters on AuNPs/SWCNTs surface can greatly enhance the sensitivity and selectivity in detecting Cu(II). The differential pulse anodic stripping voltammetry (DPASV) response of the Cu(II) at the l-cys/AuNPs/SWCNTs/GCE was ca. 6.7 and 6.5 times larger than that at the AuNPs/SWCNTs/GCE and l-cys/AuNPs/GCE without SWCNTs, respectively. The sensor demonstrated a wide linear response range and a lower detection limit of 0.02nM with a signal-to-noise of 3 using 3min of preconcentration time. The interference experiments showed that Ag(I), Pb(II), Cd(II) and Hg(II) had little influence on Cu(II) signal. The high sensitivity and excellent selectivity in contrast to the values reported previously in the area of electrochemical Cu(II) detection, demonstrated the analytical performance of the as-prepared sensor toward Cu(II) was superior to the existing electrodes. The as-prepared sensor was further applied to determine the Cu(II) in the real environmental water sample, and the results agreed satisfactorily with the certified values.

Simultaneous determination of Pb and Cd in seafood by ICP OES with on-line pre-concentration by solid phase extraction with amberlite XAD-4 after complex formation with DDTP

An on-line method for Cd and Pb pre-concentration and simultaneous determination in acid digested seafood by inductively coupled plasma optical emission spectrometry (ICP OES) was developed. The on-line pre-concentration was based on the complex formation of the analytes with the ammonium salt of O,O-diethyldithiophosphate (DDTP) and using the Amberlite XAD-4 resin as a solid support in a homemade column. Different conditions of the flow injection system, such as solutions flow rates, nebulizer pressure and eluent concentration were optimized. Three certified reference materials of lobster hepatopancreas, dogfish liver and fish protein, three samples of fish muscle and three samples of shrimp were digested with HNO3, H2O2 and H2SO4 in a microwave system under reflux. DDTP was added in the solutions obtained, and the mixture was injected in the FI system. Calibration curves for Cd and Pb were obtained using the standard solutions in the concentration range 0.05-0.5 µg mL-1 in the digestion medium, submitted to the same pre-concentration procedure. The quantification limits (3.3 x LOD) for 5 min of pre-concentration time were 0.005 mg kg-1 Cd2+ and 0.1 mg kg-1 Pb2+ in the sample of fish or shrimp in natura, considering 1.0 g of the sample in a final volume of 50 mL. The agreement of the obtained concentrations with the certified ones (Student t-test, 95% confidence) and the recoveries of spiked real samples, from 90 to 120%, demonstrated good accuracy. Precision was also adequate, with relative standard deviations from 2 to 13%. The method was accurate, precise and certainly could be applied to the digested samples of different natures.

Determination of Hg(II) in natural waters using a carbon paste electrode modified with hybrid mesostructured silica nanoparticles

Mesostructured silica nanoparticles functionalized with a 5-mercapto-1-methyltetrazole derivative (MTTZ-MSU-2) were employed to prepare a chemically modified carbon paste electrode for Hg(II) determination in aqueous media by square wave adsorptive anodic stripping voltammetry. Under optimized operating conditions, 60s of electrolysis time in HCl 0.1M, the voltammetric signal increased with increasing preconcentration time from 1 to 10min. The voltammetric responses measured (peak areas) were linear with respect to Hg(II) concentration in the range of 0.1–1μM with a detection limit of 0.099μM after 5min preconcentration time and in the range of 0.025–0.25μM with a detection limit of 0.023μM for 10min of preconcentration time. The chemically modified carbon paste electrode had good single and inter-electrode reproducibility (RSD of 2 and 12%, respectively). Applicability to spiked groundwater and river water was demonstrated without any sample pretreatment (recoveries of 99 and 92%, RSD 4–7%, respectively).

On‐line Solid Phase Extraction of Copper in Water Samples with Flow Injection Flame Atomic Absorption Spectrometry

AbstractAn on‐line solid phase extraction method for the preconcentration and determination of Cu(II) by flame atomic absorption spectrometry has been described. The procedure is based on the retention of Cu(II) ions at pH 6.0 on a minicolumn packed with Amberlite XAD‐1180 resin impregnated with chrome azurol S. After preconcentration, Cu(II) ions adsorbed on the impregnated resin were eluted by 1 mol L−1 HNO3 solution. Several parameters, such as pH, type of eluent, flow rates of sample and eluent solutions, amount of resin were evaluated. At optimized conditions, for 3.5 min of preconcentration time, the system achieved a detection limit of 1.0 µg L−1, and a relative standard deviation of 1.2% at 0.2 µg mL−1 copper. An enrichment factor of 56‐fold was obtained with respect to the copper determination. The proposed method was successfully validated by the analysis of standard reference material (TMDA 54.4 lake water) and recovery studies. The method was applied to the preconcentration of Cu(II) in natural water samples.

Development of screen-printed carbon electrodes modified with functionalized mesoporous silica nanoparticles: Application to voltammetric stripping determination of Pb(II) in non-pretreated natural waters

A screen-printed carbon electrode modified with functionalized mesoporous silica nanoparticles (MTTZ-MSU-2) was developed and evaluated for reliable quantification of trace Pb(II) ions by anodic stripping square wave voltammetry in non-pretreated natural waters. The optimal operating conditions were 5 min preconcentration time and 120 s electrolysis time in HCl 0.2 M. The electrode displayed excellent linear behavior in the concentration range examined (1–30 μg L −1) with a limit of detection of 0.1 μg L −1. The screen-printed carbon modified electrode has long service time and good single and inter-electrode reproducibility. Applicability to spiked drinking water, river water and groundwater was demonstrated without any sample pre-treatment (recoveries between 97% and 106%, RSD 4–7%). On the basis of the present data, mercury-free screen-printed electrodes modified with functionalized mesoporous silicas have the potential to become the next-generation analyzers for decentralized heavy metal monitoring in environmental samples.

Voltammetric analysis of Pb(II) in natural waters using a carbon paste electrode modified with 5-mercapto-1-methyltetrazol grafted on hexagonal mesoporous silica

A hexagonal mesoporous silica (HMS) functionalized with a 5-mercapto-1-methyltetrazole derivative was employed to prepare a chemically modified carbon paste electrode for Pb(II) detection in aqueous solution by square wave adsorptive stripping voltammetry. The optimal operating conditions were 5 min preconcentration time at pH 6.5, and 120 s electrolysis time in 0.2 mol L−1 HCl. Under these conditions, the voltammetric signal increased linearly with the preconcentration time in the range 1 to 10 min and with the Pb(II) concentration in the range 1 to 100 µg L−1. The electrode was reproducible and sensitive. Simultaneous determination of Pb, Cd and Cu was also carried out with the electrode. The accuracy of the method was validated by analysing Pb(II) in tap water and groundwater samples.

Ca 10(PO 4) 6(OH) 2-modified carbon-paste electrode for the determination of trace lead(II) by square-wave voltammetry

The analytical performance of hydroxyapatite Ca 10(PO 4) 6(OH) 2(HAp) screen-printed sensors designed for the detection of metals was evaluated. The hydroxyapatite plays an important role in modern analytical electrochemistry due to their usefulness for the preparation of sensors giving rise to improved responses from metals. The suitable HAp-modified carbon-paste electrode (HAp-CPE) for the electrochemical determination of lead is illustrated in this work using cyclic and square-wave voltammetry in the potential range between −0.3 and −0.8 V. Perchlorate acid solution (1.0 mol L −1) was employed as the supporting electrolyte. The voltammetric measurements were carried out using as working electrode HAp-CPE, and a platinum electrode and an SCE electrode as auxiliary and reference electrodes, respectively. Under the optimized working conditions, calibration graph is linear for 5 min of preconcentration time with the detection limit 7.68 × 10 −10 mol L −1. This detection limit is remarkably lower than those reported previously using other modified electrodes or amperometric detection. The results indicate that this electrode is sensitive and effective for the determination of Pb 2+.

Online preconcentration using monoliths in electrochromatography capillary format and microchips

Online preconcentration and separation of analytes using an in situ photopolymerized hexyl acrylate-based monolith stationary phase was evaluated using electrochromatography in capillary format and microchip. The band broadening occurring during the preconcentration process by frontal electrochromatography and during the desorption process by elution electrochromatography was studied. The hexyl acrylate-based monolith provides high retention for neutral analytes allowing the handling of large sample volumes and its structure allows rapid mass transfer, thus reducing the band broadening. For moderately polar analytes such as mono-chlorophenols that are slightly retained in water, it was shown that enrichment factors up to 3500 can be obtained by a hydrodynamic injection of several bed volumes for 120 min under 0.8 MPa with a decrease in efficiency of 50% and a decrease of 30% for the resolution between 2- and 3-chlorophenol. An 8 min preconcentration time allows enrichment factors above 100 for polyaromatic hydrocarbons. The interest of these monoliths when synthesized in microchip is also demonstrated. A 200-fold enrichment was easily obtained for PAHs with only 1 min as preconcentration time, without decrease in efficiency.

A Novel Sensitive Method for the Determination of Cadmium and Lead Based on Magneto‐Voltammetry

A novel method for the ultratrace determination of Cd2+ and Pb2+ based on magneto‐voltammetry was developed. In the presence of a low strength magnetic field of 0.6 T, square wave stripping voltammetry (SWSV) of Cd2+ and Pb2+ was performed in this determination. A high concentration of redox species Fe3+ was added to the analytes to generate a large cathodic current during the preconcentration step. A large Lorentz force arising from the flux of net current through the magnetic field resulted in convective solution flow due to magnetohydrodynamics. Then more metal ions deposited on the electrode surface at a faster rate and an enhancement as large as 160% for the stripping peak current was observed. Under the optimal conditions, this method exhibits high sensitivities of 5.67 µA µM−1 for Cd2+ and 6.98 µA µM−1 for Pb2+, over the 1×10−8 – 1×10−6 mol l−1 range. Detection limits as low as 9.0×10−10 and 8.6×10−10 mol l−1 for Cd2+ and Pb2+ were obtained with a 2 min preconcentration time, respectively. The method was successfully applied to detect Cd2+ and Pb2+ in real water samples and the results were in agreement with atomic absorption spectrometry.

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.