Factorial design for multivariate optimization of an on-line preconcentration system for platinum determination by ultrasonic nebulization coupled to inductively coupled plasma optical emission spectrometry

A system for on-line preconcentration and determination of platinum by ultrasonic nebulization (USN) coupled to inductively coupled plasma optical emission spectrometry (ICP-OES) was studied. It is based on the chemical sorption of platinum on a column packed with polyurethane foam loaded with thiocyanate reagent. The optimization step was carried out using two level full factorial design. Three variables (pH, loading flow rate (LFR) and eluent concentration) were regarded as factors in the optimization. Results of the two level factorial design 2³ with three replicates of the central point for platinum preconcentration, based on the variance analysis (ANOVA), demonstrated that the factors and their interactions are not statistically significant. The proposed procedure allowed the determination of platinum with a detection limit of 0.28 μg l⁻¹. The precision for 10 replicate determinations at 10.0 μg l⁻¹ Pt level was 3.8% relative standard deviation (R.S.D.), calculated from the peak heights obtained. A total enhancement factor of 100 was obtained with respect to ICP-OES using pneumatic nebulization (10 for USN and 10 for preconcentration). A sampling frequency of 50 samples per hour was obtained. The effect of other ions in concentrations agreeing with water samples was studied. The addition/recovery experiments in the samples analyzed demonstrated the accuracy and applicability of the system developed for platinum determination in spiked water 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.     

On-line complexation/preconcentration system for the determination of lead in wine by inductively coupled plasma-atomic emission spectrometry with ultrasonic nebulization

An on-line lead preconcentration and determination system implemented with inductively coupled plasma-atomic emission spectrometry (ICP-AES) with ultrasonic nebulization (USN) in association with flow injection was studied. For the preconcentration of lead, a Pb-quinolin-8-ol complex was formed on-line at pH 6.8 and retained on Amberlite XAD-16 resin. The lead was removed from the microcolumn by countercurrent elution with nitric acid. A total enhancement factor of 225 was obtained with respect to ICP-AES with pneumatic nebulization (15.0 for USN and 15.0 for the column). The detection limit for Pb for the preconcentration of a 10 mL wine sample was 0.15 microg/L. The precision for 10 replicate determinations at a Pb level of 25 microg/L was a relative standard deviation of 2.5%, calculated from the peak heights obtained. The calibration graph obtained by using the preconcentration system for lead was linear with a correlation coefficient of 0.9995 for levels near the detection limit up to > or = 1000 microg/L. The method was successfully applied to the determination of lead in wine samples.     

Determination of arsenic in plant samples by inductively coupled plasma atomic emission spectrometry with ultrasonic nebulization: a complex problem

Under well-defined conditions, the analysis of most trace elements by inductively coupled plasma atomic emission spectrometry with ultrasonic nebulization (ICP-AES-USN) leads to accurate results for environmental matrices usually studied. Due to differences in matrix composition between standards and samples, ICP-AES-USN determinations of arsenic are interfered with by changes that take place mainly within the desolvation stage of the USN device. In this work, effects of plant matrices on the determination of As in six arsenic species have been investigated. Firstly, interferences were simulated by measuring analyte (species) signals in solutions containing variable concentrations of the main matrix elements encountered in mineralized plant samples (K, Ca, Mg, P and Na). Secondly, the influence of real plant matrices on emission signals of arsenic species was also studied. In this case, the observed effects were different than for individual matrix elements considered separately: Ca and Mg always present in real samples efficiently compensate the undesirable effects. Validation of this statement has been performed using mineralized plant reference materials. In addition, ICP-AES-USN results have been compared with those obtained by Zeeman electrothermal atomic absorption spectrometry.     

Improvement of the capabilities of inductively coupled plasma optical emission spectrometry by replacing the desolvation system of an ultrasonic nebulization system with a pre-evaporation tube

The effect of replacing the desolvation system (i.e., heater/condenser (HC) and membrane desolvator (MD)) of an ultrasonic nebulizer (USN) system with a pre-evaporation tube (PET) that is heated to about 400 °C on the analytical capabilities of inductively coupled plasma optical emission spectrometry (ICP–OES) was investigated. A multivariate optimisation was conducted in each case to find operating conditions maximizing plasma robustness. Under optimum conditions, the analytical performance of ICP–OES was significantly improved (i.e., better sensitivity, detection limit and plasma robustness) with USN–PET compared to that achieved with both the commercially-available USN–HC–MD and a conventional pneumatic nebulizer/spray chamber sample introduction system. However, only the USN–PET approach allows the determination of Hg, which appears to otherwise be lost in the heater/condenser system. Using a simple external calibration, without any matrix matching, and using an argon emission line for internal standardization, the results obtained for the determination of trace elements in certified soil reference materials (SRM 2710 and 2711) by USN–PET were in good agreement with certified values. This is unlike with conventional sample introduction systems where internal standardization using an Ar line is unusual, as it does not compensate for physical interferences, and either internal standardization (with internal standards added to the sample and standard solutions) or matrix-matched calibration is required.     

Determination of selenium in blood serum by inductively coupled plasma atomic emission spectrometry with pneumatic nebulization

The possibility of determining selenium in blood serum using inductively coupled plasma emission spectrometry with conventional pneumatic nebulization was studied. A high-resolution spectrometer (SBW=6 pm) with laterally viewed ICP was employed. Analysis with conventional pneumatic nebulization could overcome laborious and demanding digestion, which is necessary for hydride generation. A pressure digestion with nitric acid at 160 degrees C was sufficient to decrease the carbon content in the serum sample to 5%-10% of its original value. Spectral interference of the CN band was observed and mathematically corrected. It was found that the carbon-induced selenium line emission enhancement occurred even under ICP optimized conditions. A method of determination was developed and applied to the analysis of blood serum. True limit of detection in real samples is 0.01-0.02 mg/L and the limit of quantification (RSD 10%) is 0.03-0.07 mg/L using Se I 196.090 nm line at an integration time of 10-2 s. The method was tested by analysis of porcine blood serum and the serum reference material Seronorm MI 0181.     

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) HNO₃ containing 0.3 μg l⁻¹ of Rh as an internal standard using ultrasonic nebulization. The detection limits (3σ) 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.     

Micro-scale flow system for on-line multielement preconcentration from saliva digests and determination by inductively coupled plasma optical emission spectrometry

A micro-scale flow system is proposed for on-line preconcentration of Cd, Cu, Mn, Ni and Pb in saliva samples and their determination by inductively coupled plasma optical emission spectrometry (ICP-OES). A small column containing 8 μl of AG50W-X8 resin was inserted into the flow system, assembled with capillary tubes and connected to a micro-concentric nebulizer. The elution of the analytes was performed with 3 mol l⁻¹ HCl at a flow rate of 82 μl min⁻¹. The ICP-OES signal acquisition program permits measurements for 5 s in the concentrated portion of the transient elution peaks. A sample volume of 1 ml was required to obtain enrichment factors of 46, 23, 17, 18 and 44 for Cd, Cu, Mn, Ni and Pb, respectively. The relative standard deviations for a 50-μg l⁻¹ multi-analyte solution were ≤6.5%. The recoveries for Cd, Cu, Mn, Ni and Pb in digested human saliva samples were between 86 and 111%. The sample throughput was 24 h⁻¹.     

On-line complexation of zinc with 5-Br-PADAP and preconcentration using a knotted reactor for inductively coupled plasma atomic emission spectrometric determination in river water samples

An on-line zinc preconcentration and determination system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) associated with flow injection (FI) was studied. The zinc was retained as zinc-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Zn-(5-Br-PADAP)) complex at pH 9.2. The zinc complex was removed from the knotted reactor (KR) with 30% v/v nitric acid. An enrichment factor of 42 was obtained for the KR system with respect to ICP-AES using pneumatic nebulization. The detection limit for the preconcentration of 10 mL of aqueous solution was 0.09 microg/L. The precision for 10 replicate determinations at the 5 microg/L Zn level was 2.3% relative standard deviation (RSD), calculated with the peak heights obtained. The calibration graph using the preconcentration system for zinc was linear with a correlation coefficient of 0.9997 at levels near the detection limits up to at least 100 microg/L. The method was succesfully applied to the determination of zinc in river water samples.     

On-line complexation of zinc with 5-Br-PADAP and preconcentration using a knotted reactor for inductively coupled plasma atomic emission spectrometric determination in river water samples

An on-line zinc preconcentration and determination system implemented with inductively coupled plasma atomic emission spectrometry (ICP-AES) associated with flow injection (FI) was studied. The zinc was retained as zinc-2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (Zn-(5-Br-PADAP)) complex at pH 9.2. The zinc complex was removed from the knotted reactor (KR) with 30% v/v nitric acid. An enrichment factor of 42 was obtained for the KR system with respect to ICP-AES using pneumatic nebulization. The detection limit for the preconcentration of 10 mL of aqueous solution was 0.09 μg/L. The precision for 10 replicate determinations at the 5 μg/L Zn level was 2.3% relative standard deviation (RSD), calculated with the peak heights obtained. The calibration graph using the preconcentration system for zinc was linear with a correlation coefficient of 0.9997 at levels near the detection limits up to at least 100 μg/L. The method was succesfully applied to the determination of zinc in river water samples. Received: 27 December 1999 / Revised: 14 March 2000 / Accepted: 15 March 2000     

Determination of heavy metals by inductively coupled plasma mass spectrometry after on-line separation and preconcentration

A method for the determination of Cu, As, Se, Cd, In, Hg, Tl, Pb and Bi in waters and in biological materials by inductively coupled plasma mass spectrometry, after an on-line separation, is described. The matrix separation and analyte preconcentration is accomplished by retention of the analytes complexed with the ammonium salt of O,O-diethyl dithiophosphoric acid in a HNO₃ solution on C₁₈ immobilized on silica in a minicolumn. Methanol, as eluent, is introduced in the conventional pneumatic nebulizer of the instrument. In order to use the best compromise conditions, concerning the ligand and acid concentrations, the analytes were determined in two separate groups. The enrichment factors were in the range from 5 to 61, depending on the analyte. The limits of detection varied from 0.43 ng L⁻¹ for Bi to 33 ng L⁻¹ for Cu. The sample consumption is only 2.3 mL for each group and the sampling frequency is 21 h⁻¹. The accuracy was tested by analysing five certified reference materials: water, riverine water, urine, bovine muscle and bovine liver. The agreement between obtained and certified concentrations was very good, except for As. The relatively small volume of methanol, used as eluent, minimizes the problems produced by the introduction of organic solvent into the plasma.     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples.     

Flow injection on-line sorption preconcentration of platinum in a knotted reactor coupled with electrothermal atomic absorption spectrometry

A flow injection on-line sorption preconcentration method for the electrothermal AAS determination of platinum has been developed. The pyrrolidine dithiocarbamate complexes of either Pt⁴⁺ or Pt²⁺, formed in 0.7 mol L^–1 HNO₃, are on-line adsorbed on the inner walls of a PTFE knotted reactor and subsequently eluted with methanol. An enhancement factor of 112 and a detection limit (3 σ) of 10 ng L^–1 along with a sampling frequency of 21 h^–1 are achieved with a 90 s preconcentration time at a sample flow rate of 8.8 mL min^–1. The relative standard deviation is 2.5% for 0.4 μg L^–1 Pt. The method has been applied to the determination of platinum in blood samples. Received: 6 October 1997 / Revised: 26 November 1997 / Accepted: 3 December 1997     

Determination of trace rare earth elements by inductively coupled plasma optical emission spectrometry after preconcentration with immobilized nanometer titanium dioxide

A simple and sensitive method is presented for the determination of dopamine with a nanoscale ceria ion-selective CMC (carboxymethyl cellulose) membrane electrode by means of the Belousov–Zhabotinsky oscillating chemical reaction. The electrode exhibits excellent potential response. If the concentration of dopamine is in the range of 4.9 × 10⁻⁵ to 2.4 × 10⁻⁷ mol · L⁻¹, the change in oscillating amplitude is proportional to the concentration of dopamine, with a correlation coefficient of 0.9987 and a standard deviation of 0.17%. A recovery of 97.5–105.0% was obtained. Interference was also studied. The use of a nanoscale ceria ion-selective membrane-working electrode improved the sensitivity of the determination method.     

Determination of rare earth elements in seawater by on-line column preconcentration inductively coupled plasma mass spectrometry

A home made column of commercially available iminodiacetate resin, Muromac A-1 (50–100 mesh) was used to concentrate rare earth elements (REEs) (15 elements: Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu) in seawater. An automated low pressure flow analysis method with on-line column preconcentration/inductively coupled plasma mass spectrometry (ICP-MS) is described for the determination of REEs in seawater. Sample solutions (adjusted to pH of 3.0) passed through the column. After washing the column with water, the adsorbed elements were subsequently eluted into the plasma with 0.7 M nitric acid. Calibration curves were accomplished by means of purified artificial seawater with a sample loading time of 120 s. Detection limits (DLs) of the on-line column preconcentration/ICP-MS by eight replicate operations were between 0.040 and 0.251 pg ml⁻¹ for REEs in the artificial seawater. The precision was less than 8.9% for REEs and one sample can be processed in 7 min using a 7 ml of sample. The proposed method was applied to determine REEs in coastal seawater of Hiroshima Bay, Japan.     

On-line preconcentration and determination of chromium in parenteral solutions by inductively coupled plasma optical emission spectrometry

A method for the preconcentration and speciation of chromium was developed. On-line preconcentration and determination were obtained using inductively coupled plasma optical emission spectrometry (ICP-OES) coupled with flow injection. To determinate the chromium (III) present in parenteral solutions, chromium was retained on activated carbon at pH 5.0. On the other hand, a step of reduction was necessary in order to determine total chromium content. The Cr(VI) concentration was then determined by difference between the total chromium concentration and that of Cr(III). A sensitivity enrichment factor of 70-fold was obtained with respect to the chromium determination by ICP-OES without preconcentration. The detection limit for the preconcentration of 25 ml of sample was 29 ng l⁻¹. The precision for the 10 replicate determinations at the 5 μg l⁻¹ Cr level was 2.3% relative standard deviation, calculated with the peak heights. The calibration graph using the preconcentration method for chromium species was linear with a correlation coefficient of 0.9995 at levels near the detection limits up to at least 60 μg l⁻¹. The method can be applied to the determination and speciation of chromium in parenteral solutions.     

Determination of cadmium by an improved double chamber electrothermal vaporization inductively coupled plasma atomic emission spectrometry

An improved double chamber electrothermal vaporization (ETV) system was designed. A new inner chamber and its bottom plate made of quartz glass were attached with carrier support gas inlet port for the determination of cadmium by inductively coupled plasma atomic emission spectrometry (ICP-AES). The use of the inner chamber in combination with the plate played important roles to transport the metal vapor efficiently into argon ICP. Ten-μl sample aliquots were dried at 100 °C and subsequently heated at 1000 °C on the tungsten boat furnace. The evolved vapor was swept into the ICP source through PTFE tubing and the inner chamber by a 0.8 l/min H₂ (7%)-Ar carrier gas. The performance parameters of ETV-ICP-AES such as temperature program and gas flow rate were evaluated using cadmium standard solution. Under the optimized experimental conditions, the best attainable detection limit at Cd II 214.438 nm line was 0.2 ng/ml with linear dynamic ranges of 50 to 10,000 ng/ml for cadmium. The instrumental precision expressed as the relative standard deviation (RSD) from ten replicate measurements of 10,000 ng/ml for cadmium by ETV-ICP-AES was 0.85%. The present method has been successfully applied to the determination of cadmium in zinc-base materials.     

Antimony speciation in environmental samples by interfacing capillary electrophoresis on-line to an inductively coupled plasma mass spectrometer

Antimony is a widely distributed trace element of ecotoxicological interest. A pathway via bioalkylation of inorganic Sb species is discussed in the literature, resulting in organically bound Sb species. Therefore, Sb speciation becomes increasingly a matter of interest for risk assessment in the environment. This contribution investigates the possibilities of CE on-line hyphenated to ICP-MS for Sb speciation. Two methods are employed, both highly resolving the species but only one preserving the species stability. The latter used Na2HPO4/NaH2PO4, 20 mM, pH 5.6 as the background electrolyte and NaOH or acetic acid as stacking electrolyte 1 or stacking electrolyte 2, respectively. Detection limits of 0.1 microgram/1-0.7 microgram/1, depending on species, were achieved. When analysing liquid phases from fouling and sewage sludge up to eight antimony species were detected. Sb (V) as well as methylated Sb species were found.     

电感耦合等离子体原子发射光谱法测定高温合金中低含量钇

建立电感耦合等离子体原子发射光谱法测定高温合金中低含量钇的方法。采用盐酸、硝酸、氢氟酸溶解样品,在优化的仪器条件下,采用基体匹配法配制系列标准工作溶液,选择分析线为360.073 nm。钇的含量在0.0005%~0.050%范围内与光谱强度具有良好的线性关系,相关系数为0.99999,检出限为0.000003%。该方法测定结果的相对标准偏差不大于6.0%(n=8),加标回收率为90.0%~104.0%。该方法简便、快速、准确,可用于高温合金中低含量钇的测定。