Determination of lead in atmospheric particulates by flameless atomic absorption spectrometry with a graphite tube

A procedure for the determination of atmospheric particulate lead by flameless atomic absorption spectrometry is described. Aerosols are collected on 10-cm Whatman 41 filters with high-volume pumps. The lead is removed from a one-eighth sector of the filter by two ultrasonic treatments in 0.1 M nitric acid for 10 and 5 min, respectively. Investigations, including comparison with samples pre-ashed at low temperature, indicated that the lead was completely recovered. Routinely 20-μ1 amounts of the solution are injected into a graphite tube and the % absorption at 283.3 nm is measured. The elements normally encountered in atmospheric aerosols do not interfere. The sensitivity for 24-h samples is 0.01 μg m^?3 of air. Sampling time can be reduced to a few minutes in urban air when a larger segment of the filter is used and a larger volume is injected. The reproducibility of the complete procedure is 3% for a typical lead concentration of 0.35 μg m^?3. The method was applied to short-period variations of the lead concentration in urban air.     

Determination of cadmium by electrothermal atomic absorption spectrometry using electrochemical separation in a microcell

Electrodeposition on the graphite electrode under conditions of controlled current in a flow-through mode, followed by electrothermal atomic absorption spectrometry, is proposed for the determination of cadmium. After electrolysis in a microcell of 2.6 μl volume, deposited metal was dissolved in 40 μl 0.2 mol l⁻¹ HNO₃ and the whole volume was direct injected into the atomizer. Using this on-line arrangement and electrodeposition from 1.75 ml of sample solution detection limit of 25 ng l⁻¹ Cd was attained. The method was applied for the determination of cadmium in a real sample of seawater.     

The direct determination of cadmium in urine by electrochemical atomic absorption spectrometry with the L'vov platform

A simple, direct procedure for the measurement of cadmium in urine is described. Graphite-furnace atomic absorption spectrometry is used in conjunction with selective atomisation at 800°C from a L'vov platform. Urine samples are diluted with an equal volume of deionised water and 20-μl aliquots are injected. Calibration is done by standard additions. The sensitivity is 0.016 μg Cd l^?1 for 1% absorption for a 20-μl sample. Within-run precision is 4.9% at 0.84 μg l^?1. The detection limit is 0.06 μg l^?1, which allows normal unexposed levels of cadmium in urine to be determined. The method is applicable to the determination of urinary cadmium levels of both occupationally non-exposed and exposed populations.     

Determination of microgram amounts of carbon in the for of carbamate by non-aqueous electrolytic conductivity detection

An absorption/detection system is described for the determination of carbon at and below microgram detection level. The carbon dioxide formed by combustion of an organic substances (solid or in solution) is led into a simple absorption/detection system containing 2.00 cm³ of an ethanolic 2 M solution of 3-methoxypropylamine. The conductivity of the carbamate solution formed is measured by means of platinum electrodes built in the absorption tube, and the integrated d.c. voltage signal obtained is fed to a precision digital voltmeter. Detector response is linear up to 6.6 μg of carbon, and the detection limit is 2 × 10^?2 μg. A single determination takes 5 min. Precision was found to be better than +? 1.0% (P-=95%) for 1–6 μg or carbon.     

Ion-pair-based surfactant-assisted dispersive liquid–liquid microextraction for the determination of cadmium in water samples: Optimization using response surface methodology

A sensitive, simple, and rapid method is developed for ion-pair-based surfactant-assisted dispersive liquid–liquid microextraction (IPSA-DLLME) and flame atomic absorption spectrometric determination of cadmium in water samples. In this procedure, trace amounts of Cd²⁺ were converted to CdI ₄ ^2– , and after addition of a tetrabutylammonium bromide (TBAB) solution as cationic surfactant the analyte was transformed to the ion-pair state. This cadmium species was extracted by fast injection of a solution containing 200 μL of chloroform and 800 μL of methanol as extraction and disperser solvents, respectively. The pH of the sample solution, concentration of iodide, TBAB amount, and the extractant volume were optimized using a 27-run Box–Behnken design with a triplicate central point. Under the optimized conditions, the calibration curve was linear in the range 1–200 μg L^–1 (R ² = 0.9959); with the detection limit (signal/noise = 3) of 0.28 μg L^–1. The relative standard deviations (RSD) for eight runs (Cd²⁺ = 10 μg L^–1) and enrichment factor were found to be 3.04 % and 50, respectively.     

Trace determination of gaseous chlorine: a comparison between an electrometric method and the methyl orange photometric method

Two methods for the determination of molecular chlorine in air are critically compared. An electrometric method based on measurement of the reduction current of chlorine to chloride is superior to the photometric determination based on bleaching of an acidic solution of methyl orange. The limit of detection for the electrometric method is 50 μg m^-3; the standard error of the mean is better than 2%, and the sensitivity is 5.9 μg m^-3 μ A^-1 at +50 mV applied potential versus SCE with a mercury cathode. The limit of detection for the photometric method is 300 μg m^-3; the precision is of the order of 5%, and the sensitivity is 80 μg m^-3 for an error of 1% in the absorption measurements. The accuracy of the electrometric method is good whereas the photometric method yields consistently low results. The electrometric method is less subject to interferences than the photometric method.     

Transport processes through track-etch membrane filters in a reagent delivery cell

A reagent delivery cell with a track-etch membrane filter for on-line dilution of concentrated salt solutions is described. The influence of several system parameters such as concentration of the stock solution, temperature, transmembrane pressure and the dependence on the diffusion coefficients of several salt components on the dilution was evaluated. As an application example, the use of the reagent delivery cell for on-line calibration of an atomic absorption spectrometer was studied. Fluxes through the membrane filter of 10 to 50 nL mm^–2 min^–1 with relative standard deviations of 0.8% within a day and 1.9% from day to day were achieved. The permeation experiments with the track-etch membrane filter for the dilution of aqueous solutions of several chlorides and sodium salts confirm a diffusion process. Flux rates can be estimated mathematically using Fick’s first law with an agreement between measured and calculated dilution factors within 86 to 113%.     

Dispersive Liquid‐Liquid Microextraction of Cu(II) Using a Novel Dioxime for Its Highly Sensitive Determination by Graphite Furnace Atomic Absorption Spectrometry

A dispersive liquid‐liquid microextraction (DLLME) technique was proposed for the enrichment and graphite furnace atomic absorption spectrometric (GFAAS) determination of Cu²⁺ in water samples. In this method a mixture of 480 μL acetone (disperser solvent) containing 26 μg S,S‐bis(2‐aminobenzyl)‐dithioglyoxime (BAT) ligand and 20 μL carbon tetrachloride (extraction solvent) was rapidly injected by a syringe into 5 mL aqueous sample containing copper ions (analyte). Thereby, a cloudy solution formed. After centrifugation, the fine droplets containing the extracted copper complex were sedimented at the bottom of the conical test tube. This phase was collected by a microsyring and after dilution by methanol, 20 μL of it was injected into the graphite tube of the instrument for analysis. Effects of some parameters on the extraction, such as extraction and disperser solvent type and volume, extraction time, salt concentration, pH and concentration of the chelating agent were optimized. The response surface method was used for optimization of the effective parameters on the extraction recovery. Under these conditions, an enrichment factor of 312 was obtained. The calibration graph was linear in the rage of 2–50 μ L⁻¹ Cu²⁺ with a detection limit of 0.03 μg L⁻¹ and a relative standard deviation (RSD) for five replicate measurements of 3.4% at 20 μg L⁻¹ Cu²⁺. The method was successfully applied to the determination of Cu²⁺ in some spring water samples.     

Application of edta to direct graphite-furnace atomic absorption analysis for cadmium in sea water

A method is described for the direct determination of cadmium in undiluted sea water by graphite-furnace atomic absorption spectrometry. The addition of EDTA ( 1 mg ml^-1) reduces the temperature of atomization of cadmium to far below that of volatilization of other matrix components. The need for very careful temperature control and accurate background compensation is thus minimized. Sea water was analyzed by the method of standard additions. A detection limit of 0.01 μg l^-1, a sensitivity of 0.034 μg l^-1 and a precision of ±10% at the 0.05 μg l^-1 level were obtained for 20-μl injections.     

Extraction—spectrophotometric determination of traces of cadmium with 4-(2-pyridylazo)resorcinol and a long-chain quaternary ammonium salt

A simple and highly sensitive extraction—spectrophotometric determination of cadmium is described. The ion-associate formed between the cadmium-PAR anionic chelate and cetyldimethylbenzylammonium chloride (CDBA) is extracted with chloroform at pH 10. The absorption maximum of the extracted species occurs at 505 nm, the molar absorptivity being (9.82 ± 0.30) × 10⁴ l mol^-1 cm^-1. The optimal concentration range for measurements is 0.2–1.0 μg Cd ml^-1; Beer's law is obeyed. The composition of the ion-associate is estimated to be CdPAR₂-2CDBA. The conditional extraction constant is log K'_ex ≈ 8. The stability constant of the cadmium—PAR chelate in aqueous solution is log β₂ = 17.5 ± 0.3. Extraction with N-benzoyl-N-phenylhydroxylamine is used to avoid several interferences. Moderate amounts of zinc are masked with sodium hydroxide.     

Simultaneous determination of tin and lead by anodic stripping voltammetry in aqueous-alcoholic medium. Application to the direct determination of these elements in canned foods

Tin and lead may be determined in mixture in a solution of 50% methanol-50% isopropanol containing l M hydrochloric acid. The solvent-electrolyte composition affects both the relative a.s.v. peak heights and peak resolution. Iron(III) in large quantities does not interfere, and mixtures of copper, lead, tin, and cadmium may be analyzed. Juice samples can be analyzed without digestion, by simple 1:5000 dilution (5 μl to 25 ml) with the above solvent electrolyte. It was demonstrated that tin gradually dissolves from cans containing the juice.     

The optimization of an ICP injection technique and the application to the direct analysis of small-volume serum samples

The optimization and the analytical properties of an injection technique for the analysis of small-volume samples (50–200 μl) by inductively coupled plasma atomic emission spectroscopy (ICP-AES) are described. Samples are injected into a small funnel connected to a concentric glass nebulizer. A 3 kW argon/nitrogen ICP with power stabilization is used as excitation source. When operating the nebulizer at an argon pressure of 5 bar, relative detection limits for calcium, copper, iron, magnesium and zinc (0.2–50 $\text{ng}\text{ml}$) are a factor of 2 to 10 higher when compared with ICP methods using continuous nebulization. However, the full power of detection of the injection method is obtained at a 50 μl sampling volume. Matrix effects caused by sodium salt concentrations of 5 $\text{g}\text{l}$ are lower than 10%. Relative standard deviations s_r,(I_X) ranged from 0.03 to 0.07. The method was applied to the sequential determination of trace elements (copper, iron and magnesium) in human serum samples after a 1 + 4 dilution with Herrmann solution. The accuracy of the method is illustrated by the analysis results for calcium, copper, iron, magnesium and zinc in a series of test serum samples.     

Microtitrimetric and photometric determination of sulphur in metals in the low μg g-1 range after wet or dry evolution of hydrogen sulphide

Wet and dry techniques have been optimized for the separation of sulphur traces from metals (e.g. Ag, Cu, Cu alloys, Pb, Sn, Fe) as hydrogen sulphide, in combination with a final microtitrimetric or spectrophotomefcric determination. The metal sample can be dissolved in a mixture of hydroiodic, formic and hypophosphorous acids, and the evolved hydrogen sulphide swept with nitrogen into an absorption vessel. Alternatively, in the hydrogenation technique, the metal sample is heated in a stream of pure hydrogen up to ?1150°C and the hydrogen sulphide produced is absorbed in sodium hydroxide solution or cadmium hydroxide suspension. The sulphide is determined in the absorption vessel by microtitration with cadmium(II) titrant and dithizone as indicator. The methylene blue colour reaction is applied for the speetrophotometric determination. Precautions are taken to avoid systematic errors (losses by absorption, contamination by laboratory air) and to lower reagent blanks, so that concentrations as low as ?0.2 μg g^-1 (sample weight ?1 g) can be determined. The coefficients of variations are ?10% and 2.5% at concentration ranges of 1–10 μg g^-1 and > 10 μg g^-1, respectively.     

Flow injection spectrophotometric determination of europium using chlortetracycline

A flow injection (FI) spectrophotometric determination of europium (III) is described, based on the complexation between europium (III), and chlortetracycline (CTC) in a Tris-buffer pH 8.0 medium. The resulting yellow-coloured complex is measured at its absorption maximum of 400 nm after 100 μl of sample or standard solution containing europium (III) are injected into the merged streams of CTC and Tris-buffer solutions. Optimum conditions for determining μg amounts of europium (III) are achieved by univariate method. Various types of reactors are also investigated. It is shown that the use of a single bead string reactor gives rise to the enhancement of peak height. A linear calibration curve over the range of 0.10-0.60 μg ml⁻¹ europium (III) is established with the regression equation (n=6) Y=34.93X+0.01 and the correlation coefficient of 0.9994 is obtained. A detection limit (3σ) of 0.01 μg ml⁻¹ of europium (III) and the relative standard deviation (R.S.D.) of 4.32% for determining 1.0 μg ml⁻¹ of europium (III) (n=7) are obtained. The recommended method has been applied to the quantitation of europium (III) in spiked water and stream sediment samples with average recoveries of 99.9 and 97.5%, respectively. The sampling rate is found to be 85 h⁻¹.     

The determination of hydrogen chloride in ambient air with diffusion/denuder tubes

A manual method for the determination of hydrogen chloride in air, based on diffusion/denuder tube separation from particulate chloride aerosol is described. When air is drawn through a tube coated with a selective absorbent (sodium fluoride), separation is achieved because gaseous hydrogen chloride diffuses much more rapidly to the tube walls than particulate chloride aerosol, which passes through virtually unabsorbed. After the sampling period (the length of which depends on the concentration of gaseous hydrogen chloride expected), the sorbed hydrogen chloride is washed from the tube and measured with a highly sensitive chloride ion-selective electrode with a mercury (I) chloride membrane. The method is examined theoretically and experimentally. The experimentally derived absorption efficiencies of the diffusion/denuder tubes were > 90% and the standard deviation of the method was 0.023 μg m^?3 for hydrogen chloride concentrations of 0.16–0.55 μg m^?3. Interference from particulate chloride salts was negligible; this was confirmed by tests with artificially generated aerosol particles from an aerosol generator. The diffusion/denuder tubes have high capacity; level as high as 330 μg m^?3 hydrogen chloride can be sampled for 60 min without affecting performance. A detection limit of (50/t) μg m^?3 can be achieved, where t is the sampling rime (min); e.g., 1μg m^?3 hydrogen chloride can be detected with a sampling period of 50 min.     

Indirect atomic absorption spectrometric determination of mixtures of chloride and iodide by precipitation in an unsegmented flow system

Chloride and iodide are injected into a carrier silver nitrate and the precipitates formed are retained on a stainless-steel filter, so that total chloride and iodide can be determined by the decrease in the atomic absorption signal for silver. The silver chloride precipitate is subsequently dissolved with ammonia and chloride only is determined. Iodide is determined by difference. Mixtures of these anions at μg ml^?1 levels can be determined for chloride/iodide ratios from 7.5:1 to 1:60, with a sampling frequency of ca. 10 h^?1. Applications to the determination of chloride in foodstuffs and wines are described. Up to 10 samples per hour can be handled and 50–100 samples can be run before the filter must be cleaned.     

A new reagent for the spectrophotometric microdetermination of cadmium

2,2′-Dipyridyl-2-pyridylhydrazone (DPPH) allows a simple, rapid, and sensitive spectrophotometric microdetermination of cadmium in aqueous solution. The yellow 1:2 metal-to-ligand complex formed has a molecular extinction coefficient of 5.5 × 10⁴ liters mole^?1 cm^?1 at the absorption maximum of 444 nm. The determination of cadmium is carried out at pH 12.3 ± 0.2. Beer's law is obeyed over the concentration range of 0.2 to 2 ppm and the Sandell sensitivity of the color reaction is 0.002 μg of cadmium/cm² for an absorbance of 0.001.     

Direct determination of Cu,Mn, Pb,and Zn in beer by thermospray flame furnace atomic absorption spectrometry

In this work, thermospray flame furnace atomic absorption spectrometry (TS-FF-AAS) was employed for Cu, Mn, Pb, and Zn determination in beer without any sample digestion. The system was optimized and calibration was based on the analyte addition technique. A sample volume of 300 μl was introduced into the hot Ni tube at a flow-rate of 0.4 ml min⁻¹ using 0.14 mol l⁻¹ nitric acid solution or air as carrier. Different Brazilian beers were directly analyzed after ultrasonic degasification. Results were compared with those obtained by graphite furnace atomic absorption spectrometry (GFAAS). The detection limits obtained for Cu, Mn, Pb, and Zn in aqueous solution were 2.2, 18, 1.6, and 0.9 μg l⁻¹, respectively. The relative standard deviations varied from 2.7% to 7.3% (n=8) for solutions containing the analytes in the 25–50 μg l⁻¹ range. The concentration ranges obtained for analytes in beer samples were: Cu: 38.0–155 μg l⁻¹; Mn: 110–348 μg l⁻¹, Pb: 13.0–32.9 μg l⁻¹, and Zn: 52.7–226 μg l⁻¹. Results obtained by TS-FF-AAS and GFAAS were in agreement at a 95% confidence level. The proposed method is fast and simple, since sample digestion is not required and sensitivity can be improved without using expensive devices. The TS-FF-AAS presented suitable sensitivity for determination of Cu, Mn, Pb, and Zn in the quality control of a brewery.     

Continuous determination of hydrogen fluoride in air with the fluoride-selective electrode

Hydrogen fluoride in a standard or sample gas stream at 200 ml min^?1 permeates through a teflon membrane (0.8 μm pore size, 0.08 mm thick) into an absorption solution (citrate/acetate buffer at pH 5.4) flowing at 30 ml min^?1. The fluoride produced is measured with the fluoride-selective electrode. The response time is about 12 min. The absorption efficiency of hydrogen fluoride is about 70% between 6.5 and 0.25 ppm by volume (5.2 and 0.2 mg m^?3). In this range, the Nernst equation is valid with a relative standard deviation of less than 1.8%. The lower determination limit for hydrogen fluoride is 0.1 ppm (0.08 mg m^?3).     

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.