Beam-injection flame-furnace atomic-absorption spectrometry (BIFF–AAS) with low-pressure sample-jet generation

Flame-furnace AAS (FF-AAS) comprises two individual, recently developed FAAS techniques remarkable for their high power of detection and the small amounts of sample required. One of these techniques is beam-injection flame-furnace AAS (BIFF-AAS), whereby the sample is introduced into a flame-heated atomization cell as a high-speed liquid jet. For the first time this sample-introduction beam has been generated at low pressure by use of a peristaltic pump and a special micro channel smooth jet nozzle developed for this application. Compared with standard FAAS a 7- to 17-fold improvement in the power of detection was obtained for six elements (Ag, Cd, Hg, Pb, Se, and Zn). The relative standard deviation (N=15) was between 0.7% and 3.4%. Sample volumes between 10 microL and 1 mL have been investigated. The applicability of the peristaltic pump for beam generation enables an optimum sampling mode for a variety of analytical tasks (continuous sample uptake, manual or automated, or different flow-injection modes). The method can also be regarded as a simple, effective interface between FIA techniques and flame AAS.     

Sample introduction assisted by compressed air in flame furnace AAS: a simple and sensitive method for the determination of traces of toxic elements

The power of detection of flame AAS for the toxic elements Cd, Hg, Pb and Tl can be improved by 1–2 orders of magnitude by using flame furnace AAS. In flame-furnace AAS, liquid samples are introduced directly into a nickel tube located in the flame, in the simplest case through a ceramic thermospray capillary. Transportation of the samples is achieved by using compressed air only. Comparatively low detection limits are achieved by both beam injection flame furnace (BIFF-AAS) and thermospray flame furnace AAS (TS-FF-AAS). For TS-FF-AAS, a pressure of less than 20 kPa (<80 in. water) is required. The TS-FF-AAS technique is very simple, robust and cheap. The detection limits were 0.2–0.4 g L^–1 (Cd), 40–100 g L^–1 (Hg), 5–9 g L^–1 (Pb) and 4–14 g L^–1 (Tl), respectively, depending on the method, flow rate and sample volume used. Pb and Cd were found at concentrations of 0.1–2 and 0.005–0.3 g g^–1, respectively, in samples of various spices.Dedicated to the memory of Wilhelm Fresenius.     

A novel analytical low-cost flow system based on a 0.6 MPa (84 psi) diaphragm pump applied to on-line trace pre-concentration in flame AAS and ICP-OES

A novel inexpensive 0.6 MPa (84 psi) flow system based on a low-cost diaphragm pump has been developed. The unfavourable strong pulsation of the pump has been overcome by using highly flexible silicone tubing as a pulse suppression coil. This results in a smooth pulse-free continuous flow of 100 mL min(-1) in circulation. This flow rate is much too high for a flow-injection system; however, with a restrictor capillary the flow rate required can be tapped off down to a range of 0.1-50 mL min(-1). By employing diaphragm pumps in an analytical flow system the pressure gap between HPLC pumps (2-40 MPa) and peristaltic pumps (<0.2 MPa), mainly used in FIA systems, can be filled. Due to the higher pressure delivered by diaphragm pumps relative to peristaltic pumps, the new flow system can be applied to on-line sample pre-concentration and matrix separation in flame AAS and ICP-OES by using standard HPLC pre-columns or small ion-exchange columns, respectively. In this way, very low detection limits in flame AAS have been reached (Cd 0.07 micro g L(-1), Cu 0.05 micro g L(-1), Co 0.9 micro g L(-1), Ni 0.8 micro g L(-1), Mn 0.7 micro g L(-1), Pb 0.8 micro g L(-1) and Tl 0.2 micro g L(-1)).     

Solid-phase extraction and preconcentration of cadmium(II) in aqueous solution with Cd(II)-imprinted resin (poly-Cd(II)-DAAB-VP) packed columns

A novel chelating resin (poly-Cd(II)-DAAB-VP) was prepared by metal ion imprinted polymer (MIIP) technique. The resin was obtained by one pot reaction of Cd(II)-diazoaminobenzene-vinylpyridine with cross-linker ethyleneglycoldimethacrylate (EGDMA). Comparing with non-imprinted resin, the poly-Cd(II)-DAAB-VP has higher adsorption capacity and selectivity for Cd(II). The distribution ratio (D) values for the Cd(II)-imprinted resin show increase for Cd(II) with respect to both D values of Zn(II), Cu(II), Hg(II) and non-imprinted resin. The relatively selective factor (α_r) values of Cd(II)/Cu(II), Cd(II)/Zn(II) and Cd(II)/Hg(II), are 51.2, 45.6, and 85.4, which are greater than 1. poly-Cd(II)-DAAB-VP can be used at least 20 times without considerable loss of adsorption capacity. Based on poly-Cd(II)-DAAB-VP packed columns, a highly selective solid-phase extraction (SPE) and preconcentration method for Cd(II) from aqueous solution was developed. The MIIP-SPE preconcentration procedure showed a linear calibration curve within concentration range from 0.093 to 30 μg l⁻¹. The detection limit and quantification limit were 0.093 and 0.21 μg l⁻¹ (3σ) for flame atomic absorption spectrometry (FAAS). The relative standard deviation of the eleven replicate determinations was 3.7% for the determination of 10 μg of Cd(II) in 100 ml water sample. Determination of Cd(II) in certified river sediment sample (GBW 08301) demonstrated that the interfering matrix had been almost removed during preconcentration. The column was good enough for Cd(II) determination in matrixes containing components with similar chemical property such as Cu(II), Zn(II) and Hg(II).     

Microanalytical concept for multicomponent analysis of airborne particulate matter

Summary A microanalytical concept is presented that permits the determination of four ionic species (NH ₄ ⁺ , Cl^–, NO ₃ ^– , SO ₄ ^2– and 16 elements (Al, As, Cd, Ca, Cu, Fe, K, Mg, Mn, Na, Ni, Pb, Se, Si, V, Zn) in minute samples of filter collected atmospheric particulate matter. The multistage procedure is based on consecutive aqueous extraction and acid digestion of the entire sample. Ion analysis of the extract is made by flow injection analysis (FIA) and single column ion chromatography (SCIC) with total consumption of only 50 l sample volume. Flame and furnace atomic absorption spectroscopy (AAS) is employed for element analysis after acid decomposition in a closed microwave digestion system. Using flow injection sample introduction for flame-AAS a liquid volume of 2 ml is sufficient for determination of 10 elements. Determination of the remaining 6 elements by graphite furnace AAS requires 1 ml. The quality assurance programme is briefly described. It includes the analysis of standard reference materials, intercomparison with other laboratories and the use of alternative methods for accuracy control.     

The use of a polymer inclusion membrane in flow injection analysis for the on-line separation and determination of zinc

This paper reports the first use of a polymer inclusion membrane (PIM) for on-line separation in flow injection analysis (FIA) involving simultaneous extraction and back-extraction. The FIA system containing the PIM separation module was used for the determination of Zn(II) in aqueous samples in the presence of Mg(II), Ca(II), Cd(II), Co(II), Ni(II), Cu(II), and Fe(III). The Fe(III) and Cu(II) interferences were eliminated by off-line precipitation with phosphate and on-line complexation with chloride, respectively. The concentration of Zn(II) was determined spectrophotometrically using 4-(2-pyridylazo) resorcinol (PAR). The optimal composition of the PIM consisted of 40% (m/m) di(2-ethlyhexyl) phosphoric acid (D2EHPA) as carrier, 10% (m/m) dioctyl phthalate (DOP) as plasticizer and 50% (m/m) poly(vinyl chloride) (PVC) as the base polymer. The optimized FIA system was characterized by a linear calibration curve in the range from 1.0 to 30.0 mg L⁻¹ Zn(II), a detection limit of 0.05 mg L⁻¹ and a relative standard deviation of 3.4% with a sampling rate of 4 h⁻¹. Reproducible results were obtained for 20 replicate injections over a 5 h period which demonstrated a good membrane stability. The FIA system was applied to the determination of Zn(II) in pharmaceuticals and samples from the galvanizing industry and very good agreement with atomic absorption spectrometry was obtained.     

A novel flow injection chemiluminescence determination of Cr(VI) with Dichlorotris(1,10-phenanthroline)ruthenium(II)

A selective novel reverse flow injection system with chemiluminescence detection (rFI-CL) for the determination of Cr(VI) in presence of Cr(III) with Dichlorotris (1,10-phenanthroline)ruthenium(II), (Ru(phen)₃Cl₂), is described in this work. This new method is based on the oxidation capacity of Cr(VI) in H₂SO₄ media. First, the Ruthenium(II) complex is oxidized to Ruthenium(III) complex by Cr(VI) and afterwards it is reduced to the excited state of the Ruthenium(II) complex by a sodium oxalate solution, emitting light inside the detector. The intensity of chemiluminescence (CL) is proportional to the concentration of Cr(VI) and, under optimum conditions, it can be determined over the range of 3-300 μg L⁻¹ with a detection limit of 0.9 μg L⁻¹. The RSD was 8.4% and 1.5% at 5 and 50 μg L⁻¹, respectively. For the rFI-CL method various analytical parameters were optimized: flow rate (1 mL min⁻¹), H₂SO₄ carrier concentration (20% w/V), Ru(phen)₃Cl₂ concentration (5 mM) and sodium oxalate concentration (0.1 M). The effect of Cr(III), Fe(III), Al(III), Cd(II), Zn(II), Hg(II), Pb(II), Ca(II) and Mg(II), was studied. The method is highly sensitive and selective, allowing a fast, on-line determination of Cr(VI) in the presence of Cr(III). Finally, the method was tested in four different water samples (tap, reservoir, well and mineral), with good recovery percentage.     

Determination of inorganic and total mercury by vapor generation atomic absorption spectrometry using different temperatures of the measurement cell

A simple and inexpensive laboratory-built flow injection vapor generation system coupled to atomic absorption spectrometry (FI-VG AAS) for inorganic and total mercury determination has been developed. It is based on the vapor generation of total mercury and a selective detection of Hg^2 + or total mercury by varying the temperature of the measurement cell. Only the inorganic mercury is measured when the quartz cell is at room temperature, and when the cell is heated to 650 °C or higher the total Hg concentration is measured. The organic Hg concentration in the sample is calculated from the difference between the total Hg and Hg^2 + concentrations. Parameters such as the type of acid (HCl or HNO₃) and its concentration, reductant (NaBH₄) concentration, carrier solution (HCl) flow rate, carrier gas flow rate, sample volume and quartz cell temperature, which influence FI-VG AAS system performance, were systematically investigated. The optimized conditions for Hg^2 + and total Hg determinations were: 1.0 mol l^− 1 HCl as carrier solution, carrier flow rate of 3.5 ml min^− 1, 0.1% (m/v) NaBH₄, reductant flow rate of 1.0 ml min^− 1 and carrier gas flow rate of 200 ml min^− 1. The relative standard deviation (RSD) is lower than 5.0% for a 1.0 μg l^− 1 Hg solution and the limit of quantification (LOQ, 10 s) is 55 ng g^− 1. Certified samples of dogfish muscle (DORM-1 and DORM-2) and non-certified fish samples were analyzed, using a 6.0 mol l^− 1 HCl solution for analyte extraction. The Hg^2 + and CH₃Hg⁺ concentrations found were in agreement with certified ones.     

Determination of lead,cadmium and mercury in blood for assessment of environmental exposure: A comparison between inductively coupled plasma–mass spectrometry and atomic absorption spectrometry

A biomonitoring method for the determination of Pb, Cd, and Hg at background levels in whole blood by inductively coupled plasma-mass spectrometry is described. While this method was optimized for assessing Pb, Cd and Hg at environmental levels, it also proved suitable for assessing concentrations associated with occupational exposure. The method requires as little as 200 μl of blood that is diluted 1 + 49 for direct analysis in the inductively coupled plasma-mass spectrometer. Method performance is compared to well-established AAS methods. Initial method validation was accomplished using National Institute of Standards and Technology (NIST) Standard Reference Material 966, Toxic Metals in Bovine Blood. Method detection limits (3s) are 0.05 μg dl^− 1 for Pb, 0.09 μg l^− 1 for Cd; and 0.17 μg l^− 1 for Hg. Repeatability ranged from 1.4% to 2.8% for Pb; 3% to 10% for Cd; and 2.6% to 8.8% for Hg. In contrast, AAS method detection limits were 1 μg dl^− 1, 0.54 μg l^− 1, and 0.6 μg l^− 1, for Pb, Cd, and Hg, respectively. Further performance assessments were conducted over a 2-year period via participation in four international External Quality Assessment Schemes (EQAS) operated specifically for toxic metals in blood. This includes schemes operated by (a) the New York State Department of Health's Wadsworth Center, Albany, NY, USA (b) L′Institut National de Santé Publique du Québec, Centre de Toxicologie du Québec, Canada, (c) Friedrich-Alexander University, Erlangen, Germany, and (d) the University of Surrey, Guildford, UK Trace Elements scheme. The EQAS data reflect analytical performance for blind samples analyzed independently by both inductively coupled plasma-mass spectrometry and AAS methods.     

Determination of trace impurities in titanium dioxide by direct solid sampling electrothermal atomic absorption spectrometry

A true direct solid sampling electrothermal atomic absorption spectrometry method with Zeeman-effect background correction (Analytik Jena ZEEnit 60 AAS) was developed for the determination of As, Cd, Hg, Pb, Sb and Zn in powdered titanium dioxide of pharmaceutical, food and cosmetics grade. The interaction of the titanium matrix and graphite surface of the sample carrier boat in a transversely heated graphite tube atomizer was investigated. Conversion of titanium dioxide to interfering TiO₂–TiC-liquid phase, running out the sampling boat, was observed at temperatures above 2000 °C. The temperature program was optimized accordingly for these volatile analytes in atomization and cleaning steps in order to prevent this interference and to prolong significantly the analytical lifetime of the boat to more than one thousand runs. For all elements, calibration by aqueous standard addition method, by wet-chemically analyzed samples with different content of analytes and/or by dosing one sample in different amounts, were proved as adequate quantification procedures. Linear dynamic calibration working ranges can be considerably expanded up to two orders of magnitude within one measurement run by applying three-field dynamic mode of the Zeeman background correction system. The results obtained by true direct solid sampling technique are compared with those of other independent, mostly wet-chemical methods. Very low limits of detection (3σ criterion) of true solid sampling technique of 21, 0.27, 24, 3.9, 6.3 and 0.9 ng g^− 1 were achieved for As, Cd, Hg, Pb, Sb and Zn, respectively.     

Preconcentration of trace metals from acidic solutions by coprecipitation with dithizone

Traces of Ag, Bi, Cd, Cu, Hg, Pb, Pd and Zn are separated by carrier precipitation with dithizone from diluted HNO₃ and HCl solutions. The separated trace elements are determined by flame AAS and/or by spectrophotometry. The preconcentration recovery is dependent on the acid concentration of the sample solution. The amount of dithizone precipitated is optimized. The detection limits (ng/ml) are 15.0 (Pb, Zn), 12.0 (Pd), 10.0 (Bi), 6.0 (Ag), 5.0 (Hg), 2.0 (Cu) and 1.0 (Cd). Aluminium, aluminium sulfate and gallium are analyzed with the method. The accuracy of the results was checked by differential pulse voltammetry.     

Mercury Speciation in Fish by High-Performance Liquid Chromatography (HPLC) and Post-Column Ultraviolet (UV)-Photochemical Vapor Generation (PVG): Comparison of Conventional Line-Source and High-Resolution Continuum Source (HR-CS) Atomic Absorption Spectrometry (AAS)

An ultraviolet-photochemical generator (UV-PVG) capable of post-column on-line transformation of both organic and inorganic mercury species to cold vapor (Hg⁰) with subsequent detection by quartz tube-atomic absorption spectrometry (QT-AAS) was developed. Mercury(II), methylmercury(I), ethylmercury(I), and phenylmercury(I) were successfully detected after separation by reversed-phase high-performance liquid chromatography (RP-HPLC). Two types of AAS detectors were compared. The first was a commonly used line-source instrument while the second was a high-resolution continuum source (HR-CS) AAS. The latter provided better limits of detection: 0.47?µg?L^?1 for Hg(II), 0.84?µg?L^?1 for methylmercury(I), 0.80?µg?L^?1 for ethylmercury(I), and 2.0?µg?L^?1 for phenylmercury(I). The repeatability at 30?μg?L^?1 was 3.6%, 4.1%, 6.2%, and 4.5% for these species (n?=?10). These figures of merit were comparable with those reported for more sensitive atomic fluorescence spectrometry. Nine sample extraction procedures were investigated. Extraction by tetramethylammonium hydroxide and HCl at 75?°C was selected as the only method compatible with the proposed separation and detection steps providing high extraction efficiency and no changes in mercury speciation. The applicability of the proposed high-performance liquid chromatography–ultraviolet-photochemical vapor generation–quartz tube-atomic absorption spectrometry method was demonstrated using fish samples and certified reference materials (CRM) DOLT-4 (dogfish liver) and ERM-CE464 (tuna fish). The results were comparable to those obtained by a reference method based on L-cysteine extraction and high-performance liquid chromatography–inductively coupled plasma-mass spectrometry (HPLC–ICP-MS) determination.     

Flow injection analysis system for monitoring of succinic acid in biotechnological processes

In this study, a flow injection analysis (FIA) system using a cartridge of immobilized isocitrate lyase (ICL) and isocitrate dehydrogenase (ICDH) was developed to monitor the concentrations of succinic acid in biotechnological processes. The ICL and ICDH immobilized on VA-Epoxy Biosynth E3-carrier had a good operational lifetime (up to 24 h) and storage stability (up to 30 days). The FIA system with the immobilized ICL/ICDH cartridge was characterized with respect to the factors affecting the activity of the immobilized enzymes, such as pH of carrier solution, temperature, sample matrix, etc. Optimal pH value of the immobilized enzymes was slightly shifted in the alkaline range, i.e. 9.0. Some components such as 10 g l⁻¹ lactose, 3 g l⁻¹ malate and 3 g l⁻¹ oxaloacetate in sample solution had significant activating effects (more than 10%) on the response of the FIA system. But the activity of the immobilized ICL and ICDH was not largely influenced by some components like imidazole (1 mM), sodium azide (10 mM) and semicarbazide (2 g l⁻¹) added to carrier buffer solution. The FIA system with an enzyme cartridge was applied to on-line monitor the concentrations of succinic acid in a continuously stirred reactor and a fermentation process of immobilized Escherichia coli, and showed good sensitivity and reliability of the FIA system developed in this work.     

Interference of nitrite and nitrogen dioxide on mercury and selenium determination by chemical vapor generation atomic absorption spectrometry

In this study, a systematic investigation was performed concerning the interference of nitrogen oxides on the determination of selenium and mercury by hydride generation atomic absorption spectrometry (HG AAS) and cold vapor atomic absorption spectrometry (CV AAS). The effect of nitrate, nitrite and NO₂ dissolved in the condensed phase was evaluated. No effect of NO₃⁻ on Se and Hg determination was observed up to 100 mg of sodium nitrate added to the reaction vessel. The Se signal was reduced by about 80% upon the addition of 6.8 mg NO₂⁻. For Hg, no interference of nitrite was observed up to 20 mg of NO₂⁻. A complete suppression of the Se signal was observed when gaseous NO₂ was introduced into analytical solutions. For Hg, a signal decrease between 8 and 13% occurred. For Se, bubbling argon or heating the solution was not able to recover the original absorbance values, whereas Hg signals were recovered with these procedures. When gaseous NO₂ was passed directly into the atomizer, Se signals decreased similarly to when NO₂ was bubbled in analytical solutions. The addition of urea, hydroxylamine hydrochloride and sulfamic acid (SA) was investigated to reduce the NO₂ effect in sample digests containing residual NO₂, but only SA was effective in reducing the interference. Based on the results, it is possible to propose the use of SA to prevent interferences in Se and Hg determinations by HG AAS and CV AAS, respectively.     

On-line determination of mercury(II) by membrane separation flow injection analysis

A rapid and inexpensive gas-diffusion (GD) flow injection method for the on-line determination of Hg(II) in aqueous samples is described. The analytical procedure involves the injection of a Hg(II) sample into a 1.5 M H₂SO₄ carrier stream which is merged with a reagent stream containing 0.6% SnCl₂ and 1.5 M H₂SO₄. Under these conditions Hg(II) is reduced to metallic mercury which partially evaporates through a Teflon membrane into an acceptor stream containing 1.75×10⁻⁴ M KMnO₄ in 0.3 M H₂SO₄. The decrease in the absorbance of the acceptor stream at 528 nm corresponding to the absorption maximum of the permanganate anion can be related to the original concentration of Hg(II) in the sample. The method is characterized by a detection limit of 4 μg l⁻¹ and a sampling frequency of 8 h⁻¹. The flow system was successfully applied to the analysis of river samples spiked with Hg(II).     

Flow injection determination of anisidine value in palm oil samples using a triiodide potentiometric detector

A flow injection analysis (FIA) procedure for the determination of anisidine value (AV) in palm olein using a triiodide detector is described. Undiluted oil sample and chloramine-T reagent were added to a reaction chamber, and reaction was accelerated by applying a short vortex action (typically for 30 s). After allowing the emulsified oil phase to be separated from the aqueous phase (bottom layer), an aliquot of the aqueous phase (containing unreacted chloramine-T) was aspirated into a carrier stream that contained I⁻ where the chloramine-T oxidized the I⁻ to form I₃⁻ which was finally detected by a flow-through triiodide potentiometric detector. Variables that affect the FIA signals such as size of the reaction chamber, oil and reagent flow rates, chloramine-T concentration, vortex time, time for phase separation, carrier stream pH and injected volume were studied. The optimized FIA procedure is linear over 1.0-23.0 AV. The method exhibits good repeatabililty (R.S.D. of ±3.16% (n = 4) for the determination of 5.0 AV) and a sampling rate of 40 samples per hour was achieved. Good correlation (r² = 0.996 (n = 4)) between the proposed method and the manual American Oil Chemists’ Society procedure was found when applied to the determination of twenty different types of palm olein samples.     

Anodic Stripping Voltammetry Combined with Sequential Injection Analysis for Measurements of Trace Metal Ions with Bismuth‐ and Antimony Film Electrodes under Comparable Conditions

Anodic stripping voltammetry combined with sequential injection analysis (ASV‐SIA) was selected to examine the use of bismuth‐ and antimony‐film plated glassy carbon electrodes under comparable conditions for the determination of Pb(II) and Cd(II) ions. Of interest were the conditions for film deposition, as well as the composition of sample/carrier solutions, including concentrations of Sb(III) or Bi(III) and HCl. Then, by the optimized procedure, one could determine Pb(II), Cd(II), and Zn(II) ions at the low µg L^?1 level and ASV‐SIA configuration with both electrodes tested on analysis of a water sample.     

Simultaneous flow injection speciation of iron(II) and iron(III) cyano complexes utilizing electrochemical and atomic absorption detectors in series

Summary A method is described for the simultaneous speciation of Fe(CN) ₆ ^4– and Fe(CN) ₆ ^3– in a flow injection (FIA) system comprising electrochemical (EC) and flame atomic absorption spectrometry (AAS) detectors in series. One of these species is detected amperometrically at a Pt-electrode by applying the required potential and measuring the resulting reduction or oxidation current of the appropriate iron cyanide complex. Total iron in both species is determined by an AAS detector. The EC detector is inherently more sensitive, with a detection limit of 0.5 g Fe l^–1 and a relative standard deviation of 1.0% for a 0.040 g Fe ml^–1 sample. The limit of detection for the AAS detector is 0.5 g Fe ml^–1, and the relative standard deviation for a 5.70 g Fe ml^–1 sample is 0.40%. The method enables up to 60 analyses (120 speciations) per hour and obviates the problem of easy oxidation of Fe(CN) ₆ ^4– .

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Simultane Speziation von Eisen(II)- und Eisen(III)-Cyanokomplexen durch Flie\injektionsanalyse mit Hilfe von hintereinander geschalteten elektrochemischen und AAS-Detektoren

     

Evaluation of high pressure oxygen microwave-assisted wet decomposition for the determination of mercury by CVAAS utilizing UV-induced reduction

The UV-induced cold vapor generation with formic acid coupled to AAS after high pressure oxygen microwave decomposition was developed for determination of total Hg in analytical samples. Certified reference materials were decomposed in 1.5 mol L^{− 1} HNO₃ and 0.6 mol L^{− 1} H₂O₂. Microwave decomposition with oxygen has allowed the use of diluted reagents. The oxygen at a pressure of ca. 15 bar was delivered during the mineralization to the closed vessel. Interference by unused residues of H₂O₂ and HNO₃ was observed. In order to overcome the negative effect of remaining oxidants pre-reduction with hydroxylammonium chloride at a concentration 0.75 mmol L^{− 1} was used. Recovery of mercury in four reference materials containing 0.20–1.99 µg g^{− 1} Hg were 99–104% of certificate values. The limits of detection and quantification in the sample solutions were determined as 0.12 and 0.38 µg L^{− 1}, which corresponds to absolute detection limits of 12 and 38 ng g^{− 1} for total mercury, respectively. The results were in good agreement with the t-test at a 95% confidence level of the certified values in the investigated reference materials. The relative standard deviation was better than 7% for most of the samples.     

Spectrophotometric study of Cd(II), Pb(II), Hg(II) and Zn(II) complexes with 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin

The reaction of 5,10,15,20-tetrakis(4-carboxylphenyl)porphyrin (TCPP) with Cd(II), Pb(II), Hg(II) and Zn(II) was studied spectrophotometrically and kinetics, equilibrium constants as well as photodecomposition of complexes were determined. It was verified that these metal ions with large radius accelerate the incorporation reaction of zinc into TCPP. On the basis of the mechanism and kinetics of this reaction, a sensitive method for the spectrophotometric determination of trace amounts of Zn(II) has been developed. The molar absorptivity of examined Zn-TCPP complex and Sandell's sensitivity at 423 nm were 3.5×10⁵ M⁻¹ cm⁻¹ and 18.3 ng cm⁻². The detection limit for the recommended procedure was 1.4×10⁻⁹ M (0.9 ng ml⁻¹) and precision in range 20-100 ng ml⁻¹ not exceeds 2.7% RSD. The proposed method applied for zinc determination in natural waters and nutritional supplement was compared with AAS results and declared value.