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Analytical and Bioanalytical Chemistry (v.370, #1)

Cyclodextrins as electrode modifiers by A. Ferancová; J. Labuda (pp. 1-10).

Complexation abilities and analytical applications of working electrodes with attached cyclodextrins (CDs) are reviewed. For the immobilization of CDs, their adsorption and formation of self-assembled monolayers, preparation of polymer films, as well as incorporation within plasticized membranes and composites such as carbon paste and gels are considered. Some electrochemical investigations of the CD interactions in solution are also reported with respect to their use at CD modified electrodes.

Critical outlook and trends for environmental reference materials at the Measurements & Testing Generic Activity (European Commission) by Ph. Quevauviller; D. Bennink; S. Bøwadt (pp. 11-15).

It is now well recognised that the quality control (QC) of all types of analyses, including environmental analyses depends on the appropriate use of reference materials. One of the ways to check the accuracy of methods is based on the use of Certified Reference Materials (CRMs), whereas other types of (not certified) Reference Materials (RMs) are used for routine quality control (establishment of control charts) and interlaboratory testing (e.g. proficiency testing). The perception of these materials, in particular with respect to their production and use, differs widely according to various perspectives (e.g. RM producers, routine laboratories, researchers). This review discusses some critical aspects of RM use and production for the QC of environmental analyses and describes the new approach followed by the Measurements & Testing Generic Activity (European Commission) to tackle new research and production needs.

A two-dimensional immune algorithm for resolution of overlapping two-way chromatograms by L. Sun; Wensheng Cai; X. Shao (pp. 16-21).

A two-dimensional immune algorithm is proposed for resolving the multicomponent overlapping two-way data matrices. The method is a development of the one-dimensional immune algorithm proposed elsewhere. When the inner product of vectors is expanded to the similar operation on matrices, the 1D immune algorithm can be expanded to the 2D algorithm which is suitable for the analysis of two-way data matrices. Both simulated and experimental two-way data sets were investigated by the method, and the results prove that the 2D immune algorithm is an effective tool for resolving the overlapping two-way signals. The effect of noise on the recoveries is also discussed.

Flow-injection spectrophotometric multidetermination of metallic ions with a single reagent exploiting multicommutation and multidetection by Fábio R. P. Rocha; B. F. Reis; Jarbas J. R. Rohwedder (pp. 22-27).

A flow system designed by computer-controlled discrete commutation devices is proposed for the multidetermination of metallic ions with a single chromogenic reagent. Intermittent addition of masking agents and changes of the reaction pH were exploited to implement selective determination of four species. Multidetection with an optical-fiber CCD-array spectrophotometer enabled simultaneous measurements at different wavelengths for multidetermination. The proposed system was applied to the determination of iron, copper, nickel and zinc in alloys and pharmaceutical preparations, yielding results in agreement with those obtained by flame atomic absorption spectrophotometry at the 95% confidence level. The sampling rate was estimated to be 80 determinations per hour. Coefficients of variation lower than 2% (n = 20) were achieved for all species.

Example of a technique for evaluation of interferences caused by complicated sample matrix elements in ICP–AES determination by P. Hautaniemi; Rose Matilainen (pp. 28-32).

An example of a useful and rapid procedure for the evaluation of interferences caused by complicated sample matrices in inductively coupled plasma atomic emission spectrometry (ICP–AES) is described. Using simple acid–base standards, all the elements investigated were determined separately in complicated matrices with satisfactory results. Multiple linear regression was used to calculate the linear correction coefficients for each matrix element analyzed. Good analytical results improved still further when this correction method was used.

Maltodextrins as new chiral selectors in the design of potentiometric, enantioselective membrane electrodes by R.-I. Stefan; J. F. van Staden; Hassan Y. Aboul-Enein; J. F. van Staden (pp. 33-37).

Maltodextrins (dextrose equivalent (DE) 4.0– 7.0, 13.0–17.0, and 16.5–19.5) are proposed as novel chiral selectors for the construction of potentiometric, enantioselective membrane electrodes. The potentiometric, enantioselective membrane electrodes can be used reliably for the assay of S-captopril as raw material and in pharmaceutical formulations such as Novocaptopril tablets, by use of direct potentiometry. The best response was obtained when maltodextrin with higher DE was used for construction of the electrode. The best enantioselectivity and time-stability was achieved for the lower DE maltodextrin. L-proline was found to be the main interferent for all the proposed electrodes. The surface of the electrodes can be regenerated by simply polishing; this furnishes a fresh surface ready for use in a new assay.

The validation of Kayzero-assisted NAA in Budapest, Řež, and Ljubljana via the analysis of three BCR certified reference materials by F. De Corte; R. van Sluijs; András Simonits; J. Kučera; Borut Smodiš; Anthony R. Byrne; Antoine De Wispelaere; D. Bossus; Jaroslav Frána; Zbyněk Horák; Radojko Jaćimović (pp. 38-41).

After installation and calibration of k₀-assisted NAA in three Central European research institutes (AEKI-Budapest, NPI-Řež, and IJS, Ljubljana), its validation was established via the analysis of three BCR certified reference materials. The matrices of choice were: CRM 277 estuarine sediment, CRM 038 coal fly ash from pulverized coal, and CRM 101 spruce needles. For some elements, e.g. Zn, Cd, and Hg, the analyses were not only performed instrumentally (INAA), but also in the radiochemical mode (RNAA). The work was performed in the framework of a European Copernicus Project.

The certification of SRM 1546 – Meat Homogenate, a new reference material for nutrients in a high protein, high fat matrix by M. J. Welch; Jennifer C. Colbert; Lisa M. Gill; Curtis S. Phinney; Katherine E. Sharpless; Lorna T. Sniegoski; Laura J. Wood (pp. 42-47).

In response to reference material needs expressed by the food industry and government regulators, the National Institute of Standards and Technology (NIST) has developed a new Standard Reference Material (SRM) consisting of a canned meat product with certified and reference values for a large number of constituents. SRM 1546 Meat Homogenate consists of a mixture of finely ground pork and chicken prepared and canned by a commercial process. NIST determined the concentration levels of cholesterol, sodium, calcium, iron, and seven fatty acids in this SRM using well defined methods and procedures. These analytes as well as 34 other constituents or properties were determined in an interlaboratory comparison exercise involving 21 laboratories, most of which are associated with the National Food Processors Association (NFPA) Food Industry Analytical Chemists Subcommittee (FIACS). From statistical analysis of the data, NIST assigned certified concentrations for the eleven analytes measured at NIST and reference concentrations for the proximates, six additional fatty acids, seven minerals, and seven water-soluble vitamins. Information values without uncertainties are provided for the concentrations of six additional constituents for which the uncertainties could not adequately be assessed. SRM 1546 will provide laboratories with a means to evaluate the accuracy of the methods they use to assign nutrient levels to processed meats and similar products.

Determination of hydrogen ion by ion chromatography (IC) with sulfonated cation-exchange resin as the stationary phase and aqueous EDTA (ethylenediamine-N,N,N′,N′-tetraacetic acid) solution as the mobile phase by W. Hu; Alexander Iles; Kiyoshi Hasebe; Hidenori Matsukami; Shunan Cao; Kazuhiko Tanaka (pp. 48-51).

An ion chromatographic (IC) method has been developed for determination of hydrogen ion (H⁺). It is based on the use of sulfonated cation-exchange resin as stationary phase, aqueous ethylenediamine-N,N,N′,N′-tetraacetic acid (dipotassium salt, EDTA-2K, written as K₂H₂Y) solution as mobile phase, and conductivity for detection. H⁺ was separated mainly by cation-exchange, but its elution was accelerated by the presence of EDTA. The order of elution for the model cations was H⁺ > Li⁺ > Na⁺ > NH₄ ⁺ > Ca²⁺ > > Mg²⁺. A sharp and highly symmetrical peak was obtained for H⁺ and this was attributed to the capacity of H₂Y₂ ^2– to receive and bind H⁺. H⁺ was detected conductiometrically and detector response (reduction in conductivity as a result of H⁺+H₂Y^2–→H₃Y^–) was linearly proportional to the concentration of H⁺ in the sample. The detection limit for H⁺ with this IC system was better than 4.7 μmol L^–1. A significant advantage of this method was the ability to separate and determine, in one step, H⁺ and other cations. The successful determination of H⁺ and other cation species in real acid-rain samples demonstrated the usefulness of this method.

Application of high-surface-area ZrO2 in preconcentration and determination of 18 elements by on-line flow injection with inductively coupled plasma atomic emission spectrometry by E. Vassileva; N. Furuta (pp. 52-59).

A flow-injection analysis (FIA) system incorporating a micro-column of ZrO₂ has been used for the development of an on-line multi-element method for the simultaneous preconcentration and determination of Al, Bi, Cd, Co, Cr, Cu, Fe, Ga, In, Mn, Mo, Ni, Pb, Tl, V, Sb, Sn, and Zn by inductively coupled plasma atomic emission spectrometry (ICP–AES). The conditions for quantitative and reproducible preconcentration, elution, and subsequent on-line ICP–AES determination were established. A sample (pH 8) is pumped through the column at 3 mL min^–1 and sequentially eluted directly into the ICP–AES with 3 mol L^–1 HNO₃. With a sample volume of 100 mL and an elution volume of 1 mL signal enhancement 100 times better than for conventional continuous aspirating systems was obtained for the elements studied. The reproducibility (RSD %) of the method at the 10 ng mL^–1 level in the eluate is acceptable – less than 8% for five replicates. Recoveries between 95.4% and 99.9% were obtained for the elements analysed. ZrO₂, with a specific surface area of 57 m² g^–1 and a capacity of approximately 5 mg g^–1 for the elements studied, was synthesized by hydrolysis of ZrCl₄. The preconcentration system was evaluated for several simple synthetic matrices, standard water samples and synthetic seawater. The effect of foreign ions on the efficiency of preconcentration of the elements studied was investigated. The application of a micro-column filled with high-surface-area ZrO₂ and flow injection inductively coupled plasma atomic emission spectrometry enables preconcentration and simultaneous determination of 18 elements at low concentrations (ng L^–1) in different water samples.

Determination of elemental sulfur in coal by gas chromatography – mass spectrometry by Grażyna Gryglewicz; Stanisław Gryglewicz (pp. 60-63).

A method for the determination of S⁰ in coal based on the extraction with cyclohexane with subsequent quantitative analysis of elemental sulfur in the extract by GC/MS is described. The quantity of elemental sulfur was determined in four coal samples with different distribution of sulfur forms. The effect of solvent and extraction time on the efficiency of sulfur removal was studied. The elemental sulfur extracted from coal occurred in the form of S₆, S₇ and S₈. Calibration solutions were prepared from freshly recrystalized elemental sulfur. It was found that the injection temperature has a crucial influence on the m/z 64 ion chromatogram.

Determination of trace amounts of lead in mussels by flow-injection flame atomic-absorption spectrometry coupled with on-line minicolumn preconcentration by M. C. Yebra; M. F. Enríquez; A. García; A. Moreno-Cid (pp. 64-68).

A minicolumn packed with poly(aminophosphonic acid) chelating resin incorporated in an on-line preconcentration system for flame atomic-absorption spectrometry was used to determine ultratrace amounts of lead in mussel samples at μg L^–1 level. The preconcentrated lead was eluted with hydrochloric acid and injected directly into the nebulizer for atomization in an air-acetylene flame for measurement. The performance characteristics of the determination of lead were: preconcentration factor 26.8 for 1 min preconcentration time, detection limit (3σ) in the sample digest was 0.25 μg g^–1 (dry weight) for a sample volume of 3.5 mL and 0.2 g sample (preconcentration time 1 min), precision (RSD) 2.3% for 25 μg L^–1 and 2.0% for 50 μg L^–1. The sampling frequency was 45 h^–1. The method was highly tolerant of interferences, and the results obtained for the determination of lead in a reference material testify to the applicability of the proposed procedure to the determination of lead at ultratrace level in biological materials such as mussel samples.

Direct mass-quantification of particulate deposits of polycyclic aromatic hydrocarbons by Fourier transform imaging microscopy by Chanan Sluszny; Vladimir V. Gridin; Valery Bulatov; I. Schechter (pp. 69-75).

Successful coupling of imaging microscopy with Fourier transform spectrometry provides a new methodological approach. This was applied to the direct analysis of particulate deposits of polycyclic aromatic hydrocarbons (PAHs). The fluorescence signals of single microscopic particulates were found to be proportional to their mass, obtained from the corresponding HPLC results. Special fluorescence characteristics related to individual particle analysis were studied. The sensitivity of the proposed method to PAHs in soil is in the sub-ppb range, similar to HPLC results. Analysis of inhomogeneous PAH-particulates was demonstrated, as well as the resolution of photochemical products of PAHs. The effects of particulate orientation relative to the detector upon quantification are discussed.

An evaluation of analytical techniques for determination of lead, cadmium, chromium, and mercury in food-packaging materials by L. Perring; Marie-Isabelle Alonso; Daniel Andrey; Bernard Bourqui; Pascal Zbinden (pp. 76-81).

Closed microwave digestion and a high-pressure asher have been evaluated for wet-oxidation and extraction of lead, cadmium, chromium, and mercury from a range of typical packaging materials used for food products. For the high-pressure asher a combination of nitric and sulfuric acids was efficient for destruction of a range of packaging materials; for polystyrene, however, nitric acid alone was more efficient. For microwave digestion, a reagent containing nitric acid, sulfuric acid, and hydrogen peroxide was used for all materials except polystyrene. Use of the high-pressure asher resulted in the highest recoveries of spiked lead (median 92%), cadmium (median 92%), chromium (median 97%), and mercury (median 83%). All samples were spiked before digestion with 40 μg L^–1 Cd, Cr, and Pb and 8 μg L^–1 Hg in solution. The use of indium as internal standard improved the accuracy of results from both ICP–MS and ICP–AES. Average recovery of the four elements from spiked packaging materials was 92 ± 14% by ICP–MS and 87 ± 15% (except for mercury) by ICP– AES. For mercury analysis by CVAAS, use of tin(II) chloride as reducing agent resulted in considerably better accuracy than use of sodium borohydride reagent.

Analytical performance of luminescent immunoassays of different format for serum daidzein analysis by M. A. Bacigalupo; A. Ius; P. Simoni; F. Piazza; A. Roda; K. D. R. Setchell (pp. 82-87).

Two sensitive competitive-type solid-phase immunoassays for serum daidzein analysis have been developed and optimized. The first is a chemiluminescent enzyme immunoassay that uses black polystyrene microtiter wells in which daidzein-specific antibodies raised in rabbits are immobilized and a daidzein derivative is coupled to horseradish peroxidase (HRP) as a label. The HRP activity of the antibody-bound tracer is measured with an enhanced chemiluminescent system (luminol/ H₂O₂/enhancer). The second immunoassay is based on the use of bovine serum albumin–daidzein derivative immobilized on microtiter plates and a secondary anti-rabbit IgG-Fc fragment conjugated with 4,7-bis(chlorosulfophenyl)-1,10-phenanthroline-2,9-dicarboxylic acid (BCPDA). Formation of the complex Eu³⁺-BCPDA enables time-resolved fluorescence-mode detection of the amount of antibody bound to the immobilized antigen. Both methods fulfilled all the requirements of accuracy and precision. The detection limit was the same for each method, 10 pg/ well; this is better than that of other immunoassays. The specificity of the two methods was different, because of their competitive-type mechanisms. The performance of the chemiluminescence method is better, because the cross-reactivity of the main interfering compound (genistein) was 5%, compared with 25% for the time-resolved fluoroimmunoassay.

Fluorescence immunoassay of α-fetoprotein with iron(III) tetrasulfonatophthalocyanine as a mimetic enzyme labeling reagent by Huang-Hao Yang; Qing-Zhi Zhu; Dong-Hui Li; P. Lin; Ma-tai Ding; J.-G. Xu (pp. 88-91).

A new fluorimetric immunoassay for α-fetoprotein (AFP) has been developed using a novel promising mimetic peroxidase, iron(III) tetrasulfonatophthalocyanine (FeTSPc), as a labeling reagent to catalyze the fluorescence reaction of P- hydroxyphenylacetic acid (P-HPA) and hydrogen peroxide (H₂O₂). In the competitive immunoassay, anti-AFP antibody was coated on a 96-well plate (polystyrene) and a constant amount of FeTSPc-labeled AFP and a known amount of test solution were added. Non-labeled and FeTSPc-labeled AFP compete for binding to the plate-bound antibody. After the immunoreaction, the immunochemically adsorbed FeTSPc–AFP conjugate moiety was determined by measuring the fluorescence produced in a solution containing P-HPA and H₂O₂. AFP can be determined in the concentration range of 1–300 ng mL^–1 with a detection limit of 0.5 ng mL^–1.

HPLC-based method using sample pre-column clean-up for the determination of methanethiol and ethanethiol in parenteral amino acid solutions by P. C. do Nascimento; Denise Bohrer; A. L. B. Rohlfes; Leandro M. de Carvalho; Adrain Ramirez (pp. 92-96).

A method has been developed for the chromatographic determination of methanethiol (MT) and ethanethiol (ET) as contaminants in amino acid parenteral nutrition (PN) solutions. The clean-up of the samples before chromatographic analysis was investigated by solid-phase extraction (SPE) on pre-columns filled with polyethylene powder (PE), aluminium oxide (AlOx), silica (SiOx), or polyurethane foam (PUF) as adsorbents. The thiols were more efficiently separated from the matrices by SPE on PUF pre-columns. Simultaneous derivatization and elution with DTNB (5,5′-dithiobis(2-nitrobenzoic acid)) enabled further discrimination between MT and ET by reversed-phase HPLC with spectrophotometric detection. The retention times for the derivatized MT and ET species were 12.5 and 23.0 min, respectively. Recoveries from spiked PN samples were calculated to be approximately 90%, and the MT and ET content of commercial PN solutions was determined using the methodology described. Detection limits of 15 and 10 μg L^–1 were calculated for MT and ET, respectively.

2-Chloroacetaldehyde induces εdA DNA adducts in DNA of Raji cells as demonstrated by an improved HPLC–fluorimetry method by B. Zielinski; M. Hergenhahn (pp. 97-100).

Etheno adducts in DNA are promutagenic lesions and are formed from vinyl chloride, urethane, and lipid peroxidation-derived products such as 4-hydroxynonenal. Such adducts were induced in a B-lymphoid cell line (Raji) by a metabolite of vinyl chloride, 2-chloroacetaldehyde. By modification of a method of Bedell et al., etheno dA was determined in 20 μg DNA by HPLC–fluorimetry. Our method has a detection limit of 5 fmol which is one two-hundredth that of the original method. By use of this method initial evidence was found that cigarette smoke can also induce etheno dA adducts in Raji cell DNA.

Voltammetric determination of cadmium(II) using a chemically modified electrode by Shengshui Hu; Kangbing Wu; Hongchao Yi; Xuan Dai; Dafu Cui (pp. 101-103).

An 1-(pyridylazo)-2-naphthol modified glassy carbon electrode has been investigated as sensor for the measurement of trace levels of Cd²⁺. Cd²⁺ is deposited on the surface of a PAN modified glassy carbon electrode at –1.10 V (vs. SCE) via forming Cd²⁺–PAN and subsequent reduction at the electrode. In the following step, Cd-PAN is oxidized, and voltammograms are recorded by scanning the potential in a positive direction. Calibration plots were found to be linear in the range 2 × 10^–8 mol/L to 8 × 10^–7 mol/L. The detection limit was 5 × 10^–10 mol/L, and the coefficient of variation, determined on one single electrode at a concentration of 5 × 10^–7 mol/L, was calculated to be 3.2% (n = 5). Using this new kind of modified electrode, trace levels of Cd(II) in water samples were determined; the average recovery was calculated to be 98.78%.

A simple and rapid in situ preconcentration method for the determination of phosphate in environmental waters by use of solid-phase extraction, and its applications to brackish lake waters by M. Okumura; L. Tong; Kaoru Fujinaga; Yasushi Seike (pp. 104-107).

A simple and rapid in situ preconcentration method for the determination of phosphate in environmental waters has been developed for field analysis. This method is based on solid-phase extraction on a zirconium-loaded Sep-Pack Accell CM cartridge (Zr-SP) and is applicable to studies in which sampling is performed by use of a graduated syringe to prevent contamination and to ensure easy operation at sampling sites. The Zr-SP cartridge was prepared by passing 0.1 mol L^–1 zirconium solution through a Sep-Pak Accell CM cartridge, packed with cation exchange sorbent based on a silica matrix. The adsorption of phosphate and its desorption depend only on the pH of the solution. A water sample containing phosphate was adjusted to pH 2 and passed through the Zr-SP cartridge to collect it. The retained phosphate was quantitatively eluted with 0.5 mol L^–1 sodium hydroxide solution. The phosphate retained in the Zr-SP cartridge was stable for at least one month. The established preconcentration method was successfully applied to brackish lake waters to investigate seasonal changes in the distribution and behavior of phosphate in a brackish lake.

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Analytical and Bioanalytical Chemistry (v.370, #1)