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Analytica Chimica Acta (v.542, #2)
Enzymatic protein digest in chip-based nanovials with immobilized proteolytic enzymes by Å. Emmer; J. Roeraade (pp. 137-143).
In the present work, protein digest reactions in silicon-based microchips, coated with immobilized proteolytic enzymes, have been carried out. The performance of such vials, modified with trypsin or chymotrypsin, was tested with myoglobin as a substrate. Capillary electrophoresis and matrix-assisted laser desorption/ionization mass spectrometry were utilized for analysis of the digests, and the influence of different instrumentation setups, immobilization procedures and reaction conditions are discussed.
Keywords: Protein digest; Immobilized enzymes; Nanovials; Capillary electrophoresis; MALDI-TOF MS
Functionalized semiconductor nanocrystals for ultrasensitive detection of peptides by Xudong Chen; Xinbo Wang; Lin Liu; Dacheng Yang; Li Fan (pp. 144-150).
Semiconductor CdS nanoparticle have been prepared and modified with thiovanic acid. The functionalized nanoparticles are water-soluble. They were used as the fluorescence probes in the ultrasensitive detection of peptides. This method is based on the fluorescence enhancement of functionalized nano-CdS in the presence of peptide with mercapto groups (GN-9) and the fluorescence quenching of functionalized nano-CdS in the presence of peptide (GA-8 and MT-25). Excitation and emission wavelengths were 360 and 530nm, respectively. Under optimum conditions, the calibration graphs are linear over the range of 0.15–3.5, 0.2–4.0, and 0.2–3.8μgml−1 for GN-9, GA-8 and MT-25, respectively. The corresponding detection limits were 0.010μgml−1 for GN-9, 0.018μgml−1 for GA-8 and 0.022μgml−1 for MT-25, respectively. This method has been proved to be a simple, rapid and sensitive method.
Keywords: Peptides; Semiconductor nanocrystals; Detection; Fluorescence
Classification of edible and lampante virgin olive oil based on synchronous fluorescence and total luminescence spectroscopy by Konstantina I. Poulli; George A. Mousdis; Constantinos A. Georgiou (pp. 151-156).
Total luminescence and synchronous fluorescence spectroscopies were tested as regards their ability to differentiate edible from lampante virgin olive oils. Total luminescence spectra were recorded by measuring the emission spectra in the range 350–720nm at excitation wavelengths from 320 to 535nm. The synchronous fluorescence spectra of 41 edible and 32 lampante virgin olive oils were acquired by synchronous scanning the excitation and emission monochromator maintained at an offset value of 80nm. Classification of virgin olive oils based on their synchronous fluorescence spectra was performed by hierarchical cluster analysis and principal component analysis using the spectral range of 429–545nm. Principal component analysis provided better discrimination between the two classes, without any classification error, while hierarchical cluster analysis allowed 97.3% correct classification. These results indicate the capability of fluorescence techniques to differentiate virgin olive oils according to their quality.
Keywords: Synchronous fluorescence spectroscopy; Total luminescence spectroscopy; Principal component analysis; Hierarchical cluster analysis; Virgin olive oil
Enzyme coated glass pH-electrode: Its fabrication and applications in the determination of urea in blood samples by Rachana Sahney; B.K. Puri; S. Anand (pp. 157-161).
A new enzyme coated electrode for the determination of urea in blood samples has been developed. It is based on the encapsulation of urease enzyme in the porous silicate matrix by the sol–gel technique on a glass electrode for the purpose of sensing urea in blood samples. Various parameters like the effect of pH, selection of a suitable buffer of appropriate concentration and interference of common substances in blood samples have been evaluated to optimize the conditions for the determination of urea. The electrode can be used for the determination of urea in the concentration range 0.03–30.0mM in a solution. The detection limit of the present enzyme-coated electrode is found to be 52μg/ml of urea. The relative standard deviation for the electrode-to-electrode reproducibility is found to be 2.4% for the determination of 0.1mM of urea (six replicate electrodes). Sol–gel matrix containing immobilized enzyme was stable for about 25 days at ∼4°C with 80% urease activity. Urea content in various clinical blood samples has been estimated using this electrode and the results are found to be in good agreement with the standard clinical methods as reported in the literature.
Keywords: Enzyme-coated electrode; Urea sensor; Sol–gel technique; Urea determination; Blood samples
Photoelectrochemical investigation of methylene blue immobilised on zirconium phosphate modified carbon paste electrode in flow injection system by Yusuf Dilgin; Zekerya Dursun; Gurel Nisli; Lo Gorton (pp. 162-168).
The adsorption of methylene blue (MB) onto zirconium phosphate (ZrP) was studied and the adsorption capacity value and isotherms were determined. The adsorption capacity of ZrP was increased after being exposed to gas phase n-butyl amine. The adsorbed MB on ZrP was used as a modifier material in carbon paste electrode (MCPE), which in turn was used in voltammetric investigations and flow injection (FI) amperometric determination of ascorbic acid (AA). A quasi-reversible electrode reaction of adsorbed MB was exhibited. A home made flow-through electrochemical cell with a suitable transparent window for irradiation of the electrode surface was constructed and used for amperometric FI studies. The photoamperometric-FI conditions were optimised as 1.5mLmin−1 flow rate, a 25cm transmission tubing length, a 100μL injection volume, and a constant applied potential of +100mV versus SCE. The calibration curve for AA was linear over the concentration range from 1.0×10−6 to 4.0×10−5M. The relative standard deviation of four replicate injections of 3.0×10−5M AA was 1.2%. The results obtained for AA determination in pharmaceutical products are in good agreement with those obtained using the procedure involving the reaction between triiodide and AA.
Keywords: Flow injection analysis; Modified electrode; Photoelectrocatalysis; Adsorption of methylene blue; Ascorbic acid; Zirconium phosphate
1H NMR-based metabonomics for the diagnosis of inborn errors of metabolism in urine by Maria A. Constantinou; Evangelos Papakonstantinou; Manfred Spraul; Sophia Sevastiadou; Christos Costalos; Michael A. Koupparis; Kleopatra Shulpis; Anna Tsantili-Kakoulidou; Emmanuel Mikros (pp. 169-177).
1H NMR-based metabonomics was used for the detection and diagnosis of inborn errors of metabolism from urine samples. 1D1H NMR spectra from 47 normal, 9 phenylketonuric (PKU) newborns and 1 maple syrup urine disease (MSUD) child were obtained and investigated. Urine1H NMR spectra of normal, PKU and MSUD samples exhibited differences concerning the phenylalanine (Phe) and branched-chain amino acids (leucine, valine, isoleucine) resonances, respectively. Principal component analysis (PCA) and partial least squares discriminant analysis (PLS-DA) were applied in order to establish adequate models for discrimination between pathological and normal samples. Normalization of the spectra was based to the total spectral intensity or to creatinine peak. Different data transformation procedures were used. Discrimination of PKU and MSUD samples from normal samples was achieved by the different models produced by PCA and PLS-DA. Comparing the two methods of statistical analysis, PLS-DA was found to lead to a most proper discrimination when all pathological samples were used, while PCA proved suitable to identify every single pathological sample among the physiological ones. Thus,1H NMR in urine can be considered as an alternative to blood spots in order to develop a mass-screening method, which does not require sample pre-treatment and avoids any painful procedure for the newborns.
Keywords: Nuclear magnetic resonance spectroscopy (NMR); Urine; Phenylketonuria (PKU); Maple syrup urine disease (MSUD); Principal component analysis (PCA); Partial least squares discriminant analysis (PLS-DA)
Strategies for organic impurity quantification by1H NMR spectroscopy: Constrained total-line-shape fitting by Pasi Soininen; Jorma Haarala; Jouko Vepsäläinen; Matthias Niemitz; Reino Laatikainen (pp. 178-185).
A constrained total-line-shape (CTLS) fitting strategy for organic impurity analysis from1H NMR spectra was developed and assessed by studying two examples. In general, total-line-shape fitting allows integration of overlapping lines without suffering from baseline artifacts as much as traditional integration methods. It is shown here that the constrained total-line-shape fitting, where the spectral structures of the multiplets to be fitted are taken into account in form of constraints, allows quantification of seriously overlapping lines and when the signals are close to the root of major signals. Also, a method for removal of13C satellite signals is described. The results indicate that our approach significantly improves the usefulness of qNMR in impurity analysis and that impurity levels of 0.1mol%, which in some cases means down to 0.01wt%, can be easily determined with relative standard error smaller than 10%.
Keywords: Drug impurity; 1; H NMR; Quantitative NMR; qHNMR; Deconvolution; Total-line-shape fitting
A computational and experimental investigation of the interaction between the template molecule and the functional monomer used in the molecularly imprinted polymer by Wenguo Dong; Ming Yan; Minlian Zhang; Zheng Liu; Yanmei Li (pp. 186-192).
A computational approach to screening monomer for preparing molecularly imprinted polymer (MIP) was proposed, using the binding energy, Δ E, of a template molecule and a monomer as a measure of their interaction. For a specified template molecule, a monomer of higher Δ E is suitable for preparing the MIP. To examine the validity of this approach, theophylline (THO) was chosen as the template molecule and methacrylic acid (MAA), acrylamide (AA) and 2-(trifluoromethyl)acrylic acid (TFMAA) were as the functional monomers, respectively. Density functional theory (DFT) at B3LYP/6-31+G**//B3LYP/3-21G level was used to calculate Δ E. It was shown that TFMAA gave the largest Δ E while AA gave the smallest. The details of the interaction between the THO with these monomers were also given by this computing approach. The adsorption of THO on the MIP synthesized using different monomers was studied. The MIP synthesized using TFMAA as monomer showed the highest selectivity to THO while the MIP from AA gave the lowest, as predicted from the Δ E calculation.1H NMR spectroscopy showed that, compared to MAA and AA, a stronger H-bond interaction is formed between TFMAA and THO. FT-IR analysis of the MIPs prepared using these three monomers confirmed the existence of CO and OH groups, which forms H-bond with THO. The results described above have given an insight into the interaction between THO and the monomers, and shown the use of Δ E to facilitate the selection of monomers for the synthesis of MIP.
Keywords: Molecularly imprinted polymer; Binding energy; Density functional theory; Theophylline
Adsorption properties of mesoporous silicas for organic pollutants in water by Y.X. Zhao; M.Y. Ding; D.P. Chen (pp. 193-198).
Synthesis of mesoporous silica materials is performed respectively using self-assembling micellar aggregates of two surfactants: cetylpyridinium bromide (CPB) and cetyltrimethylammonium bromide (CTAB). The retention properties have been studied of these two kinds mesoporous silicas towards environmental pollutants (mono-, di-, tri-chloroacetic acid, toluene, naphthalene and methyl orange). LC and suppressed ion chromatography have been used to evaluate the retaining amount of analytes on the mesoporous silica materials. The effect of the composition (presence and absence of surfactants, different kinds of surfactants) on the sorption performance has been considered. As-prepared materials show excellent retention performance toward chloroacetic acids, toluene, naphthalene and methyl orange. The materials without surfactants does not show, if any, affinity for ionic and non-ionic analytes.All this provides the basis for potential applications of these mesoporous silica materials as preconcentrators and sorptive chromatographic substrates for selective separation and/or enrichment (removal) of specific classes of analytes.
Keywords: Mesoporous silicas; Environmental pollutants; Sorption; Chromatography
Modelling of the association mechanism of a series of rodenticide molecules with lipid membrane investigated by computational chemistry and biochromatography by C. André; L. Ping; M. Thomassin; J.F. Robert; Y.C. Guillaume (pp. 199-206).
The increase of pest rodents population in urban and rural areas is tackled by dissemination of baits poisoned with anticoagulant compounds. In order to modelize the cell membrane transport of these rodenticides, which have toxic effect on human keratynocytes and break the vitamin K cycle, a new general model based on the perturbation method was developed to describe the association process between these rodenticide and an immobilized artificial membrane (IAM). The thermodynamic functions of the rodenticide transfer from the bulk solvent to the IAM surface were also determined. The variation plots of the solute transfer data versus the salt concentration ( x) in the bulk solvent allow to demonstrate that the rodenticides—IAM surface association mechanism was governed by both the hydrophobic effect and the van der Waals interactions/hydrogen bonds between the rodenticide polar groups with the polar headgroups of phospholipid monolayers (polar retention effect). This result was also corroborated by a comparison of the number of water molecules surrounded the rodenticide in the medium (obtained by computational chemistry) and the number of water molecule release at the IAM—rodenticide interface (obtained thanks to the Tanford's equation).
Keywords: Biochromatography; IAM surface; Rodenticide; Polar retention effect; Hydrophobic effect; Computational chemistry
Synthesis of chitosan resin possessing 3,4-diamino benzoic acid moiety for the collection/concentration of arsenic and selenium in water samples and their measurement by inductively coupled plasma-mass spectrometry by Akhmad Sabarudin; Koji Oshita; Mitsuko Oshima; Shoji Motomizu (pp. 207-215).
A chitosan resin functionalized with 3,4-diamino benzoic acid (CCTS-DBA resin) was newly synthesized by using a cross-linked chitosan (CCTS) as base material. The adsorption behavior of trace amounts of elements on the CCTS-DBA resin was examined by the pretreatment with a mini-column and measurement of the elements by inductively coupled plasma-Mass spectrometry (ICP–MS). Arsenic(V) could be retained on the CCTS-DBA resin at pH 3 as an oxoanion of H2AsO4−. Selenium(VI) is strongly adsorbed at pH 2 and pH 3 as an oxoanion of SeO42−, while selenium(IV) as HSeO3− is adsorbed on the resin at pH 3. The sorption capacities are 82, 64, and 88mgg−1resin for As(V), Se(IV), and Se(VI), respectively. The effect of common anions and cations on the adsorption of As(V), Se(IV), and Se(VI) were studied; there was no interference from such anionic matrices as chloride, sulfate, phosphate, and nitrate up to 20ppm, as well as from such artificial river water matrices as Na, K, Mg, and Ca after passing samples through the mini-column containing the resin. The CCTS-DBA resin was applied to the collection of arsenic and selenium species in bottled drinking water, tap water, and river water.
Keywords: Cross-linked chitosan; 3,4-Diamino benzoic acid; Arsenic; Selenium; ICP–MS
Enrichment of rare-earth elements (REE) and Gd-DTPA in surface water samples by means of countercurrent chromatography (CCC) by Kristina Hennebrüder; Werner Engewald; Hans-Joachim Stärk; Rainer Wennrich (pp. 216-221).
An analytical scheme was developed for the determination of rare-earth elements and gadolinium diethylenetriaminepentaacetate (Gd-DTPA) in river water by ICP-MS. Since the concentration of Gd-DTPA and the rare-earth elements in river water is often lower than the limits of detection in quadrupole ICP-MS applying pneumatic nebulization, a preconcentration procedure is essential.In this work, the capabilities of countercurrent chromatography (CCC) for preconcentration of REE were investigated. For preconcentration ethylhexylphosphates as stationary phase had been used. Acidified aqueous samples (pH 2) and river water spiked with REE and Gd-DTPA were under study. The procedure was compared with solid phase extraction (SPE) using the same samples and ethylhexylphosphates as stationary phase. The recovery of the light and middle REE was found to be at about 100%, which was found to be more efficient than applying SPE. In contrast, the recovery rates for Yb and Lu were low (and poorly reproducible) using CCC (57% and 73%, respectively) while significant better results were obtained with SPE (89% and 84%, respectively).The recoveries of Gd applying Gd-DTPA were 80±4% in the investigation of river water samples.
Keywords: Gd-DTPA; REE; ICP-MS; Preconcentration procedures; Countercurrent chromatography; River water
Polyelectrolyte complexes of poly(methacryloxyethyl trimethylammonium chloride) and poly(ethylene oxide)-block-poly(sodium methacrylate) studied by asymmetrical flow field-flow fractionation and dynamic light scattering by Gebrenegus Yohannes; Susanna Holappa; Susanne K. Wiedmer; Toni Andersson; Heikki Tenhu; Marja-Liisa Riekkola (pp. 222-229).
Polyelectrolyte complex (PEC) formation between cationic poly(methacryloxyethyl trimethylammonium chloride) (PMOTAC) and anionic poly(ethylene oxide)-block-poly(sodium methacrylate) (PEO- b-PMANa) was studied by asymmetrical flow field-flow fractionation and dynamic light scattering. The influence of ionic strength and mixing ratios of the charged units of the polyelectrolytes on the complex formation was evaluated. The diffusion coefficients and the hydrodynamic diameter distributions of the free and complexed polyelectrolytes were measured. In the absence of salt, the weight averaged hydrodynamic diameters were 48 and 28nm for PMOTAC and PEO- b-PMANa, respectively. In the presence of salt, the particles were smaller, with weight averaged hydrodynamic diameters of 44–45 and 8–10nm, respectively. In salt-free solution, at 1:1 mixing ratio of the charged monomer units of PMOTAC and PEO- b-PMANa, polydisperse particles with diameters of 2000–4000nm were formed. In the presence of 20, 80, and 160mM of sodium chloride, the 1:1 complexes were relatively monodisperse particles with weight averaged hydrodynamic diameters of 93, 124, and 120nm, respectively.
Keywords: Polyelectrolyte complexes; Asymmetrical flow field-flow fractionation; Dynamic light scattering; Particle size; Mixing ratio; Salt
Measurement and computation of zinc binding to natural dissolved organic matter in European surface waters by Tao Cheng; Karel De Schamphelaere; Steve Lofts; Colin Janssen; Herbert E. Allen (pp. 230-239).
The zinc binding characteristics of natural dissolved organic matter (DOM) from five representative European surface freshwater sources were studied by square wave anodic stripping voltammetry (SWASV) and model simulation. Water samples were titrated with zinc and free zinc ion activity {Zn2+}, was calculated from the measurement of labile zinc by SWASV and other system conditions. Measured values of {Zn2+}, which were in the range 10−7 to 10−5M, were compared with those simulated using Humic Ion-Binding Models V and VI. It was assumed that zinc speciation was controlled by the organic matter, represented by fulvic acid (FA), together with inorganic solution complexation. The models were calibrated by adjusting the parameter DOMFA, the proportion of DOM considered to behave as FA. Two modeling scenarios were used to obtain DOMFA values, both considering and not considering the competitive effects of Al, Fe(II) and Fe(III). The default Zn–DOM binding strength in Model VI (log KMA=1.6) was not able to provide realistic values of DOMFA and a log KMA of 1.8 was tentatively proposed as a more plausible value in these waters. Models V and VI gave very similar fits to the data after optimization of DOMFA, in contrast to recent findings for copper. This may be due to the fact that the additional strong binding sites provided by Model VI are not important in complexing Zn in the Zn concentration range investigated in this study. Computed free Zn activities from both modeling scenarios were very similar; however, the consideration of Al and Fe competition is more realistic for natural waters.
Keywords: Zinc complexation; Natural organic matter; Speciation modeling; WHAM
A study of complexation thermodynamic of humic acid with cadmium (II) and zinc (II) by Schubert's ion-exchange method by Hutaf Baker; Fawwaz Khalili (pp. 240-248).
The complexation of humic acid from Azraq Oasis with two heavy metal ions Cd(II) and Zn(II) was investigated at pH 4 and 5 under constant ionic strength of 0.1 and at different temperatures (25, 35, 45, 55 and 65°C). This investigation was done by using Schubert's ion-exchange equilibrium method, and its modified version.The derived conditional stability constants (log β n) for these two metal–humate complexes were determined; they formed 1:1 and 1:2 complexes. It was found that the conditional stability constants (log β n) increased by increasing pH and temperatures for all metal–humate complexes. It was found that the conditional stability constant log β1 for Cd–humate is bigger than Zn–humate at all the desired temperatures and at pH 4 and 5.The derived constants and their temperature dependences have been used to calculate the corresponding thermodynamic parameters Δ G, Δ H, and Δ S, the results indicate that the stability of these complexes derives from very favorable entropy.
Keywords: Humic acid; Schubert's method; Metal complexation; Equilibrium: Thermodynamic
Study of quantitative structure–mobility relationship of the peptides based on the structural descriptors and support vector machines by Huanxiang Liu; Xiaojun Yao; Chunxia Xue; Ruisheng Zhang; Mancang Liu; Zhide Hu; Botao Fan (pp. 249-259).
Support vector machines (SVM), as a novel learning machine, was used to develop the non-linear quantitative structure–mobility relationship model of the peptides based on the calculated descriptors for the first time. The molecular descriptors representing the structural features of the compounds included the constitutional and topological descriptors calculated by CODESSA program, which can be obtained easily without optimizing the structure of the molecule, and CPSA (charged partial surface area) descriptors obtained by SYBYL software. The MLR method was used to select the descriptors responsible for the electrophoretic mobility of peptides and develop the linear model. The prediction result of the SVM model ( ɛ=0.04, γ=0.002 and C=100) is much better than that obtained by MLR method. The RMS error of the training set, the test set and the whole set is 0.0569, 0.0553, 0.0565 and the prediction correlation coefficient is 0.925, 0.912 and 0.922, respectively. The prediction results are in agreement with the experimental values. This paper provided a new and effective method for predicting the electrophoretic behavior of peptide and some insight into what structural features are related to the electrophoretic mobility of peptides. Moreover, it also offered an idea about dealing with the structural optimization and obtaining their structural descriptors for biomacromolecules.
Keywords: Peptides; Quantitative structure–mobility relationship; Support vector machine; Electrophoretic mobility; Prediction
Fast GC analysis of major volatile compounds in distilled alcoholic beverages by Kevin Mac Namara; Riccardo Leardi; Andrew Sabuneti (pp. 260-267).
The principal secondary flavour compounds in distilled spirits can be successfully quantified by split injection to a 0.15mm internal diameter (I.D.) capillary column. Initial conditions for split ratio, gas velocity, initial oven temperature and oven ramp rate are given by method translation from a similar method on a standard 0.25mm internal diameter column with the same phase. These parameters were then investigated in an experimental design comprising a series of experiments in which the responses were the resolution of two critical peak pairs, the analysis time and the limit of quantification (LOQ) of the eight major compounds. The LOQ is the concentration corresponding to a signal 10 times greater than the noise. The experiments were replicated at two different concentration levels, which encompassed the natural levels of the compounds of interest found in distilled spirits. From the chemometric evaluation of these data, a validated model was constructed, which allowed the prediction of conditions for optimum chromatographic analysis. Three additional concentration levels were then added to the model to establish linearity, repeatability and sensitivity. Modern gas chromatographic hardware allows the use of these narrow-bore capillary columns for routine use without operational difficulties. Major advantages are a substantial decrease in analysis time allowing high throughput processing of samples.
Keywords: Distilled spirits; Narrow-bore column; Gas chromatography; Flavour compounds; Experimental design
Preparation and evaluation of n-octadecylphosphonic acid-modified magnesia–zirconia stationary phases for reversed-phase liquid chromatography by Hai-Bo He; Yu-Qi Feng; Qu-Li; Shi-Lu Da; Zhi-Xiong Hu (pp. 268-279).
Three n-octadecylphosphonic acid-modified magnesia–zirconia reversed stationary phases (C18PZM) are prepared via the strong Lewis base interactions between organophosphonate and magnesia–zirconia composite. And two of them are end-capped by using trimethylchlorosilane as end-capping agent in different procedures. Stability studies at extreme high pH conditions (pH 9–12) show that both the non-endcapped and endcapped columns are quite stable at pH 12 mobile phase. The reversed-phase liquid chromatographic behavior of three C18PZM stationary phases are comparatively investigated in detail using a variety of basic compounds as probes. The retention of basic compounds on the three phases is studied over a wide range of pHs. And the possible retention mechanisms of basic compounds on the three stationary phases are discussed. The results show that the basic solutes retain by a hydrophobic and cation-exchange interaction mixed mechanism on three stationary phases when they are operated in eluents at pH values near to the p Ka of the Brönsted conjugate acid form of the analyte, suggesting that inherent zirconol groups on ZM are not expected to interact with bases via cation-exchange interaction at lower pH. Nonetheless, the non-endcapped phase differs markedly from the edncapped ones in retention and selectivity of basic solutes using eluents at pH 4.1, implying a complex retention mechanism at this pH. The cation-exchange sites under such conditions are more likely due to the adsorbed Lewis base anionic buffer constituents (acetate) on accessible ZM surface sites than the chemisorbed phosphonate. Although the three phases exhibit very similar chromatographic behavior with eluents at pH 10.1, and show in general satisfactory separation of basic compounds and alkaloids studied, the performance for a specific analyte, however, differs largely from column to column.
Keywords: Stationary phases; Reversed-phase liquid chromatography; Magnesia–zirconia; Octadecylphosphonic acid-modified; Basic compounds; Alkaloids
Molybdenum, Mo–Ir and Mo–Ru coatings as permanent chemical modifiers for the determination of cadmium and lead in sediments and soil samples by electrothermal atomic absorption spectrometry by Orhan Acar (pp. 280-286).
Molybdenum, Ir, Ru, Mo–Ir, Mo–Ru thermally coated on to platforms inserted in pyrolytic graphite tubes as permanent modifiers and Pd+Mg(NO3)2 conventional modifier mixture have been employed for the determination of cadmium and lead in dissolved sediments and soil samples by electrothermal atomic absorption spectrometry (ETAAS). Optimum masses and mass ratios of permanent modifiers for the analysis of Cd and Pb in sample solutions have been investigated. The 280μg of Mo, 200μg of Ir, 200μg of Ru, 280μg of Mo+200μg of Ir or 280μg of Mo+200μg of Ru has been found as efficient as 5μg of Pd+3μg of Mg(NO3)2 for increasing thermal stabilization of analytes and for decreasing the most serious interferences. Pyrolysis and atomization temperatures, atomization and background signal shapes, characteristic masses and detection limits of analytes in dissolved samples with or without permanent and conventional modifiers have been compared. The detection limits and characteristic masses obtained with Mo–Ir coated platform are 0.01μgg−1 and 1.1pg for Cd and 0.09μgg−1 and 19pg for Pb, respectively. Long-term stabilities for analytes in samples with Mo, Mo–Ir, Mo–Ru and Pd+Mg(NO3)2 have been studied. Cadmium and lead contents have been determined in certified and standard reference materials by using optimum conditions investigated and the results obtained with Mo–Ir or Mo–Ru were in agreement with the values of certified reference materials.
Keywords: Permanent chemical modifiers; ETAAS; Cadmium; Lead; Soil; Sediment
Microwave-assisted alkaline digestion combined with microwave-assisted distillation for the determination of iodide and total iodine in edible seaweed by catalytic spectrophotometry by Diego Gamallo-Lorenzo; María del Carmen Barciela-Alonso; Antonio Moreda-Piñeiro; Adela Bermejo-Barrera; Pilar Bermejo-Barrera (pp. 287-295).
Microwave energy has been novelty applied to speed up a tetramethylammonium hydroxide (TMAH) alkaline digestion of seaweed samples and to assist distillation of iodine from seaweed alkaline digests. Iodide in the alkaline digests from seaweed and distilled iodine, reduced back to iodine in a hydroxylamine hydrochloride solution, was determined by a catalytic spectrophotometric method based on the catalytic effect of iodide on the oxidation of As(III) by Ce(IV) in H2SO4/HCl medium (Sandell–Kolthoff reaction). The determination of iodide was directly performed in the alkaline digests, while total iodine was assessed by analyzing the hydroxylamine hydrochloride solution after the distillation process. Microwave-assisted alkaline digestion was performed using 7.5mL of TMAH and irradiating samples at 670W for two 5.5min steps. Microwave-assisted distillation was carried out using 4.0mL of the alkaline digest and 3mL of a 2.2M hydrochloric acid and 0.05% (m/v) sodium nitrite solution, with a microwave power at 670W for two 90s steps. The distillate (iodine vapor) was bubbled in 10mL of a 500μgmL−1 hydroxylamine hydrochloride solution (accepting solution). The linear calibration ranges were 0.30–20.0 and 0.40–20.0μgL−1 for iodide determination and total iodine determination, respectively. The limit of detection was 9.2μgg−1 for iodide and 28.5μgg−1 for total iodine. Repeatability of the overall procedures, expressed as R.S.D. for 11 determinations, was 2.6% for 196.3μgg−1 of iodide measured after microwave-assisted alkaline digestion, and 5.8% for 954.3μgg−1 of total iodine by microwave-assisted alkaline digestion followed by microwave-assisted distillation. Finally, accuracy of the methods was assessed by analyzing the NIST-09 (Sargasso) certified reference material and the methods were applied to the determination of iodide and total iodine in different Atlantic edible seaweed samples with satisfactory results.
Keywords: Iodide; Total iodine; Microwave-assisted distillation; Edible seaweed; Catalytic spectrophotometry