Check out our New Publishers' Select for Free Articles

Analytical and Bioanalytical Chemistry (v.366, #1)

Chemical measurement and the law by P. De Bièvre (pp. 1-2).

In-situ monitoring of protein labeling reactions by matrix-assisted laser desorption/ionization mass spectrometry by Jianzhong Lu; Renato Zenobi (pp. 3-9).

Taking the labeling reaction of horse heart cytochrome c or ubiquitin with biotinamidocaproate N-hydroxysucchinimide ester (biotin-NHS) as test cases, this report demonstrates the usefulness of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry for in-situ monitoring of the labeling process and for determining the composition of the labeled products without the need for prior separation. The effects of pH and starting materials concentration on the labeling process were investigated in detail. Our MALDI MS results show that: (1) labeled products are always mixtures of different conjugates, which may explain peak broadening found in chromatographic studies of labeling reactions; (2) the higher conjugate fractions become more prominent as the labeling reaction proceeds, with a concomitant exponential decline of the lower conjugate fractions; (3) biotin-NHS can be incorporated into peptides and protein in a stepwise and controlled manner simply by adjusting the molar ratio of the starting materials.

An immune algorithm for resolution of multicomponent overlapping chromatograms by X. Shao; Z. Chen; X. Lin (pp. 10-16).

A novel immune algorithm for resolution and quantitative determination of the components in overlapping chromatograms was proposed by imitating biological immune systems. The algorithm takes an overlapping chromatogram as its input and subtracts the chromatograms of standard samples from the input by iteration of a network. When the residual does not change, the network will converge and chromatographic information of the components in overlapping chromatogram will be obtained. Both simulated and experimental data sets were investigated by the method. Results showed that both resolved results and recoveries of quantitative determination are satisfactory. Comparing with conventional least-square method, the immune algorithm is fast in calculation.

Application of artificial neural networks in multifactor optimization of an FIA system for the determination of aluminium by Yongyao Zhou; Huaiwen Wang; Gang Sun; Yuquan Fan; Xingguo Chen; Zhide Hu (pp. 17-21).

A methodology based on the coupling of experimental design and artificial neural networks (ANNs) is proposed in the optimization of a new flow injection system for the spectrophotometric determination of Al(III) with Arsenazo DBM, which has for the first time been used as chromogenic reagent in the quantitative analysis of aluminium. An orthogonal design is utilized to design the experimental protocol, in which three variables are varied simultaneously. Feedforward-type neural networks with faster back propagation (BP) algorithm are applied to model the system, and then optimization of the experimental conditions is carried out in the neural network with 3-7-1 structure, which have been confirmed to be able to provide the maximum performance. In contrast to traditional methods, the use of this methodology has advantages in terms of a reduction in analysis time and an improvement in the ability of optimization. The method has been applied to the determination of Al(III) in steel samples and provided satisfactory results.

Characterizing dissolved organic matter fractions using spectral fluorescent signatures and post processing by principal component analysis by T. F. Marhaba; R. L. Lippincott; D. Van (pp. 22-25).

Using modern computer enhanced control and acquisition systems, it is possible to process and analyze the entire usable portion of a spectral region in a reasonable amount of time. This paper describes the creation of a three dimensional fluorescent spectral library of dissolved organic matter (DOM) fractions in water obtained by solid phase adsorption. Although analysis of the response surface and the emission characteristics can be documented manually, this process is subjective in nature and prone to errors. A more efficient method is to conduct post processing using multi-variate analysis of the response surface to identify specific characteristics of the sub-fraction of DOM in water.

Investigation of microwave assisted drying of samples and evaporation of aqueous solutions in trace element analysis by B. Maichin; P. Kettisch; G. Knapp (pp. 26-29).

Investigations of microwave assisted drying of sample materials and microwave assisted evaporation of aqueous sample solutions and acidic digestion residues were accomplished by means of special rotors for the microwave digestion system MULTIWAVE. To check the results obtained by microwave assisted drying, the samples were also conventionally dried at 105 °C in an oven. The following samples have been dried: 10 g each of meat, fish, apple, cucumber, potato, mustard, yogurt, clay and marl; 1 g each of certified reference material TORT 2 (lobster hepatopancreas), BCR 278 (mussel tissue) and BCR 422 (cod muscle); 500 g garden mould. Microwave assisted drying takes 40 min for organic samples and ¶30 min for inorganic material. Important is a slow increase of microwave power during the first 20 min. The results agree well with conventional drying at 105 °C. Losses of As, Se and Hg have been investigated for ¶3 CRMs. Only Se shows losses in the range of 20%. Losses of As, Be, Cd, Co, Cr, Cu, Fe, Hg, Li, Mg, Mn, Mo, Ni, Pb, Sb, Se, Sr, Ti, Tl, V and Zn after evaporation of aqueous samples and acidic solutions after wet digestion, respectively, have been investigated. 50 mL aqueous solution was evaporated almost to dryness within 25 min. The recovery of Hg is 40–50%, of Se 90–95% and of the other elements 97–102%. 0.2 g each of TORT 2, BCR 278 and BCR 422 have been digested with 4 mL nitric acid and 1 mL hydrochloric acid by means of the microwave digestion system MULTIWAVE. The digestion residue was evaporated almost to dryness and dissolved again in 10 mL diluted nitric acid. In this case no element losses have been observed. The measured concentration of As, Cd, Cu, Fe, Mn, Hg, Pb, Mo, Ni, Se, Sr, V and Zn agree very well with the certified values. An important prerequisite for good recoveries is not to evaporate the solutions to complete dryness.

Experimental derivation of Auger transition probabilities from X-ray excited Auger electron spectra in XPS by A. Tanaka; T. Nakamura; K. Hirokawa (pp. 30-35).

Auger transition probabilities were experimentally derived from dominant XAES and related XPS peaks observed in XPS spectra. Some values of derived probabilities were higher than 1, because of addition or subtraction of background signal from the XAES or/and XPS peak intensity. However, the probabilities obtained are recognized to be useful for practical quantification by XAES and AES.

Analysis of non-conducting powders by direct current glow discharge atomic emission spectrometry and application to the determination of rare earth elements by W. Huang; B. Hu; Z. Jiang; L. Wang (pp. 36-40).

Some characteristics for the analysis of non-conducting powders by direct current glow discharge atomic emission spectroscopy (dc-GD-AES) were investigated. Copper powder was chosen as a suitable host conducting material for the analysis of mixtures of rare earth oxides. The influences of sample preparation and discharge parameters on the sputtering rate, discharge stability and emission intensity of the analyte were investigated systematically. The sample-to-sample reproducibility was discussed, and the average RSDs were in the range from 4% to 5%. The proposed method was applied to the analysis of a mixture of rare earth oxides and the results obtained were in good agreement with those obtained by ICP-AES.

Al and Ti secondary neutral and secondary ion emission from oxide samples in the high-frequency sputtering mode of HF-plasma SNMS by X. Ai; H. Hutter; M. Gritsch; H. Börner; J. D. Sunderkötter; H. Bubert; H. Jenett (pp. 41-47).

A strong Al⁺ and a minor Ti⁺ peak without a proportional increase of the O⁺ signal in SNMS high-frequency sputtering mode (HFM) time profiles of an insulating µm-thick oxide layer on Ti-48Al-2Cr-2Nb led us to check for a possible contribution of positive secondary ions (SI⁺). SI⁺ and SI^– (negative secondary ions) can be detected in ion energy spectra. This is shown using Al⁺, O^–, AlO^–, and AlO₂ ^– ions sputtered from massive Al₂O₃. Similarly, and depending on stoichiometry, also Ti⁺ from mixed sintered, microscopically inhomogeneous Al₂O₃-TiO₂-SiO₂ pellets has been identified to be partly SI⁺. The subtraction of an assumed contribution of ionized secondary neutrals (SN⁺) suggests that SI⁺ may form several 10% of the detected ions obtained in the HFM sputtering and plasma processes. However, the positive surface potential of some 10 V being necessary to cause detectable SI⁺ contributions does not build up on µm-thin insulating layers. Therefore, we have to conclude that the Al⁺ and Ti⁺ peaks in the sputter time profiles of the µm-thick oxide layer on Ti-48Al-2Cr-2Nb which are accompanied by an O⁺ deficiency cannot have been caused by SI⁺. Instead, their more probable origin is the inhomogeneous Al₂O₃ interlayer itself. Together with the residues of a topmost TiO₂ layer which has strongly been depleted in O by preferential sputtering, the relative O⁺ deficiency may be explained without assuming SI⁺ contributions.

Mercury determination with ICP-MS: signal suppression by acids by L. Jian; W. Goessler; K. J. Irgolic (pp. 48-53).

When mercury is quantified by ICP-MS under routine conditions (external calibration) in reference materials, which require mineralization with nitric acid, the experimental concentrations are almost always unacceptably low in comparison to certified values. Sorption of mercury on the Teflon surfaces of the digestion vessels, changes in the viscosity of the aspirated solutions, in the efficiency of the nebulization, in the aerosol transport, and memory effects cannot be responsible for the low results. The intensity of a mercury signal is strongly dependent on the concentration of nitric acid (and other mineral acids) in the measured solutions. Correct results for mercury in the SRM GBW-90101 (Chinese human hair; 2.16 ± 0.21 mg Hg/kg certified) can only be obtained, when the solutions, with which the external calibration curves were established, have exactly the same nitric acid concentration as the aspirated digests (2.03 ± 0.01 mg Hg/kg; n = 5), when mercury is determined by the standard addition method (2.10 ± 0.01 mg Hg/kg; n = 5), or when the experimental mercury concentration obtained at a nitric acid concentration in the digest, different from the concentration in the external calibration solutions, is corrected mathematically based on a pre-established function [Hg²⁺] = f [HNO₃]. The concentrations found by this mathematically based correction 2.04 ± 0.01 mg Hg/kg (n = 5) is in good agreement with the values obtained by acid matched calibration or by the standard addition method. For practical work with large numbers of samples the mathematical correction appears to be the method of choice. For occasional mercury determinations, the standard addition method seems to be the most practicable.

Determination of thorium and uranium in activated concrete by inductively coupled plasma mass spectrometry after anion-exchange separation by K. Kato; M. Ito; K. Watanabe (pp. 54-58).

A sensitive analytical method was established for the determination of Th and U in activated concrete samples. The method combines an anion-exchange separation step with an ICP-MS determination technique. In the ICP-MS measurement, a few μg mL^–1 of Al and Ca, a few ng mL^–1 of Mn, La, Ce, Nd and Pb and pg mL^–1amounts of Li, Zr, Nb and Ba coexisting in the anion-exchange fraction of Th and U did not interfere. No adverse interference effects were observed in real sample analyses. The obtained detection limits (3σ, n = 10) of Th and U were 2.3 and 1.8 pg mL^–1, respectively. The analytical precisions for ca. 5 μg g^–1 Th and ca. 1 μg g^–1 U in real activated concrete samples were equally less than 7% RSD. The accuracies obtained by the analysis of GSJ rock standard samples were –18.1 to 0.4% for the Th determination and –14.0 to –5.7% for the U determination. The method uses the conventional absolute calibration curve. The internal standard calibration is unnecessary.

Direct potentiometric titration of chloride and fluoride ions in reversed micelles of an ethoxylated surfactant by A. I. Bulavchenko; E. K. Batishcheva; T. Yu. Podlipskaya; V. G. Torgov (pp. 59-63).

The possibility of the potentiometric titration of Cl^– and F^– ions directly in reversed micelles of the ethoxylated surfactant (Neonol APh₉-4) in n-decane is shown. The potential change of the indicator electrode (silver chloride and lanthanum fluoride) only depends on the ion concentration in the aqueous pseudophase of the reversed micelles and is independent of the aqueous phase concentration in n-decane in the region of concentrations from 4 to 0.2 vol %. The determination of the micelle size of Neonol APh₉-4 in the precipitation titration of Cl^– and F^– ions by photon correlation spectroscopy showed the formation of nanoparticles of AgCl and LaF₃ of dimensions limited by original micelle size (r_hd = 6 to 11 nm). The growth of AgCl and LaF₃ nanoparticles was studied at a shortage and excess of the titrant and in the point of equivalence.

Routine analysis of ultra pure water by ICP-MS in the low- and sub-ng/L level by R. Hoelzl; L. Fabry; L. Kotz; S. Pahlke (pp. 64-69).

The chemical analysis with inductively coupled plasma-mass spectrometry (ICP-MS) can help to examine the purity of ultra pure water (UPW) down to 10 part per trillion (ng/L) and lower. For a proper determination of a high number of samples per week the analysis must be divided into two parts: the routine analysis and the reference water analysis. The routine analysis is done by direct measurement of the ultra pure water samples. Applying a standard addition method under particular clean conditions, the reference water analysis leads to the definition of the accurate zero. A quick evaluation scheme is also presented for the reference water analysis. The method is tested for its fitness for application by examining LOD (for relevant element < 2 ng/L), reproducibility and linearity of calibration. The ICP-MS was optimized according to the methodology of G. Taguchi to improve reproducibility and LOD.

Stability of reactive low boiling hydrocarbons on carbon based adsorbents typically used for adsorptive enrichment and thermal desorption by K. Dettmer; Th. Knobloch; W. Engewald (pp. 70-78).

In the context of evaluating air sampling methods, laboratory experiments were performed to investigate the stability of eleven selected low boiling hydrocarbons (e.g. 1,3-butadiene, isoprene) adsorbed on four different carbon based adsorbents. The carbon molecular sieves Carboxen 569, Carboxen 1003, Carbosieve SIII and the graphitized carbon black Carbotrap X were tested. The influence of storage duration on the recovery of the analytes was examined by loading the adsorbent tubes with the test compounds via a sample loop under inert gas. Furthermore, the influence of sampling the hydrocarbons continuously from air on the recovery of the analytes was investigated using a simple experimental set-up providing a flow of synthetic air spiked with the hydrocarbons. Analysis of the loaded adsorbent tubes was performed by thermal desorption and capillary gas chromatography. Losses up to 80% of 1,3-butadiene and isoprene were observed for the carbon molecular sieves, occurring even immediately after the sampling step. In contrast, no significant losses of these reactive constituents were detected for Carbotrap X over a storage time of seven days. The laboratory investigations were confirmed in a field experiment.

Direct solid sample analysis of sediments, soils, rocks and advanced ceramics by ETV-ICP-AES and GF-AAS by W. Schrön; A. Liebmann; G. Nimmerfall (pp. 79-88).

Methods for the direct solid sample trace element determination in complex composed inorganic powder samples, e.g. sediments, soils, rocks, minerals and similar technical materials, are systematically investigated by SS-ETV-ICP-AES and SS-GF-AAS. High-grade homogeneity of the sample powder even at milligram and sub-milligram levels is required due to small sample weights. All the investigations are carried out with CRMs and RMs. SS-ETV-ICP-AES, which has been improved by high temperature vapor halogenation, is used for the determination of Cr, Cu, Ni, Pb, and Zn in the trace element range < 10 to > 500 μg/g. No significant influence of matrix components is observed using this method. SS-GF-AAS is used for the determination of Cd, Pb, and Zn in the 0.006 to 150 μg/g range. Precision and accuracy of SS-GF-AAS are improved by application of 3D-calibration plots in comparison to conventional 2D-calibration. In this way, the two methods SS-ETV-ICP-AES and SS-GF-AAS complement one another concerning their analytical performance.

Application of ion-chromatography for the determination of the organic-group parameters AOCl, AOBr and AOI in water by J. Oleksy-Frenzel; S. Wischnack; M. Jekel (pp. 89-94).

A method of differential AOX-analysis, i.e. the simultaneous determination of AOCl, AOBr and AOI is described. Individual steps of the method including enrichment at activated carbon, combustion in an oxygen stream and ion-chromatographic detection were optimized. In most cases quantitative recoveries of various organic Cl, Br and I containing substances of different polarity and structure were obtained. The method was applied to the determination of AOX-fractions in municipal and hospital wastewater. A good agreement between conventional coulometric and the described ion-chromatographic determination was found. High concentrations up to 130 μg/L I of organic iodine compounds were measured in the influent and effluent of a municipal treatment plant in Berlin and up to 10 mg/L I in a hospital wastewater.

Analytical fractionation of aquatic humic substances by metal affinity chromatography on iron(III)-coated cellulose by R. Kuckuk; P. Burba (pp. 95-101).

The chromatographic fractionation of aquatic humic substances (HS) onto iron(III)-coated cellulose (Cell-Fe(III)) as a metal-loaded adsorbent is described, analogously to the separation principle of the well-established metal affinity chromatography (MAC). For that purpose the sorption of HS from different aquatic origin on that collector was characterized by their kinetics and equilibrium distribution coefficients Kd. Based on Kd values of 10³ to 10⁴^,mL/g, and fast sorption kinetics a preparative HPLC procedure, using stepwise increased pH-values (pH 8–12.5, borate buffer) as an eluent, was developed for the fractionation of dissolved HS (up to 7 fractions of different amount). The fractions obtained by this MAC procedure from selected aquatic HS samples were different in their Cu(II) complexation capacity, absorbance ratio E_{265 nm}/E_{365 nm} and Fourier transform infrared spectra.

Quantification of sterols, 5α- and 5β-stanols in sewage sludge, manure and soils amended with these both potential fertilizers by E. Ibañez; S. Borrós; Ll. Comellas (pp. 102-105).

A method for the quantitative determination of sterols, 5α- and 5β-stanols is proposed to characterize the lipid fraction of two potential organic fertilizers, like sewage sludge and manure, as well as soils amended by them. It was possible to determine the kind of fertilizer added to the soil. Further studies were conducted to determine the accumulative effects of steroids in soils treated with manure and different doses of sewage sludge.

Application of solid phase micro extraction for the rapid analysis of chlorinated organics in breast milk by L. Röhrig; H. -U. Meisch (pp. 106-111).

The method presented here allows the monitoring of persistent organochlorine compounds in breast milk using the solid phase microextraction technique (SPME) and gas chromatography with electron capture detection (GC-ECD). It describes the determination of hexachlorobenzene (HCB), α-, β-, and γ-hexachlorocyclohexane (HCH), dichlorodiphenyltrichloroethane (DDT) and its derivatives, and some important congeners of the polychlorinated biphenyls (PCB). Also included are more polar substances such as tri-, tetra- and penta-chlorophenols, which can be analyzed simultaneously with the afore-mentioned less polar compounds without the need of a derivatization for the determination of the phenolic compounds. The reproducibility of the results is very good down to the lower μg/L-region. The method is very fast and of low cost compared to the classic extraction and determination procedures.

Spectrophotometric flow injection determination of total phosphorus in beer using on-line UV/thermal induced digestion by S. M. V. Fernandes; J. L. F. C. Lima; A. O. S. S. Rangel (pp. 112-115).

A flow injection system for the automatic determination of total phosphorus in beer is described. The developed manifold uses a two-stage photooxidation/thermal digestion procedure together with oxidizing and hydrolyzing reagents to convert all forms of phosphorus compounds to orthophosphate. Polyphosphates are hydrolyzed by acid and heat, and organo-phosphates are digested by UV-catalyzed peroxodisulfate oxidation. The orthophosphate formed is then spectrophotometrically determined by the phosphomolybdenum blue reaction, using stannous chloride as reducing agent. The results obtained for a set of 19 beer samples (with concentrations from 120 to 735 mg P/L) were in good agreement with the reference method, the maximum relative deviation found being 4.7%. Relative standard deviations for ten consecutive determinations were lower than 1.5%, and a detection limit of 1 mg P/L was achieved.

Analytical characterization of paintings on pre-Roman pottery by means of spectroscopic techniques. Part II: Red, brown and black colored shards by L. Sabbatini; M. G. Tarantino; P. G. Zambonin; G. E. De Benedetto (pp. 116-124).

As a part of a systematic study aimed at assessing the chemical composition of ancient pigments as well as at collecting information useful for the understanding of the technical aspects related to pottery preservation and decoration, the results of analysis performed on red, brown and black pigments decorating pre-Roman pottery excavated in thirteen different tombs unearthed in the archaeological zone of Canosa (Puglia, Italy) are presented. Both surface (XPS) and bulk (FT-IR) spectroscopies were used which gave complementary information and XRD was used in some cases to further support the spectral assignments. Results suggested that the shards characterized by “nominally” the same color could be differentiated by the chemical composition of the pigmented layers; in particular, the shards exhibiting the red pigment could be divided into three groups containing, respectively, either hematite or ochre plus other substances not related to the color but of great concern for the understanding of ancient techniques used for color preparation. Manganese oxides were found to be the basis of the brown pigments, which could be divided into three groups on the basis of Mn and Fe contents. Either magnetite or carbon of vegetable origin was found in the black-pigmented layers. Furthermore, an attempt was made to find a possible correlation between this classification and the results of a provenance study carried out on the same pool of shards analyzed in the present investigation.

Sections

Personal tools

Analytical and Bioanalytical Chemistry (v.366, #1)

Sections

Personal tools

Local resources

Analytical and Bioanalytical Chemistry (v.366, #1)