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Analytical and Bioanalytical Chemistry (v.365, #7)
New Members of the Editorial and Advisory Boards Shakers and Makers in Analytical Science
(pp. 567-568).
Comparability and recognition of chemical measurement results – an international goal by Wolfgang Richter (pp. 569-573).
As a consequence of the globalisation of trade and industry and other human activities, reliability of and confidence in measurement results is increasingly required, also in the field of chemical analysis, so that measurements made in one country will be accepted in other countries without the necessity to repeat them. The prerequisite for confidence is comparability on the basis of known uncertainties which in turn are based on traceability to recognised references. Traceability structures for chemical measurements are required which, by providing calibration means traceable to national standards, allow uncertainty statements to be made at field level, thus establishing comparability. Such traceability structures are now being developed in all industrialised countries. To ensure international comparability, mutual recognition of the national activities in metrology in chemistry is required in addition. The Mutual Recognition Agreement (MRA) for national measurement standards and calibration certificates issued by national metrology institutes, which is currently under way within the framework of the Metre Convention, aimes at providing the necessary international confidence for all kinds of measurements. The field of chemical analysis is included in the international metrological infrastructure through the new Consultative Committee for Amount of Substance (CCQM). Carefully selected key comparison measurements, which cover the most important areas where traceability is required, and which are carried out by national metrology institutes in cooperation with other national institutes entrusted with the provision of part of the national references for chemical measurements, form the basis for declarations of equivalence under the MRA. The results of the first key comparisons and studies carried out so far clearly show that the group of laboratories involved in the key comparisons is capable of establishing the international references (key comparison reference values) for chemical measurements with sufficient accuracy, also in complicated matrices.
Complementary use of inter-laboratory certification study data by W. Hässelbarth (pp. 574-576).
The agreed purpose of an inter-laboratory certification study is to characterise a certified reference material (CRM). In addition to this, any (successful) certification study may also be utilised as a laboratory/method performance study by the participants. The intention of this note is to emphasise the complementary use of certification study data by the participants of the certification study and to explain the options involved. On this occasion, an apparent paradox arising in the interpretation of certification study data is resolved. The procedures for bias correction and estimation of bias-related uncertainty contributions discussed on this occasion are, however, generally applicable to normal CRM use.
Adsorption of mercury on gold and silver surfaces by M. Levlin; E. Ikävalko; T. Laitinen (pp. 577-586).
In order to study the adsorption mechanism of Hg on Au and Ag substrates, thin film Au(111) and Ag(111) substrates were exposed to gaseous metallic mercury, while the mercury concentration, substrate temperature, and exposure length were varied. The resulting changes in the surface morphology of the substrates were studied with scanning tunneling microscopy (STM). The amount of adsorbed Hg required to cause saturation, i.e. a decrease in the adsorption rate was found to be dependent on the mercury concentration and substrate temperature. The observations lead to the conclusion that the adsorption includes place exchange processes and concerted adsorption of more than one Hg atom in one process. The results show that the collection efficiency of single-crystalline surfaces is a function of both mercury concentration and temperature. Therefore, results from measurements performed at different conditions using single-crystalline surfaces may not be comparable.
An Ni(chitin)2 modified nitric oxide microsensor by Yuezhong Xian; Jian Xue; Song Zhang; Xiangyang Ying; Litong Jin (pp. 587-591).
The development of a simple, sensitive, selective, and stable amperometric nitric oxide microsensor is described. It is based on Ni(chitin)2 mediators immobilized on a platinum, Nafion modified electrode. The detection of NO is based on the Ni(chitin)2 catalysis of NO oxidation at an anodic potential of +0.74 V (vs. SCE). The catalytic peak current is linear for a NO concentration in the range of 8.5 × 10–8 mol/L to 1.5 × 10–5 mol/L, with a correlation coefficient of 0.9992. The detection limit of the microsensor is 5.0 × 10–8 mol/L. It is suitable for the direct measurement of NO in biological systems.
Studies on the use of XeF2 as digestion reagent by E. Hoffmann; C. Lüdke; J. Kürner; H. Scholze; E. Ullrich; H. Stephanowitz (pp. 592-596).
A digestion procedure was developed for the determination of selected elements (Al, Ba, Ca, Ce, Cd, Co, Cr, Cu, Fe, La, Mg, Ni, Sr, Pb, Zn) in sediments using XeF2. The use of XeF2 has some interesting features but this reagent should be handled only under dry gas which is a severe limitation of the methodology. In a first step the sediment sample (0.1 g) is dried (120 °C) and digested by XeF2 (1.5 g) in the vapor phase (190 °C; 9 × 106 Pa). Then the dry residue is dissolved in aqua regia and the solution digested at high pressure once again (aqua regia digestion). Subsequently the digested solution is diluted with sub-boiling distilled water and is ready for the analysis by ICP-MS. The sediment standard CRM 320 was analyzed to verify the procedure. A comparison of the results with those obtained by the normally used fluoric acid digestion showed that the recovery rates of each investigated element agreed within a confidence interval of 95%, except Cr. The recovery rate of Cr was lower for the XeF2 digestion than for the fluoric acid digestion by more than 5%. Further studies were focussed on the possible digestion of SiC by XeF2 as first step for the trace element determination. In the gaseous reaction products Si could be detected by ICP-MS which gives evidence to a decomposition of SiC. A digestion procedure for small Si samples (0.010 g) was developed. Detection limits (DL) determined for selected elements of analytical interest (Al, Ca, Cd, Cr, Co, Cu, Fe, Mg, Ni, Pb) were between 1 to 12 ng/g. For most of the elements this is an improvement in comparison to the HF vapor phase digestion. The verification of the method was carried out with GFAAS.
Determination of oxygen in oxides by carrier gas hot extraction analysis with simultaneous COx detection by Wolfgang Gruner (pp. 597-603).
The determination of oxygen by carrier gas hot extraction is the most popular method for oxygen analysis, but its application to high oxygen contents in oxides requires a critical look at the basic assumptions of the method. The process was studied for various oxides (Al2O3, Bi2O3, Cr2O3, Fe2O3, MoO3, NiO, TiO2, WO3, Y2O3, and ZrO2) using a modern analyser with IR-detectors for CO2 and CO. There was a difference specific to oxides that must be known to get the required analytical results with high precision and accuracy. High amounts of CO2 were formed particularly from Bi2O3, Fe2O3, MoO3, NiO, and WO3. The reaction rate can be controlled with delayed heating of the furnace, so that an oxide sample weight of up to 100 mg can be used.
Determination of haloacetic acids by the combination of non-aqueous capillary electrophoresis and mass spectrometry by Werner Ahrer; W. Buchberger (pp. 604-609).
The applicability of capillary electrophoresis (CE) in combination with atmospheric pressure ionization mass spectrometry (API-MS) is demonstrated for the determination of organic acids and in particular for haloacetic acids. CE-conditions, sheath flow and MS-parameters were optimized with respect to the separation of the analytes and mass spectrometric sensitivity.CE/MS turned out to be an attractive alternative for the determination of haloacetic acids to existing methods based on GC-ECD. Employing CE/MS derivatization is not necessary which saves time and avoids possible sources of errors. In the present work the sample pre-treatment is performed by liquid-liquid extraction using methyl tert.-butyl ether as the extraction solvent. The organic phase is brought to dryness in a stream of nitrogen gas and the residue is dissolved in methanol and analyzed by CE/MS using a mixture of 2-propanol/water 80 : 20 containing triethylamine as the sheath liquid in the interface. Best results for the separation of all nine possible bromo- and chloroacetic acids together with two internal standards are obtained with a carrier electrolyte consisting of ammonium acetate/acetic acid in methanol; to resolve the strongly acidic trihaloacetic acids as well as the less acidic monohaloacetic acids, a careful optimization of the acetic acid content is necessary. The method was applied to the determination of haloacetic acids in real water samples. With optimized CE and MS conditions detection limits between 0.3 and 7.6 μg/L in the original water samples were achieved, employing a sample volume of 30 mL.
Direct methylation at the surface of Carbopack B Part II: Determination of phenoxyalkanoic acid herbicides by J. Nolte; R. Krüger (pp. 610-614).
The determination of phenoxyalkanoic acids in different types of water within the limits of the European drinking water guideline is described. Most of these acids are used world-wide as herbicides and growth regulators. Compounds having an acidic hydrogen in their structure are very strongly adsorbed on Carbopack B, a special graphitized carbon black. This effect was used for the transformation of analytes to methyl esters directly on the surface of the adsorbent, using trimethylsulfonium hydroxide (TMSH) as derivatization reagent. After elution with ethyl acetate the derivatives were identified and quantified by gas chromatography/mass spectrometry (GC/MS). The interaction between analyte and adsorbent and the yields of the derivatization step are influenced by the length of the alkanoic chain.
Analysis of organomercuric species in soils from orchards and wheat fields by capillary gas chromatography on-line coupled with atomic absorption spectrometry after in situ hydride generation and headspace solid phase microextraction by B. He; G. B. Jiang (pp. 615-618).
A convenient procedure for the determination of organomercuric compounds in soils from orchards and wheat fields is described based on the aqueous derivatization of the polar organomercuric halides in 0.1 M HAc-NaAc (pH 4) buffer into their hydrides by addition of 1 mL of 6% KBH4 with subsequent headspace solid phase microextraction (SPME) of the volatile derivatives. The volatile derivatives are separated by gas chromatography (GC) with a Supelco SPB-1 capillary column and on-line detected by electric heated quartz furnace atomic absorption spectrometry (AAS). The relative standard deviations for ten replicate measurements are 2.1%, 2.8% and 3.5% for methyl-, ethyl- and phenylmercury with absolute detection limits of 16 ng, 12 ng and 7 ng, respectively. This method is applied to the analysis of organomercuric compounds in soil samples and 0.04–0.64 μg/g of organomercuric species are detected in soils from different sites. The recoveries after standard addition are between 93–106%.
A simple solid phase spectrofluorimetric method combined with flow analysis for the rapid determination of salicylamide and salicylic acid in pharmaceutical samples by A. Ruiz Medina; M. L. Fernández de Córdova; A. Molina Díaz (pp. 619-624).
A new, sensitive and very simple spectrofluorimetric biparameter sensor is described for the determination of salicylamide and/or salicylic acid in pharmaceutical preparations. The method integrates the transitory retention and fluorescence detection of both compounds on Sephadex QAE A-25 resin packed into a conventional flow-through cell. A monochannel manifold with two alternative carriers is used. At pH 2.0 (first carrier) salicylic acid is selectively retained on the solid support and after developing the analytical signal it is desorbed. At pH 11.0 (second carrier) both salicylic acid and salicylamide are simultaneously and transitorily retained on the solid, the analytical signal now corresponding to both analytes. The monochromators were tuned at 260 (excitation) and 415 (emission) nm, respectively. The calibration graph for salicylamide is linear over the range 0.01 to 0.32 μg mL–1 and for salicylic acid from 0.04 to 1.0 μg mL–1 in the presence of each other. The relative standard deviation and the sampling frequency for the determination of salicylamide (0.20 μg mL–1) and salicylic acid (0.50 μg mL–1) were 1.1% and 35 h–1, and 0.9% and 45 h–1, respectively. Good results on application to individual determination or mixture resolution in pharmaceutical samples testify to the usefulness of the proposed sensor.
Analysis of nucleotides directly from TLC plates using MALDI-MS detection by Donna T. Isbell; Arkady I. Gusev; Nelli I. Taranenko; C. H. Chen; D. M. Hercules (pp. 625-630).
The methodology for the detection of picogram quantities of nucleotides directly from TLC plates without the use of radioactive labeling has been developed. The method couples thin-layer chromatography (TLC) separation with matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) detection. The TLC/MALDI coupling protocol was studied and optimized for the separation and detection of deoxyribonucleotides. Several ammonia based solvents were examined as potential extraction solvents for the TLC/MALDI coupling protocol. It was found that in order to obtain maximum MALDI signal intensity and minimal analyte spreading, the extraction solvent should produce Rf-values for the analytes in the range of 0.3–0.4. Rf-values above this range led to extensive analyte spreading and those below this range resulted in poor extraction. Various MALDI matrices and co-matrices were investigated, the best results were obtained using 2′,4′,6′-trihydroxyacetophenone (THA) as a matrix. The extraction solvent chosen was an ammonium hydroxide/methanol (100 mM/30%, Rf = 0.28–0.38) solvent system which was found to provide the best sensitivity, minimal lateral spreading and excellent matrix transfer. Using the optimized coupling protocol, the detection limits for the deoxyribonucleotide monophosphates were established at or better than 10 picograms.
A robust technique for the group classification of the C-13 NMR spectra of natural products from Meliaceae by L.-A. Fraser; Dulcie A. Mulholland (pp. 631-634).
Neural networks have been found to be good general classifiers of the binned C-13 NMR spectra of limonoids and associated extractives from the Meliaceae family. 5 ppm binning of the C-13 NMR spectra was found to be superior to 10 ppm binning. The excellent results obtained by developing the system on real extractives using the 5 ppm binning, revealed that the system developed was robust and general enough to tolerate the inherent problems associated with natural product extraction. Experiments concerning the effect of noise and missing bins were also conducted and documented. A literature-sourced sample set was also added in order to ensure the system was not specifically designed to cope only with the unique data set on which it had been trained.