| 1. |
- Andersson, Patrik, et al.
(författare)
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Ultraviolet absorption spectra of all 209 polychlorinated biphenyls evaluated by principal component analysis
- 1997
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 357:8, s. 1088-1092
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Tidskriftsartikel (refereegranskat)abstract
- The ultraviolet absorption spectra of all 209 polychlorinated biphenyls (PCBs) were recorded in the range 200-300 nm and displayed two important absorption maxima, viz., the main-band, lambda(max) 200-225 nm, and the kappa-band, lambda(max) 245-265 nm. By utilising principal component analysis, substitution related spectral characteristics of the PCBs, underlying the main patterns of the spectra, were examined. Captured in the multivariate evaluation were e.g., the importance of chlorine atoms in ortho positions, determining the intensity and existence of the kappa-band, chlorine substitution in para-para position, and the total number of chlorine atoms. The measured UV-spectra of all 209 polychlorinated biphenyls provide important physico-chemical descriptors for use in future quantitative structure-activity and structure-property relationship (QSAR/QSPR) studies.
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| 2. |
- Dahlén, Johan, et al.
(författare)
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Analysis of low molecular weight organic acids in water with capillary zone electrophoresis employing indirect photometric detection
- 2000
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 366:5, s. 488-493
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Tidskriftsartikel (refereegranskat)abstract
- A capillary zone electrophoretic method for the analysis of low molecular weight carboxylic acids in water was developed. The application uses the chromophore trimellitic acid that allows for indirect photometric detection at 254 nm. Selectivity control by the addition of Ca2+ to the carrier electrolyte made possible a baseline resolved separation of 14 carboxylic acids. Good linearity and repeatability were obtained for both electrokinetic and hydrostatic injection modes. The usefulness of the method is demonstrated by the analysis of a snow sample.
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| 3. |
- Feng, Xinbin, et al.
(författare)
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Modified on-line monitoring of total gaseous mercury in flue gases using a Semtech 2000 Analyzer
- 2000
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Ingår i: Fresenius Journal of Analytical Chemistry. - 0937-0633. ; 368:5, s. 528-533
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Tidskriftsartikel (refereegranskat)abstract
- The Semtech Hg 2000 analyzer continuously monitors the Hg0 content in flue gas. An on-line measurement method of total gaseous mercury in flue gas developed in our laboratory is described, which uses the absorption cell of the Semtech Hg Analyzer connected to a converter that is located in a furnace heated up to 650 °C. The converter can be heated up to 800 °C by both the furnace and an extra heating of a Ni-Cr alloy heating wire. Both the absorption cell and the converter are made of quartz. All gaseous Hg2+ species in flue gas are thermally reduced to Hg0 by the converter and detected by the Semtech Hg 2000 analyzer. The thermal reduction efficiencies of different conversion materials, which were filled in the converter, such as quartz chips, granular MgO, Ni and CoO powder, were tested using different flue gas conditions. Studies have shown that HCl is the major factor to inhibit the thermal reduction of Hg2+ to Hg0, and in the converter and the absorption cell Hg0 will react readily with HCl to form HgCl2. Both MgO and Ni could be used in the converter to absorb HCl in the flue gas, but Ni has better absorption efficiency. By using an original Semtech and a modified one, both Hg0 and total gaseous Hg contents in flue gas could be monitored simultaneously and continuously.
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| 4. |
- Haupt, Dan, et al.
(författare)
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Optimization of the chiral resolution of four hydrophobic amines on CHIRAL-AGP by a central composite face design (CCF)
- 1995
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Ingår i: Fresenius' Journal of Analytical Chemistry. - 0937-0633 .- 1432-1130. ; 352:7-8, s. 705-711
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Tidskriftsartikel (refereegranskat)abstract
- A three-factor central composite face design (CCF) has been used for the optimization of the chiral resolution of the enantiomers of alprenolol, oxprenolol, trimipramine and propranolol on CHIRAL-AGP. The variables (factors) investigated were pH and concentrations of the micellar agent Tween((R)) 20 and heptanoic acid. The responses evaluated were resolution (R(S)), capacity factor (k') of the last eluted enantiomer and a chromatographic response function (CRF) defined as CRF = P-5/log t(ret), where P is the peak-valley ratio according to Kaiser and t(ret), is the retention time. The computed models, one for each substance and one for each response (in total 12 models), showed that the main factor for the regulation of R(S) as well as k' and CRF in the experimental domain is the pH. The optimal pH for the substances could be found between pH 5.5 and 6.5. The optimum was evaluated by generating contour plots for the CRF models. The computed mathematical models were statistically evaluated and the predictive power of the models was tested by ex perimentation
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| 5. |
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| 6. |
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| 7. |
- Nordmark, Ulrika, et al.
(författare)
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Optimum conditions for pulse generation in diaphragm-free Karl Fischer coulometry
- 2000
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer. - 0937-0633 .- 1432-1130. ; 368:5, s. 456-460
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Tidskriftsartikel (refereegranskat)abstract
- A flexible instrument was designed in order to investigate the influence of current magnitude, current duration and the frequency of the pulse generation on the error obtained in coulometric Karl Fischer titrations carried out in diaphragm-free cells. For a given current magnitude the lowest errors were obtained for current durations more than 60% of the total time for the pulse cycle. No significant influence of the pulse frequency (5-1000 Hz) was found independently of the pulse current duration for three different types of reagents intended fur diaphragm-free coulometry. For all reagents, the errors obtained with the home-built instrument were significantly smaller than those obtained with an optimized commercial titrator based on pulsed current generation. Using optimum conditions for the former instrument, in combination with an imidazole-buffered reagent at pH 10 containing chloroform as modifier, the accuracy was close to 100%. Thus, it is now possible to achieve the same high accuracy with diaphragm-free coulometry as with the conventional diaphragm based technique. The precision of the water determinations was affected by the size of the background.
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| 8. |
- Nordmark, Ulrika, et al.
(författare)
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Progress in pulsed-current Karl Fischer coulometry using diaphragm-free cells
- 2000
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer. - 0937-0633 .- 1432-1130. ; 367:6, s. 519-524
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Tidskriftsartikel (refereegranskat)abstract
- Factors influencing the accuracy of water determinations using diaphragm-free, pulsed current Karl Fischer (KF) coulometry were investigated with the new Metrohm 756 instrument. Results obtained with commercially available reagents from Riedel-deHaen and Merck were compared with home-made ones that were especially designed to minimize the formation of iodine-consuming reduction products generated in the cathode reaction. Positive errors in the range 2-5% were found for the commercial reagents as compared to 0.2-1% for the home-made ones which were buffered at about pH 10 containing modifiers like chloroform, hexanol or ethylene glycol. Except for the composition of the KF-reagent, the cathode current density and the titration rate were found to be critical parameters for the accuracy of the determinations. For all reagents investigated, the best results were obtained for the maximum generator current 400 mA (corresponding to a current density of 1400 mA cm(-2)) in combination with a maximum titration rate of 2000 mu g min(-1). Surprisingly, the errors found under optimum conditions for the pulse technique were always somewhat larger than the corresponding values obtained with continuous coulometry.
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| 9. |
- Nordqvist, Yvonne, et al.
(författare)
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Comparison of denuder and impinger sampling for determination of gaseous toluene diisocyanate (TDI)
- 2001
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Ingår i: Fresenius´ Journal of Analytical Chemistry. - Berlin : Springer. - 0937-0633 .- 1432-1130. ; 371:1, s. 39-43
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Tidskriftsartikel (refereegranskat)abstract
- An air-sampling method employing denuders coated inside with a chemisorptive stationary phase has been evaluated for analysis of the hazardous gaseous 2,4 and 2,6 isomers of toluene diisocyanate (TDI). The denuder stationary phase consisted of polydimethylsiloxane (SE-30) to which dibutylamine (DBA) was added as a reagent for derivatization of TDI. The accuracy and precision of sampling by means of denuders were shown to differ only slightly from those of the established impinger method. The denuder method was, however, also shown to be suitable for long-term measurements (up to 8 h). The limit of determination (LOD) of the method, including LC-APCI-MS-MS analysis, was found to be 1.9 µg m-3 and 1.2 µg m-3 for 2,4- and 2,6-TDI, respectively, for short-term measurements (15 min). Significant lower LOD was obtained for long-term measurements.This is well below the Occupational Safety and Health Administration (OSHA) 8-h TWA (time weighted average) exposure limit, which is 40 µg m-3 for the sum of the TDI isomers. The denuder method was also found to be robust and easy to handle. The samplers can be prepared several days before sampling with no loss in performance. The contents of denuders should, on the other hand, be extracted immediately after sampling to prevent degradation of the isocyanate derivatives formed.
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| 10. |
- Qian, J, et al.
(författare)
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Efficiency of solvent extraction methods for the determination of methyl mercury in forest soils.
- 2000
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Ingår i: Fresenius J Anal Chem. - 0937-0633. ; 367:5, s. 467-73
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Tidskriftsartikel (refereegranskat)abstract
- Methyl mercury was determined by gas chromatography, microwave induced plasma, atomic emission spectrometry (GC-MIP-AES) using two different methods. One was based on extraction of mercury species into toluene, pre-concentration by evaporation and butylation of methyl mercury with a Grignard reagent followed by determination. With the other, methyl mercury was extracted into dichloromethane and back extracted into water followed by in situ ethylation, collection of ethylated mercury species on Tenax and determination. The accuracy of the entire procedure based on butylation was validated for the individual steps involved in the method. Methyl mercury added to various types of soil samples showed an overall average recovery of 87.5%. Reduced recovery was only caused by losses of methyl mercury during extraction into toluene and during pre-concentration by evaporation. The extraction of methyl mercury added to the soil was therefore quantitative. Since it is not possible to directly determine the extraction efficiency of incipient methyl mercury, the extraction efficiency of total mercury with an acidified solution containing CuSO4 and KBr was compared with high-pressure microwave acid digestion. The solvent extraction efficiency was 93%. For the IAEA 356 sediment certified reference material, mercury was less efficiently extracted and determined methyl mercury concentrations were below the certified value. Incomplete extraction could be explained by the presence of a large part of inorganic sulfides, as determined by x-ray absorption near-edge structure spectroscopy (XANES). Analyses of sediment reference material CRM 580 gave results in agreement with the certified value. The butylation method gave a detection limit for methyl mercury of 0.1 ng g(-1), calculated as three times the standard deviation for repeated analysis of soil samples. Lower values were obtained with the ethylation method. The precision, expressed as RSD for concentrations 20 times above the detection limit, was typically 5%.
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| 11. |
- Rodushkin, Ilya
(författare)
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Capabilities of high resolution inductively coupled plasma mass spectrometry for trace element determination in plant sample digests
- 1998
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 362:6, s. 541-546
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Tidskriftsartikel (refereegranskat)abstract
- The analytical performance of inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of plant sample digests was evaluated using double focusing sector field ICP-MS (ICP-SMS). Instrumental detection limits of ICP-SMS are superior to those obtained by quadrupole systems (ICP-QMS) and reach the fg mL-1 range for elements with high m/z ratios. Matrix effects caused by a plant digest after sample preparation resulting in 200-fold dilution were found to be negligible. The usefulness of high mass resolution for overcoming some spectral interferences is demonstrated. Mathematical correction possibilities could be necessary to improve accuracy. The concentrations of more than 20 elements can be determined in 5 min and only one internal standard is necessary to correct for instrumental drift.
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| 12. |
- Rodushkin, Ilia, et al.
(författare)
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Multielement analysis of whole blood by high resolution inductively coupled plasma mass spectrometry
- 1999
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : Springer Science and Business Media LLC. - 0937-0633 .- 1432-1130. ; 364:4, s. 338-346
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Tidskriftsartikel (refereegranskat)abstract
- An analytical method using double focusing sector field inductively coupled plasma mass spectrometry (ICP-SMS) for rapid simultaneous determination of 50 elements in digested human blood is described. Sample preparation consisted of microwave digestion with nitric acid followed by dilution with ultrapure water. The importance of controlling possible contamination sources at different sample preparation and analysis stages in order to achieve adequate method detection limits (MDL) is emphasised. Correction for matrix effects was made using scandium, indium and lutecium as internal standards. Accuracy of the data for elements suffering from spectral interferences was improved by applying either a high resolution capability of the ICP-SMS or mathematical corrections. Different approaches for accuracy assessment in blood analysis are evaluated. Additional information on trace elements concentration in selected blood reference materials is given. The between-batch precision was assessed from replicate analysis (including sample preparation) of reference materials and was better than 10% RSD for 21 elements and better than 30% RSD for 36 elements under consideration. A statistical summary for results obtained for 31 blood samples from non-exposed subjects is presented. The majority of elements tested was found in the samples at concentrations higher than MDL.
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| 13. |
- Sarkar, P, et al.
(författare)
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Application of dual-step potential on single screen-printed modified carbon paste electrodes for detection of amino acids and proteins
- 1999
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Ingår i: Fresenius' Journal of Analytical Chemistry. - : SPRINGER VERLAG. - 0937-0633 .- 1432-1130. ; 364:02-jan, s. 154-159
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Tidskriftsartikel (refereegranskat)abstract
- A novel screen-printed biosensor for protein and amino acid (AA) estimation is reported. A rhodinised carbon paste working electrode (WE) was used in. the three-electrode configuration. Bromine was generated by the electrolysis of an acidic potassium bromide electrolyte on the working electrode when poised at an appropriate potential. The consumption of bromine by the protein and amino acid was then measured at a lower-potential. This sensor was used to detect most of the amino acids and some common proteins. The method is highly sensitive and can even detect L- and D- proline which give no response with enzyme electrodes. This sensor has also been used to detect protein/amino acid in fruit juice, milk, and urine. The unique feature of the sensor is that it does not require any reagent/chemical other than buffer. No surface treatment or modification of the WE is necessary and hence the sensor is stable for the lifetime of the basic screen-printed electrode, which is about a year. A very small amount of analyte (10 mu L) is required for direct detection. The sensor is inexpensive and disposable and may also be used for continuous-flow systems. This sensor may have useful application in process monitoring and control during the production of amino acids.
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