| 1. |
- Cedergren, Anders, et al.
(författare)
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Determination of water in NIST reference material for mineral oils
- 2000
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Ingår i: Analytical Chemistry. - 0003-2700 .- 1520-6882. ; 72:14, s. 3392-3395
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Tidskriftsartikel (refereegranskat)abstract
- The accuracy of the reference concentrations of moisture in electrical insulating oil RM 8506 and lubricating oil RM 8507 (both of mineral type) and specified by the National institute of Standards and Technology (NIST) as containing 39.7 and 76.8 ppm (w/w) water, respectively, has recently been the subject of debate in this journal. To shed some further light on this controversy, we report in this correspondence results for these oils obtained by two additional methods, one based on specially designed reagents for diaphragm-free Karl Fischer (KF) coulometry and the other based on the concept of stripping at elevated temperature/continuous KF coulometry. A positive interference effect was shown to take place for RM 8506 when the direct coulometric method was used. If the results are corrected for this, the values including six different procedures varied in the range 13.5-15.6 ppm (w/w). For RM 8507, all values were between 42.5 and 47.2 ppm (w/w), which means that the values recommended by NIST for both reference oils using volumetric titration are about twice as high as those obtained with the other techniques. A possible explanation for this discrepancy is presented.
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| 2. |
- Nordmark, Ulrika, et al.
(författare)
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Conditions for Accurate Karl Fischer Coulometry Using Diaphragm-Free Cells
- 2000
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Ingår i: Analytical Chemistry. - Washington, D. C., USA : American Chemical Society. - 0003-2700 .- 1520-6882. ; 72:1, s. 172-179
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Tidskriftsartikel (refereegranskat)abstract
- Factors influencing the extent of formation of oxidizable reduction products in coulometric cells used for Karl Fischer (KF) determination of water were investigated. For methanolic KF reagents buffered with imidazole (Im) or diethanolamine (DEA) (separately or in combination), three parameters were found to be of outmost importance: the cathodic current density, the pH, and the concentration of protonated base (ImH+ or DEAH+). For reagents buffered with only Im, the relative formation of oxidizable reduction products varied in the range 2-40%; i.e., 51-70 g of water was found for a 50 g water sample, depending on the above-mentioned parameters. The lowest values were observed for reagents having a pH around 10 in combination with cathodic current densities in the range 2000-5000 mA cm-2. For all the Im-buffered reagents investigated, the addition of modifiers such as chloroform, hexanol, and carbon tetrachloride was found to decrease the formation of oxidizable reduction products significantly. For example, a reagent buffered at pH 10 containing 1 M hexanol gave less than 0.3% formation in the current density interval from 200 to 4000 mA cm-2. The best reagents based on the above-mentioned modifiers were tested in the continuous coulometric mode with errors typically in the interval 0-0.5% using optimum conditions. One prerequisite for obtaining such small errors with diaphragm-free continuous coulometry is to use a cathode area no larger than 0.002 cm2. For some of the reagents based on both Im and DEA, the formation of oxidizable reduction products was close to zero at certain current densities, although the analytical performance was not as good as for the reagents buffered solely by Im due to longer conditioning and titration times.
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| 3. |
- 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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| 4. |
- 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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| 5. |
- Nordmark, Ulrika
(författare)
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Quantitative determination of resin mixtures in coating colours for paper by multivariate analysis of data from pyrolysis-gas chromatography
- 2000
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Ingår i: Journal of Analytical and Applied Pyrolysis. - : Elsevier. ; 55:1, s. 93-103
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Tidskriftsartikel (refereegranskat)abstract
- Pulp and paper industries are interested in a technique for analysing the purchased resins used in coating colours. The concept of pyrolysis-gas chromatography in combination with chemometrics, i.e. principal component analysis and principal least squares, was used to develop improved methods for the quantitative analysis of tertiary mixtures based on latex resins. A principal least square model was made based on pyrolysis-gas chromatography data and a mass spectrometer was used to identify pyrolysis fragments. It was shown that the model accurately predicted the concentration of a resin in a tertiary mixture. The average error of prediction, for resin mixtures not previously shown for the model, was less than 4% by weight for each of the investigated resins.
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