摘要 :
New non-toxic Karl Fischer reagents for water determination based on ethanol as solvent has been developed in the last year. To prove their suitability in the ambiguous filed of food analysis a variety of samples were analysed usi...
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New non-toxic Karl Fischer reagents for water determination based on ethanol as solvent has been developed in the last year. To prove their suitability in the ambiguous filed of food analysis a variety of samples were analysed using conventional methanol-based reagents and the new ethanolic reagents. Since the most kind of food consists of polar substances the methanolic reagents give faster results. The non-toxic ethanol-based reagents are preferred for non-polar samples as butter.
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The Karl Fischer titration is indicated voltametrically or amperometrically by polarising a double platinum electrode. The end-point is recognised by a strong decrease of the resistance of the solution, caused by a small excess of...
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The Karl Fischer titration is indicated voltametrically or amperometrically by polarising a double platinum electrode. The end-point is recognised by a strong decrease of the resistance of the solution, caused by a small excess of iodine molecules. A minimum conductivity of the KF solutions is necessary for indicating the endpoint. In conventional methanolic Karl Fischer solutions, dissolved components assure a sufficient conductivity. But substitution of methanol by less polar solvents can lead to indication problems. The relationship between conductivity and indication for various volumetric one-and two-component systems is shown. For the coulometric method, the conductivity of KF solutions is of especial importance. The generation of iodine at the cathode requires a higher conductivity than is necessary for indicating the endpoint. The aim of further developments is to adjust new-reagent compositions to standard parameters of the instrument. Some examples of new Karl Fischer solvents are given.
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The authors investigated Karl Fischer coulometric titration using a diaphragmless cell. Many samples, such as hydrocarbons, alcohols and polymers, were analyzed by the pre- sent method and the conventional method using a cell with...
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The authors investigated Karl Fischer coulometric titration using a diaphragmless cell. Many samples, such as hydrocarbons, alcohols and polymers, were analyzed by the pre- sent method and the conventional method using a cell with a diaphragm. The relation- ship between both methods showed good agreement (relation coefficient, r= 0.99996). Compounds containing a nitro group showed higher analytical values, because the prod- ucts electrolyzed at the cathode reacted with the iodine produced at the anode. Present method is suitable for the coulometric titration/the moisture vaporization method in which the moisture in samples is introduced into the electrolyzing cell by heating and purging.
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This study evaluated the efficiency of Karl Fischer titration and coulometry for measurement of water content in small intact and defective cartilage specimens. Cartilage from the main weight-bearing zone of the medial condyle of ...
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This study evaluated the efficiency of Karl Fischer titration and coulometry for measurement of water content in small intact and defective cartilage specimens. Cartilage from the main weight-bearing zone of the medial condyle of 38 fresh sheep knees was used. Of these, 20 condyles had an intact cartilage, while defects (14 grade Ⅰ and 4 grade Ⅱ) were found in the rest. The mechanical hardness was determined as Shore A. Cartilage specimens of approximately 5 mg were analyzed in special devices for moisture measurement and then continuously heated up to 105℃. The actual measurement was performed in an electric cell (coulometry). An electrode was laminated with hygroscopic phosphorus pentoxide. In the electrochemical reaction, H and O are liberated from the electrode. The requirement for electric energy correlates with the amount of water in the specimen. The water content in intact cartilage was 66.9%. Grade Ⅰ (72.6%) and grade Ⅱ (77.8%) defects had significantly higher water content. Significantly higher and faster spontaneous evaporation was observed in cartilage defects at room temperature. The water content and spontaneous water evaporation correlated with significantly lower mechanical hardness. The experimental design (combined method of thermo-gravimetry, Karl Fischer titration, and coulometry) was sufficient for evaluating the water content in small cartilage specimens. It is also possible to measure the temperature-dependent water liberation from cartilage specimens.
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A modified Karl Fischer (KF) titration method (measurements at 50 degreesC instead of room temperature) for the precise determination of the water content in honey has been developed together with the adjustment of a drying method...
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A modified Karl Fischer (KF) titration method (measurements at 50 degreesC instead of room temperature) for the precise determination of the water content in honey has been developed together with the adjustment of a drying method using an infrared (IR) technique. The results obtained by this IR method applying a temperature between 98-100 degreesC were found to be very similar to those obtained by the KF technique. In the second part of the study, the water concentration was determined in 39 authentic honey samples from various geographical and botanical origins using four different techniques: KF titration, refractive index measurements, official oven-drying method and a special oven method. Significant differences could be observed (maximum differences were in the range 0.9-5.1% absolute). The results obtained by KF titration were found to have the lowest standard deviations. With the exception of a few honey varieties., this method led to the highest values.
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Drying techniques are very frequently used and in many cases official methods for moisture determination. These methods, however, do not yield the water content as a result but a mass loss which is caused not only by the evaporati...
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Drying techniques are very frequently used and in many cases official methods for moisture determination. These methods, however, do not yield the water content as a result but a mass loss which is caused not only by the evaporation of water but by all substances volatile under the drying conditions, be they original components of the product or be they produced by decomposition reactions during the drying process. This mass loss varies therefore with the parameters applied like time, temperature, form of energy transfer, atmospheric pressure or surrounding humidity. To shorten determination times of many hours in common air ovens with convective heating techniques with more efficient heating principles have been developed. One of these is infrared drying. With such methods, however, the danger of product decomposition and, consequently, of wrong results rises, particularly when the water content is low. It could be shown, however, that analyses are possible, even for beverage instant powders with very low water contents. Moreover, parameter sets could be found to match the infrared results exactly with the true water content determined by Karl Fischer titration. Another essential finding was that not only the parameters for the drying programme itself like time, temperature and end-point criterion are important, but also, and this to a surprisingly great extent, the number of consecutive measurements and the duration of the intervals between analyses. This effect again depends extremely on the type of apparatus.
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Water content was determined in 11 samples of white yoghurts. Several techniques, namely Karl Fischer (KF) volumetric titration, near and middle infrared spectroscopy (MIR), oven drying and moisture analyser were used. Optimisatio...
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Water content was determined in 11 samples of white yoghurts. Several techniques, namely Karl Fischer (KF) volumetric titration, near and middle infrared spectroscopy (MIR), oven drying and moisture analyser were used. Optimisations of solvent, titration temperature and extraction time were carried out for the KF titration. Methanol at room temperature with 5 min extraction period was used as final conditions. For the infrared spectroscopy (FTIR) the suitable solvent and the appropriate wavenumbers for water analysis were chosen. The measurement in the near infrared (NIR) region at the wavenumber 10270 cm~(-1) using acetonitrile as solvent and transmission method was evaluated as the best of the FTIR methods. Based on the comparison of individual methods the oven drying at 105 ℃ seems to be the most suitable, but it is the most time consuming. However, KF volumetric titration and especially FTIR methods appear to be good alternatives to the drying methods.
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A new method for the fast (less than 5 min) and accurate (better than 0.5% error in water content) measurement of water in sultana raisins without the need for sample weighing has been developed. The method is based on a commercia...
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A new method for the fast (less than 5 min) and accurate (better than 0.5% error in water content) measurement of water in sultana raisins without the need for sample weighing has been developed. The method is based on a commercially available water sensor and probe. Additionally, a raisin press has been developed to prepare the sample for analysis in one step. The results obtained with the proposed method correlate well (R~2 = 0.999) with those obtained using a high speed blending Karl Fischer auto-titrator. The method shows good analytical characteristics, the analysis time is short, and no expensive or dangerous chemical consumables are used. The method can thus be used easily by non-experienced personnel, either on site, or in the laboratory.
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The determination of water content of lactose and the water activity, which is related to it, are important to assess its microbiological stability as well as its technical and commercial quality. Lactose is a very important produ...
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The determination of water content of lactose and the water activity, which is related to it, are important to assess its microbiological stability as well as its technical and commercial quality. Lactose is a very important product in the dairy sector, but also in the pharmaceutical domain. The moisture content in milk products is often determined by gravimetric oven drying at 102 ±2 ℃ until an approximate constant mass is reached. All substances volatile under the conditions applied contribute to the mass loss observed, however, a difference between water and other volatiles is not made. Strongly bound water may, on the other hand, escape detection. This is particularly the case for lactose monohydrate, which occurs in nearly all dairy products. To avoid errors caused by this fact, a method on the basis of the Karl Fischer titration was developed and tested in an international inter-laboratory trial in cooperation with the International Dairy Federation (IDF) and the International Organization for Standardization (ISO). The method is in the final stage for publication as an international standard.
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