Distillation methods, such as ASTM D95 and D provide better . This innovative KF technique is incorporated in ASTM D (Method B) and is applicable. If a crackle test is positive, further testing is needed to quantify the amount of water by using The Karl Fischer Water titration by ASTM D A measured. Feb 24, The KF Coulometer from Metrohm is the perfect instrument to satisfy ASTM D
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Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present. The two types of volumetric KF differ in the exact composition of titrant and solvent. The end-point determination in KF titration occurs by asttm of bivoltametric indication. However, due to solubility and reactivity issues described above, analysts often drastically d63304 sample size, which tends to reduce the reproducibility of test results.
Distillation methods, such as ASTM D95 and D provide better quantitative data in the range of approximately ppm to 25 percent, but require large sample sizes and involve long analysis times, typically 60 to minutes. Reactivity Certain compounds ashm the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents.
Water in oils can occur in dissolved, emulsified and free states.
Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF. However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction.
As a guideline, sample sizes shown in Table 1 are recommended for volumetric and coulometric KF, respectively.
Coulometric KF Titration for ASTM D
In one-component KF, the titrant usually referred to as a CombiTitrant or a composite contains all the ingredients needed for the KF reaction, namely iodine, sulfur dioxide, base and a suitable alcohol, while the solvent is typically dry methanol. The subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes water in a 1: Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives.
A number of lubricating oil additives are reactive and are known to interfere with direct KF titration. Used oils may also contain contaminants that can potentially interfere with direct KF analysis, such as trace metals, polyaromatic hydrocarbons, polychlorinated biphenyls, as well as various products of incomplete combustion.
Modern Instrumental Methods and Techniques. In other words, the larger d634 sample, the less error is introduced into the analysis by sample weighing, transfer and other handling. It is estimated that nearlyKF determinations d63304 performed daily around the world. Volumetric or coulometric KF methods, utilizing either direct titration or the oil evaporator technique, can be d630 to quantify water in oil samples f6304 trace amounts to percent.
Toggle navigation Toggle search. That is, while the iodine in the KF reagent is reacting with water, there is no free iodine present in the titration cell, and a high voltage is required to maintain the set polarization current at the double platinum pin indicator electrode.
Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample 0. The technique also offers other substantial advantages over more conventional hot plate crackle test and distillation methods, and it has been incorporated into numerous ASTM standards.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water. Fundamentals of Volumetric Karl Fischer Titration. Best Ways to Test for Water in Oil.
Since its invention by German petroleum chemist Dr. Current Issue Archive Advertise. The distillation component of the indirect titration method ensures that the hard-to-dissolve oil samples, or those containing potentially interfering compounds, are not introduced to the titration cell, while the KF titration component of the method accurately quantifies the water content of the azeotropic vapor carried into the titration cell by the dry gas. Techniques for Successful KF of Oil Samples Direct Titration Sample solubility issues may be overcome by using co-solvents such as chloroform, toluene or xylene to increase the solvent capacity of conventional KF reagents in the titration cell.
Analyzing Water in Oil
With both types of volumetric KF, imidazole is the c6304 used most frequently as a buffer to maintain optimal v6304 for the reaction. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. These include aldehydes, higher phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides. Finding the Source of Water Contamination in Oil. The procedure involves adding the oil sample to the solvent present in the evaporation chamber where it dissolves in the solvent, and in the process forms a binary azeotrope between the solvent and the sample’s water content.
The following reactions represent this two-step mechanism. The KF method does not suffer from the same issues and limitations associated with the other techniques described above, and a number of recent advances in titrator instrumentation and reagent formulations have further improved the accuracy and reproducibility of KF analyses.
These include corrosion, erosion, etching and hydrogen embrittlement. Chemistry and Principles Karl Fischer titration proceeds according to a reaction with a two-step mechanism in which sulfur dioxide initially reacts with an alcohol ROH to form an ester intermediate which is neutralized, or buffered, by an appropriate organic base RN. Oils have limited solubility in alcohols, such as methanol, which are typically used in common KF reagent formulations, while they are fully soluble in organic solvents like chloroform, toluene and xylene.