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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The two types of volumetric KF differ in the exact composition of titrant and solvent. Coulometric KF In coulometric KF, the iodine needed by the KF reaction is not present in the KF reagent, but is instead generated electrochemically in situ from iodide at the anode of the generator electrode, a component of the coulometric titration cell Figure 2.
As a guideline, sample sizes shown in Table 1 are recommended for volumetric and qstm KF, respectively.
In coulometry, the quantity of iodine generated corresponding to the amount of water present is calculated by the titrator on the basis of current mA and time sec.
Coulometric KF is most accurate in the range asfm 1 ppm to 5 percent water. 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. Fundamentals of Volumetric Karl Fischer Titration. 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.
However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to reduce the reproducibility of test results.
It is estimated that nearlyKF determinations are performed daily around the world.
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 aatm. The KF method does not suffer from the same issues and limitations associated with the other techniques described above, and a number r6304 recent advances in titrator instrumentation and reagent formulations have further improved the accuracy and reproducibility of KF analyses.
Strategies for Removing Water from Oil. With both types of volumetric KF, imidazole is the base used most frequently as a buffer to maintain optimal pH for the reaction. In other words, the larger the sample, the less error is introduced into the analysis by sample weighing, transfer and other handling.
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. Key Components of a Modern Volumetric KF Titrator Coulometric KF In coulometric KF, the iodine needed by the KF reaction is not present in the KF reagent, but is instead generated electrochemically in situ from iodide at the anode d3604 the generator electrode, a component of the coulometric titration cell Figure 2.
Karl Fischer inKarl Fischer KF analysis has progressed from an esoteric laboratory procedure to a widely accepted instrumental method routinely used for water determination in the petrochemical industry. For those oil samples which fail to adequately dissolve even when using KF reagents formulated with organic co-solvents, or those that are suspected of containing interfering compounds, an indirect KF analysis using an oil evaporator is recommended, as described below.
The end-point determination in KF titration occurs by means of bivoltametric indication. A number of lubricating oil additives are reactive and are known to interfere with direct KF titration. The Best Gets Better: However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction.
Chemistry and Principles Karl Fischer titration proceeds according to a reaction with a two-step mechanism in which sulfur d66304 initially reacts with an alcohol ROH to form an ester intermediate which is neutralized, or buffered, by an appropriate organic base RN.
Some of the modes by which water exists in lubricating oils can lead to catastrophic equipment failure.
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.
Water in oils atm occur in dissolved, emulsified and free states.
Once all the water has reacted with the iodine, trace quantities of free iodine appear in the titration cell, causing a drop in voltage necessary to keep the polarization current constant, which in turn signals the end-point of the titration.
The distillation component of the indirect titration method ensures that astj 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. Reactivity Certain compounds in the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents.
Volumetric KF is most accurate in the range of ppm to percent water. The subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes water in a 1: High water content of d6034 oils negatively impacts the operation and longevity of the oils and the mechanical equipment components being lubricated.
Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF.
KF analysis is a versatile and robust analytical tool for water content analysis in oil samples, and can detect water in any of three states commonly found in oils. The following reactions represent this two-step mechanism. Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample 0.
These include corrosion, erosion, etching and hydrogen embrittlement. 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.
Coulometric KF Titration for ASTM D
Volumetric or coulometric KF methods, utilizing either direct titration or the oil evaporator technique, can be used to quantify water in oil samples from trace amounts d3604 percent. Visual indication is reliable for quantifying water content only in the free state, while the hot plate crackle test can be used to detect free and emulsified water. Modern Instrumental Methods and Techniques.
Recommended Sample Sizes for KF Analysis Sample Size Selection For both direct and indirect KF methods, sample size selection is critical for minimizing errors associated with sample weighing, transfer and injection.
Analyzing Water in Oil
axtm Best Ways to Test for Water in Oil. Since its invention by German petroleum chemist Dr. However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water.