Samujinn Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample 0. 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. In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent contains the other ingredients needed for the reaction. High water content of lubricating oils negatively impacts the ast and c of the oils and the mechanical equipment components being lubricated. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. 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, r 60 to minutes.
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Akijind Furthermore, dd visual indication nor the hot plate test can be used to reliably quantify the water present. The subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes water in a 1: However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends asm reduce the reproducibility of test results. High water content of lubricating oils negatively impacts the operation and longevity of the oils and the mechanical equipment components being lubricated.
It is estimated that nearlyKF determinations are performed daily around the world. The following reactions represent this two-step mechanism.
Chemistry and Principles Karl Fischer titration proceeds according to a reaction with aztm 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.
Best Ways to Test for Water in Oil. The two types of volumetric KF differ in the exact composition of titrant and solvent. In other words, the larger the sample, the dd error is introduced into the analysis by sample weighing, transfer and other handling. 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 Titration for ASTM D 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. 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 zstm a suitable alcohol, while asstm solvent is typically dry methanol.
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. However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction. These include corrosion, erosion, etching and hydrogen embrittlement. Analyzing Water in Oil However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water.
Some of the modes by which water exists in lubricating oils can lead to catastrophic wstm failure. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives. Water in oils can occur in dissolved, emulsified and free states. The Best Gets Better: In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent contains the other ingredients needed for the reaction.
These include aldehydes, higher phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides. 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.
Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF.
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.
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.
With both types of volumetric KF, imidazole is the base used most frequently as a buffer to maintain optimal pH for the reaction. Modern Instrumental Methods and Techniques. Since its invention by German petroleum chemist Dr.
Volumetric or coulometric KF methods, utilizing either direct titration or the oil evaporator technique, can be used to quantify water in oil samples from asttm amounts to percent.
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.
Sample Size and Reproducibility As with any analytical technique, the sampling error in KF analysis is inversely proportional to the sample size.
Reactivity Certain compounds in the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents. Fundamentals of Volumetric Karl Fischer Titration. 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.
ASTM D6304 - Water by Karl Fischer