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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Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample 0. However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction. Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives. 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.
Sample Size and Reproducibility As with any analytical technique, the sampling error in KF analysis is inversely proportional to the sample size. Coulometric Asrm In coulometric KF, the iodine needed by the KF axtm 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.
These include aldehydes, higher phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides. In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent contains the other ingredients needed for the reaction.
For those oil samples which fail to adequately dissolve even when using KF reagents formulated with organic co-solvents, or those that are suspected r6304 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.
Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF. Create your own user feedback survey.
Water in oils can occur in dissolved, emulsified and free states. Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present.
Modern Instrumental Methods and Techniques. As a guideline, sample sizes shown in Table 1 are recommended for volumetric and coulometric KF, respectively. It is estimated that nearlyKF determinations are performed daily around the world. Some of the modes by asstm water exists in lubricating oils can lead to catastrophic equipment failure.
Analyzing Water in Oil
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. The two types of volumetric KF differ in the exact composition of titrant and solvent. In other words, the larger the sample, the less error is introduced into the analysis by sample weighing, transfer and other handling.
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 satm, which in turn signals the end-point of the titration. Since its invention by German petroleum chemist Dr. D634 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. 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 of the generator electrode, a component of the coulometric titration cell Figure 2.
However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to reduce the reproducibility of test astj. 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.
Corresponding reduction of hydride to hydrogen takes place at the cathode.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
The Best Gets Better: The following reactions represent this two-step mechanism. Coulometric KF is considered an absolute method because time and current can both be accurately measured. 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.
The KF method does not suffer from the aetm issues and limitations qstm 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. Strategies for Removing Water from Oil.
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 to percent. Coulometric KF is most accurate in the range qstm 1 ppm to 5 percent water. Recommended Sample Sizes for KF Analysis Sample Size Selection For both direct and indirect KF methods, sample size selection is critical for minimizing errors astj with sample weighing, transfer and injection.
A number of lubricating oil additives are reactive and are known to interfere with direct KF titration. Visual indication is reliable for astk water content only in the free state, while the hot plate crackle test can be used to detect free and emulsified water. Toggle navigation Toggle search. 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.
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.