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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A number of lubricating oil additives are reactive and are satm to interfere with direct KF titration. KF analysis is a versatile and robust analytical tool for water content analysis in oil samples, and can detect water in ashm of three states commonly found in oils. 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.
Analyzing Water in Oil
The Best Gets Better: 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. These include aldehydes, higher phenols, modified asgm, ketoacids, polysiloxanes, sulfides and metal oxides. Fundamentals of Volumetric Karl Fischer Titration. The subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes water in a 1: Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF.
Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present. Once s6304 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.
Types of Titration Volumetric KF Volumetric KF proceeds in the conventional manner of a classic titration, in that the titrant containing iodine is added mechanically to the solvent containing the sample by the titrator’s burette Figure 1.
Best Ways to Test for Water in Oil. However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction. Additionally, d604 has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives.
The following reactions represent this two-step mechanism. Modern Instrumental Methods and Techniques. Strategies for Removing Water from 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.
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.
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. Understanding Oil’s Saturation Point. 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.
Some of the modes by which water exists in lubricating oils can lead to catastrophic equipment failure. Toggle navigation Toggle search. 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. Volumetric KF is most accurate in the range of ppm to percent water. However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to reduce the reproducibility of test results.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
Corresponding reduction of hydride to hydrogen takes place at the cathode. 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. Sample Size and Reproducibility As with any analytical technique, the sampling error in KF analysis is inversely proportional to the sample size.
The end-point determination in KF titration occurs by means of bivoltametric indication. 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. d63004
Create your own user feedback survey. Key Awtm 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.
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.
Analyzing Water in Oil
Karl Fischer inKarl Fischer KF analysis has progressed from an esoteric laboratory procedure to atsm widely accepted instrumental method routinely used for asym determination in the petrochemical industry. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. Since its invention by German petroleum chemist Dr. Reactivity Certain compounds in the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents.
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.