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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Since its invention by German petroleum chemist Dr. With both types of volumetric KF, imidazole is the base used most frequently as a buffer to maintain optimal pH for the reaction. Toggle navigation Toggle search. The subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes wstm in a 1: Karl Fischer inSstm 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.
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. 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.
KF analysis is a versatile and robust analytical tool for water content analysis in oil samples, and can detect water in any ast three states commonly found in oils. Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample 0. The end-point determination in S6304 titration occurs by means of bivoltametric indication.
Reactivity Certain compounds in the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents.
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.
Sample Size and Reproducibility As with any analytical technique, the sampling error in KF analysis is inversely proportional to the sample size. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water.
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.
Analyzing Water in Oil
The Best Gets Better: Coulometric KF is considered an absolute method because time and current can both be accurately measured. 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, ast, phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides.
Volumetric KF is most accurate in the range of ppm to percent water. Understanding Oil’s Saturation Point. The two types of volumetric KF differ in the exact composition of titrant and solvent.
Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF.
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. 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.
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.
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.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
A number of lubricating oil additives are reactive and are known to interfere with direct KF titration. However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction. 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. Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives.
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. 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.
Analyzing Water in Oil
These include corrosion, erosion, etching and hydrogen embrittlement. It is estimated that nearlyKF determinations are performed daily around the world.
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. Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present. High water content of lubricating oils negatively impacts the operation and longevity of the oils and the mechanical equipment components being lubricated.
The following reactions represent this two-step mechanism. 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.
In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent contains the other ingredients needed for the reaction. However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to reduce the reproducibility of test results.
Finding the Source of Water Contamination in Oil. Best Ways to Test for Water in Oil.
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 d63044 from iodide at the anode of the generator electrode, a component of the coulometric titration cell Figure 2. Fundamentals of Volumetric Karl Fischer Adtm.
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.
Current Issue Archive Advertise. 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.
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 zstm chloroform, toluene and xylene.
Coulometric KF Titration for ASTM D
Some of the modes by which water exists in lubricating oils can lead to catastrophic equipment failure. 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.
Strategies for Removing Water from Oil. In other words, the larger the sample, the less error is introduced into the analysis by sample weighing, transfer and other handling. Modern Instrumental Methods and Techniques. Corresponding reduction of hydride to hydrogen takes place at the cathode. Create your own user feedback survey.