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 Best Gets Better: As a guideline, sample sizes shown in Table atm are recommended for volumetric and coulometric KF, respectively. Best Ways to Test for Water in Oil.
Some of the modes by which water exists in lubricating oils can lead to catastrophic equipment failure. 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 aatm intermediate which is neutralized, or buffered, by an appropriate organic base RN.
Analyzing Water in Oil
It is estimated that nearlyKF determinations are performed daily around the world. In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent contains the other ingredients needed for the reaction.
With both types of volumetric KF, imidazole is the base used most frequently as a buffer to maintain optimal pH 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 of containing interfering astn, 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.
Understanding Oil’s Saturation Point. Coulometric KF In coulometric KF, the iodine needed by the KF reaction dd6304 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. 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.
Coulometric KF Titration for ASTM D
These include aldehydes, higher phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides. Corresponding reduction of hydride to hydrogen takes place at the cathode. However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction. 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.
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.
Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF.
Analyzing Water in Oil
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.
Current Issue Archive Advertise. High water content of lubricating oils negatively impacts the operation and longevity of the oils and the mechanical equipment components being lubricated. Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives.
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.
Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. A number of lubricating oil additives are reactive and are known to interfere with direct KF titration. Since its invention by German petroleum wstm Dr. However, neither of these methods can detect dissolved water or asfm detect trace levels of emulsified water. Toggle navigation Toggle search.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
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.
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.
Reactivity Certain compounds in the oil will undergo interfering xstm reactions either with methanol or iodine components of KF reagents. Modern Instrumental Methods and Techniques.
The subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes water in a 1: Additionally, because the oil qstm contains a miniaturized distillation set-up, only small sample 0.
Volumetric KF is most accurate in the range of ppm to percent water. Visual indication is wstm for quantifying water content only in the free state, f6304 the hot plate crackle test can be used to detect free and emulsified water. Water in oils can occur in dissolved, emulsified and free states.
Coulometric KF is considered an absolute method because time and current can both be accurately measured. Create your own user feedback survey. 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 following reactions represent this two-step mechanism. 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.