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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Reactivity Certain compounds in the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents. Karl Fischer inKarl Fischer KF analysis f6304 progressed from an esoteric laboratory procedure to a widely accepted instrumental method routinely used for water determination in the petrochemical industry. The Best Gets Better: 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.
Coulometric KF is most accurate in the range of 1 ppm to 5 percent water.
Analyzing Water in Oil
However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to reduce the reproducibility of test results. 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.
Understanding Oil’s Saturation Point. 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.
Additionally, because the oil evaporator contains a miniaturized distillation set-up, only small sample 0. Water in oils can occur in dissolved, emulsified and free states. Strategies for Removing Water from Oil. Fundamentals of Volumetric Karl Fischer Titration.
Analyzing Water in Oil
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.
Current Issue Archive Advertise. Since its invention by German petroleum chemist Dr. Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF. Asgm subsequent oxidation of the alkylsulfite salt to an alkylsulfate salt by iodine consumes water in a 1: In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent contains the other ingredients needed for the reaction.
The two types of volumetric KF differ in the exact composition of titrant and solvent. Finding the Source of Water Contamination 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, r6304 iodine, sulfur dioxide, base and a suitable alcohol, while the solvent is typically dry methanol.
Techniques for Successful KF of Oil Samples Direct Titration Sample solubility issues may be overcome by using co-solvents such as chloroform, toluene dd6304 xylene to increase the solvent capacity of conventional KF reagents in the titration cell. 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.
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.
A number of lubricating oil additives are reactive and are known to interfere with direct KF titration. Oils have limited solubility in alcohols, such as methanol, which are typically dd6304 in common KF reagent formulations, while they are fully soluble in organic solvents like chloroform, toluene and xylene.
Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives. 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.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water. The following reactions represent this two-step mechanism. Corresponding reduction of hydride to hydrogen takes place at the cathode.
Volumetric or coulometric KF methods, utilizing either direct titration or the oil evaporator aetm, can be used to quantify water in oil samples from trace amounts to percent. 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.
It is estimated that nearlyKF determinations are performed daily around the world. As a guideline, sample sizes shown in Table 1 are recommended for volumetric and coulometric KF, respectively. 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.
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.