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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Some of the modes by which water exists in lubricating oils can lead to catastrophic equipment failure.
Metrohm: Coulometric Karl Fischer Titration for ASTM D6304
Corresponding reduction of hydride to hydrogen takes place at the cathode. Sample Size and Reproducibility As with any analytical technique, the sampling error in KF analysis is inversely proportional to the sample size. 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.
Modern Instrumental Methods and Techniques. Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present. These include corrosion, erosion, etching and hydrogen embrittlement. 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.
Coulometric KF is considered an absolute method because time and current can both be accurately measured. 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.
However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water. 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.
Create your own user feedback survey. 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.
Volumetric KF is most asym in asttm range of ppm to percent water. Reactivity Certain compounds in the oil will undergo interfering side reactions either with methanol or iodine components of KF reagents. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. 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.
However, alcohols cannot be completely removed from KF reagents, because the presence of alcohol is required by the mechanism of the KF reaction. In two-component KF, the titrant contains only an alcoholic solution of iodine, while the solvent asmt the other ingredients needed for the reaction.
Analyzing Water in Oil
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. 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. 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 Best Gets Better: 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.
High water content of lubricating oils negatively impacts the operation and longevity of the oils and the mechanical equipment components being lubricated. The two types of volumetric KF differ in the exact composition of titrant and solvent.
The end-point determination in KF titration occurs by means of bivoltametric indication. With both types of volumetric KF, imidazole is the base used most frequently as a buffer to maintain optimal pH for the reaction.
Best Ways to Test for Water in Oil. Strategies for Removing Water from Oil.
d3604 Current Issue Archive Advertise. However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to satm the reproducibility of test results. Additionally, water has been known to cause certain oil additives to precipitate out, as well as to chemically attack some additives.
These include aldehydes, higher phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides. It is estimated that nearlyKF determinations are performed daily around the world. 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.
In other words, the larger the sample, atm less error is introduced into the analysis by sample weighing, transfer and other handling.
Techniques for Successful KF of Oil Samples Direct Titration Sample solubility issues may be overcome by using adtm such as chloroform, toluene or xylene to increase the solvent capacity of conventional KF reagents in the titration cell. Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF. 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.
As a guideline, sample sizes shown in Table 1 are recommended for volumetric and coulometric KF, respectively.