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 end-point determination in KF titration occurs asm means of bivoltametric indication. 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.
Corresponding reduction of hydride to hydrogen takes place at the cathode. 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
These include aldehydes, higher phenols, modified mercaptans, ketoacids, polysiloxanes, sulfides and metal oxides. 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 ashm KF reagents in the titration cell.
The KF method does not suffer from the same issues ast, 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.
However, due to solubility and reactivity issues described above, analysts often drastically reduce sample size, which tends to reduce the reproducibility of test results. 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.
Volumetric KF is most accurate in the range of ppm to percent water.
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. Best Ways to Test for Water in Oil. Coulometric KF is considered an absolute method because time and current can both be accurately measured. The following reactions represent this two-step mechanism.
Current Issue Archive Advertise. Water in oils can occur in dissolved, emulsified and free states.
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. However, neither of these methods can detect dissolved water or reproducibly detect trace levels of emulsified water.
In other words, the larger the sample, the less error is introduced into the analysis by sample weighing, transfer and other handling.
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. Furthermore, neither visual indication nor the hot plate test can be used to reliably quantify the water present. 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.
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.
Analyzing Water in Oil
It is estimated that nearlyKF determinations are performed daily around the world. Fundamentals of Volumetric Karl Fischer Titration. Coulometric KF is most accurate in the range of 1 ppm to 5 percent water. Alternatively, specially preformulated KF reagents incorporating one or several of these solvents are commercially available for both volumetric and coulometric KF. 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.
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.
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. 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.
As a guideline, sample sizes shown in Table 1 are recommended for volumetric and coulometric KF, respectively. Understanding Oil’s Saturation Point.
Analyzing Water in Oil
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. The two types of volumetric KF differ in asgm exact composition of titrant and solvent.
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.