Certification by the Karl Fischer method of the water content in SRM 2890, Water Saturated 1-Octanol, and the analysis of associated interlaboratory bias in the measurement process

The calibration of Karl Fischer instruments and reagents and the compensation for instrumental bias are essential to the accurate measurement of trace levels of water in organic and inorganic chemicals. A stable, non-hygroscopic standard, Water Saturated Octanol, which is compatible with the Karl Fischer reagents, has been prepared. This material, Standard Reference Material (SRM) 2890, is homogeneous and is certified to contain 39.24 ± 0.85 mg water/mL (expanded uncertainty) of solution (47.3 ± 1.0 mg water/g solution, expanded uncertainty) at 21.5?°C. The solubility of water in 1-octanol has been shown to be nearly constant between 10?°C and 30?°C (i.e., within 1% of the value at 21.5?°C). The results of an interlaboratory comparison exercise illustrate the utility of SRM 2890 in assessing the accuracy and bias of Karl Fischer instruments and measurements.     

Interlaboratory assessment of measurement precision and bias in the coulometric Karl Fischer determination of water

The precision and bias of the coulometric Karl Fischer ASTM method D1533-00 have been assessed in a collaborative ASTM round robin program for a group of 34 laboratories. The test materials used in this study included water saturated 1-octanol (WSO), water saturated 1-butanol (WSB), and a series of new and used transformer oil samples. Fundamental systematic biases have been demonstrated in the accuracy of the measurement of water in the WSO, WSB, and transformer oil samples. The systematic bias in the measurement of the WSO and WSB standards indicates that for some laboratories either the instruments were not accurate or the quantity of the standard was not measured accurately. A second type of systematic bias consisted of measurement errors associated with the selection of the Karl Fischer solvent that was used with each instrument, and this was superimposed upon the error in the measurement of the water in the standards. Using the statistical calculation method ASTM D 6300 the repeatability and reproducibility for water in transformer oil were found to be 7 mg/kg and 14 mg/kg respectively. The method detection limit of water was 8 mg/kg oil. The method bias was estimated based on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 2890, WSO, since no suitable reference material for water in transformer oil was available for this study.     

Karl Fischer titration A method for determining the true water content of cereals

A variation of the Karl Fischer titration was developed to measure the water content of cereals such as various grains and flours. The presented method is based on an elevated working temperature. It can even reach the boiling point of the working medium which contains methanol as solvent. The influence of different sample preparations is also discussed. A standardized procedure could be found to achieve highly reproducible and statistically safe results. The proposed titration method can be carried out with titrators of different manufacturers. The method may serve as a reference technique for these products and, by consequence, as calibration method for other more rapid methods, which may then be used in the daily laboratory practice or in industrial production lines. Received: 28 April 1997 / Revised: 17 July 1997 / Accepted: 24 July 1997     

Youden analysis of Karl Fischer titration data from an interlaboratory study determining water in animal feed, grain, and forage

Data from a recent interlaboratory study of the determination of water (moisture) in animal feed, grain, and forage (plant tissue) by Karl Fischer titration were re-analyzed using Youden plots. The purpose was to show the unique ability these plots possess of separating random and systematic errors visually while providing numerical estimates of the precision and the systematic error of the method. Furthermore, the usefulness of the technique is underscored because AOAC INTERNATIONAL allows the use of matched pairs in collaborative studies to obtain estimates of repeatability and reproducibility.     

Determination of the water content of amphiphilic liquid crystals by coulometric Karl Fischer titration

An apparatus is described, which allows the precise determination of the water content of amphiphilic liquid crystals by means of coulometric Karl Fischer titration. The scope and limitations of this method are described.     

A coulometric method for determining substances that interfere with the measurement of water in oils and other chemicals by the Karl Fischer method

In order to fulfill a need to measure water in crude oils containing materials that interfere with the measurement of water by the Karl Fischer method, by reacting with iodine or iodide, a coulometric method has been developed and validated using 0.1 mol L(-1) Sodium thiosulfate as a calibrant. These interfering substances were measured in water-mass-equivalents, which were expressed as the mass of water that reacts with an equal mass of iodine in the Karl Fischer method. The SO(2)-free reagent that has been modified reacts quantitatively with sodium thiosulfate, cysteine and ascorbic acid but does not react with vinyl acetate. The level of interfering substances was measured in five transformer oils (including Reference Materials RM 8506 and RM 8507), a high and a low sulfur crude oil (Standard Reference Materials SRM 2721 and SRM 2722 respectively), a white oil, a high-vacuum oil and a high-viscosity base-stock oil. One oil contained less than 10 mg kg(-1) (water-mass-equivalents of interfering substances in oil) and two oils (RM 8507 and Drakeol 35) contained no measurable amount of interfering material (<0.2 mg kg(-1)). SRM 2271, a sour crude oil contained 834 mg kg(-1) (standard deviation (SD)=25 mg kg(-1)) (water-mass-equivalents of interfering substances in oil). Approximately 20% of this material was volatile and an additional 20% appeared to undergo some degradation (possibly oxidation) once the oil was exposed to air. These results indicate that this is a general method for measuring substances in oils that react with iodine and that it is capable of measuring in a variety of oils, using commercial instrumentation, interfering substances that inflate water measurements.     

Determination of total water content in inulin using the volumetric Karl Fischer titration

A new sample preparation method for the water content determination of inulin by volumetric Karl Fischer (KF) titration was developed and compared to the usual method of introducing the sample directly in the methanol-based working medium, modified or not by formamide (1:3, v/v) in order to increase sample solubility. In the proposed method, inulins were externally prepared by dissolving them in pure formamide (2.5:7.5, w/w). The time of analysis of the liquid/liquid reaction of the new method between the dissolved sample and the reaction medium is about 1–2 min, while the usual KF method is stopped after the 10 min delay time. The developed method permits the determination of water included in the crystals of the sample, confirmed by analysing both crystalline and amorphous inulin samples. Another advantage of this new method is its applicability for the water content determination of other polysaccharides that are not readily soluble in the working medium. Moreover, water content determination can be done by any type of volumetric KF titrator, as this proposed technique is not dependent on any additional tools such as a built-in homogeniser or a heatable titration beaker.     

Comparison of standards in the Karl Fischer method for water determination.

The use of 4-(5-nonyl)pyridine oxide and trioctylamine oxide for the extraction of niobium(V) from different mineral acid solutions is described. The influence of the concentration of the solvents, acids and salting-out agents is discussed. Separations of niobium(V) from tantalum(V) and zirconium(IV) have been achieved.     

Assessment and assurance of quality in water measurement by coulometric Karl Fischer titration of petroleum products

The precise and accurate determination of water in petroleum products—gasoline, diesel oil and aromatic hydrocarbons—is of significant importance for their normal functional and operational characteristics for economics as well as in meeting international requirements. The standard method ISO 12937 for the measurement of water by the coulometric Karl Fischer titration method was subject to within-laboratory assessment. Thereby it was established that the analytical procedure could not always be relied upon, especially when low levels of water were determined. The aim of this work is to assess each stage of the test procedure depending on the particular problems defined by the samples, using high-reactive Karl Fischer reagents and coulometric cells with and without a diaphragm, and to indicate the major factors causing the uncertainty. A reduced combined uncertainty was achieved by modifying the sample preparation step, the administration of the moisture in the coulometric cell, and sample injection manipulation. Experiments showed that the cell without the diaphragm ensures lower and uniform uncertainty of the measurements in the range of 0.01 to 10 mg H₂O in comparison to the cell with a diaphragm and therefore is more appropriate for the determination of low water levels in the petroleum products. A procedure that utilized a mixture of the reagent and toluene (10:6) was able to resolve the problem of two phases of formation and reduced conductivity of the reagent in direct titration of diesel oils. The results suggest that the modified procedure ensures relative expanded uncertainty equal to or less than 2.0% (n=5, confidence interval close to 95%) and 99.4% recovery for petroleum products investigated in repeatability conditions.     

Comparison between amperometric and true potentiometric end-point detection in the determination of water by the Karl Fischer method

A rapid and sensitive method using true potentiometric end-point detection has been developed and compared with the conventional amperometric method for Karl Fischer determination of water. The effect of the sulphur dioxide concentration on the shape of the titration curve is shown. By using kinetic data it was possible to calculate the course of titrations and make comparisons with those found experimentally. The results prove that the main reaction is the slow step, both in the amperometric and the potentiometric method. Results obtained in the standardization of the Karl Fischer reagent showed that the potentiometric method, including titration to a preselected potential, gave a standard deviation of 0.001(1) mg of water per ml, the amperometric method using extrapolation 0.002(4) mg of water per ml and the amperometric titration to a pre-selected diffusion current 0.004(7) mg of water per ml. Theories and results dealing with dilution effects are presented. The time of analysis was 1-1.5 min for the potentiometric and 4-5 min for the amperometric method using extrapolation.     

Application of the Karl Fischer method to the determination of the moisture content in insulating papers

Summary A modified extraction method has been developed for the determination of the moisture content of insulating papers used in condensers and transformers. The water is extracted from the paper sample with methanol continuously titrated with Karl Fischer reagent by means of the special apparatus devised. The method can advantageously be used to measure the adsorption isotherms of paper samples containing 0.05–2 % water.

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Zusammenfassung Eine modifizierte Extraktionsmethode für die Feuchtigkeitsbestimmung in Isolierpapier, wie es für Kondensatoren und Transformatoren verwendet wird, wurde ausgearbeitet. Das Wasser wird aus der Papierprobe mit Methanol extrahiert, das kontinuierlich mit Karl Fischer-Reagens in einer speziellen Apparatur titriert wird. Das Verfahren kann vorteilhaft zur Messung der Adsorptionsisothermen von Papierproben mit einem Wassergehalt von 0,05–2% verwendet werden.

     

无吡啶卡尔.费休试剂微库仑法测定石油产品中微量水分的研究

研究了无吡啶卡尔·费休试剂的组成及特性，并建立了利用无吡啶卡尔·费休的微库仑法测定石油产品中水含量的分析方法。方法用二乙醇胺代替吡啶制备成新的卡氏试剂、无臭味、操作方便、分析速度快、灵敏度高、重复性好，其检测下限为１．０μｇ／ｇ，实际样品测定的相对标准偏差小于５％。方法应用于石油产品中水分的测定，结果令人满意。     

Water determination of precursor solutions with oxidant cations by the Karl Fischer method: the YBCO-TFA case

Uncontrolled water content in non-aqueous precursor solutions can be a source of irreproducibility in thin film performance through changes in the gel network. Towards gaining control on the solution properties, water determination in metalorganic solutions of YBCO-TFA has been studied by the Karl Fischer titration in a volumetric-type unit. However, oxidizing cations usually present when preparing functional oxides by chemical solution routes severely interfere in the Karl Fischer analysis. In the case of YBCO-TFA, cupric ions in the initial solution oxidize the iodide produced in the Karl Fischer reaction back to iodine, which in turn feeds the titration reaction and consumes more water, causing a negative error in the analysis, which can be as large as 70%. However, such chemical interference of cupric salts can be modelled and quantified. A corrected Karl Fischer methodology is proposed for accurately measuring water content in YBCO-TFA solutions, which could be potentially extended to other precursor solutions containing oxidant cations.     

Determination of water in organic solvents by flow-injection analysis with Karl Fischer reagent and a biamperometric detection system

A flow-injection system with a biamperometric flow-through detector provided with two platinum plate electrodes was tested for the determination of water with a two-component pyridine-free Karl Fischer reagent. The response was shown to be linear in the concentration range 0.03-0.11% water in methanol, ethanol or 2-propanol, with methanol as the carrier solvent. The maximum sampling frequency was about 150 samples per hr. It appeared to be possible to introduce a membrane separation step, thus allowing for the determination of water in fouled process streams. To avoid direct contact between the Karl Fischer solution and the pumping tubes, and thus extend the lifetime of the tubes, an indirect delivery system, based on replacement of the solution by pumped silicone oil, was also applied.     

Thermodynamics of the Solubility of Water in 1-Hexanol, 1-Octanol, 1-Decanol, and Cyclohexanol

Summary. The solubility of water in 1-hexanol, 1-octanol, 1-decanol, and cyclohexanol was determined as a function of water activity by the isopiestic method at 298.2K. The solubility of water in the alcohol was expressed by a Setchenov type of equation and the correlation coefficients were related to the virial coefficients of the McMillan-Mayer theory of solution. From the solubility data both the activities and the osmotic coefficients of the alcohols were calculated. The Henrys law constants for the solubility of water in the alcohols are given. They depend linearly on the Gibbs energy of hydration. The excess Gibbs energy of mixing of water and alcohols is positive as a consequence of the strong intermolecular interactions of the two pure components of the mixture.     

Certification of the methylmercury content in SRM 2977 mussel tissue (organic contaminants and trace elements) and SRM 1566b oyster tissue

The methylmercury content in two new marine bivalve mollusk tissue Standard Reference Materials (SRMs) has been certified using results of analyses from the National Institute of Standards and Technology (NIST) and two other laboratories. The certified concentrations of methylmercury were established based on the results from four and six different (independent) analytical methods, respectively, for SRM 1566b Oyster Tissue (13.2 +/- 0.7 microg/kg) and SRM 2977 Mussel Tissue (organic contaminants and trace elements) (36.2 +/- 1.7 microg/kg). The certified concentration of methylmercury in SRM 1566b is among the lowest in any certified reference material (CRM).     

Certification of the methylmercury content in SRM 2977 Mussel Tissue (organic contaminants and trace elements) and SRM 1566b Oyster Tissue

The methylmercury content in two new marine bivalve mollusk tissue Standard Reference Materials (SRMs) has been certified using results of analyses from the National Institute of Standards and Technology (NIST) and two other laboratories. The certified concentrations of methylmercury were established based on the results from four and six different (independent) analytical methods, respectively, for SRM 1566b Oyster Tissue (13.2 ± 0.7 μg/kg) and SRM 2977 Mussel Tissue (organic contaminants and trace elements) (36.2 ± 1.7 μg/kg). The certified concentration of methylmercury in SRM 1566b is among the lowest in any certified reference material (CRM).     

Significant improvements in the analysis of perfluorinated compounds in water and fish: Results from an interlaboratory method evaluation study

The 2nd international interlaboratory study (ILS) on perfluorinated compounds (PFCs) in environmental samples was organized to assess the performance of 21 North American and European laboratories on the analysis of PFCs in water and fish. A study protocol was provided to assess accuracy, precision, matrix effects and to study the use of in-house standards. The participants used shared native and mass-labelled standards that were provided for this study to quantify the PFC concentrations in the samples. Matrix effects in the determination of PFCs can be considerable and can decrease the sensitivity, the accuracy and internal standard recoveries. Therefore, two quantification methods were evaluated by all laboratories: standard addition quantification (SAQ) and solvent-based calibration curve quantification (SBCCQ; using mass-labelled internal standards (IS)). The between laboratory reproducibility (i.e. coefficient of variance) was smaller for the SBCCQ results (except for PFBS and PFHxS for which no mass-labelled analogues were available) compared to those obtained by the SAQ method. The within laboratory precision of individual laboratories is good (mean for all PFCs in water 12% and 6.8% in fish). The good performance is partially attributable to the use of well-defined native- and mass-labelled standards. Therefore, the SBCCQ method is recommended. The results show that analytical methods for PFCs in water and fish have improved considerably. Critical steps identified in this study are (i) the use of well-defined native standards for quantification, (ii) the use of mass-labelled internal standards (preferably one for each target compound) and (iii) minimization of matrix effects by a better clean up.     

Determination of water (moisture) and dry matter in animal feed, grain, and forage (plant tissue) by Karl Fischer titration: collaborative study

A Karl Fischer method for determining water (dry matter) in animal feed and forages was collaboratively studied. Water was extracted from animal feed or forage material into methanol-formamide (1 + 1) directly in the Karl Fischer titration vessel by high-speed homogenization. The water was titrated at 50 degrees C with one-component Karl Fischer reagent based on imidazole. Ten blind samples were sent to 9 collaborators in the United States, Canada, and Germany. The within-laboratory relative standard deviation (repeatability) ranged from 1.14 to 6.99% for water or from 0.09 to 0.56% for dry matter. Among-laboratory (including within-) relative standard deviation (reproducibility) ranged from 5.35 to 10.73%, or from 0.44 to 0.77% for dry matter. The authors recommend that the method be adopted as Official First Action by AOAC INTERNATIONAL. A comparable alternative extraction procedure using boiling methanol is also recommended for Official First Action.