Determination of water content in bee’s pollen samples by Karl Fischer titration

It was analyzed the water content of three pollen samples from three different sources, using the classical chemical method (Karl Fischer). It is very important for this method to select the proper work conditions because pollen has a complex composition. For Karl Fischer’s method we selected the most adequate solvents, temperature and particle size. The Karl Fischer titration in a mixture of solvents (Hydranal^® solvent and n-octanol) at high temperature (50 °C) is the most indicated for the determination of water content in these products.     

Efficient,precise and fast water determination by the Karl Fischer titration

One of the most widely used techniques for the water content determination in food is Karl Fischer (KF) titration. The primary advantage with respect to methods based on loss of weight is its high selectivity to water. On the other hand, KF titration is only possible when water in food samples is freely available. Thus, a suitable sample preparation to release water completely has to be selected and done prior to the KF titration. Although KF titration itself is a fast method (1–2 min for a single analysis), the sample preparation step is time-consuming, e.g. 1–2 h when performing an external extraction. The use of a high-speed stirrer for internal homogenization, in addition to fast control algorithms in automatic KF titrators, offers a fast, quick and efficient alternative to more traditional sample preparation techniques. Sample preparation and stirring time can be considerably reduced, and auxiliary solvents can be avoided. The whole analysis is completely automated. In this contribution the use of high-speed homogenizers in KF titration will be discussed in detail.     

Uncertainty evaluation and validation of the test specimen size reduction in the determination of water content in crude oils by coulometric Karl Fischer titration

The authors aim to evaluate the uncertainty and to validate the test specimen size reduction in the determination of water content in crude oils by coulometric Karl Fischer titration. The most relevant uncertainty sources are the volume of the microsyringe (resolution and temperature effect) and the repeatability. F-test and t-test show that there is no significant effect in the reduction of the test specimen size.     

Comparison between Karl Fischer and refractometric method for determination of water content in honey

The aim of this work was to compare refractometric index (RI) and Karl Fischer (KF) titration methods for water content measurement in honeys. In addition, the effectiveness of two different solvents (methanol (M) and methanol:formamide in the ratio 1:1 (M + F)) was evaluated.Results indicated that RI and KF methods yielded similar results for water content determination in honeys; mainly, when the solvent M + F was used. This solvent mixture (M + F) also allowed a reduction in titration time which may be a potential advantage for measuring water content in honey.     

Quality versus economical aspects in determination of water in crude oils: Centrifuge method or potentiometric Karl Fischer titration

The authors’ objective is to evaluate economical aspects versus quality of three different approaches to determine water in crude oils. The first two are based on potentiometric Karl Fischer titration, normal and reduced size (lower reagent consumption) of the test sample, and the last one is the centrifuge method. To help the best understanding of the potentiometric Karl Fischer titration method, the authors detail its uncertainty evaluation. When their results are compared by analyses of variance, it is not observed statistical differences among these approaches. Finally, the costs are described in order to shed light on which one to choose once all of them show compatible quality.     

New Karl Fischer reagents for the water determination in food

New non-toxic Karl Fischer reagents for water determination based on ethanol as solvent has been developed in the last year. To prove their suitability in the ambiguous filed of food analysis a variety of samples were analysed using conventional methanol-based reagents and the new ethanolic reagents. Since the most kind of food consists of polar substances the methanolic reagents give faster results. The non-toxic ethanol-based reagents are preferred for non-polar samples as butter.     

卡尔菲休库仑法水分测量影响因素分析

针对使用卡尔菲休库仑法测量水分,研究了环境水分、样品预热处理和取样量对卡尔菲休库仑法测量水分的影响。结果表明:环境水分是导致卡尔菲休法测量水分结果出现误差的最主要因素;经过预热处理的样品水分测量结果的准确性好于未经过预热处理的;取样量的多少影响到水分测量结果的重复性和准确性,取样量大则测定的准确性高、重复性好,环境水分对结果的影响就减弱了。     

采用非水滴定法测定羧基丁腈橡胶中的羧基含量

建立了一种采用非水滴定法测定羧基丁腈橡胶中羧基含量的方法,并考察了该方法的准确度和精密度。该方法以非水溶剂丁酮溶解试样,然后以KOH-乙醇标准溶液中和,滴加酚酞作指示剂,并用盐酸标准溶液返滴定过量的KOH。测试结果表明,该方法的回收率为97.3%～103.4%,标准偏差不大于0.040%。     

弹性石英毛细管和卡尔费休库仑法测定乙烯、丙烯中微量水

以弹性石英毛细管作为节流和气化元件,采用卡尔费休库仑法测定聚合级乙烯、丙烯中微量水,方法准确可靠,检测限可达1μg/g,相对标准偏差不大于5%,回收率为94%～110%,并与电容式湿度计的测定结果进行对比,结果吻合。     

无苯溶剂-等量电位滴定法测定油品中碱性氮化物含量

以乙酸-丙酸混合物(二者体积比为1∶3)为高氯酸滴定剂溶剂,石油醚-乙酸混合物(二者体积比为1∶1)为样品溶剂,同时采用两步溶解方式,运用等量电位滴定法测定油品中的碱性氮化物含量。结果表明,新溶剂配方的0.02 mol/L高氯酸滴定液,在凝固点下降同时,标定终点清晰,稳定性良好;以原油为基体,蜡油为标准物,通过回收率实验进行了方法准确度测定,回收率为98.6%~103.0%,表明该方法的准确度高;无论是浅色油品还是深色油品,最大相对标准偏差为1.83%,实际样品的5次测定结果的最大差值仅为允许差值(SH/T 0162标准规定的重复性指标)的25%~100%。     

Main and side reactions in the Karl Fischer solution

The new investigations show that in Karl Fischer (KF) solutions various equilibria compete depending on the reaction conditions. In alcoholic media mainly alkyl sulphite is oxidised. The oxidation of hydrogen sulphite has only a small influence, which increases with rising water concentrations and proceeds via SO₃ as intermediate product. The oxidation of the SO₂ by aerial oxygen takes place as a side reaction in the KF reagents. In here alkyl sulphate and sulphate are formed in almost equal concentration, indicating, that hydrogen sulphite is oxidised.     

原子荧光光谱法测定生活水中硒含量

测定硒含量是生活饮用水中的重要分析项目,使用原子荧光光谱测定硒具有多种优点,但是对仪器的操作条件非常苛刻,设置不当会影响测定结果的准确度。依照《生活饮用水标准检验方法金属指标》,寻找测定生活饮用水中硒的最佳条件。     

Reliable Determination of Water Contents of Bitumen and Vacuum Residua via Coulometric Karl Fischer Titration Using Tetrahydrofuran

Standard methods for water content analysis in crude oil are difficult to apply or even fail for bitumen and residual samples that are routinely enriched in water contents. A fast and simple coulometric Karl Fischer (KF) determination of water contents in heavy oil samples was conceived. Tetrahydrofuran was selected for bringing oil and bitumen samples spanning any water percentages into homogeneous solution. Analysis repeatability was deemed reasonable (less than 1.6% relative standard deviation). Correction factors were found mandatory for getting accurate results, as electrode symmetry overtitration effects were observed to affect the analysis.     

紫外分光光度法测定炼油废水中的石油类含量

采用红外、紫外、荧光3种方法测定炼油厂废水中石油类的含量，并对测定结果进行归纳分析，讨论了3种方法的准确度和优缺点，认为紫外分光光度法测定炼油厂废水中的石油类含量是可行的。     

Determination of the water content in different sugar syrups by halogen drying

Sugars are heat sensitive. The determination of the water content by drying methods is therefore problematic, particularly when vigorous heating principles are used. A method is described for determining the water content of invert sugar and fructose syrups by halogen drying, a new variation of infrared drying. Parameter sets could be found in a way that the mass loss measured corresponded to the water content found by Karl Fischer titration that served as reference method. In these situations two opposed sources of error account for each other, the additional determination of other volatiles than water formed by the heat treatment on the one hand, and, on the other hand, the non-detection of strongly bound water or water trapped in the sample by a crust formed on the sample surface at the end of the drying process.     

Determination of water content in crude oil emulsion by LF-NMR CPMG sequence

Transverse relaxation times (T2) and T2 spectrum for crude oil emulsions with different water content are obtained by low field nuclear magnetic resonance Carr-Purcell-Meiboom-Gill sequence and various methods to determine the water content are investigated. The results show that there are three methods to accurately determine the water content. When water content is greater than 20.0wt%, determination through T2 value of emulsions is fastest with the relative error below 2.5%. T2 spectrum show the characteristics of multiple peaks, and T2 value of the peaks originated from water are suitable for determination of water content for O/W emulsions. A method is developed and optimized to determine the water content by using the peak-area ratio in T2 spectrum, which is not limited by the water content and the form of emulsion.     

自动电位滴定法测定炼油厂酸性水中氯离子的含量

介绍自动电位滴定法测定炼油厂酸性水中氯离子含量。炼油厂酸性水样品经加热煮沸、双氧水氧化等预处理后,以硝酸银标准溶液为滴定剂,在自动电位滴定仪上进行电位滴定。实验表明,本方法可以用来测定浑浊带色度的炼油厂酸性水,且对样品的酸碱度没有苛刻要求,过量的双氧水对测定结果没有影响。     

Karl Fischer Titration to determine moisture in honey: A new simplified approach

Honey, produced by Apis mellifera from nectar or honeydew, contains a discrete quantity of water (about 17%). The variability of water content influences the quality, the stability, the workability and the storage of honey. Moisture in honey is usually measured via determination of refractive index (RI); from the value measured, the percentage is calculated by an empirical formula or by “conversion” table. A possible alternative approach is the Karl Fischer Titration (KFT). The objective of this work was to find the optimal parameters for water determination in honey with KFT without any heat treatment of sample or working medium and the measurement of water content in more than 100 honeys of different botanical origin, using RI and KFT determinations. The water content, obtained with KFT, was usually higher than that determined by RI analysis. According to our results KFT seems to be the most reliable method.