Karl Fischer titrator, automatic

Although the DL 40 was capable of performing Karl Fischer water titrations and Mettler developed a separate microprocessor-controlled push-button operated DL 18 KF titrator, they also introduced as an all-purpose apparatus the improved DL 40 RC (see Fig. 5.11) with a dual titration head and with a modified software program to handle the new two-component titrants for Karl Fischer titration (see pp. 204-205). The instrument can also be expanded into an automatic series titrator by connecting the RT 40 sample transport for 16 samples and storage of 50 sample weights from a connected balance this series routine can be interrupted at any time after completion of the titration in progress. 

IL. Dilute solution viscosity measurements were done at 30 with the appropriate Ostwald-Fenske capillary viscometers. The water content of all organic solvents, used as the liquid phase in solid-liquid PTC runs was analyzed by potentiometric Karl Fischer titration using a Metrohm AG CH 9100 model automatic titrator. 

Karl Fischer titration assembly, automatic (Metrohm 701 or 758, Brinkmann or... 

The water analyses were carried out using an automatic Karl Fischer titrator (Aquatest II) and normally no problems were encountered. However, for the benzene-water-hydrochloric acid system, the acid strongly interfered with the water analyses. With a slight modification of operating procedure, reasonably satisfactory, but low precision, results were obtained For these analyses, the sample was introduced into the analyzer by injection with the syringe needle below the surface of the vessel solution and every benzene injection was preceded by a 100 yl methanol sample. 

An end point in a Karl Fischer titration can be observed visually based on the brown color of the excess reagent. More commonly, however, end points are obtained from electroanalytical measurements. Several instrument manufacturers offer automatic or semiautomatic instruments for performing Karl Fischer titrations. All of these are based on electrometric end point detection. The details of operation of Karl Fischer titrators are discussed in Chapter 22. 

The Karl Fischer test method ASTM D-6304) can be applied to the direct determination of water in lubricating oil. In this method, the sample injection in the titration vessel can be done volumetrically or gravimetrically. The instrument automatically titrates the sample and displays the result at the end of the titration. Viscous samples can be analyzed by using a water vaporizer accessory that heats the sample in the evaporation chamber, and the vaporized water is carried into the Karl Fischer titration cell by a dry, inert carrier gas. 

Karl Fischer titration is specified for use in plasticizers. The method determines free and Itydration water in solid and liquid samples. In most cases, automatic titration is used and this is the main subject of standard but manual titration method is also included in the appendix. The sample containing a maximum of 100 mg of water is dissolved in a suitable solvent and titrated with Karl Fischer reagent which consists of iodine, sulfur dioxide, organic base, and solvent. The titration end-point is determined amperometrically. The ASTM method lists numerous substances in which the presence of water can be determined. There is also a list of substances which interfere with measurements. 

Karl Fischer titrations are frequently used for the analysis of water content in such samples as food materials, pharmaceuticals, and solvents used in industrial applications, or for the determination of hydration water in crystals. Dedicated units are commercially available and many automatic titra-tors or pH meters feature a connector for current biased voltage measurements labeled Karl-Fischer or simply KF . 

Figure 6 Close-up of Karl Fischer titration vessel containing Karl Fischer reagent, electrodes, automatic stirrer, and portable hygrometer. 

Presently there is available on the market commercial Karl Fischer titration assemblies, some of which automatically stop the titration at the end point Instructions for operation of these devices are provided by the manufacturer and not described herein. This test method is not intended for use with coulometric Karl Fischer titrators. 

Considering the related Mettler DL 40 and DL 40 RC MemoTitrators, the DL 40 can be used for ten different volumetric and potentiometric methods titration to a pre-selected absolute (EPA) or relative (EPR) end-point equilibrium titration (EQU)-recording titration (REC)-incremental titration (INC) Karl Fischer water determination (KF)-controlled dispensing (DOSE) pH and pX measurements (pX/E) multi-level titrations and back-titrations with automatic calculation (CALC) and manual titration (MAN)-automatic calibration of electrodes (CAL). 

Metrohm have also designed the 672 Titroprocessor with the 655 Dosimat (Fig. 5.14 and p. 319) as a rapid routine titrator with three functions SET as an end-point titration, GET as a titration to find one or more equivalence points and KFT for Karl Fischer or other titrations with polarized electrodes it can be expanded into an automatic series titrator by connecting the 624 Sample Changer for ten samples. 

A number of instrument manufacturers offer automatic coulometric titrators, most of which employ a potentiometric end point. Some of these instruments are multipurpose and can be used for the determination of a variety of species. Others are designed for a single type of analysis. Examples of the latter are chloride titrators, in which silver ion is generated coulometrically sulfur dioxide monitors, where anodically generated bromine oxidizes the analyte to sulfate ions carbon dioxide monitors, in which the gas, absorbed in monoethanolamine, is titrated with coulometrically generated base and water titrators, in which Karl Fischer reagent (see Section 20C-5) is generated electrolytically. 

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