SCIENCE BEHIND ANALYTICAL INSTRUMENTS - BASICS

1.0 ABSTRACT Based on the experiment objectives, which is to conduct the simple experiments regarding liquid-liquid extraction and to determine the distribution of coefficient and mass transfer coefficient with the aqueous phase as the continuous medium through liquid-liquid extraction. This experiment is based on the solubility. First experiment, we used separators funnel to separate two solutions of different solubility and densities, and then titrate with 0.1M of NaOH. The values for distribution coefficient by titration with 0.1M are 3.36 in 1.0 ml of propionic acid, 2.70 in 3.0 ml propionic acid and 1.88 in 5.0 ml propionic acid. Second experiment, we used liquid-liquid extraction column to obtain feed, raffinate and extract samples. The samples were titrated with different of NaOH concentration (0.1M and 0.025M). The value of mass transfer coefficient from liquid-liquid extraction are; 0.242 mol/Lmin if titrated with 0.1M NaOH and 0.662 mol/Lmin if titrated with 0.025M NaOH. The experiment was completely and successfully done. 2.0 INTRODUCTION Liquid-liquid extraction also known as solvent extraction and partitioning is a method to separate compounds based on their relative solubility in two different immiscible liquids, usually water and an organic solvent (Propanoic Acid). It is an extraction of a substance from one liquid phase into another liquid phase. Liquid-liquid extraction is a basic technique in chemical laboratories, where it is performed using a separator funnel. This type of process is commonly performed after a chemical reaction as part of the work-up. In other words, this is the separation of a substance from a mixture by preferentially dissolving that substance in a suitable solvent. By this process a soluble compound is usually separated from an insoluble compound. The basic principle behind extraction involves the contacting of a solution with another solvent that is immiscible with the original. The solvent is also soluble with a specific solute contained in the solution. The two phases are formed after the addition of the solvent, due to the differences in densities. The solvent is chosen so that the solute in the solution has more affinity toward the added solvent. Therefore, mass transfer of the solute from the solution to the solvent occurs. Further separation of the extracted solute and the solvent will be necessary. However, these separation costs may be desirable in contrast to distillation and other separation processes for situations where extraction is applicable.

Sample Preparation Techniques for Chemical Analysis, 2021

Comprehensive Analytical Chemistry, 2002

Extraction is normally a laboratory procedure prior to analysis. It is expected to be performed in a reproducible manner, in the fastest possible time and at low cost. Subsequent analysis is then supposed to capitalise on the effectiveness of this process to generate good quality data. However, the weakest link in this process is often neglected as unimportant and time-consuming. It might involve a journey to a site of interest some distance away. The weather might be unfavourable-wet, windy and cold. However, the sampling strategy performed and the nature of the sample type probably have the greatest influence on the result obtained than the rest of the process. Sampling inherently requires a strategy of how best to obtain a representative sample from the location. Then, how best to remove the sample; it is not necessarily a surface sample, but may be sub-surface. Also, how to effectively store the sample, i.e., type of container and method of preservation required. And, finally, how to safely transport it back to the laboratory. It may be that some preliminary sample pre-treatment is necessary, or that the sample requires drying at room temperature, or not for fear of losing volatile compounds. All these stages are necessary to obtain a homogenous and representative sample of appropriate size for the selected extraction techniques.

Analytica Chimica Acta, 2013

h i g h l i g h t s • MINE device-promising step in direct liquid sample preparation. • Solubility parameter applied for prediction of MINE device effectiveness. • Solubility parameter for different compositions of monolithic material.

Journal of Chromatography A, 2013

In chromatographic columns, when the eluting strength of the sample solvent is larger than that of the carrier liquid, a deformation of the analyte zone occurs because its frontal part moves at a relatively high velocity due to a low retention factor in the sample solvent while the rear part of the analyte zone is more retained in the carrier liquid and hence moves at a lower velocity. The influence of this solvent strength effect on the separation of analytes is studied here theoretically using a mass balance model describing the spatio-temporal evolution of the eluent, the sample solvent and the analyte. The viscosity of the sample solvent and carrier fluid is supposed to be the same (i.e. no viscous fingering effects are taken into account). A linear isotherm adsorption with a retention factor depending upon the local concentration of the liquid phase is considered. The governing equations are numerically solved by using a Fourier spectral method and parametric studies are performed to analyze the effect of various governing parameters on the dispersion and skewness of the analyte zone. The distortion of this zone is found to depend strongly on the difference in eluting strength between the mobile phase and the sample solvent as well as on the sample volume.

Analytica Chimica Acta, 2012

THE 5TH INTERNATIONAL CONFERENCE ON MATHEMATICS AND SCIENCE EDUCATION (ICoMSE) 2021: Science and Mathematics Education Research: Current Challenges and Opportunities

Two experimental laboratory procedures for determining the distribution coefficient of analyte between two immiscible solvents have been used as teaching material in an analytical chemistry laboratory. The two teaching materials are the distribution of acetic acid between water & diethyl ether and the distribution of I2 between water and chloroform. Students were assigned to determine the analyte distribution coefficient (Kd) and the effect of analyte concentration on the Kd value. The assessment of experimental procedure performance was based on some criteria (1) visual clarity of chemical changes, (2) the level of laboratory work difficulty, (3) ability of students to determine the appropriate Kd value, (4) ability of students to explain the effect of analyte concentration on the Kd value. The initial trial of the procedure did not demonstrate the optimal expected outcome. Students struggled to experiment smoothly and precisely, implying the necessity to refine the procedure for the next purpose. For example, students failed to determine the correct Kd value and improperly explained the relationship between analyte concentration and Kd value. The students' difficulty in employing the procedure are discussed and considered to produce a valid and reliable procedure.