Thursday, April 23, 2020

What is the difference between LC and HPLC?

High-performance liquid chromatography (HPLC) is a widely used separation technique for the qualitative and quantitative analysis of compounds. HPLC, also known as high-pressure liquid chromatography, it is an advanced version of LC. In HPLC, we inject the sample solution through the syringe into the injector, the mobile phase carries it through a stationary phase (column) that isolates the molecule based on its affinity.HPLC has a wide range of applications, such as pharmaceuticals, forensics, clinical, and food analysis.
The major difference between traditional LC and HPLC is that the mobile phase of liquid chromatography moves by the gravity force while the mobile phase of HPLC flows through the high pressure that is created by the pump, which decreases the analysis time.

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Sunday, April 12, 2020

What is the stationary phase in thin-layer chromatography?

Thin Layer Chromatography is a type of chromatography that is used to separate the non-volatile molecules. The separation process of TLC is executed on the sheet of aluminum, plastic, or glass. This sheet is usually formed by a thin layer of silica gel, aluminum oxide, or cellulose and acts as a stationary phase. The analytes are move by the mobile phase in the capillary action and they separate based on their affinity towards the stationary phase.
The uncoated silica gel is one of the most commonly used stationary phases in thin layer chromatography (TLC). Silica gel is a kind of silicon dioxide. The silica gel remains the significant adsorbent for different types of chromatography, such as high-performance liquid chromatography (HPLC), column chromatography, high-performance thin-layer chromatography (HPTLC), and thin-layer chromatography (TLC). The significant benefit of silica is its incredible affinity for adsorption. Silica gel is a slightly acidic and polar adsorbent in nature that has a high ability to adsorb basic compounds. The alumina also used as a stationary phase in TLC since it has a high ability to retain acidic components because it is slightly acidic. This is ideal to isolate the weak or moderately polar components.

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What is the stationary phase in column chromatography?

Column chromatography is a type of chromatography used to separate and purification of sample components. It is a solid-liquid method where the solid stationary phase and mobile phase is a liquid that is used in the process of separation. The principle of column chromatography is based on the differential adsorption of the analytes by the adsorbent.
The stationary phase of column chromatography is the adsorbent. The stationary phase of column chromatography generally is a solid (adsorption) or a liquid (partition) the material used in the stationary phase depends on the compounds want to separate. Generally, silica, alumina, calcium phosphate, calcium carbonate, starch, and magnesium are used. Solvent or mobile phase selection is dependent on both the solvent and the adsorbent nature. The rate of separation of the analytes of a sample mixture depends on the solvent polarity and activity of the adsorbent. If the adsorbent activity is high and the polarity of the solvent is low, the separation is very slow however providing a good separation.

Advantages of TLC over column chromatography

The thin-layer chromatography and column chromatography both are the types of chromatography that are used to separates the compounds. The basic principle of TLC and column chromatography is the adsorption of the solutes. The column chromatography and TLC are one of the most commonly used techniques in analytical techniques since they have many advantages and applications. Both techniques have the same stationary and mobile phases hence the TLC is used to find an appropriate mobile phase or solvent system and Rf value.
Here are mentioned some advantages of TLC over column chromatography.
  • The Rf value in TLC can be easily calculated.
  • TLC has a broad range of solvents than column chromatography.
  • The results of thin-layer chromatography have more specific individual spots; therefore it becomes easier to differentiate them.
  • TLC required fewer amounts of solvents to separate the analytes than the column chromatography.
  • The molecules in TLC have to travel distance less as compared with column chromatography, hence it saves time.
  • The preparation of samples in thin layer chromatography is easy as compared to column chromatography, the column chromatography required a large amount of sample.

Why silica gel is used as a stationary phase in column chromatography?

Column chromatography is the most efficient technique of separating and purifying components, in which the solid stationary phase and a liquid mobile phase used. In the process of separation, the column is filled with silica gel, a sample compounds placed on top of the column, and then the mobile phase moves from the solid support under the force of gravity. Depending on differing affinity of molecules to the stationary phase they are isolated and separated into fractions.
Silica gel as a stationary phase is largely accepted as one of the top adsorbents used in column chromatography as well as other separation techniques. One of the major advantages is its tremendous affinity for adsorption. Additionally, it is commercially very readily available in several different sizes and types and there is a huge of information and research that is given by producer on its many uses, particularly in chromatography. The major significant reason for silica gel used as a stationary phase in column chromatography is that it has feasible to obtain the extract essential size of the particle size for a particular method.
Silica gel is a polar adsorbent that is slightly acidic and has a strong capacity to adsorb the basic substance. Alumina is slightly basic and has a strong capacity to retain acidic molecules. This is better to separate the analytes that are moderately or weak polar. The silica gel is most widely used in the reversed-phase partition chromatography and it has broad applications that consist of separation of steroids, amino acids, lipids, alkaloids, and several pharmaceutical processes.

What are the 4 types of titration?

A titration is a method by which a known concentration solution is used to determine the concentration of an unknown solute. The titrant is usually applied from a burette to a known compound quantity unless the reaction is complete. The titrations can be classified into four types, acid-base titrations, redox titrations, precipitation titrations, and complexometric titrations, etc.
1. Acid-base titrations: The acid-base titration is used to find out the unknown acid or base concentration, which is neutralized with a known concentration acid or base. The concentration can be measured using the stoichiometry of the reaction. It uses the neutralization reaction that takes place amongst the acid and the base and how it will react when the acid and base formulas are known.
2. Redox Titrations: Redox titration is a technique of measuring the concentration of a given compound due to a redox reaction between titrant and compound. Sometimes, these forms of titrations include the use of a redox indicator or potentiometer. It works based on the reaction of oxidation-reduction between the compound and the titrant. Determining the concentration of unknown compounds is one of the most common laboratory methods. 
3. Precipitation Titrations: Precipitation titration is a titrimetric method that involves the formation of precipitates during the process of titration. In which the titrant reacts with the compound and forms an insoluble matter and this titration continued until the final drop of the compound is consumed. If the titrant is excess it will react with the indicator and indicate to end the titration process.
4. Complexometric Titrations: In this type of titration the metal ion reacts with the indicator and forms metal indicator complex. Subsequently, ethylenediaminetetraacetic acid is added that reacts with a metal ion to form a metal-EDTA complex that is extra stable than the metal-indicator complex. Hence the metal-indicator complex subsequently breaks down and gives free metal ions to react with EDTA. Free metal ions are not present at the equivalent point and therefore free indicator ion provides a color that is distinct from the metal indicator complex color. 

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