HPLC- Overview

HPLC (High-performance liquid chromatography) – what is it?

High-performance liquid chromatography, or HPLC for short, is an analytical procedure utilised to isolate, differentiate, or quantify any element in a combination.

The combination is isolated based on the principles of column chromatography, and spectroscopy is used to identify and quantify it.

The development of column chromatography from low-pressure compatible glass columns to high-pressure compatible metal columns occurred in the 1960s.

In essence, HPLC is a much enhanced variation of column liquid chromatography. A solvent is forced via a column under high pressures ranging up to 400 atmospheres, as opposed to being allowed to flow through it under the influence of gravity.

The Principle of High-Performance Liquid Chromatography (HPLC)

• Purification occurs in an isolation column between a fixed and portable phase.
• The stationary portion of a separation column consists of a granular material with very minute porous granules.
• The mobile phase, on the other hand, is a solvent or solvent mixture which is forced via the isolation column at high pressure.
• The specimen is introduced into the portable phase circulation from the pump to the isolation column via a valve containing a sample loop, including a microtube or stainless steel capillary.
• As a result of interactions with the stationary phase, the various components of the sample are maintained to variable degrees, which causes them to migrate across the column at various speeds.
• After exiting the column, each chemical is identified by an appropriate detector, which sends information to the HPLC application on the computer.
• During the completion of this operation or run, the computer’s HPLC software generates a chromatogram.
• The chromatogram enables the detection and measurement of the various solutions.

Instrumentation for High-Performance Liquid Chromatography (HPLC)

The Pump

• The pump system has been created as a consequence of the evolution of HPLC.
• The pump generates a stream of extractant from the tank into the system and is located in the upper stream of the liquid chromatography system.
• A “typical” need of pumps is the ability to generate high pressure. However, the pump should also be able to maintain a steady pressure under all conditions and a consistent flow rate.
• The majority of pumps utilised in contemporary LC systems generate flow by moving a motor-driven piston back and forth (reciprocating pumps). Because of the piston motion, it produces “pulses.”

Injector

• Located adjacent to the pump is an injector.
• The sample is injected into the eluent flow using the simplest approach, which involves a syringe.
• Sampling loops are the foundation of the most popular injection technique.
• The usage of the autosampler (auto-injector) technology, which enables repeated injections at certain scheduled times, is also quite common.

Column

• Within the column, isolation is performed.
• Rather than glass, contemporary columns are frequently encased in stainless steel.
• As opposed to calcium carbonate, silica or polymer gels are the most commonly used wrapping materials.As LC eluents, acidic to basic solvents may be used.
• Since stainless steel is robust to a large variety of solvents, it is often used for column housing.

Detector

• Within the column, analyte separation is performed, and the obtained isolation is evaluated by a detector.
• Whenever an analyte is absent, the composition of the eluent stays unchanged. When the eluent’s composition is altered by the analyte’s presence, A detector performs measurement of these differences.
• As a kind of electrical signal, this discrepancy is tracked. There are several detectors available.

Recorder

• Since a detector detects the change in eluent as an electrical impulse, it still isn’t visible to the human eye.
• Historically, pen (paper) chart recorders were commonly used. A computer-based data processor (integrator) is increasingly popular these days.
• In addition to data acquisition, there are numerous types of data processors, varying from simple systems with an integrated printer and word processor to those with software designed specifically for a liquid chromatography (LC) system and including features such as peak-fitting, baseline correction, automatic concentration calculation, molecular weight determination, etc.

Degasser

Human-invisible gases, such as oxygen, may be present in the eluent utilized for LC analysis.

• An unstable baseline results from the detection of gas as noise in the eluent.
• Degasser removes gases using special polymer membrane tubing.
• The surface of the polymer tube has many very tiny holes that let air pass through, but do not permit liquid to do the same.

Column Heater

Frequently, the column temperature has a substantial effect on the LC isolation.

• Maintaining constant temperature conditions is crucial for getting reproducible outcomes.
• With higher temperatures (50 to 80 °C), particular analyses, like sugar and organic acid, may also achieve better resolutions.
• In the column oven, columns are often retained as a result (column heater).

Types of High-Performance Liquid Chromatography (HPLC)

1. Normal phase

Silica is an example of a polar column packed, whereas water is a non-polar mobile phase. It is employed with chiral substances, geometric isomers, cis-trans isomers, and water-sensitive substances.

2. Reverse phase:

The mobile phase is water with a miscible solvent, and the non-polar column packing is C18 (e.g., methanol). It may be used to sample polar, non-polar, ionizable, and ionic. 

3. Ion exchange

Column packing comprises ionic groups, and the mobile phase is a buffer. Anions and cations are separated using this.

4. Size exclusion

In a porous medium, molecules diffuse into the pores and are segregated based on how big they are compared to the pores. Large molecules elute first, followed by smaller ones.

Applications of High-Performance Liquid Chromatography (HPLC)

In practically all branches of chemistry, biochemistry, and pharmacology, HPLC has evolved into a generally applicable approach.

• Drug evaluation
• An examination of artificial polymers
• Pollutant analysis in environmental analytics
• Drug detection in biological matrices
• Isolation of priceless goods
• Controlling the purity and quality of delicate chemicals and industrial items
• biopolymer separation and purification, such as those of enzymes or nucleic acids
• purifying of water
• Trace component pre-concentration
• Chromatography using ligand exchange
• Protein ion-exchange chromatography
• Carbohydrate and oligosaccharide high-pH anion-exchange chromatography

Advantages of High-Performance Liquid Chromatography (HPLC)

1. Speed
2. Efficiency
3. Accuracy
4. versatile and very accurate in recognising and quantifying chemical constituents.

Limitations

• Cost: Despite its benefits, HPLC may be expensive since it calls for significant quantities of pricey organics.
• Complexity
• Some substances are difficult to identify using HPLC because they are permanently adsorbed, while others are just weakly detectable.
• Gas chromatography is more effective in separating volatile compounds.

References

• https://www.shodex.com/en/kouza/a.html
• https://www.alphacrom.com/en/hplc-basics
• https://laboratoryinfo.com/hplc/
• https://sciencing.com/disadvantages-advantages-hplc-5911530.html
• https://www.slideshare.net/krakeshguptha/hplc-26970638
• https://www.chemguide.co.uk/analysis/chromatography/hplc.html
• https://www.azom.com/article.aspx?ArticleID=8468
• https://www.ru.ac.za/media/rhodesuniversity/content/nanotechnology/documents/chromatography%20Augustus.pdf