High-Performance Liquid Chromatography

HPLC Full Form in English, letter by letter

HPLC is a laboratory technique that separates, identifies and measures the components of a liquid mixture by pumping it through a packed column.

HPLC Full Form in Indian Languages

When a medicine batch is cleared in an Indian quality-control lab, an HPLC instrument has often given the number. The term is short for High-Performance Liquid Chromatography, and its name in six Indian languages is below.

The principle in one paragraph

High-Performance Liquid Chromatography separates the parts of a mixture by pushing a liquid sample through a column packed with very fine particles. Each component interacts differently with the packing, called the stationary phase, so each travels at its own speed and comes out of the column (elutes) at its own retention time.

A detector at the end records each component as a peak. The retention time tells you what the compound is, and the area under the peak tells you how much of it there is, once compared with a standard of known strength. The liquid is pumped at high pressure, often several hundred bar, so the separation is fast and sharp. That is the 'high performance' in the name. Older books call the technique high-pressure liquid chromatography, and both names refer to the same method.

The instrument, part by part

Pump, injector and column

The pump delivers the mobile phase at a precise flow rate. It can keep a fixed mixture (isocratic) or change the mixture during the run (gradient) to bring out strongly held compounds. An autosampler injects a few microlitres of sample. The column is where the separation happens. A common choice is a C18 reverse-phase column, about 150 to 250 mm long, packed with particles of 2.5 to 5 micrometres. It is the most expensive consumable in the lab.

Detector and data system

A UV-visible detector, which measures absorbance at a chosen wavelength, is the standard. Fluorescence and refractive-index detectors serve special cases. Joining an HPLC to a mass spectrometer (LC-MS/MS) gives both identification and very high sensitivity, which is why pesticide-residue and anti-doping work depends on it. The software integrates the peaks and keeps an audit trail, as regulated laboratories require.

Where HPLC is used in India

Pharmaceutical quality control is the largest user. Drug makers test the strength of active ingredients and look for related impurities by HPLC, following methods in the Indian Pharmacopoeia or the USP. The National Dope Testing Laboratory in New Delhi, which is accredited by WADA, uses LC-MS/MS to screen athletes' samples.

Food-testing laboratories check for antibiotic and pesticide residues, in line with FSSAI limits, and environmental laboratories measure contaminants in water. Hospital and reference laboratories use LC-MS/MS for some drug-level and vitamin tests, where the gap between a useful dose and a toxic dose is small.

Method validation and sample preparation

A method can be used for reporting only after validation. Analysts have to show specificity, linearity, accuracy, precision, limit of detection, limit of quantitation and robustness, following the ICH Q2 guideline. Many Indian laboratories also hold NABL accreditation, which requires reference standards, calibrated instruments and trained staff.

Sample preparation is the unglamorous half of the work: filtering, extracting and diluting. It is also the usual source of bad results. A clogged column or a badly prepared sample can give neat-looking peaks that mean nothing. Experienced analysts spend more time on preparation than on the run itself.

A short worked example shows the use. A tablet is labelled as 500 mg. The analyst grinds several tablets, dissolves them in a measured volume of solvent, filters the liquid and injects it. The peak area is compared with that of a reference standard of known strength, and the result is reported as a percentage of the label claim, which must usually fall within limits set in the pharmacopoeia.

HPLC compared with GC and UHPLC

HPLC handles molecules that do not vaporise easily or break down on heating, which covers most drug substances. Gas chromatography needs the sample to turn into a gas, so it suits volatile compounds such as solvents. Each technique answers a different question, and a pharma lab usually has both.

The trade-offs are cost and skill. An LC-MS/MS system costs crores, method development needs real expertise, and columns wear out. Ultra-high-performance liquid chromatography (UHPLC) uses particles below 2 micrometres and pressures above 400 bar to cut a thirty-minute run to a few minutes. Waters launched the first commercial UHPLC system in 2004. The whole field goes back to Mikhail Tsvet, who separated plant pigments in a glass column in 1903 and gave chromatography its name.

If you are heading into a chemistry laboratory, learn the column first, because that is where the separation and most of the cost sits. After that, practise reading a chromatogram until retention time and peak area make sense.

HPLC Full Form: Common Questions