HPLC (high-performance liquid chromatography)

HPLC stands for High-Performance Liquid Chromatography, a laboratory analytical technique that separates the individual compounds in a liquid mixture by pumping it under high pressure through a packed column, then detects each as it emerges. In air monitoring it is the standard method for measuring polycyclic aromatic hydrocarbons (PAHs), especially benzo(a)pyrene — large, heavy organic molecules that are collected on filters, extracted into a solvent, and then quantified by HPLC.

HPLC is a laboratory, not a field, method: the air sample is collected over the averaging period, taken to a lab, the PAHs extracted and concentrated, and then run through the instrument. It is highly sensitive and specific, capable of measuring benzo(a)pyrene at the NAAQS level of 1 ng/m³ and distinguishing it from the dozens of related PAH compounds — a separation that simpler methods cannot achieve.

For recyclers, HPLC is the method behind the benzo(a)pyrene and PAH figures in ambient air reports and in any occupational or environmental PAH assessment. PAHs are a defining hazard of thermal processing of plastics, rubber and tyres — concentrated in char, heavy pyro-oil and soot — so for pyrolysis operators the HPLC-derived PAH number is the parameter that quantifies one of their most serious carcinogenic risks.

The practical relevance is interpretive and procedural: a recycler will not run HPLC in-house, but should ensure that PAH/benzo(a)pyrene monitoring required by the SPCB or by occupational-safety good practice is carried out by an NABL-accredited laboratory using HPLC (or GC-MS) on properly collected samples. Knowing that PAH measurement is lab-based and not instantaneous also sets realistic expectations for turnaround and cost in compliance planning.