Aliphatic Hydrocarbon (ALI) analysis is a quantitative technique used for the determination of normal alkanes with 10 to 34 carbons (C10 to C34), and the isoprenoids pristane and phytane, in extracts of sediment and water. This technique is very sensitive for "fingerprinting" petroleum and for following its degradation in the environment. Quantitation is performed by high-resolution capillary gas chromatography with flame ionization detection (GC/FID). Method detection limits for compounds determined using this method are very low (< 0.02 mg/dry g for sediment, and < 0.32 mg/L for water).

The gas chromatograph is temperature-programmed and operated in split mode. The capillary column is a Restek Scientific RTX-1 (30 m long by 0.25 mm ID and 0.25 mm film thickness) or equivalent. Carrier flow is regulated by electronic pressure control. Dual columns and FIDs are used and the data acquisition system is HP Chemstation software, capable of acquiring and processing GC data.

An analytical set consists of standards, samples, and quality control samples (method blank, duplicate, matrix spike, matrix spike duplicate and standard reference material).

A calibration curve is established by analyzing each of 5 calibration standards (1.25, 10, 25, 40 and 50 mg/ml), and fitting the data to a straight line using the least square technique. For each analyte of interest, a response factor (RF) is determined for each calibration level. All 5 response factors are then averaged to produce a mean relative response factor for each analyte. Calibration check standards are interspersed throughout an analytical batch in order to insure the instrument's integrity. A diluted oil standard is used as a retention index solution for compounds not found in the calibration solution.