Determination of Picogram Nitroglycerin Plasma Concentrations Using Capillary Gas Chromatography with On-Column Injection

A specific, sensitive, and precise capillary gas chromatographic (GC) assay capable of analyzing picogram concentrations of nitroglycerin in human plasma was developed. The analytical procedure involves a double extraction of 1mL of plasma with pentane, after the addition of internal standard (1ng of 2,6-dinitrotoluene), followed by evaporation and reconstitution in 50 μL of heptane. The extract (1 μL) was injected onto a capillary column using the on-column injection technique. The GC oven temperature was programmed from 120°C to 180°C at a rate of 5°C/min. The oven temperature was then programmed to 250°C and was maintained for 10min. The nitroglycerin and internal standard retention times were 8.6 and 11.4 min, respectively. The position of the end of the capillary column inside the detector is a critical determinant of sensitivity: the column exit must be positioned such that nitroglycerin adsorption to the detector is minimized (i.e., sensitivity maximized). The assay limit of quantitation was 25 pg/mL (CV = 7.6%) using 1mL of plasma. This GC assay, specific for nitroglycerin in the presence of its metabolites, isosorbide dinitrate, and several other drugs, may be used to quantitate plasma levels obtained after therapeutic nitroglycerin doses.