Analysis of histamine and N tau-methylhistamine in plasma by gas chromatography-negative ion-chemical ionization mass spectrometry.

ABSTRACT

Current methods of quantitation of histamine and its major metabolite N tau-methylhistamine are inaccurate and insensitive to the very low concentrations that exist in plasma samples. Therefore, an accurate and sensitive method for quantification in plasma has been developed using the stable isotope dilution assay with negative ion-chemical ionization mass spectrometry. For histamine, after the addition of [2H4]histamine to 2 ml of plasma, the plasma sample is deproteinized, extracted into butanol, back extracted into HCl, derivatized to the pentafluorobenzyl derivative (CH2C6F5)3-histamine, purified on silica gel columns, and then quantified with negative ion-chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions m/z 430/434. For N tau-methylhistamine, after the addition of N tau-[2H3]methylhistamine to 2 ml of plasma, the plasma sample is deproteinized, extracted into butanol, back extracted into HCl, derivatized to the heptafluorobutyryl derivative (C3F7CO2)2-N tau-methylhistamine, purified on silica gel columns, and then quantified with negative ion-chemical ionization mass spectrometry by selected ion monitoring of the ratio of ions m/z 497/500. The precision of the histamine assay is 3.1% and the accuracy is 95.5 +/- 2.5% while the precision of the N tau-methylhistamine assay is 1.9% and the accuracy is 106.8 +/- 1.9%. The lower limits of sensitivity are 1 pg for histamine and 6 pg for N tau-methylhistamine injected on column. Using the assay in three normal human volunteers, plasma concentrations of histamine were 130, 92, and 85 pg/ml, and of N tau-methylhistamine were 229, 228, and 216 pg/ml. This assay provides a very sensitive and accurate method of quantitation of histamine and N tau-methylhistamine in plasma samples.