DETERMINATION OF ORGANIC-ACIDS BY ION CHROMATOGRAPHY IN RAIN WATER INTHE STATE OF ZULIA, VENEZUELA

Ion-exchange chromatography with a Dionex Model QIC system was used to identify and determine formic and acetic acid in event rains collecte d at the La Esperanza site (Zulia, Venezuela). Pyruvic acid was observ ed infrequently and always at very low concentrations. The method can be adapted for the routine determination of these acids, giving result s in less than 12 min (only the chromatogram without column clean-up). A set of calibration graphs for mixed standards with different concen tration ranges (0.5-80 mu M) with a good linear regression (R(2) = 0.9 992-1.0000) were used. The estimated limit of quantification was <0.2 mu M for both acids. Replicate analyses of four different fractions of a certain sample taken and preserved with chloroform showed relativel y good reproducibility (R.S.D. ca. 7%) for both acids, and the results were well within acceptable data quality limits. Both the absolute or ganic acid concentrations and the ratio of organic acid concentrations to inorganic acid concentrations were significantly lower in La Esper anza than those reported at other rural Venezuelan sites. Organic and inorganic anion balances revealed a low potential contribution (ca. 7% ) of formic and acetic acid to the acidity of the rain (volume-weighte d average pH = 4.1). In other rural Venezuelan sites these acids contr ibuted over 60% to the free acidity.