DETERMINATION BY ION CHROMATOGRAPHY OF SELECTED ORGANIC AND INORGANICACIDS IN RAINWATER AT MARACAIBO, VENEZUELA

Chemically suppressed ion chromatography with a Dionex Model 2000i/sp, IonPac AS11, IonPac AG11, ASRS-I system was used for the analysis of major organic and inorganic acids in precipitation samples collected i n the city of Maracaibo during a one-year period. Two different isocra tic methods were used. First, inorganic (sulfuric, nitric and hydrochl oric) acids were adequately determined by using 21 mM NaOH as eluent. Second, organic (formic and acetic) and hydrofluoric acids were determ ined by using 0.5 mM NaOH as eluent; however, occasional poor resoluti on of acetic and hydrofluoric acid peaks were obtained. The methods sh owed good reproducibility (R.S.D. ca. 5%) for primary inorganic anions plus formate and relatively poor reproducibility (R.S.D. ca. 15%) for fluoride plus acetate. In the Maracaibo rainwater system, the concent rations of the typical urban pollutants (SO4, NO3-, Cl*, H+) are sign ificantly larger than those found in Caracas precipitation, suggesting that Maracaibo is affected to a greater extent by air pollution. NO3- and Cl- dominated the anionic composition. About 92% (as SO4) and 50 % (as Cl) of the total each ion concentration was represented by non- marine derived species. Organic and inorganic anion balances showed th at potential acid rain (volume-weighted average pH=5.35) in Maracaibo is mainly caused (ca. 90%) by sulfuric, nitric and hydrochloric acids. Only about 4% of the original acidity of the rainwater was found to b e fr ee acidity, indicating a high degree of neutralization in the Mar acaibo precipitation. (C) 1998 Elsevier Science B.V.