Trace analysis of volatile organic compounds in water by GC and HPLC

Abstract

<p>Low-molecular weight aldehydes and ketones were concentrated by a hydrophobic zeolite, ZSM-5. The carbonyl compounds (100 ppb) were desorbed with a small volume of acetonitrile and converted to the 2,4-dinitrophenylhydrazones. The derivatized analytes were recovered by solvent extraction (pentane) followed by microdistil- lation. The 2,4-dinitrophenylhydrazones were analyzed by reversed phase HPLC on a C(,18) column at 254 nm. Good recoveries were obtained for the model compounds, except formaldehyde. The method was applied to the analysis of drinking water from Ames, IA (no aldehydes or ketones) and from Des Moines, IA (1.6 ppb butanone);Other polar low-molecular weight compounds (100-200 ppb), diethyl ether, acetates, nitriles, alcohols, aldehydes, ketones and acids were concentrated by the ZSM-5 and Silicalite. Except for methanol, formaldehyde, acetic acid, and propionic acid good recoveries were obtained for model compounds. Concentration factors of 50 to 500 were achieved. Satisfactory desorbing solvents were 1-propanol, acetone, methanol and acetonitrile. The concen- trated solution was injected into a capillary (DBWax, 0.525 mm I.D.) column. The analytes were quantitated by GC with FID;The method of distillation with gas purging (helium) concentrated a variety of classes of organic (amines, alcohols, ketones, aldehydes, esters, phenols, nitriles, chlorinated compounds and polynuclear aromatic) compounds (25 ppm to 25 ppb). The entire apparatus was heated to 85(DEGREES)C or greater. The concentrating column (Tenax) was cooled. For safety a slow heating procedure was devised. The analytes were desorbed from the concentrating column by solvent elution with methanol or acetonitrile. The concentrated solution was injected into a capillary (methyl silicone, 0.525 mm I.D.) column and the analytes were quantitated by GC with FID;Recovery of the analytes was primarily dependent on the water solubility and molecular weight of the analyte. Less sample (more;headspace) was used for the strawberry jello, instant decaffeinated coffee, and shale oil retort water; ('1)DOE Report IS-T-1265. This work was performed under Contract No. W-7405-Eng-82 with the Department of Energy.</p>