1631
Anal. Chem. 1082, 54, 1631-1633
Determination of Trace Levels of Quaternary Ammonium Compounds in River Water by Liquid Chromatography with Conductometric Detection Vlctorlo T. Wee* and ,tulle M. Kennedy The Procter & Gamble Company, Environmental Safety Department, Ivorydale Technlcal Center, Cincinnatl, Ohio 452 17
An analytical method has been developed to isolate and concentrate trace levels of long alkyl chain quaternary ammonium compounds fromi river water. The extracted quaternary ammonium compounds are separated and quantified by using high-performance liquid chromatography with a conductivity detector. Thia unique feature of this method Is the chromatographic system. For the first time, non-UV absorbing long alkyl chain qiuaternaries are determined at submicrogram quantity without any form of derlvatlratlon. I n addition, Ion chromatography is performed in a nonaqueous media, wtthout lon pairing, and in the absence of a suppressor column. The new method was used to determine two non-UV absorbing quaternaries, dlltallowdimethyiammoniumchloride and dodecyltrimethylamnronium chloride, and two UV-absorbing quaternaries, steairyldlmethylbenrylammonlumchloride and 1-hexadecylpyrlldinlum chloride, In several river waters.
Quaternary ammonium compounds containing at least one long hydrophobic alkyl chain are used commercially as disinfectants, fabric softening agents, foam (depressants,and antistatic agents ( I ) . As ingredients in consumer products, the quaternaries are gene rally discharged to surface waters via wastewater treatment plants. While there are currently several metholds (2-13) for the determination of quaternaries, none can offer the desired combination of being rapidl, direct, quantitative, specific, and sensitive. Gas chromatography (GC), for instance, is rapid and sensitive, but involves the analysis of degraded intermediates (6-8). A combined colorimetric/thin-layer chromatography (TLC), although direct, is semiquantitative, long, and tedious (11). By far the most promising and convenient approach has been high-performance liquid chromatography (HPLC). The application of HPLC, however, has been limited to UV-absorbing quaternaries because of the absence of a universal, sensitive detector (2-4). A review of some of these methods is presented in a recent article (14). This paper presents a new analytical procedure for the quantitation of both UV and non-UV absorbing quaternaries. The procedure includes a simple and efficient scheme to extract the quaternary ammonium compound from river water matrices. An interesting feature of this analytical procedure is the chromatographic system that consists of an HPLC coupled with a conductivity detector. This combination had been used in the past for the determination of inorganic ions (15) and low molecular weight, water soluble, pH dependent, organic ions (16). Chromatography was always performed in this type of analysis with an aqueous mobile phase where the p H of the solution could be altered to vary sensitivity and selectivity. An aqueous medium was also necessary in order to induce ionization since the sensitivity of the conductivity detector is directly proportional to the degree of ionization. Furthermore, suppressor columns (16) or aqueous media of 0003-2700/82/0354-1631$01.25/0
low conductivity (15) were normally used to increase detector sensitivity by reducing background conductivity of the eluent. HPLC separation of the materials was usually achieved through ion pairing ( 2 , 3 , 5 )or in the presence of inorganic salts (4). The HPLC procedure described in this paper eliminates the use of suppressor columns, separates without ion pairing, utilizes a nonaqueous medium, and, for the first time, permita determination of submicrogram quantities of non-UV absorbing quaternaries. This is possible because long alkyl chain quaternaries are both soluble and ionized in organic solvents. In this medium quaternaries can be separated on a cyanoamino bonded phase column and the ionic species can be detected by conductivity. This procedure was used here to determine the concentration of some commonly used quaternaries, ditallowdimethylammoniumchloride (DTDMAC), dodecyltrimethylammonium chloride (DOTMAC), l-hexadecylpyridinium chloride (HDPC), and stearyldimethylbenzylammonium chloride (STEDBAC), in several river waters.
EXPERIMENTAL SECTION Quaternary Ammonium Compounds and Reagents. Dodecyltrimethylammonium chloride (DOTMAC) and l-hexadecylpyridinium chloride (HDPC) were obtained from Eastman Organic Chemicals, Rochester, NY. Stearyldimethylbenzylammonium chloride (STEDBAC) was obtained from Rohm & Haas Co., Philadelphia, PA. Ditallowdimethylammonium chloride (DTDMAC) was obtained from Sherex Co., OH. The quaternary ammonium compounds were used without further purification. The linear alkylbenzenesulfonate (LAS) used was commercial grade. The methanol used was a HPLC grade (distilled in glass) obtained from Burdick & Jackson. All other chemicals and solvents used were reagent grade. Sample Collection Preparation. Grab samples of river water were collected randomly from four different locations. All samples were preserved with 1% formalin. No additional chemicals were added to minimize the adsorption of quaternaries to the container walls since
