Environ. Sci. Technol. 1994, 28, 497-503
Determination of Secondary Alkane Sulfonates in Sewage Wastewaters by Solid-Phase Extraction and Injection-Port Derivatization Gas Chromatography/Mass Spectrometry Jennifer A. Fleld,' Thomas M. Field, Thomas Polger, and Walter Glger
Swiss Federal Institute for Environmental Science and Technology (EAWAG), CH-8600 Dubendorf, Switzerland Secondary alkane sulfonate (SAS) surfactants were determined in aqueous samples from sewage treatment plants using solid-phase extraction (SPE) and a single-step procedure that combines elution and injection-port derivatization for sample analysis using gas chromatography/ mass spectrometry (GUMS). A tetrabutylammonium ion pair reagent was applied both to elute SAS from CIS bonded-silica disks as their ion pairs and to derivatize SAS ion pairs under GC injection-port conditions. SAS was effectively recovered from samples of raw sewage (>92%)andfromprimary(>98%)andsecondary(>85%) sewage effluents. No sample cleanup steps were necessary because the identification and quantitation of SAS isomers and homologs were performed using mass selective detection. The overall precision of the method, indicated by the relative deviation, for SAS in raw sewage, primary effluent, and secondary effluents was 7.1,5.2, and 10.4%, respectively. The concentration of SAS in municipal wastewaters ranged from 0.69 to 0.98 mg/L in raw sewage, from 0.54 to 0.89 mg/L in primary effluents, and from below detection to 0.02 mg/L in secondary effluents. Linear alkylbenzene sulfonate (LAS) concentrations also were determined in wastewater samples.
Introduction The fate of surfactants in aquatic environmentshas been the focus of continual attention due to the large quantities used worldwide in consumer, industrial, and institutional cleaning products. Environmental acceptability plays an increasingly important role in the manufacture and marketing of surfactants, particularly in Europe (1). The behavior of surfactants is also a key issue in the application of surfactants for remediating contaminated aquifers (2). Secondary alkane sulfonates (SAS) are anionic surfactants that are primarily produced and consumed in Europe as components in liquid cleaning formulations (3, 4). Recent interest in SAS is centered around its potential as a substitute for linear alkylbenzene sulfonate (LAS) surfactants. In 1990, LAS comprised 45% of the US. surfactant market at 4.1 X los kg (1). Cox estimated European SAS consumption in 1985 at only 8.2 X 106 kg (3). European SAS production capacity in 1991 was 1.5 X lo8kg, although production is estimated to be somewhat lower (5). Of the 2.3 X lo6 kg of SAS consumed in Switzerland in 1991, approximately 89 % was consumed in the form of household products and 11% as industrial products (6). Production of SAS is accomplished by two processes: sulfoxidation accounts for two-thirds and sulfochlorination accounts for one-third of the European SAS production (5). In addition to monosulfonated SAS, disulfonated
materials (6% by dry weight) also are present in SAS commercial formulations (4). Technical SAS contains a range of homologs typically with alkyl chain lengths from C13 to CIS. Each homolog is comprised of isomers defined by the location of the sulfonate group on the alkyl chain. For example, a 2-Cls-SAS [2-(hexadecyl)sulfonatel describes a 16-carbonalkyl chain with the sulfonic acid gtoup attached to the second carbon as follows: H,C-CH(SO,-)-[CH,]
13-CH3
Solid-phase extraction (SPE) has developed into an important technique in environmental analytical chemistry by reducing the time, cost, and quantity of organic solvents associated with sample preparation. Both hydrophobic and ion-exchange SPE phases have been used for isolating sulfonated compounds from aqueous environmental samples (7-12).The utility and versatility of SPE is reflected by the range of hydrophobic and ionexchange phases that are available in different sizes (sample capacities) and formats (disk or membrane vs cartridges). The advantages of disks include higher sample application rates and recovery reproducibilities due to the characteristicsof high cross-sectional area, smaller particle size,and embedded particles, which improve mass transfer and eliminate bed channeling (13). The versatile disk format can be eluted either with liquid solvents (7,14) or by supercritical fluids (15). Conventional derivatization methods for sulfonates are generally time-consuming procedures that require a minimum of two or three steps and are sensitive to trace amounts of water. Ion pair derivatization, also known as flash-heater esterification, is a rapid, simple, and robust alternative to conventional derivatization methods for aliphatic and aromatic sulfonated surfactants (16). Ion pair derivatization is preceded by the reaction of SAS [RSOsNa+I with tetrabutylammonium hydrogen sulfate [N(Bu)4+HS04-1to form SAS ion pairs [RSO~-N(BU)~+I in solution (eq 1). RSOcNa'
+ N(Bu);HSO;
s
RSO;N(Bu),+ + Na'HSO; (1) Upon introduction to a high temperature (300 "C) GC injection port, SAS is esterified to its butyl esters [RS03Bul (eq 2).
A
* Corresponding author present address: Department of Agricultural Chemistry, Oregon State University, Corvallis, OR 97331.
RSO
