Aqueous solubility of PAH

Data on the aqueous solubility of PAHs in the presence of a third component, such as an electrolyte, are also very important. The practical implications are that the presence of this third component may substantially change the solubility, an example being the salting-out effect of sodium chloride and other salts present in seawater (7). 

This method worked well for the fairly soluble compounds being studied. Interlaboratory precision was good. Therefore, this basic methodology, with minor modifications, such as the use of gas chromatography (GC) or fluorescence spectroscopy for analysis of the aqueous solutions has been generally adopted for the determination of the aqueous solubilities of PAHs (23-32), even though the solubilities of some PAHs differ from that of benzene by a factor of more than 106. In the remainder of this section some of the modifications that have been made on this basic method and some new approaches to the measurement of the aqueous solubility of aromatic hydrocarbons will be briefly reviewed. 

The solubilities reported by Sutton and Calder were 5%-20% higher than those determined by McAuliffe. This is not surprising since the McAuliffe method is susceptible to serious losses due to adsorption of the hydrocarbons on the walls of the syringe. (See Accommodation section.) Sutton and Calder injected concentrated organic extracts rather than dilute aqueous solutions. This reduced the chances for adsorptive losses during injection and increased the sensitivity of the method. However, neither McAuliffes nor Sutton and Calders method is sufficiently sensitive for determination of the aqueous solubility of PAHs. 

Locke s method provides a rapid and simple means for estimating the aqueous solubilities of PAHs. Individual solubility values can be estimated to within 200%. However, these extrapolated values differ too greatly from measured solubilities for this procedure to be categorized as a valid method of determining the aqueous solubility of PAHs. 

Summary. Methods for determining the aqueous solubilities of PAHs are subject to errors associated with the preparation, extraction, and quantitative analysis of saturated solutions. There is no one method that has addressed the problems associated with each of these processes. Systematic errors associated with quantitative analyses of saturated solutions should be reduced in methods where selective analytical measurement techniques are used. Chromatographic methods allow separation of nonanalyte signals-in-time from those of the analyte. Fluorescence spectroscopy allows greater selectivity than UV spectroscopy, though less than gas or liquid chromatography. 

Although there are values for the aqueous solubility of many PAHs in the literature, they have been reported at only one temperature. The agreement between values determined by different methods is sometimes poor. Furthermore, there have been few determinations of the aqueous solubility of PAHs in seawater. Because of the increasing need for information about these systems, a study was undertaken to investigate the solubility behavior of PAHs in aqueous systems. 

Development of Dynamic Coupled-Column Liquid Chromatography— An Accurate Method for the Determinations of the Aqueous Solubility of PAHs... 

Critical Evaluation of the DCCLC Method. The development of an accurate method for determining the aqueous solubility of PAHs is contingent upon the ability of that method to prepare, maintain, transfer, and analyze saturated solutions. In this section some of the problems associated with PAH solubility methodology in general are discussed along with explanations of how these problems are circumvented by the DCCLC approach.. ... 

Problems Associated with the Preparation and Stabilization of a PAH-Water SRM. Preparation of aqueous PAH solutions of known concentration by gravimetric procedures is difficult because of the extremely low aqueous solubilities of PAH. As shown in Table IX many PAHs have aqueous solubilities of less than 500 /xg/kg (ppb). Preparation of aqueous solutions of known concentration by serial dilutions of a more concentrated organic solution is both hazardous and wasteful. After small aliquots are taken, large volumes of organic solvent containing toxic and expensive chemicals remain to be disposed of. 

Figure 1. Structure and aqueous solubility of PAH s in agAt-9 (Data taken from ref. 20)...

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