V. Gómez

Determination of non-ionic and anionic surfactants in environmental water matrices.

Solid-phase extraction (SPE) combined with liquid chromatography electrospray mass spectrometry (LC-(ESI)MS) was used to determine 16 non-ionic and anionic surfactants in different environmental water samples at ng L(-1) levels. The proposed method is sensitive and simple and has good linear range and detection limits (less than 50 ng L(-1)) for most compound classes. The effect of ion suppression was studied in aqueous matrices from several treatment plants-including urban and industrial wastewater treatment plants (WWTPs), drinking-water treatment plants (DWTPs) and seawater desalination plants (SWDPs)-and it was considered when quantifying our samples. In addition, conventional treatments and tertiary treatments that use advanced membrane technologies, such as ultrafiltration (UF) and reverse osmosis (RO) were evaluated in order to determine their efficiency in eliminating these compounds. The concentrations of non-ionic surfactants in the raw waters studied ranged from 0.2 to 100 μg L(-1). In effluents, the concentrations ranged from 0.1 to 5 μg L(-1), which reflects consistent elimination. Anionic surfactants were present in all waters studied at higher levels. Levels up to 3900μgL(-1) of linear alkylbenzene sulfonates (LASs) and 32,000 μg L(-1) of alkyl ethoxysulfates (AESs) were detected in urban WWTP influents, while levels up to 25 μg L(-1) of LASs and 114 μg L(-1) of AESs were found in drinking-water and desalination treatment plants. The results indicate that conventional processes alone are not sufficient to completely remove the studied surfactants from waste streams. Tertiary treatments that use advanced membrane technologies such as UF and RO can further reduce the amount of target compounds in the effluent water.

Sequential injection analysis with second-order treatment for the determination of dyes in the exhaustion process of tanning effluents.

A sequential injection (SI)-DAD spectrophotometric method to control the exhaustion of dyes in a mixture of three dyes from a tanning industry process has been developed. It is based on an interdiffusion process of the sample and reagents which leads to a gradual fall in pH through the channel to the detector recording a data matrix. The aim of this paper is to develop a second-order calibration model that is unaffected by interferents by applying multivariate curve resolution with alternating least squares (MCR-ALS). We obtained a linear calibration in the 5-30mgl(-1) range with a correlation coefficient of 0.999 for each dye with detection limits of 2.6, 3.9 and 2.1mgl(-1) for Acid Red, Acid Brown and Acid Orange, respectively. The simultaneous determination of the three dyes from tanning samples showed a satisfactory precision for the three analytes. The method has been validated comparing the concentration of some spiked samples with the expected concentration using a t-paired test. When we used this method to study the exhaustion of dyes, we found that there were several stages in this process. These data may be the key to optimising the exhaustion process.

Modeling the adsorption of dyes onto activated carbon by using experimental designs

We used experimental design methodologies to obtain the response surface of the adsorption process for three acid dyes used in the dyeing step of a tanning process. The dyes were Acid Red 97, Acid Orange 61 and Acid Brown 425. The adsorption process was evaluated determining the concentrations of individual and total dyes remaining in solution at the end of the process. These concentrations were determined simultaneously in a single step using sequential injection analysis with multivariate curve resolution alternating least squares (SIA-MCR-ALS). This method involves fractional factorial designs and the steepest ascent method to find a zone of efficient adsorption and a response surface-modeling step to fit the relevant adsorption factors for the response.