Advances in stir bar sorptive extraction for the determination of acidic pharmaceuticals in environmental water matrices: Comparison between polyurethane and polydimethylsiloxane polymeric phases

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Abstract

Stir bar sorptive extraction with polyurethane (PU) and polydimethylsiloxane (PDMS) polymeric phases followed by high-performance liquid chromatography with diode array detection [SBSE(PU or PDMS)/HPLC-DAD] was studied for the determination of six acidic pharmaceuticals [o-acetylsalicylic acid (ACA), ibuprofen (IBU), diclofenac sodium (DIC), naproxen (NAP), mefenamic acid (MEF) and gemfibrozil (GEM)], selected as non-steroidal acidic anti-inflammatory drugs and lipid regulators model compounds in environmental water matrices. The main parameters affecting the efficiency of the proposed methodology are fully discussed. Assays performed on 25 mL of water samples spiked at the 10 μg L−1 level under optimized experimental conditions, yielded recoveries ranging from 45.3 ± 9.0% (ACA) to 90.6 ± 7.2% (IBU) by SBSE(PU) and 9.8 ± 1.6% (NAP) to 73.4 ± 5.0% (GEM) by SBSE(PDMS), where the former polymeric phase presented a better affinity to extract these target analytes from water matrices at the trace level. The methodology showed also excellent linear dynamic ranges for the six acidic pharmaceuticals studied, with correlation coefficients higher than 0.9976, limits of detection and quantification between 0.40–1.7 μg L−1 and 1.5–5.8 μg L−1, respectively, and suitable precision (RSD <15%). Moreover, the developed methodology was applied for the determination of these target analytes in several environmental matrices, including river, sea and wastewater samples, having achieved good performance and moderate matrix effects. In short, the PU foams demonstrated to be an excellent alternative for the enrichment of the more polar metabolites from water matrices by SBSE, overcoming the limitations of the conventional PDMS phase.

Introduction

Pharmaceuticals became recognized as relevant environmental contaminants in the course of the last decade [1]. The occurrence of these pollutants has been widely evident in recent years since the improvement of the analytical methodologies lowered the limits of detection. Unfortunately, the consequences of the continuous presence of low concentrations of pharmaceuticals in the ecosystem are still not fully known [2]. A discussion of various aspects of ecotoxicology of pharmaceuticals in the environment can be found in recent reports [3], [4], [5]. Pharmaceuticals in their native form or as metabolites are continually being introduced into sewage waters, mainly indirectly by excreta, through disposal of unused or expired drugs, or directly in discharges from pharmaceutical-manufacturing plants. A number of studies have revealed that pharmaceuticals are ubiquitous in the aquatic environment, mainly because some compounds are not efficiently removed during wastewater-treatment processes reaching surface, ground and consequently drinking water systems [6]. Several pharmaceuticals have been detected at trace level in wastewaters throughout Europe, and some have been measured at sub-trace contents in rivers and drinking water sources [1], [3], [4], [6], [7], [8]. From all the pharmaceuticals reported in literature, the classes of non-steroidal acidic anti-inflammatory drugs (NSAIDs) such as o-acetylsalicylic acid (ACA), ibuprofen (IBU), diclofenac sodium (DIC), naproxen (NAP) and mefenamic acid (MEF), etc., or even lipidic regulators [e.g. gemfibrozil (GEM)], are the most frequently mentioned as environmental contaminants. NSAIDs are commonly used to relieve the symptoms of arthritis, bursitis, gout, swelling, stiffness and joint pain and their annual prescription in developed countries achieved several hundreds of tons. Nevertheless, some of these pharmaceuticals are sold as non-prescription drugs and therefore, not controlled. Additionally, a variety of lipidic regulating drugs are used to lower levels of blood cholesterol among people at risk of heart attack or stroke [7]. Several analytical methodologies proposed for quantifying pharmaceuticals in environmental matrices use gas chromatography (GC), high-performance liquid chromatography (HPLC) or capillary electrophoresis with conventional detectors or hyphenated to mass spectrometry [2]. Since GC requires a previous derivatization step, HPLC has been used successfully to analyze pharmaceuticals in aqueous media [2]. The trace levels usually found in the environment makes the enrichment step a must, prior to instrumental analysis. Solid-phase extraction has been the most used sample preparation technique to monitor NSAIDs and lipidic regulators [6], [8] and besides this technique minimizes the use of toxic solvents when compared to the conventional liquid–liquid extraction, requires substantial amounts of sample (0.2–2 L) during trace analysis. In the last decade, sorptive extraction techniques have become popular solventless approaches for enrichment purposes and have been applied to the analysis of these type of drugs, namely solid-phase microextraction (SPME) [9] and liquid-phase microextraction [10], [11]. Recently, stir bar sorptive extraction (SBSE) has been proposed as a novel sample preparation method for the enrichment of priority organic compounds from aqueous matrices at trace level [12]. This analytical approach has, however, been inspired in the use of polydimethylsiloxane (PDMS), which is a polymeric phase with higher affinity for non-polar compounds, presenting limitations concerning the extraction of the more polar ones such as NSAIDs. To overcome this limitation, several authors have proposed new strategies, such as in situ derivatization [13], the dual-phase stir bar involving PDMS combined with specific adsorbents (e.g. activated carbons) [14], as well as, a glass fiber strip coated with polyacrylate [15] to recover compounds with higher polarity. Nevertheless, these analytical approaches presented a limited range of applicability, which proved to be more acceptable for the headspace analysis of particular matrices or classes of compounds. More recently, a novel polymeric phase based on polyurethane (PU) foams proved to be more indicated for the enrichment of the more polar analytes in aqueous media [16], [17]. The present contribution aims the application and comparison of SBSE(PU) and SBSE(PDMS) followed by HPLC with diode array detection (DAD) for the determination of ACA, NAP, IBU, DIC, MEF and GEM, selected as NSAIDs and lipidic regulators as model compounds in water matrices. The performance of the proposed methodology was evaluated in terms of precision, linearity and detection limits. The application of the optimized methodology to monitor these priority pollutants in environmental water samples is also addressed.

Section snippets

Standards and reagents

HPLC-grade methanol (MeOH, 99.9%) and acetonitrile (ACN, 99.9%) were supplied by Sigma–Aldrich (Steinheim, Germany). Sodium chloride (AnalaR grade, 99.9%) was obtained from BDH (Poole, UK). Ultra-pure water was obtained from Milli-Q water purification systems (Millipore, Bedford, MA, USA) and phosphoric acid (85%) was supplied by Riedel-de Haën (Seelze, Germany). IBU was provided by Shasun Chemicals and Drugs (Genéris Farmacêutica S.A., Portugal). DIC, MEF and GEM were purchased from

HPLD-DAD conditions

The HPLC-DAD parameters were evaluated in order to attain suitable instrumental conditions for the simultaneous analysis of ACA, NAP, DIC, IBU, MEF and GEM. Under optimized instrumental conditions, a very good response was attained for these compounds by HPLC-DAD, showing enough resolution within convenient analytical time (< 32 min), as shown in Fig. 1a. It can also be observed that the wavelengths that provided maximum response to DAD (λmax) were 230 nm for NAP, 220 nm for MEF and 205 nm for the

Conclusions

The SBSE-LD/HPLC-DAD analytical approach offers the opportunity of a new practical and reliable methodology for the determination of six NSAIDs and lipidic regulators (ACA, IBU, DIC, NAP, MEF and GEM) selected as model compounds in environmental water matrices. The capability and potential application of PU foams compared to the conventional PDMS during SBSE of these compounds from water samples have been evaluated in this study. Under optimized experimental conditions a good analytical

Acknowledgements

Ana R.M. Silva (BD/40926/2007) and Fátima C.M. Portugal (BD/24598/2005) acknowledge Fundação para a Ciência e a Tecnologia for the Ph.D. grants, Engª Manuela Justino for her prompt availability to provide us the wastewater samples and Generis Farmacêutica S.A. (Portugal) for the ibuprofen standard.

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