Impact of Different Water Matrices on Analysis of Chlorinated Phenols

Marijana Kragulj1, Jelena Tričković, Jelena Molnar, Aleksandra Tubić, Snežana Maletić, Jasmina Agbaba and Božo Dalmacija

 

 

¹ Corresponding author: Marijana Kragulj, Address: University of Novi Sad Faculty of Sciences, Trg Dositeja Obradovića 3, 21000 Novi Sad, Republic of Serbia, E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it , tel: +381214852725; fax: +38121454065

 

 

 

Abstract

This study investigates method validation for the determination of chlorinated phenols (CPs) in water matrices by derivatization with acetic anhydride followed by liquid-liquid extraction with hexane and analyzed by gas chromatography-mass spectrometry. Three water matrices were used: synthetic matrix, Zrenjanin groundwater and Danube surface water. Accuracy expressed as recovery was determined at CP concentrations of 300 µg/l and 600 µg/l in all water matrices and precision was determinated as relative standard deviations (RSD). Method detection limit (MDL) values were in the range from 0.09 to 0.533 µg/L for all water matrices. Method validation has shown that lower recoveries and higher RSD are obtained for natural water matrices in comparison with the synthetic matrix. The lower recovery of natural matrices can be explained by the fact that selected natural waters have high dissolved organic carbon (DOC) content. Since all investigated CPs are hydrophobic organic compounds (logKOW > 3) they are likely to interact with DOC, leading to less efficiency of extraction in natural matrices. Additionally, for natural water matrices a negative correlation between molecular hydrophobicity and recovery was found. Method validation showed that this method is sensitive and precise for the analysis of CPs in different water matrices.

Keywords: chlorinated phenols, method validation, organic matter, water matrices

 

 

Introduction

 

Chlorinated phenols (CPs) comprise a family of 19 organohalide compounds that have been used as herbicides, pesticides and wood preservatives (Armenante et al., 1999). In addition to their industrial use, CPs can be formed during the purification of drinking water and from the degradation of other chlorinated biocides (Pritchard et al., 1987). Phenols are present in the wastewater of various industries, such as refineries (up to 6–500 mg/L), coking operations (28–3900 mg/L), coal processing (9–6800 mg/L) and the manufacture of petrochemicals (2.8–1220 mg/L). The release of phenol-containing wastewater into natural water bodies is forbidden without prior treatment because of the toxicity of phenol and its derivatives (Lončar et al., 2011; Michałowicz et al., 2009; 2010).

Chlorinated organic compounds, in particular, are found to be resistant to biochemical degradation. Monochlorophenols, among other phenol compounds, serve as intermediates in the production of pesticides. These are also used as antimicrobial agents in a wide array of products, such as adhesives, oils, textiles and pharmaceutical products. The US Environmental Protection Agency (EPA) and Water Framework Directive (WFD) classified pentachlorophenol (PCP) as a priority pollutant (http://www.epa.gov/waterscience/methods/pollutants.htm; WFD, 2000). In addition, the limit value for the first class of surface waters, according to Serbian regulation, is set to 1 µg/l (Serbian regulation, Official Gazette of the Republic of Serbia No. 30/10, 2012).

With the known health risks linked to CPs exposure and the importance placed on these xenobiotics by the EPA and WFD, it is not surprising that many analytical methods exist for monitoring CPs in different types of water such as drinking water, surface water and wastewater (Favaro et al., 2008; González-Toledo et al., 2001; Peng et al., 2007).

The most widely used approach for analysis of CPs is gas chromatography-mass spectrometry (GC/MS). However, the GC/MS method causes thermal decomposition of phenols. To surmount this limitation, one of the most common and easily integrated approaches is derivatization. A variety of reagents have been utilized for CP derivatization such as acetic anhydride and activated silanols (Wang et al., 2009; Regueiro et al., 2009; Kovács et al., 2008; Padilla-Sánchez et al., 2010; Ho et al., 2008). The employment of acetic acid anhydride in basic conditions (K2CO3) offers several advantages since the reaction times are short, and the reagent itself is cheaper when compared to other derivatizing reagents (Padilla-Sánchez et al., 2010). On the other hand, survey of available literature showed us that data on precision and accuracy of the method, together with data on the presence of CPs in the environment are widely available, however, mostly, without an attempt to compare recovery values for different matrices. Comparison of recovery values for CPs in reagent and surface water was found in US EPA 528 (US EPA 528 for determination of phenols in drinking water by solid phase extraction and capillary column gas chromatography/mass spectrometry (GC/MS), 2000). It showed slightly higher values in recovery for reagent water for some of analytes.

With this consideration in mind, the scope of the current study was (1) to validate a simple, sensitive, specific and low-cost sample preparation technique for analysis of 2,4-dichlorophenol (2,4-DCP); 2,4,6-trichlorophenol (2,4,6-TCP); 2,3,4,5-tetrachlorophenol (2,3,4,5-TeCP) and PCP in water by GC/MS, and (2) to investigate the effect of different water matrices on the efficiency of extraction.

Materials and methods

Reagents and chemicals

2,4-DCP, 2,4,6-TCP, 2,3,4,5-TeCP were purchased as 1000 µg/mL stock solutions in MeOH; Sigma–Aldrich Chemical Company. PCP was purchased as neat and stock solution was made measuring certain weight of pentachlorophenol (Sigma-Aldrich Chemical Company) to give a concentration of about 1500 µg/mL. All solvents used were for organic residue analysis (J.T. Baker). The derivatisation reagent (acetic anhydride, ReagentPlus®, ≥99%) was purchased from Sigma–Aldrich Chemical Company.

The four chlorinated phenols (2,4-DCP, 2,4,6-TCP, 2,3,4,5-TeCP and PCP) differ in hydrophobicity, electron polarizability, polarity, molecular size and number of chlorine atoms. The relevant properties of the chosen CPs are summarized in Table 1.

 

Table 1: Physicochemical properties of the investigated CPs

Tab01

 

Characterisation of water matrices

Three water matrices were used in this work: a clean water matrix (synthetic matrix), Zrenjanin groundwater and Danube surface water.

The synthetic matrix was deionized water of ASTM Type I (American Society for Testing and Materials), which was obtained by the LABCONCO (WaterPro RO/PS Station) system.

Characterization of all water matrices included determination of pH, electroconductivity, total organic carbon (TOC) and dissolved organic carbon (DOC). The content of TOC and DOC was determined using the TOC analyzer (Elementar LiquiTOCII) after acidification with cc. HCl. The content of DOC was determined after filtration through a 0.45 μm membrane filter. pH measurements were made using the WTW pH InoLab. Water electroconductivity was measured by the Hanna electroconductivity meter (Model HI 933000).

 

Sample and calibration preparation

The method was developed on the basis of the method for the determination of CPs in water matrices by derivatization with acetic anhydride and liquid-liquid extraction (Schuster, 1994). Method validation was performed by determining accuracy and precision expressed as relative standard deviation (RSD) for measurements made in 3 series in duplicates at CP concentrations of 300 µg/l and 600 µg/l in all water matrices.

These concentrations were chosen in order to cover the linear calibration range for these substances. The method detection limit (MDL) of CPs was determined at 1 µg/L in 6 replicates.

Calibration standards of all chlorinated phenols were prepared as follows: flasks containing premeasured 50 ml of deionized water were spiked with a certain volume of CPs methanol working solutions with CPs concentrations from 50 to 1500 µg/mL resulting in final solutions with CPs concentrations from 20 to 1200 µg/L. Further procedure for the preparation of calibration standards and spiked water matrices for analysis of CPs was as follows: for the derivatization step 0.05 g of K2CO3 was measured in glass vials of 10 ml, and 4 ml of investigated sample and 1 ml of acetic anhydride were added. The samples were shaken for 15 min. After derivatization, for the extraction step, 0.15 g of NaCl and 3 ml of hexane were added to vials and the mixture was shaken for 15 min. Then, 0.5 ml of hexane extract was transferred to vials for GC analysis and analyzed using GC/MS.

 

Chromatographic and MS conditions

Configuration of GC/MS and GC/MS parameters used for analysis of CPs are given in Table 2.

 

Table 2: GC/MS parameters for analysis of CPs

Tab02