Determination of Surfactants in Environmental Samples
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DOI: 10.2478/eces-2013-0005 ECOL CHEM ENG S. 2013;20(1):69-77 Ewa OLKOWSKA 1, Marek RUMAN 2, Anna KOWALSKA 3 and Żaneta POLKOWSKA 1* DETERMINATION OF SURFACTANTS IN ENVIRONMENTAL SAMPLES. PART I. CATIONIC COMPOUNDS OZNACZANIE SURFAKTANTÓW W PRÓBKACH ŚRODOWISKOWYCH. CZ ĘŚĆ I. ZWI ĄZKI KATIONOWE Abstract: Compounds from the group of cationic surfactants are widely applied in household, industrial, cleaning, disinfectant, cosmetic and pharmaceutical products as their specific properties (antimicrobial, emulsifying, anticorrosion, softening). After use, cationic surfactants are disposed to wastewater-treatment plants and finally with effluent water to surface waters due to their incomplete degradation. Moreover, they can freely circulate in different environmental compartments including living organisms. It becomes indispensable to recognize in more detail behavior, fate and biological effects of cationic surfactants. This analytical problem can be solved with use sensitive and reliable analytical techniques at sample preparation step and final determination step. In recent years, during isolation analytes from environmental samples mainly were used liquid-liquid extraction (LLE) - liquid matrices or solid-liquid extraction (SLE) - solid matrices. This technique involves application of toxic solvents (chloroform), is time-consuming and interferences are co-extracted. Nowadays, in scientific centers are carried out research to replace this traditional technique. So far, the following techniques were applied: solid-phase extraction (SPE) or it modification (HF-LPME) - liquid samples; accelerated solvent extraction (ASE) and supercritical fluid extraction (SFE) - solid samples. During the determination of total content of cationic surface active agents in environmental samples were used a traditional spectrophotometry technique and potentiometric titration technique. But those techniques are susceptible of interferences on analysis results (anionic and non-ionic compounds). The chromatographic technique (liquid chromatography) applied at the final determination step gives possibility to determine individual cationic surfactants in solvent extracts of environmental samples. The LC systems coupled with mass spectrometers are most powerful tools during such analysis. Keywords: cationic surfactants, isolation and/or enrichment, final determination, environmental samples Introduction Surfactants (usually referred to as surface active substances) are specific organic compounds that contain hydrophilic and hydrophobic group in the molecule. An exhibition of a double affinity (polar - non-polar duality) is typical for amphiphilic substances (Fig. 1). 1 Gdansk Univeristy of Technology, ul. G. Narutowicza 11/12, 80-233 Gda ńsk, Poland, phone +48 58 347 21 10, fax +48 58 347 26 94 2 Faculty of Earth Sciences, University of Silesia, ul. Będzi ńska 60, Sosnowiec 41-200, Poland 3 Department of Forest Ecology, Forest Research Institute, S ękocin Stary, ul. Braci Le śnej 3, 05-090 Raszyn, Poland *Corresponding author: [email protected] 70 Ewa Olkowska, Marek Ruman, Anna Kowalska and Żaneta Polkowska The amphiphilicity is a term derives from the Greek word amphi and it is meaning both. The non-polar hydrophobic part of surfactants molecules usually are a straight or branched hydrocarbon or fluorocarbon chain containing from 8 to 18 carbon atoms [1, 2]. Non-polar group Polar group (ionic or non-ionic) Lipophobic in aqueous media Lipophilic in aqueous media Lipophilic in hydrocarbon media Lipophobic in hydrocarbon media Fig. 1. The schematic structure of compounds from the group of surfactants [1, 2] The hydrophilic part of surfactants may be [2]: - negatively charged -> anionic compounds; - positively charged -> cationic compounds; - both positively and negatively charged ->amphoteric compounds; - without formal charge -> non-ionic compounds. Cationic surface active agents often contain the nitrogen atoms carrying positive charge (mainly in an amine or quaternary ammonium group), which are coupled with one or several long chain of the alkyl type. Quaternary ammonium compounds (QACs) are one of the widest applied group of cationic surfactants. They are organic compounds in which + positively charged nitrogen atom is attached covalently to four groups (R 1R2R3R4N ). Different types of functional groups (R 1-4) can be attached: one long chain alkyl group and the rest are either methyl or benzyl groups [3]. During the last decade dialkyl dimethyl ammonium salts ( eg DTDMAC) used in fabric softeners for household application were replaced by compounds from the group of alkyl ester ammonium salts. They are containing one or more weak ester linkages in the molecular structure [4]. In Table 1 are shown examples of compounds from the group of cationic surfactants. Table 1 The examples of compounds from the group of cationic surfactants [5] Quaternary Esters of quaternary ammonium Derivatives of Derivatives of ammonium compounds (EQAC) pyridine imidazolines compounds (QAC) + + + + R1R2R3R4N X (RCO-O-CH 2CH 2)2-N -R1R2 [NC 5H5] R1-C=N-(CH 2)2-N -R2 R2 R1 R N + + R2 N R4 N + N R3 n R1 This class of compounds is dissociated in aqueous solution into amphiphilic cations and mainly the halogen type anions. The amphiphilic structures of surfactants cause their special properties like ability to concentration at surfaces, reduction of the surface tension or formation of micelles. Therefore, they can be applied in various areas of human activity. Cationic surfactants have gained importance because of its bacteriostatic properties. For that reason they are applied as disinfectants and antiseptic agents in different products (cosmetics, medicine, laundry detergents). Determination of surfactants in environmental samples. Part I. Cationic compounds 71 Table 2 The effect of several cationic surfactants to different organisms Toxic parameter Class of Acro nym of EC * or Litera- Structure of molecule Test organisms 50 LD * analytes analytes EC /LD * 50 ture 50 50 [mg/kg] [mg/dm 3] Selenastrum capricornutum 0.19 (96 h) Microcystis aeruginosa 0.12 (96 h) [8] C ATMAC 12 Navicula pelliculosa 0.20 (96 h) Rat 250-300 [9] Gammarus sp. 0.1 (48 h) Drugesia sp. 0.68 (48 h) [10] C16 ATMAC Alkyl Dero sp. 0.22 (48 h) trimethyl Rat 410 [11] ammonium Rat 1000 [9] C ATMAC chloride 18 Mouse 633 [12] Dunaliella sp. 0.38 (24 h) C [13] 16-18 Chlorella pyrenidosa 0.28 (96 h) ATMAC Rat >500 [9] Daphnia magna 1.2-5.8 C 12-22 Planorbis corneus 0.73-23 [14] ATMAC Idus melanotus 0.36-8.6 Alkyl Selenastrum capricornutum 0.09 (96 h) [8] trimethyl C ATMAB Microcystis aeruginosa 0.03 (96 h) ammonium 16 Rat 1000 [11] bromide Dunaliella sp. 18 (24 h) [13] Chlorella pyrenidosa 6 (24 h) Slenastrum capricornutum 0.06 (96 h) [8] Dialkyl Microcystis aeruginosa 0.05 (96 h) dimethyl C 0.16-1.06 (48 16-18)2 Daphnia magna [15,16] ammoniu DADMAC h) salts Chironomus riparius 9.02 (96 h) R= two alkyl chains [17] Lymnaes stagnalis 18 (96 h) Lepomis macrochirus 0.62 (96 h) [15] Gasterosteus aculeatus 4.5 (96 h) [17] C LC : 3.5 12 Leuciscus idus melanotus 0 [14] ADMBAC LC 100 : 8.0 C Dunaliella sp. 1.8 (24 h) Alkyl 12-14 [13] ADMBAC Chlorella pyrenidosa 0.67 (96 h) dimethyl C benzyl 12-18 Rat 525 (Oral) ADMBAC ammonium [12] 150-340 salts Mouse C14-18 (Oral) ADMBAC 1420 Rat [18] (Dermal) Selenastrum Alkyl ester 2.9 (96) DEEDMAC capricornnutum [19] ammonium Daphnia magna 14.8 (24 h) salts DEQ Daphnia magna 7.7 (48 h) [20] * EC 50 (h) - effective concentration (concentration of the toxic substance that causes specific biological effect of 50% of its maximum value after 24, 48 or 72 hours * LD 50 (h) - lethal dose (concentration of the toxic substance, which kills 50% of the population after defined hours) 72 Ewa Olkowska, Marek Ruman, Anna Kowalska and Żaneta Polkowska Cationic compounds from the group of surfactants have high adsorptivity to different types of surfaces and they might be applied as: fabric softeners, antistatic agents, corrosion inhibitors or flotation agents [6, 7]. After use, compounds from the group of surfactants and their degradation products are discarded to wastewater-treatment plants (WWTPs). Sometimes surfactants are discarded directly to surface waters and they might be dispersed into different environmental compartments. In wastewater-treatment plants they are completely or partially removed by a combination of different processes ( eg sorption, biodegradation). But some surfactants have a low biodegradability or their biodegradation products are more toxic than initial compounds. Examples of toxic effect on living organisms are given in Table 2. After appropriated processes in wastewater-treatment plants the effluents in which can occurred different types of surfactants or their degradation products, are discharged into surface waters [21, 22]. Due to their widespread use and freely migration between phases surfactants (and degradation products) have been detected at various concentrations in different part of environment. The occurrence of surface active agents was confirmed in atmospheric precipitation and deposits, surface waters, sediments, soils, living organisms. Moreover, because of positive charge of the cationic surfactants they are sorbed strongly to the negatively charged solid surfaces of sludge, soil, sediments, metals, plastics and cells membranes [23, 24]. It is become necessary to understand behavior, fate and biological effects of these surfactants in the environment [24-26]. For several reasons, it is complicated to detect, identify and quantify the levels of surfactants