Detergents present a major environmental problem due to large quantities of surfactants released from laundries. For this reason, it is important to apply an appropriate analytical method for their determination. In this work, we propose two simple, fast and inexpensive analytical methods for anionic, cationic and non-ionic surfactant determination: thin layer chromatography (TLC) separation for qualitative screening and quantitative potentiometric determination with ion-selective electrodes. These methods have been chosen because of their many advantages: rapidity, ease of operation, low cost of analysis and a wide variety of TLC application possibilities. The advantage of potentiometric titration is its very high degree of automation and very low detection limits obtained with different ion-selective electrodes applied for different surfactants

Bokic, Lj.

Pusic, T.

Rezic, I.

Directory of Open Access Journals

Preliminary Testing for Anionic, Cationicand Non-ionic Surfactants DeterminationI. Reziæ,* T. Pušiæ, and Lj. BokiæFaculty of Textile Technology, Prilaz Baruna Filipoviæa 30, 10 000 Zagreb, CroatiaDetergents present a major environmental problem due to large quantities of surfactants releasedfrom laundries. For this reason, it is important to apply an appropriate analytical method for theirdetermination. In this work, we propose two simple, fast and inexpensive analytical methods foranionic, cationic and non-ionic surfactant determination: thin layer chromatography (TLC) sepa-ration for qualitative screening and quantitative potentiometric determination with ion-selectiveelectrodes. These methods have been chosen because of their many advantages: rapidity, ease ofoperation, low cost of analysis and a wide variety of TLC application possibilities. The advantageof potentiometric titration is its very high degree of automation and very low detection limits ob-tained with different ion-selective electrodes applied for different surfactants.Key words: Surfactants, potentiometric determination, detergentsIntroductionDifferent anionic, non-ionic, cationic and amphoteric sur-factants (or surface-active species) are used nowadays in dif-ferent institutions, industries and households in very largeamounts. Their industrial application is widespread in thecosmetics, metal-working, mining, paper and leather indu-stries, which is why the surfactants present in detergents re-present a major environmental pollutant. They present aserious environmental problem especially in laundrieswhere huge amounts are applied daily: for example, inWestern Europe 4 250 000 tons of detergent products and1 190 000 tons of softener products are used every year.1Many commonly used surfactants are highly toxic and dan-gerous for the environment and human health. This is whythe regulations for wastewaters are very strict: in Croatia,the limit for releasing synthetic surfactants into wastewatersis g = 0.05–0.1 mg L–1.2 Both the toxicity of surfactants andtheir biodegradation in the environment are influenced bya variety of interacting physical, chemical and biologicalfactors. The complexity of detergent products with whichsurfactants are mixed may also lead to a synergistic effect.Furthermore, detergent products can interact with the bio-degradation and toxicity of other compounds in the envi-ronment.Chemical analysis of surface-active species is of interest formany applications, such as in process monitoring, biomedi-cal applications, environmental monitoring and surfacescience investigations.3 Analysis of surfactants is carried outgenerally by either chromatographic procedures that needderivatisation like gas or liquid chromatography. Improvedanalytical procedures for the determination of the entiregroup of surfactants require optimization of the samplepre-treatment steps. Recent research reports the use of so-lid-phase micro extraction and solid-phase extraction withdifferent sorbents such as alkyl-bonded silica, graphitizedcarbon black and styrene-divinylbenzene resins. Sequentialsolid-phase extraction combined with liquid chromatogra-phy mass spectrometry has been successfully employed forthe extraction of surfactants.4Thin layer chromatography is a potentially powerful techni-que for the separation of surfactants. Reversed phase thinlayerchromatographycanbeusedtoseparateentireclassesof surfactants (i. e. anionics from non-ionics from cationics).Conversely, silica gel can be used to separate individualanionic or cationic surfactants from other similarly chargedsurfactants.5 Thin layer chromatography has advantages be-cause of its numerous positive characteristics: low cost,ease of operation, rapidity, wide choice of adsorbents andsolvents, and diversity of techniques and equipment.6Surfactants have the ability to lower surface tension due totheir specific structure. All typical surfactant propertiescan be linked to their structure and to the presence ofhydrophilic and hydrophobic groups in the molecule. Thehydrophilic group in a surfactant primarily determines itsapplication as well its analytical properties.7 Since an entirerange of instrumental analytical techniques may be used forsurfactant analysis, depending on the surfactant class andthe problem to be solved, a differentiation must be made asto whether the analysis is to be carried out in the frameworkfor controlling raw materials, quality assurance of manufac-tured ionic or non-ionic surfactants, monitoring of com-petitors, quality assurance of formulations, monitoringcompetitor formulations, environmental samples investi-gation, investigation of electroplating baths, checking thesurfactant content of water-soluble cooling lubricants, ortesting anionic surfactants and soaps in washing powders.The standard method of anionic, cationic and non-ionicsurfactant determination is UV/VIS determination and thetime-consuming standard flask extraction with chloroform,I. REZIÆ et al.: Preliminary Testing for Surfactants Determination, Kem. Ind. 56 (11) 557–560 (2007) 557KUI – 30/2007Received February 15, 2007Accepted September 12, 2007* Corresponding author:Iva Reziæ, e-mail: iva_rezic@net.hr, iva.rezic@ttf.hrin which very large quantities of harmful organic solvent areemployed.This research was a preliminary study on coupling twosimple analytical methods (thin layer chromatography withpotentiometric titration) for surfactant analysis that can beuseful in many applications such as in process monitoring,biomedical applications, environmental monitoring andsurface science investigations.8 Similar advanced methodsare being tested recently.9 Thin layer chromatography wastested since it is a potentially powerful technique for the se-paration of surfactants. While reversed phase thin layerchromatography can be used to separate entire classes ofsurfactants, silica gel can be used to separate the individualanionic or cationic surfactant from other similarly chargedsurfactants.5 In our preliminary experiments, silica gel andaluminium oxide plates were tested. Thin layer chromato-graphy was developed for separation and identification ofdifferent anionic, non-ionic and cationic surfactants.10 Thisresearch focuses on their quantitative determination afterchromatographic separation and identification. For thispurpose, a potentiometric titration with ion-selective elec-trodes was tested as a highly automated method that ena-bles very low detection limits for different surfactants.11ExperimentalSample preparationFor the purpose of this work,1go fanionic, cationic andnon-ionic surfactant standards were investigated: SDS (so-dium dodecyl sulphate), HDTMAC (cetyltrimethylammo-nium chloride) and Kemonecer NI (alkylarylpolyglycolet-her) were dissolved in 1000 mL of distillated water.Chromatographic separationFor chromatographic determination, 3 L of sample stan-dard solutions were spotted with a Pt syringe on 20 · 20 cmglass pre-coated TLC plates with 0.25 mm layers of silica gel60 F254 (Merck, Darmstadt, Germany). Development wascarried out in the Camag chromatographic chamber by theascendingtechniquetothedistanceof8cmwithnumerousorganic solvents and their mixtures with water. Solvent mix-tures investigated included: propanol, dichloromethane,ethyl acetate, chloroform, acetonitrile, benzene, tetrachlor-methane, buthanole, hexane, and iso-amyl alcohol. Afterthe development, the plates were dried thoroughly and thespots were detected under UV light at l = 254 nm.Qualitative determinationA potentiometric titration applying ion-selective electrodewas performed by TITRINO 736 GP, Metrohm, Switzer-land. The basis of potentiometric titration was a precipita-tion titration, in which the analyte was being precipitatedwith the titrant. All surfactant electrodes were sensitive toboth cationic and anionic surfactants. Cationic surfactantswere titrated with 0.004 mol L–1 anionic titrant, sodium do-decyl sulphate (SDS), at pH 10. Anionic surfactants were ti-trated with the c = 0.004 mol L–1 cationic surfactant, Hy-amine 1622, at pH 3. Non-ionic surfactants were titratedwith c = 0.01 mol L–1 tetraphenylborate (STPB) at pH 10.Addition of BaCl2 was necessary to compile the non-ionicinto the pseudo-cationic surfactant according to eq. (1) and(2), in which NIO represents a non-ionic tenside andNaTPB sodium tetraphenylborate.NIO + x Ba2+ ® [NIOBax]2+ (1)[NIOBax]2+ + 2 NaTPB ® [NIOBax]TPB2x +2N a + (2)Results and discussionTable 1 presents calculated RF values obtained at the silicagel60F S 254 platesforanumberofchromatographicsystemsinvestigated. Detection was performed under UV light (l =254 nm), with the fluorescent indicator impregnated withinthe pre-coated plates. This research does not include appli-cation of different reagents for visualization that are propo-sed in literature12–18 because detection under UV light ismuch faster and simpler. RF values were determined fromthe recorded plates for all components investigated.Table 1 –R F values obtained on the silica gel 60 F S 254platesTablica 1 –R F vrijednosti na podlozi silikagela 60 F S 254Solvent systemSustav otapala t/minRFSDSRFHDTMACRFKemonecer NI1 CCl4 13 0 0 02C H 2Cl2 6 – – 0.483C 4H8O2 6 0.88 0.95 0.774C 2H3N (ACN) 5 0.87 0.92 0.835C 4H10O (BuOH) 39 0.87 0.97 0.756C 6H6 5 0 0 0.987C 3H7OH 30 0.65 0.90 0.648C 5H12O 55 0.86 0.94 0.669C 6H14 60 0 010 2-propanol/H2O 67 0.57 0 –Developments in the organic non-polar solvents were veryfast, but unfortunately, the separations in those systemswerenotefficientenough.Sincetheadsorptionoftheparti-cular surfactant component depends on the present func-tional groups (surface-active groups), length of the carbonchain in the hydrophobic part and molecular mass of thecomponent, and on the solubility and polarity of the mole-cules in the stationary and mobile phases, we tested somemixturesoforganicsolventswithwater,butthisdidnotpro-duce better results.Iso-amyl alcohol was chosen as the best developer for sepa-ration and detection of investigated surfactant samples, be-cause it took 55 min for sufficient separation. Since all thecomponentswenttotheupperpartofthechromatographicplate, this system will be further optimized in our subse-quent investigations. The best separation of the investigatedcompounds was obtained on the silica gel 60 chromato-graphic plates, as presented in Table 2.Results of the linear range of the surfactant potentiometrictitration are presented in Fig. 1–3. Titrations were carried558 I. REZIÆ et al.: Preliminary Testing for Surfactants Determination, Kem. Ind. 56 (11) 557–560 (2007)out in a dynamic mode, in which the added volume incre-ments were calculated by microprocessor according to thechange in electrode potential until the iso-electric point(IEP) was achieved. One of the advantages of this instru-mental method is the possible detection of substances intrace amounts. The main criterion for testing the applica-tionofpotentiometrictitrationforthesurfactantsquantitati-ve determination was very low detection and quantificationlimit.Limitsofdetectionexpressedind =gL –1wereintherange from 0.07 (HDTMAC) to 0.26 (SDS) and 0.32(KEMONECER NI). Linear curves were obtained with veryhigh correlation coefficient for each individual surfactanttested. Potentiometric titration proved to be a very goodanalytical technique for determination of surfactants pre-sent in laundry wastewaters in very low concentrations.ConclusionThe goal of this investigation was to test two simple andinexpensive methods for identification and determinationof anionic, non-ionic and cationic surfactants. To that end,potentiometric titration was used for quantification of sur-factants after thin layer chromatographic identification. Wefound that the best identification and separation solvent sy-stem for the investigated surfactants is iso-amyl alcohol onthesilicagel60F254sadsorbent,detectionunderUVlightofl = 254 nm. The quantitative determination follows withthe potentiometric titration. These two investigated met-hods proved to be a very successful combination for anio-nic, cationic and non-ionic surfactant determination. Theadvantage of potentiometric titration was its very high de-gree of automation and very low detection limits obtainedwith ion-selective electrodes for different surfactants. Thinlayer chromatography offered advantages because of its nu-merous benefits such as low cost, ease of operation, and ra-pidity of the analysis.I. REZIÆ et al.: Preliminary Testing for Surfactants Determination, Kem. Ind. 56 (11) 557–560 (2007) 559Table 2 – Optimal chromatographic procedure for deter-mination of the investigated surfactantsTablica 2 – Optimalni kromatografski proces odreðivanjaispitivanih površinski aktivnih tvariAdsorbentAdsorbensSolventOtapaloTime ofdevelopment,t/minVrijemerazvijanja, t/minDetectionDetekcijasilicagel 60F254ssilikagel 60F254sisoamylalcoholizoamil--alkohol5555UV light254 nmUV-svjetlo,254 nm(tenside) / mg L–1(tenside) / mg L–1Fig . 2 – Linear curve for investigated HDTMAC surfactant ob-tained with ion selective electrodeSlika 2– BaÞdarni pravac dobiven za površinski aktivnu tvarHDTMAC (y = 0.2354x + 0.0246, R2 = 0.9988)Fig . 1 – Linear curve for investigated SDS surfactant obtainedwith ion selective electrodeSlika 1– BaÞdarni pravac dobiven za površinski aktivnu tvarSDS (y = 0.927x + 0.0224, R2 = 1.0000)(tenside) / mg L–1Fig . 3 – Linear curve for investigated KEMONECER NIsurfactant obtained with ion selective electrodeSlika 3– BaÞdarni pravac dobiven za površinski aktivnutvar KEMONECER NI (y = 0.1456x + 0.0876,R2 = 0.9781)ReferencesLiteratura1. A. Pettersson, M. Adamsson, G. Dave, Chemosphere 41(2000) 1611.2. Uredba o opasnim tvarima iz voda, Narodne Novine 78/98,(1998) 1774.3. G. F. Longman, The Analysis of Detergents and Detergent Pro-dutcs, Wiley, London, 1977.4. M. Castillo, Journal of Chromatography A 889 (2000) 195.5. D. W. Armstrong, G. Y. Stine, Journal of Liquid Cromatogra-phy 6 (1983) 23.6. J. C. Touchstone, J. Sherma, Techniques and Applications ofThin-Layer Chromatography, Wiley, United Kingdom, 1985.7. R. Schultz, Titrimetric Determination of Surfactants and Phar-maceuticals, Metrohm, Herisau, 1999.8. D. R. Karsa, M. R. Porter, Biodegradability of Surfactants, Blac-kie Academic & Professional, London, 1995.9. I. Reziæ, Lj. Bokiæ, Tenside Surf. Det. 42 (2005) 274.10. I. Reziæ, Lj. Bokiæ, Book of Proceedings, 2nd International Tex-tile, Clothing and Design Conference-Magic World of Texti-les, 3rd –6 th October 2004, Dubrovnik, Croatia, 1020–1023.11. R. Matešiæ-Puaæ, Kemija u industriji 49 (2000) 383.12. B. W. Topping, Tenside Detergents 19 (1982) 164.13. S. Janeva, J. Jordanova, Zeitschrift fur die Gesamte Hygieneund Ihre Grenzgebiete, 26 (1980) 346.14. E. R. Michelsen, Seifen Öle Fette Wachse 104 (1978) 93.15. H. König, Fresenius Zeitschrift für Analytische Chemie, 254(1971) 337.16. H. König, Fresenius Zeitschrift für Analytische Chemie, 251(1970) 167.17. A. Mohammad, H. Shahab, Tenside, Surfactants, Detergents44 (2007) 82.18. A. L. Lobachev, A. A. Kolotvin, Journal of Analytical Chemistry61 (2006) 622.List of symbolsPopis simbolac – concentration, mol L–1– koncentracija, mol L–1R2 – correlation coefficient– koeficijent korelacijeRF – value at the silica gel plates– vrijednost na podlozi silikagelat – time, min– vrijeme, minV – volume, mL– obujam, mLd – mass concentration, mg L–1– masena koncentracija, mg L–1l – wavelength, nm– valna duljina, nm560 I. REZIÆ et al.: Preliminary Testing for Surfactants Determination, Kem. Ind. 56 (11) 557–560 (2007)SAÝETAKMetode za preliminarna odreðivanja anionskih, kationskih i neionskih surfaktanataI. Reziæ, T. Pušiæ i Lj. BokiæDanas se razlièite površinski aktivne tvari (anionske, neionske, kationske i amfoterne) upotreblja-vaju u ogromnim kolièinama u razlièitim industrijama i domaæinstvima, što èini velik problem zaokoliš. Njihova je industrijska primjena proširena na proizvodnju kozmetike, metala, papira ikoÞe, pa se oni zbog toga mogu nalaziti u otpadnim vodama tih industrija u velikim kolièinama. UEuropiseupotrebljava4250000tonadetergenatai1190000tonaomekšivaèagodišnje.Mnogeod uobièajenih površinski aktivnih tvari imaju izrazito toksièno i štetno djelovanje na okoliš i naljudsko zdravlje, pa su zakonski propisi koji kontroliraju njihovo postojanje u otpadnim vodamadosta strogi: granice za otpuštanje površinski aktivnih tvari u tokove otpadnih voda u Hrvatskojkreæu se u rasponu od d = 0,05 do 0,10 mg L–1. Na toksiènost i biorazgradivost tih tvari u okolišuutjeèu mnogi fizikalni, kemijski i biološki èimbenici u meðudjelovanju. Kompleksan sastav deter-genata u kojima se površinski aktivne tvari miješaju s ostalim komponentama takoðer dovodi dosinergistièkog uèinka. Nadalje, detergenti odnosno površinski aktivne tvari u njihovom sastavumogu utjecati na biorazgradivost i toksiènost ostalih komponenata u okolišu. Zbog toga je vrlovaÞnorazvitiiprimijenitiodgovarajuæuapritomeneskupuanalitièkumetoduzaodreðivanjepo-vršinski aktivnih tvari u detergentima.Ovim radom predlaÞu se dvije jednostavne i brze analitièke metode za odreðivanje anionskih,kationskih i neionskih površinski aktivnih tvari: tankoslojnu kromatografiju za kvalitativno odreði-vanje te njihovo kvantitativno odreðivanje potenciometrijskom titracijom s ionsko selektivnimelektrodama. Pokazano je da je najbolja separacija i identifikacija istraÞivanih komponenata po-stignuta pomoæu razvijaèa izoamil alkohola na podlozi silikagela 60 F254s, detekcija je provedenapod UV luènicom pri l = 254 nm. Nakon kromatografske identifikacije komponenata, obavljenaje potenciometrijska titracija surfaktanata uz primjenu razlièitih ion selektivnih elektroda i titrana-ta (kationski je titriran sa c = 0,004 mol L–1 natrij dodecil sulfatiom pri pH 10, anionski sa c =0,004 mol L–1 Hiaminom 1622 kod pH 3, a neionski sa c = 0,01 mol L–1 tetrafenilboratom kodpH10).Tedvijemetodepokazalesusekaovrlodobrakombinacijazaodreðivanjeanionskih,ka-tionskih i neionskih površinski aktivnih tvari. Prednost potenciometrijske titracije je visok stupanjautomatizacijeivrloniskegranicedetekcijekojepostiÞurazlièiteionselektivneelektrode.Tanko-slojna kromatografija takoðer pruÞa mnoge prednosti nad ostalim analitièkim metodama: niskitroškovi, brzina te jednostavnost analize omoguæuju uvoðenje ove metode u mnoge laboratorijekoji se bave analizom detergenata.Tekstilno-tehnološki fakultet, Prilaz baruna Filipoviæa 30, Prispjelo 15. veljaèe 2007.10 000 Zagreb, Hrvatska Prihvaæeno 12. rujna 2007.

Preliminary Testing For Anionic, Cationic and Non-ionic

Abstract

Similar works

Full text

Available Versions

Directory of Open Access Journals