Eadens, D. P., Connolly, J. W.. Naval Air Rework Facility, Alameda, Calif., private communication, 1974. Napier, D. H., Wong, I. W., Br. Polym. J., 4, 45-52 (1972). Sax, N. I., "Dangerous Properties of Industrial Materials," 3rd ed, Reinhold, New York, N.Y., 1968. Stone. J. P., Hazlett, R. N., Johnson, J. E., Carhart, H. W., J. Fire FlammabiC ity, 4, 42 (1973). Sumi, K., Tsuchiya, Y., J. Fire Flammabiiity, 4, 15 (1973).
Tatem, P. A., Gann. R. G.. Carhart, H. W., Combust. Sci. Techno/.. 7, 213 (1973). Woolley, W. D., Br. Polym. J., 4, 27 (1972).
Received for review January 29,1975 Accepted May 22,1975
Determining Cationic Surfactant Concentration Lawrence K. Wang' and David F. Langley Departmeot of Chemical and Environmental Engineering, Rensseher Polytechnic Institute, Troy, New York 12181
The objective of this research was to introduce a methyl orange method for the accurate colorimetric determination of cationic surface-active agents in the 0.10 to 1.25 mg/l. range. The basic principles of the methyl orange method include complexation of cationic surfactant with methyl orange at acidic condition, chloroform extraction, water-chloroform phase separation, and spectrophotometric measurement. More specifically, the water sample to be analyzed is treated with 50 ml of chloroform and an excess of methyl orange reagent in the presence of a pH 3 buffered solution. The methyl orange reacts with the cationic surfactant forming a chloroform soluble complex. The complex is dissolved in the chloroform phase by rapidly shaking the separatory funnel for a short time. Since chloroform is heavier than water, the chloroform phase can be separated from the water phase simply by gravity separation. The intensity of yellow color in the chloroform layer is directly proportional to the methyl orange complex; thus, the intensity of the yellow color can be subsequently measured by the use of a spectrophotometer (light path = 10 cm). The absorbance curves for the surfactant (cetyldimethylbenzylammonium chloride) samples treated show an absorbance maximum of 415 nm.
Introduction Quantitative chemical methods for determining cationic surface-active agents include: (a) diphasic titration against an anionic surfactant by using a dye-transfer method to detect the end point (Wang et al., 1974); (b) precipitation of an insoluble derivative, e.g., phosphotungstate or ferricyanide, with subsequent determination of the excess of precipitating agent or of a constituent of the precipitate; (c) ultraviolet spectroscopy; (d) infrared absorption (Cross, 1965); (e) paper chromatography (Drewry, 1963); (f) ion flotation (Love11 and Sebba, 1966); and (g) absorptionmetric measurement of a colored complex (Scott, 1968). The objective of this research was to introduce a methyl orange method for the rapid colorimetric determination of cationic surface-active agents in the 0.10 to 1.25 mgb. range. The basic principles of the methyl orange method include complexation of cationic surfactant with methyl orange at acidic condition, chloroform extraction, waterchloroform phase separation, and spectrophotometric measurement. Briefly stated, the water sample to be analyzed is treated with 50 ml of chloroform and an excess of methyl orange reagent in the presence of pH 3 buffered solution. The methyl orange reacts with the cationic surfactant forming a chloroform soluble complex. The complex is dissolved in the chloroform phase by rapidly shaking the separatory funnel for a short time. Since chloroform is heavier than water, the chloroform phase can be separated from the water phase simply by gravity separation. The intensity of yellow color in the chloroform layer is directly proportional to the methyl orange complex; thus, the intensity of the yellow color can be subsequently measured by the use of a spectrophotometer. The absorbance curves (Figure 1) 210
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cover a wavelength range of 300-500 nm. The absorbance curves for both 50- and 1O-wg micrograms surfactant (cetyldimethylbenzylammonium chloride) samples treated show an absorbance maximum a t 415 nm.
Experimental Section Reagents. Methyl Orange Solution. Dissolve 0.10 g of methyl orange powder in a small amount of distilled water. Dilute this volume to 100 ml, so that the concentration is 0.1% by weight. Buffer Solution. Dissolve 52.5 g (0.25 mol) of citric acid (HOC-COOH-(CHZCOOH)~-HZO) in 200 m! of distilled water, heating slightly if necessary. Dilute this volume to 500 ml so that the citric acid concentration is 0.5 M . Dissolve 26.80 g (0.1 mol) of disodium hydrogen orthophosphate (NazHP04.7HzO) in another 200 ml of distilled water, heating if necessary. Dilute this volume to 500 ml so that the disodium hydrogen orthophosphate concentration is 0.2 M . Combine the citric acid and disodium hydrogen orthophosphate solutions to form 1000 ml of pH 3 buffer solution. Chloroform. This was anhydrous and reagent grade. Apparatus. The following apparatus is needed: (a) volumetric pipets of various sizes (1-50 ml); (b) 500-ml separatory funnels; (c) spectrophotometer providing a 10-cm light path, at a wavelength of 415 nm; and (d) two 10-cm glass spectrophotometer cells. (Note: Although the light path of 10 cm is recommended, other light paths in the 1-10 cm range can also be used.) Calibration Curve Preparation. Prepare a series of separatory funnels with 0, 0.10, 0.25, 0.50, 0.75, 1.00, and 1.25 ml of a 50 mg/l. standard cationic surfactant solution (see Discussion). Add distilled water to make a total vol-
“.*r----
LIGHT PATH:
0.3
0.2
10 iH
-
10 UlCROGRAHS COBAC
I NAVELENGlh ( M N O M E T L R S )
Figure 1. Absorbance vs. wavelength for CDBAC-methyl orange complex.
ume of 50 ml in each separatory funnel, so that the corresponding surfactant concentrations in the series of separatory funnels are O,O.lO, 0.25,0.50,0.75,1.00, and 1.25 mgA., respectively. Treat each sample as described in Analytical Procedure (c) through (e). Plot a calibration curve showing mg/l. of cationic surfactant versus absorbance (or mgh. cationic surfactant versus percent transmittance). Analytical Procedure. (a) Prepare a reference Cell A of pure chloroform and adjust the spectrophotometer to zero absorbance, or 100% transmittance, a t 415 nm. (Note: For more accurate cationic surfactant determination, 50 ml of distilled water is treated as described in Analytical Procedure (c) through (d). Then drain the separated chloroform layer into the reference Cell A, and adjust the spectrophotometer to zero absorbance, or 100% transmittance.) (b) Pipet a determined amount of the water sample into a separatory funnel, record the sample size in milliliters, and then adjust as needed to 50 ml with distilled water. (c) Add 5 ml of buffer solution, 0.5 of methyl orange reagent, and 50.0 ml of chloroform to the separatory funnel, stopper, and shake vigorously for 30 sec to allow equilibrium to be established. (d) Let the chloroform and water separate completely by gravity separation for about 20 min or until the chloroform layer is not cloudy. (e) Drain the separated chloroform layer in to the sample Cell B and measure the absorbance (or percent transmittance). (f) Determine the measured amount of cationic surfactant from the calibration curve described previously, and calculate the cationic surfactant concentration by the following equation: mgh. of cationic surfactant = (mg/l. of cationic surfactant read from calibration curve) X 50/(ml of sample size).
Discussion The methyl orange method can be used to determine various cationic surface-active agents, such as, cetyldimethylbenzylammonium chloride, ethylhexadecyldimethylammonium bromide, dodecylamine hydrochloride, trimethyloctadecylammonium chloride, cetyltrimethylammonium bromide (CTAB), etc. It is conceivable that the known type of cationic surfactant to be quantitatively measured should be selected as the reference standard for the preparation of a calibration curve. A water sample containing a known type but, unknown concentration of cationic surfactant can then be quantitatively determined by the methyl orange method using the specifically prepared Calibration curve. Figure 2 shows the calibration curve of a
0
0 25
I 0 50
I 0 75
I 1.09
COBAC C D h C L N ~ R A l I O N , P G I L
Figure 2. Calibration curve of methyl orange-cationic surfactant complex. specific cationic surfactant, cetyldimethylbenzylammonium chloride (CDBAC). It has been evaluated that this method can be used to determine CDBAC mass down to about 5 wg, which, when using a typical 50-ml water sample, corresponds to 0.1 mg/l. The calibration curve, shown in Figure 2, was found to be linear down to this range, provided that a light path of 10 cm is used. As mentioned earlier in the section of Apparatus, the light path of 10 cm is recommended for accurate cationic surfactant determination in the 0.10-1.25 mg/l. range. Although other light paths in the 1-10 cm range can also be used, the light path shorter than 10 cm will provide wider surfactant determination range, but less precision and accuracy. Besides, if a light path equal to or shorter than 5 cm is used, the amount of chloroform to be used should be reduced to 25 ml per sample.. The amounts of other chemical reagents, however, should be kept the same. I t should be noted that the methyl orange method developed is applicable to the quantitative measurement of a single type of cationic surfactant in water, It is not possible to differentiate between two quaternary ammonium compounds, between two amines, or between a quaternary ammonium compound and an amine compound. For environmental water quality control, technically any pure cationic surface-active agent can be selected as the reference standard to represent various cationic surfactants present in a water or wastewater sample. The use of either CDBAC or CTAB as the reference standards for unknown cationic surfactant samples is recommended. Both CDBAC and CTAB can be supplied by Fine Organics, Inc. (205 Main Street, Lodi, N.J. 07644) in pure powdered forms. A similar methylene blue method (APHA, 1971; EPA, 1974; Wang, 1975; Wang et al., 1975) has been used by environmental chemists for decades for analyzing anionic surface-active agents in water and wastewater. Since the methylene blue method can not differentiate linear alkylate sulfonate (LAS) and branched-chain alkyl benzene sulfonate (ABS) or other isomers of this type compounds, the environmental chemists have defined the anionic surfactants measured by the methylene blue method to be MBAS (Le., the abbreviation of methylene blue active substances). Similarly, if the cationic surfactants present in water or wastewater are of unknown type, the cationic surfactant concentration measured by the suggested methyl orange method can be generally reported to be “mg/l. MOAS” (i.e., the abbreviation of methyl orange active substances). Ind. Eng. Chem., Prod. Res. Dev., Vol. 14, No. 3, 1975
211
Literature Cited American Public Health Association, "Standard Methods for the Examination Of Water and Wastewater," 13th ed, pp 334-342, APHA. Washington* D.C.. 1971. Cross, J. T., Analyst, 90 (1071), 315 (1965). Drewry, J., Analyst, 86, 225 (1963). Environmental Protection Agency, "Methods for Chemical Analysis of Water and Wastes," 2nd ed, pp 157--158, EPA, Washington, D.C., 1974. Lovell, V. M., Sebba, F., Anal. Chem., 38 (13),1926 (1966).
Scott, G. V., Anal. Chem., 40 (4), 768 (1968). Wang, L. K., J. Am. Water Works Assoc., 67 (l),19 (1975). wang,L, K,, et J, A,,.,, water works A ~ ~67 (4), ~ ~182, (1975), , Wang, M. H.. et at., J. Environ. Eng. Div., Proc. Am. Soc. Civil Eng., 100 (EE3), 629 (1974).
Receiued for review March 21,1975 Accepted May 16,1975
Photoelectron Spectra of Halogeno(tolyl isocyanide)iron(II) Complexes John W. Schindler' PPG Industries, lnc., Research Center, Coatings 8 Resins Division, Allison Park, Pennsylvania 15 10 1
John R. Luoma Department of Chemistry, The Cleveland State University, Cleveland Ohio 44 1 15
James P. Cusick Computational Services Department, N.A.S.A. Lewis Research Center, Cleveland, Ohio 44 135
Introduction Both X-ray photoelectron spectroscopy and Mossbauer spectrometry began their developments in the late 1950's. Both fields have progressed so satisfactorily as to become well established. X-Ray photoelectron spectroscopy deals with the determination of the binding energies of an element's electrons as they are ejected by nearly monochromatic X-radiation in a classical example of Einstein's photoelectric effect. Mossbauer spectrometry is based on the observance, by recoilless resonance fluorescence, of an isotope's nuclear parameters, and is particular to the element's chemical environment. When atoms are brought together to form a molecule, the electron orbitals of each atom are then perturbed in a manner characteristic of the bonding and structure involved (Siegbahn, 1973). It follows that the nuclear energy levels are then also perturbed. Both of these methods are thus proving themselves adept in investigations of molecular bonding. Transition metal inorganic complexes containing triply bonded octahedrally coordinating ligands have been extensively studied because of the exceptional u- and s-bonding capabilities of these ligands. The spectroscopic tools most heavily relied upon during the last decade to study both bonding and structure in complexes of this type have been infrared, NMR, and Mossbauer methods. More recently, Adams et al. (1972) suggested that there exists a linear correlation between the 57Fe Mossbauer Center Shift and the Fe 2p and 3p binding energies obtained by photoelectron spectroscopy (XPES or ESCA). Having investigated bonding and structure in dihalotetrakis(toly1 isocyanide)-iron(11) complexes by infrared, NMR, and Mossbauer spectroscopic methods, we (Schindler et al., 1974) set out to test this correlation. 212
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Experimental Section The isocyanides used were 0- and p-tolyl, hereafter referred to as OTI and PTI. The instrument utilized for obtaining the ESCA data was a Varian 1-15. Photoionization was accomplished with Mg KLYX-radiation (1253.6 eV). The gold 4f7/2 calibration line was taken to be 83.8 eV. Synthetic techniques and Mossbauer instrumentation have been discussed previously (Schindler et al., 1974). Table I shows the analytical data for a number of the complexes which we studied during the course of this work. The analyses were performed for us by Alfred Bernhardt Mikroanalytisches Laboratorium, 5251 Elbach uber Engelskirchen, Fritz-Pregl Strasse 14-16, West Germany. There is excellent agreement for the cis and trans isomers which were the main objective for our earlier work (1974). There is also excellent agreement for the iodopentakis(PT1)iron triiodide, which was the first by-product isolated and extensively characterized (Schindler et al., 1973). The last complex empirically analyzes to be dichlorobis(OT1)iron(II), although the analysis appears to be high in organic ligand and low in FeC12. Discussion The previously unreported dichlorobis(OTI)iron(II) complex is of particular interest since structure cannot be assigned on the basis of the empirical formula. The pyridine analog has, however, been reported. Tominaga et al. (1966) identified dichlorobispyridineiron(I1) as an intermediate in the thermal decomposition of dichlorotetrapyridineiron(I1). We (1974) suspect a similar thermal decomposition when using the method of Malatesta et al. (1953) to form the cis isomer, during which synthesis this by-product was isolated. Little and Long (1974) identified the pyridine
