Measurement of Critical Micelle Concentration of Technical Grade Non-Ionic Detergent In Presence of Chloramine-T using Dye Solubilization Technique

Introduction

The critical micelle concentration of technical grade non-ionic surfactants has been determined in the past by three different methods¹, viz., from the break in the turbidity Vs. concentration curve, from the break in the static surface tension Vs. logarithm of concentration curve and by the iodine solubilization technique². Thus CMC determinations are usually on the basis of sharp change in the colligative properties like clouding, surface tension, solubilization of a hydrophobic dye (Orange-OT).

Ionic surfactants are easier to obtain in the pure form than ethoxylated non-ionic surfactants. Commercially available technical grade ethoxylated surfactants have a istribution in the degree of ethoxylation as well as in the hydrophobe.  For non-ionic surfactants large variation is observed in the CMC values determined by different methods. Also for non-ionic surfactants a clear break in the surface tension Vs. concentration curve is not usually obtained due to presence of impurities and a broad molecular weight distribution^3,4. CMC’s of surfactants can be determined by number of methods^5,6

The CMC of non-ionic detergents are much less than those ionic detergents of comparable hydrocarbon chain length because of which the time required to reach equilibrium in each measurements of surface tension can be several hours⁷. The surface tension method thus becomes not only time consuming but may involve uncertainties⁸ due to evaporation from the surface and stagnant layer formation⁹.  The experimental difficulties involved in the precision determination of clouding are well known¹⁰, though not insurmountable. The iodine solubilization technique is convenient but presumably involves chemical reaction leading to the formation of hydrogen iodides¹¹ and therefore cannot be considered to be reliable as compared to dye solubilization method. The solubilizing power is one of the most important properties of surfactants. The solubilization of water insoluble dye Orange-OT in the surfactant micelles was studied in order to determine CMC of the surfactants. The amount of the dye solubilized was insignificant up to the CMC of each surfactant or with additive and thereafter a sudden steep rise was observed with the formation of micelles in the bulk.

Polysorbates are a class of emulsifiers used in some pharmaceuticals and food preparations. They are often used in cosmetics to solubilize essential oils in to water based products. Tween-40 (TW-40) is one of the polysorbate. TW-40 is nonionic detergent used for cell lysis, nuclei isolation and cell fractionation. It is also widely used in cosmetics and some pharmaceutical preparations. It has been shown earlier that CMC of ionic or non-ionic surfactants get affected (decreased) by the addition of salts¹². Some inorganic and organic compounds are added to detergents in order to make detergent cheap, user friendly and to boost its power¹³, these compounds are called as “builders”. Chloramine-T (CAT) is used as disinfectant, algaecide, bactericide, germicide for parasite control and for drinking water disinfection. Due to these properties CAT can be used as a “builder” in detergents.

The present paper reports the effect of Chloramine-T (CAT) on CMC of pure non-ionic surfactant Tween-40 at various concentrations of CAT by using dye solubillization technique. These studies are important in the field of medicinal preparations, agrochemicals, detergents etc.

Materials and Methods

The non-ionic surfactant Tween-40 (M.Wt.1283.65) and Chloramine-T trihydrate (M.Wt.281.69) were the products of Sigma-Aldrich, USA and these were used as received. The dye Orange-OT (1-o-tolyl azo- 2-napthol, M.Wt.262.3) prepared from o-toluidine and 2-napthol was purified twice by precipitating it from acetone solution with water followed by recrystallization from ethyl alcohol. Doubly distilled water with specific conductance 2-4 μScm^-1 at 303.15K is used in the preparation of all solutions of different concentrations.

Dye Solubilization

The insoluble dye Orange-OT was shaken with an aqueous solution of the surfactant for 48 hours at room temperature by using mechanical stirrer and then the residue was removed by means of centrifugation and filtration. The absorbance of the resultant solution was measured by using Eqiptronics Digital Spectrophotometer Model: EQ-820 at λmax = 470nm and at 303.15K

 

Scheme 1 Click here to View Scheme

 

The absorbance for pure surfactant increases with increase in concentration for surfactant Tween-40. The absorbance values of surfactant solutions at 470nm wavelength are plotted as a function of surfactant concentration in weight percentage to measure the extent of dye uptake (Fig.1)

Figure 1 Click here to View Figure

Figure 2 Click here to View Figure

 

Below the CMC, the rise in absorbance is small, where as above the CMC, the rise in absorbance is sharp. For non-ionic surfactant the micellization process is known to be less sharp than for ionic surfactant hence the rise in absorbance varies strongly over a range of surfactant concentration. The absorbance Vs concentration curve get flattened at high enough surfactant concentration as most of the dye forms micelles, depleting the continuous-phase dye. The linear portion near the inflection point is extrapolated to the point where the absorbance matches that of the dye in the absence of any surfactant. This concentration is defined as the CMC. The observed CMC value for pure surfactant Tween-40 was 0.0241 which is very close to the reported CMC value 0.027¹⁴.

 Tween-40 and Chloramine-T systems:

The absorbance for mixed system also increases slowly with increase in concentration up to CMC and then increases sharply with increase in concentration above CMC. The absorbance values of mixed systems of Tween-40 and Chloramine-T at λmax = 470nm wavelength are plotted as a function of surfactant concentration in weight percentage to measure the extent of dye up take (Fig.2)

Surfactant Tween-40 in presence of additive Chloramine-T shows that the amount of dye solubilized rise slowly up to the CMC, thereafter a sudden and sharp rise was observed with the formation of micelles in the bulk. The CMC Tween-40 surfactant was found to be decrease with increase in the concentration of added solute Chloramine-T. Thus the solubilizing power of surfactants increases in the presence of Chloramine-T. The CMC values obtained for mixed systems are shown in Table 1

Table 1: Influence of [CAT] on CMC of detergent at λmax = 470nm      

Detergent with [CAT] wt%	CMC(mM) of Detergent at 303.15K
0.0001	0.0239
0.001	0.0179

                                 

Acknowledgement

The author (A. A. Patil) is thankful to Dr. A.Z. Patil, Hon’ble Chairman, JET’s Z.B.Patil College, Dhule,  Hon’ble Principal; Z.B.Patil College, Dhule, Head, Department of Chemistry and all colleagues of Department of Chemistry, Z.B.Patil College, Dhule for their kind co-operation.

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