Dioctyl sodium sulfosuccinate

Description and assay

Specification history

Prepared at the 37th JECFA (1990), published in FNP 52 (1992) superseding specifications prepared at the 27th JECFA (1983), published in FNP 28 (1983). Metals and arsenic specifications revised at the 55th JECFA (2000). An ADI of 0-0.1 mg/kg bw was established at the 44th JECFA (1995)

Chemical names

Sodium 1,4-bis-(2-ethylhexyl)-sulfosuccinate; butanedioic acid, sulfo-1,4-bis-(2-ethylhexyl) ester sodium salt; dioctyl sodium sulfosuccinate

C.A.S. number

577-11-7

Chemical formula

C 20 H 37 NaO 7 S

Formula weight

444.56

Assay

Not less than 98.5% on the dried basis

DESCRIPTION

White, wax-like, plastic solid, having a characteristic odour suggestive of octanol, but free from odour of other solvents

FUNCTIONAL USES

Emulsifying agent, wetting agent

METHOD OF ASSAY

Solutions - Sample solution: Transfer about 3.8 g of the sample, previously dried at 105 o for 2 h and accurately weighed, into a 500-ml volumetric flask, dissolve in chloroform. Dilute to volume with the same solvent, and mix. - Tetra-n-butylammonium iodide solution: Transfer 1.250 g of tetra-n-butylammonium iodide to a 500-ml volumetric flask, dilute to volume with water, and mix. - Salt solution: Dissolve 100 g of anhydrous sodium sulfate and 10 g of sodium carbonate in sufficient water to make 1000 ml Procedure Pipet 10.0 ml of the "Sample solution" into a 250-ml flask, and add 40 ml of chloroform, 50 ml of "Salt solution", and 10 drops of bromophenol blue TS. Titrate with "Tetra-n-butylammonium iodide solution" to the first appearance of a blue colour in the chloroform layer after vigorous shaking. Calculate the percentage of C 20 H 37 NaO 7 S by the formula: where V = the volume, in ml of tetra-n-butylammonium iodide solution required 444.6 = formula weight of dioctyl sodium sulfusuccinate W = the weight, in g, of the sample taken 369.4 = formula weight of tetra-n-butylammonium iodide

Identification

Solubility (Vol. 4)

Sparingly soluble in water; freely soluble in ethanol and glycerol

Infrared absorption

The infrared spectrum of a potassium bromide dispersion of the sample corresponds with that of a reference standard preparation (USP dioctyl sulfosuccinate reference standard obtainable from: United States Pharmacopoeia, 12601 Twinbrook Parkway, Rockville, Md 20852, USA).

pH (Vol. 4)

5.8 - 6.9 (1 in 100 soln)

Purity criteria

Loss on drying (Vol. 4)

Not more than 2% (105 o for 2 h)

Clarity of solution

Dissolve 25 g of the sample in 94 ml of ethanol. The solution does not develop a haze within 24 h

Sulfated ash (Vol. 4)

Between 15.5% and 16.2%. Test 1 g of the sample (Method I)

Bis-(2-ethylhexyl)- maleate

Not more than 0.4% See description under TESTS

Lead (Vol. 4)

Not more than 2 mg/kg Determine using an atomic absorption technique appropriate to the specified level. The selection of sample size and method of sample preparation may be based on the principles of the method described in Volume 4, “Instrumental Methods.”

Test: Bis-(2-ethylhexyl)- maleate

Reagents - Supporting electrolyte: Dissolve 21.2 g of anhydrous lithium perchlorate (LiClO 4 ) in 175 ml of water in a 250-ml beaker. Adjust the pH of this solution to 3.0 by the dropwise addition of glacial acetic acid (usually 1 or 2 drops is sufficient), using a suitable pH meter. Quantitatively transfer the solution into a 200-ml volumetric flask, dilute to volume with water, and mix. - Standard solution: Transfer 100-110 mg of bis-(2-ethyl-hexyl)-maleate (a suitable grade of bis-(2-ethylhexyl)-maleate is available as OT-35 from American Cyanamid Company, Pine Chemicals Department, Pearl River, New York 10965, USA), accurately weighed, into a 100-ml volumetric flask. Record the exact weight, to the nearest 0.1 mg, as W A . Dilute to volume with water, and mix. - Sample stock solution: Transfer 12.5 g of the sample, accurately weighed, into a 150-ml beaker. Record the exact weight, to the nearest 10 mg as W s . Add 80-90 ml of isopropanol, and stir with a glass stirring rod until the sample is dissolved. Quantitatively transfer this solution, with the aid of isopropanol, into a 250-ml volumetric flask. Dilute to volume with isopropanol, and mix. - Test solution A: Pipet 50.0 ml of the "Sample stock solution" and 20.0 ml of the "Supporting electrolyte" into a 100-ml volumetric flask. Dilute to within 15 mm of the graduated volume line with isopropanol, stopper, shake to facilitate solution, and set aside for 2 min. Dilute to volume with isopropanol, and mix. A completely clear solution should be obtained. - Test solution B: Pipet 50.0 ml of the "Sample stock solution", 10.0 ml of the "Standard solution", and 20.0 ml of the "Supporting electrolyte" into a 100 ml volumetric flask, and complete the preparation as described for "Test Solution A". - Blank: Pipet 20.0 ml of the "Supporting electrolyte" into a 100-ml volumetric flask, dilute to volume with isopropanol, and mix. Procedure Rinse a polarographic H-cell several times with small portions of "Test solution A", then fill the cell half-full with the solution, place a paper tissue in the top of the sample side of the cell and pass a moderate stream of nitrogen through the solution for 15 min. (NOTE: The nitrogen should first be saturated by passing it through a suitable scrubber containing isopropanol). After 15 min, divert the nitrogen stream over the surface of the solution, and remove the tissue from the cell. Set the polarizing voltage of a suitable, previously calibrated polarograph (Metrohm Polacord E-261 or equivalent) at -1.3 volts. Adjust the current sensitivity to the lowest range (most sensitive) at which the current oscillations will remain on scale, and record the polarogram, scanning a voltage range of -0.9 to -1.5 volts at this sensitivity and using a saturated calomel electrode as the reference electrode. Record the average oscillations, in mm, at -1.3 volts as A, and those at -1.0 volt as B. (NOTE: If a manual polarograph is used, record the average oscillations of the solutions at -1.3 volts and -1.0 volt respectively). Repeat the entire procedure using Test solution B, recording the average oscillations at -1.3 volts as D, and those at -1.0 volt as E. Similarly, repeat the entire procedure using the "Blank", recording the average oscillations at -1.3 volts as G, and those at -1.0 volt as H. Calculation Make the following preliminary calculations (in mA): where C is net diffusion current of "Test solution A", and S 1 is current sensitivity used for "Test solution A" where F is net diffusion current of "Test solution B", and S 2 is current sensitivity used for "Test solution B" where I is net current introduced by the "Blank", and S 3 is current sensitivity used for the "Blank" where J is diffusion current due to added maleate, added to Test Solution B from the Standard Solution where K is the diffusion current due to maleate present in Test Solution A Finally, calculate the percentage of bis-(2-ethylhexyl)-maleate in the original sample taken by the formula: