FAO Nutrition Meetings
Report Series No. 38A
SPECIFICATIONS FOR IDENTITY AND
PURITY AND TOXICOLOGICAL EVALUATION
OF SOME ANTIMICROBIALS AND
The content of this document is the result of the deliberations of the
Joint FAO/WHO Expert Committee on Food Additives which met 8-17
a Eighth Report of the Joint FAO/WHO Expert Committee on Food
Additives, Wld Hlth Org. techn. Rep. Ser., 1965, 309; FAO
Nutrition Meetings Report Series 1965, 38.
CHEMICAL NAMES 3,3-thiodipropionic acid; ß,ß'-thiodipropionic
acid; thiodihydracrylic acid; diethyl sulfide
EMPIRICAL FORMULA C6H10O4S
CH2 - CH2 - COOH
CH2 - CH2 - COOH
MOLECULAR WEIGHT 178.21
DEFINITION Contains not less then 98.5% of C6H10O4S and
conforms to the following specifications.
DESCRIPTION Thiodipropionic acid is a white crystalline
solid having a slight characteristic odour.
USE As an antioxidant for fats and other
A. Solubility: Water: 1 g is soluble in about 30 ml
Acetone: Freely soluble
Ethanol: Freely soluble
B. Melting range: Between 130° and 134°
C. Sulfur contents: Between 17.5% and 18.5%
Weigh 0.700 g of thiodipropionic acid and add 100 ml of acetic
acid and 50 ml of ethanol and heat the mixture gently until the
sample dissolves completely. Add 3 ml of hydrochloric acid and
4 drops of p-ethoxychrysoidin TS and immediately titrate with
0.1 N bromide-bromate TS. As the endpoint is approached (pink
colour) add 4 more drops of the indicator solution and continue
the titration dropwise, to a colour change from red to pale
yellow. Perform a blank determination and make any necessary
correction. Each ml of 0.1 N bromide-bromate TS is equivalent to
1.603 mg of S.
Sulfated ash: Not more than 0.2%.
Heavy metals: Not more than 10 mg/kg.
Place 2 g, accurately weighed, in a porcelain crucible, add sufficient
nitric acid to wet the sample, and ignite carefully at a low
temperature until thoroughly charred, covering the crucible loosely
with a porcelain lid during the ignition. When carbonization is
complete, add 2 ml of nitric acid and 5 drops of sulfuric acid, heat
cautiously until white fumes are evolved and then ignite, preferably
in a muffle furnace at 550° ± 50°C until the carbon is removed. Cool,
add 4 ml of diluted hydrochloric acid (1 in 2), cover, and digest on a
steam bath for 15 minutes. Remove the cover and evaporate on steam
bath to dryness. Moisten the residue with 0.05 ml of hydrochloric
acid, add 10 ml of hot water and digest on a stem bath for 5 minutes.
Filter, if necessary, add dilute to 25 ml.
Arsenic: Not more than 3 mg/kg.
Selenium: Not more than 30 mg/kg.
Sample solution. Transfer 2 g of thiodipropionic acid into a 250-ml
conical flask and cautiously add 10 ml of 30% hydrogen peroxide.
After the initial reaction has subsided, add 6 ml of 70% perchloric
acid and heat slowly until white fumes of perchloric acid are
copiously evolved. If the solution is brownish in colour due to the
undecomposed organic matter, add a small portion of peroxide solution
and heat again to white perchloric acid fumes, repeating if necessary
until decomposition of the organic matter is complete and a colourless
solution is obtained. Cool, add 10 ml of water and filter the
solution into a 200 × 25 mm test-tube. Wash the filter until the
filtrate measures 20 ml and add 20 ml of hydrochloric acid.
Selenium stock solution. Transfer 120.0 mg of metallic selenium
(Se) into a 1000-ml volumetric flask, add 100 ml of dilute nitric acid
(1 in 2), warm gently on a steam bath to effect the solution and
dilute to volume with water. Transfer 5.0 ml of this solution into a
200-ml volumetric flask, dilute to volume with water and mix. Each
ml. of this solution contains 3 micrograms of selenium ion (Se).
Standard solution. On the day of use, transfer 20.0 ml of selenium
stock solution (60 micrograms Se) into a 125-ml conical flask and add
20 ml of hydrochloric acid.
Procedure. Place the test-tubes containing the standard solution
and the sample solution in a water bath and heat until the temperature
of the solution reaches 40°. To each tube add 400 mg of ascorbic
acid, stir until dissolved and maintain both at 40° for 30 minutes.
Cool the solutions, dilute with water to 50 ml and mix. Any pink
colour produced by the sample does not exceed that produced by the
Weigh 0.350 g, dissolve in 40 ml of water, add phenolphthalein TS and
titrate with 0.1 N sodium hydroxide to the first appearance of a
faint pink colour that persists !or at least 30 seconds. Each ml of
0.1 N sodium hydroxide is equivalent to 8.910 mg of C6H10O4S.