ASTM D500 Test Methods of Chemical Analysis of Sulfonated and Sulfated Oils
ORGANICALLY COMBINED SULFURIC ANHYDRIDE
Method A. Titration Test (For Sulfated Oils)
15. Scope
15.1 This test method covers the determination of the organically combined sulfuric anhydride existing in a sample of sulfated oil by boiling the sample with sulfuric acid and determining the acidity of the reaction mixture. This method is applicable only to oils that split off their combined SO3 upon boiling with mineral acids and that do not contain compounds that cannot be accurately titrated in water solution with methyl orange as the indicator.

16. Apparatus
16.1 The apparatus required consists of a glass flask provided with a glass stopper and an air condenser. The connection between the flask and the condenser shall be a ground joint. Perforated glass beads shall be used to prevent bumping.
16.1.1 Flask - An Erlenmeyer flask (Fig. 2) made of a borosilicate glass, having a capacity of approximately 300 mL and provided with a glass stopper.

16.1.2 Condenser - The condenser required consists of a glass tube, 915 mm (36 in.) in length, and 8 mm (5/16 in.) in outside diameter. The lower end of the tube shall be flared and ground to fit the mouth of the Erlenmeyer flask.

16.1.3 Glass Beads - Perforated glass beads, made of chemically-resistant glass, approximately 4 mm (5/32 in.) in diameter. Before using, the glass beads shall be boiled thoroughly in several portions of water or until the wash water reacts neutral to methyl orange indicator.

17. Reagents
17.1 Ethyl Ether.

17.2 Methyl Orange Indicator Solution (1 g/L) - Dissolve 0.1 g of methyl orange in 100 mL of water.

17.3 Sodium Chloride (NaCl), solid.

17.4 Sodium Hydroxide, Standard Solution (1 N) - Accurately prepare and standardize a 1 N sodium hydroxide (NaOH) solution. Express the strength or concentration of the solution as milligrams of KOH per millilitre; 1 mL of 1 N NaOH solution is equivalent to 56.1 mg of KOH.

17.5 Sodium Hydroxide, Standard Solution (0.5 N) - Accurately prepare and standardize a 0.5 N NaOH solution. Express the strength of the solution as milligrams of KOH per millilitre; 1 mL of 0.5 N NaOH solution is equivalent to 28.05 mg of KOH.

17.6 Sulfuric Acid, Standard (0.5 N) - Accurately prepare and standardize a 0.5 N sulfuric acid (H2SO4) solution. Express the strength of the solution as milligrams of KOH per millilitre; 1 mL of 0.5 N H2SO4 is equivalent to 28.05 mg of KOH.

17.7 Sulfuric Acid (1 + 19) - Carefully mix 1 volume of concentrated sulfuric acid (H2SO4, sp gr 1.84) into 19 volumes of water while stirring.

18. Procedure
18.1 The procedure consists of two determinations: namely, (a) the alkalinity of the sample, designated as A, and (b) the increase in acidity after boiling the sample with sulfuric acid, designated as F.
18.1.1 Alkalinity, A - Dissolve 10 g of the sample in 100 mL of water in the 300-mL glass-stoppered Erlenmeyer flask, warming to obtain solution if necessary. After cooling, add 30 g of NaCl, 25 mL of ether, and 5 drops of methyl orange indicator solution; then add 0.5 N H2SO4 with frequent but gentle shaking until the mixture is slightly acid. Shake the contents of the flask vigorously, and complete the titration by adding first 0.5 N NaOH solution several drops at a time until the solution is alkaline and then the acid 1 or 2 drops at a time until the end point is reached. Shake the solution vigorously after each addition of reagent. Drain burets for 3 min before taking readings. Calculate the alkalinity, A, as follows:
A = [(B x D) - (C x E)]/W
where:
A = total alkalinity, mg of KOH/g,
B = millilitres of H2SO4 required for titration of the sample,
C = millilitres of NaOH solution required for titration of the sample,
D = strength of H2SO4, mg of KOH/mL,
E = strength of NaOH solution, mg of KOH/mL, and
W = weight of sample, g.

18.1.2 Increase in Acidity upon Boiling, F - Weigh 10 g of the sample into the Erlenmeyer flask and boil under the air condenser with H2SO4 (1+19) for 1 1/2 h or until both the oil and water layers are perfectly clear, using glass beads to prevent bumping. The volume of H2SO4 added shall be sufficient to neutralize the total alkalinity, A, of the sample plus 25 mL in excess. Regulate the heating so that the solution boils rather vigorously but with very little evaporation taking place. At the end of the heating period allow the contents to cool, wash the condenser with a spray of water from a wash bottle, and disconnect the condenser. Add 30 g of NaCl, 25 mL of ether, 50 mL of water, and 5 drops of indicator solution and titrate the solution with 1 N NaOH solution to the same end point as in the total alkalinity titration, 18.1.1. During the titration stopper the flask frequently and shake the contents of the flask thoroughly. Drain the burets for 3 min before readings are taken.

NOTE 2 - Reserve the titrated solution for the subsequent determination of total desulfated fatty matter (Sections 29-32).

18.1.2.1 Make a blank determination simultaneously with the sample, using the same amount and strength of the H2SO4, approximately the same weight of glass beads, and heating and titrating under the same conditions as the sample.

18.1.2.2 Calculate the increase in acidity upon boiling, F, as follows:
F = [(S - B)N]/W
where:
F = increase in acidity (Note 3) upon boiling, mg of KOH/g,
S = millilitres of NaOH solution required for titration of the sample,
B = millilitres of NaOH solution required for titration of the blank,
N = strength of NaOH solution, mg of KOH/mL, and
W = weight of sample, g.

NOTE 3 - The increase in acidity, F, may be negative, in which case retain the sign obtained from the above equation in Section 19.

19. Calculation
19.1 Calculate the percentage of organically combined sulfuric anhydride as follows:
Organically combined sulfuric anhydride, % = 0.1426(A + F)
where:
0.1426 = one tenth of the molecular ratio of SO3:KOH,
A = total alkalinity, mg of KOH/g, and
F = increase in acidity upon boiling, mg of KOH/g. Retain the sign of F as obtained in 18.1.2.

Method B. Extraction-Titration Test (For Sulfated Oils)
20. Scope
20.1 This test method covers the determination of the organically combined sulfuric anhydride existing in a sample of sulfated oil by extracting the undecomposed sulfated fat and other fatty matter over an acidulated, concentrated salt solution, boiling the residue with sulfuric acid after evaporating the solvent, and titrating the products of reaction. This method is applicable only to sulfated oils that split off their combined SO3 upon boiling with mineral acids, including samples containing sodium acetate or other compounds that cannot be accurately titrated in water solution with methyl orange as the indicator.

21. Apparatus
21.1 The apparatus shall be the same as described for Test Method A in Section 16.

22. Reagents
22.1 The solutions shall be the same as described for Test Method A in Section 17.

23. Procedure
23.1 The procedure consists of isolating and purifying the fatty matter as it exists in the original oil by dissolving the sample in a solvent, acidifying and washing with saturated brine, and determining the increase in acidity upon boiling the isolated product with sulfuric acid. This increase in acidity is designated as F.
23.1.1 Separation of Purified Oil - Weigh 5 to 10 g of the sample, depending upon the concentration of the fatty matter, into a 250-mL separatory funnel containing 50 mL of concentrated NaCl solution, some solid NaCl, 5 drops of methyl orange indicator solution, and 50 mL of ether. Shake the mixture and neutralize with H2SO4 (1+19) until the lower layer is distinctly pink (about 0.2 mL in excess). Highly sulfated oils at this stage may form three layers instead of two. In such cases, use a fat solvent consisting of a mixture of 2 parts of ether and 1 of alcohol. Allow the mixture in the separatory funnel to settle for at least 5 min, draw off the lower layer into another separatory funnel, and wash the ether layer with 25-mL portions of NaCl solution until practically neutral to methyl orange, that is, until 1 drop of 0.5 N NaOH solution turns the wash water strongly alkaline. Allow all separations to settle for at least 5 min. Combine the water layers, and extract with two 25-mL portions of ether. Combine the last two ether extractions and wash with NaCl solution until free from acid, as in the case of the ether layer in the first funnel. Combine all the ether layers in the decomposition flask and evaporate the ether.

23.1.2 Increase in Acidity upon Boiling, F - Determine the increase in acidity upon boiling in accordance with the procedure described for Test Method A in 18.1.2. Reserve the titrated solution for the subsequent determination of total desulfated fatty matter (Sections 29-32). Make a blank determination as described for Test Method A in 18.1.2. Calculate the increase in acidity F in accordance with 18.1.2.

24. Calculation
24.1 Calculate the percentage of organically combined sulfuric anhydride as follows:
Organically combined sulfuric anhydride, % = 0.1426 x F
where:
0.1426 = one tenth the molecular ratio of SO3:KOH, and
F = increase in acidity upon boiling.

Method C. Ash-Gravimetric Test (In the Presence of True Sulfonates)
25. Scope
25.1 This test method covers the determination of the organically combined sulfuric anhydride existing in a sample of sulfonated or sulfated oil, or both, by extracting the undecomposed sulfonated or sulfated fat and other fatty matter over an acidulated, concentrated salt solution, and ashing the purified extract. This test method is applicable to all types of sulfonated and sulfated oils, including true sulfonic acid oils and those containing sodium acetate or similar partially titratable compounds.

26. Reagents
26.1 Ethyl Ether.

26.2 Hydrogen Peroxide (30 %) - Concentrated hydrogen peroxide (H2O2).

26.3 Methyl Orange Indicator Solution (1 g/L) - Dissolve 0.1 g of methyl orange in 100 mL of water.

26.4 Sodium Chloride (NaCl), solid.

26.5 Sodium Sulfate (Na2SO4), anhydrous.

27. Procedure
27.1 The procedure consists of isolating and purifying the fatty matter as it exists in the original oil by dissolving the sample in a solvent, acidifying and washing with saturated brine, and ashing the purified extract. If the sample contains ammonia, the ammonia shall first be expelled before the determination is made on the sample.
27.1.1 In the Absence of Ammonia - Proceed as described in the separation of purified oil (23.1.1), combining the ether layers in the first funnel rather than in the decomposition flask. Carefully remove any water that may settle and dehydrate the ether layer as follows: add 5 g of anhydrous Na2SO4, shake vigorously for 5 min, and filter directly into a 150-mL beaker placed in a bath of warm water. Wash the flask and filter with ether until free from fat (absence of oil stains on the filter paper after drying) and add the filtrate to the beaker. To avoid creeping of the oil, the volume in the beaker should at no time during the filtering and washing exceed 50 mL (one third full). Evaporate the ether solution until the volume has been reduced to about 20 mL and transfer the residue to a tared 50-mL crucible (high form). Immerse the crucible in a 100-mL beaker containing warm water until practically all of the ether has evaporated. Rinse the beaker with two 10-mL and three 5-mL portions of ether, or until all of the oil has been transferred to the crucible; allow each portion of rinsing ether to evaporate before the next rinsing is made. Burn gently the solvent-free residue, and finally ignite at a dull red heat to constant weight. To prevent creeping of the oil and to hasten evaporation, stir the solution with a glass rod; before the oil is burned, wipe the rod clean with ashless filter paper and add the paper to the crucible. To oxidize traces of carbon or sodium sulfide that might form, moisten the ash with H2O2 and again carefully ignite to constant weight. Calculate the percentage of ash as follows:
Extracted ash, % = (A/B) x 100
where:
A = weight of ash, g, and
B = weight of sample, g.

27.1.2 In the Presence of Ammonia - Dissolve 5 to 8 g of the sample in 80 mL of water in a 300-mL beaker. Add 10 mL of 1 N NaOH solution and boil the solution gently until wet litmus paper no longer indicates ammonia. Cool the solution, transfer to a 300-mL separatory funnel, and add about 35 g of solid NaCl or enough to make the final solution a 25 % NaCl solution. Add 5 drops of methyl orange solution and complete the neutralization, extraction, etc., in accordance with the procedure described in 27.1.1.

28. Calculation
28.1 Calculate the percentage of organically combined sulfuric anhydride as follows:
Organically combined sulfuric anhydride, % = 1.1267 A
where:
A = extracted ash, %, and
1.1267 = molecular ratio of 2SO3:Na2SO4.