Oxidizing, Bleaching, and AACC Method 48-42Maturing Agents Page 1 of 3

Quantitative Method for BromatesFinal approval April 13, 1961Reapproval November 3, 1999

ObjectiveThis method determines the amount of potassium bromate, a flour improver, in

white and whole-wheat flour.

Apparatus1. Glass stirrer, motor-driven, variable-speed.2. Beaker, 800-ml.3. Erlenmeyer flask, 200-ml.4. Filter paper, Whatman no. 12, 24-cm, fluted.5. Buret, 10-ml, graduated in 0.05 ml.

Reagents1. Zinc sulfate solution. Dissolve 20 g ZnSO4⋅7H2O in water and dilute to 1

liter.2. NaOH, 0.4N. Dissolve 17 g NaOH in water and dilute to 1 liter (Method 70-

70). Titrate against standard acid and adjust to 0.4 ± 0.01N.3. NaOH, 0.5N. Dissolve 21 g NaOH in water and dilute to 1 liter (Method 70-

70). Titrate against standard acid and adjust to 0.5 ± 0.01N.4. Dilute H2SO4. Add 112 ml concentrated H2SO4 to 800 ml water. Cool and

dilute to 1 liter.5. KI solution. Dissolve 25 g KI in 30 ml water; dilute to 50 ml. Store in amber

bottle in cool place. Discard solution showing yellow tinge of free iodine.6. Ammonium molybdate. Dissolve 3 g (NH4)6Mo7O24⋅4H2O in 80 ml water;

dilute to 100 ml.7. Potassium bromate stock, 5 mg/ml. Dissolve 5.000 g KBrO3, dried 1 hr at

110° in about 800 ml water. Dilute to 1 liter.8. Potassium bromate standard, 0.25 mg/ml. Dilute 25 ml stock solution to 500

ml.9. Potassium iodate stock, 0.0898N. Dissolve 3.204 g KIO3, dried 1 hr at 110°

in about 800 ml water. Dilute to 1 liter.10. Potassium iodate standard, 0.00359N. Dilute 10 ml stock solution to 250

ml. Prepare fresh daily.11. Starch solution. Mix 1 g soluble starch with enough cold water to make a

thin paste. Add 100 ml boiling water and boil 1 min.12. Sodium thiosulfate stock. Dissolve 22.5 g Na2S2O3⋅5H2O and 0.06 g

anhydrous Na2CO3 in 800 ml water. Dilute to 1 liter. Dilute 10 ml to 250 ml.Transfer 5 ml diluted solution to 200-ml Erlenmeyer flask. Add 100 ml water, 10ml dilute H2SO4, and 1 ml KI solution. Add 5 ml freshly prepared starch solution(reagent11), and titrate with 0.00359N KIO3 from 10-ml buret graduated in 0.05-ml increments. Adjust Na2S2O3⋅5H2O stock solution so that 10 ml diluted to 250ml is 0.00359N. Store stock solution in amber bottle in cool place.

Oxidizing, Bleaching, and AACC Method 48-42Maturing Agents Page 2 of 3

Quantitative Method for Bromates (continued)

13. Sodium thiosulfate standard, 0.00359N. Dilute 10 ml stock solution to 250ml. Prepare fresh daily and check at least monthly.

Procedure1. Transfer quantitatively 200 ml ZnSO4 solution to 800-ml beaker and stir by

means of variable-speed stirrer with glass agitator. (Sufficient agitation todisperse flour will be obtained with vortex about 1.5 in. deep that does notextend quite to bottom.) Transfer 50 ± 0.1 g sample to stirred ZnSO4 solution in2- to 5-g portions. Continue stirring 5 min or until all dry flour on surface is uni-formly dispersed. With continued stirring, add 50 ml 0.4N NaOH. Decrease stir-rer speed and stir for another 5 min.

2. Filter or centrifuge, clarifying supernatant by filtering through Whatman no.12, if necessary.

3. Transfer 50 ml of this solution to 200-ml Erlenmeyer flask, or, if smalleraliquot is taken, dilute to about 50 ml with water. Add 10 ml 4N H2SO4, 1 ml KI,1 drop ammonium molybdate solution, and 50 ml water. With continuousagitation, add excess of 0.00359N Na2S2O3 (5–10 ml).

4. Add 5 ml freshly prepared starch solution and titrate excess thiosulfate with0.00359N KIO3 from 10-ml buret graduated in 0.05-ml increments. As end pointapproaches, add KIO3 slowly, 1–2 drops at a time, swirling and viewing flask onwhite surface after each addition. Take first reddish or purplish tinge as endpoint, read buret, and add 1–2 drops to confirm.

5. Add another 1 ml thiosulfate and again titrate to end point. Add two differ-ences between amounts of thiosulfate and KIO3 used in titrations. KBrO3 (ppm)= 10 × (ml 0.0359N Na2S2O3 – ml 0.00359N KIO3).

6. Correct results by recovery factor determined as follows: Dilute known vol-ume (X ml), > 3 ml but < 10 ml, of standard KBrO3 to 250 ml. Using 50-ml ali-quot, proceed as in paragraphs 3 and 4 above. “Added bromate” in ppm = 10 ×(ml 0.00359N Na2S2O3 – ml 0.00359N KIO3).

7. Suspend 50-g portions of nonbromated flour in two separate 200-ml por-tions ZnSO4 solution by stirring as above.

8. To one (blank) suspension, add 10 ml water; to other (recovery) suspensionadd X ml standard KBrO3 and (10 – X) ml water. Continue as above, except add40 ml 0.5N NaOH with continuous stirring. Use 5 ml standard Na2S2O3 for blankand 10 ml for recovery suspension. Deduct blank value, if any, from value ofKBrO3 found in “recovery” data and multiply result by 10 to obtain ppm recov-ered bromate.

Calculation

Recovery factoradded bromate

recovered bromate=

Oxidizing, Bleaching, and AACC Method 48-42Maturing Agents Page 3 of 3

Quantitative Method for Bromates (continued)

References1. AOAC International. 1995. Official Methods of Analysis of AOAC International, 16th ed.

Method 956.03. The Association, Arlington, VA.2. Rainey, W. L. 1954. Report on potassium bromate in flour. J. Assoc. Off. Agric. Chem. 37:395.