ASTM D4423 Standard Test Method for Determination of Carbonyls in C4 Hydrocarbons
8. Procedure
8.1 Prepare a sample flask by pouring 50 mL of alcoholic hydroxylamine hydrochloride into a 250 mL Erlenmeyer flask.
8.2 Prepare a flask for use as a sample blank by pouring 50 mL of methanol into a 250 mL Erlenmeyer flask.
8.3 Add about 0.5 mL of thymol blue indicator solution to each flask.
8.4 Carefully add 0.05 N alcoholic KOH or alcoholic HCl to each flask until matching colors are obtained. The desired color is a yellow color with a slight, but distinct, orange coloration. It is important that this orange color is present at this point of the test. If the color is more yellow at this point, it would be easy to obtain a result of less than 1 mg/kg carbonyls on a sample containing over 100 mg/kg of carbonyls.
8.5 Stopper the flasks with the Bunsen valves. (This keeps the CO2 vapor out of the flasks). Set the flasks on some crushed dry ice for a few minutes to cool the liquid contents. The color in the flasks may turn more yellow when cold, but this is not significant at this point. From this step forward, all operations must be carried out in a well-ventilated hood.
8.6 Cool a 100 mL graduated cylinder by holding it in the cooling bath for a few seconds. Then, when it is cold, collect 100 mL +/- 1 mL butadiene into the graduated cylinder. Quickly, using a clean thermometer, measure the sample's temperature to the nearest 1 °C. Record this temperature as "T" for use later to obtain the sample weight. Pour this sample into the sample flask containing the alcoholic hydroxylamine hydrochloride solution. Replace the Bunsen valve on the flask and set aside. Again, collect 100 mL +/- 1 mL of sample into the graduated cylinder. Pour this sample into the sample blank flask containing only the methanol. Replace the Bunsen valve and set aside.
8.7 Sample and sample blank can be titrated after 15 min while cold butadiene is in the flasks. If done, be careful to avoid vigorous agitation because some of the contents may boil over and be lost. It is advisable to allow as much of the butadiene as possible to evaporate before titration begins.
8.8 Titrate the sample flask's contents back to the original coloration, as described in 8.4, by using the alcoholic KOH. Record this value as "A". Set the flask aside in the hood for 5 min before pouring out the contents. If it turns red, the carbonyl concentration may be high or there is contamination in the flask. Continue the titration until the flask's contents will not turn red after standing 5 min.
8.9 Titrate the sample blank flask's contents. If the solution is red, use the standard KOH solution. If it is yellow, use the standard HCl solution. In either case, unless the sample blank's contents are still at the original coloration, titrate with the appropriate titrant back to the same, original coloration as described in 8.4. Record this value as "E".
