ASTM D1157 Standard Test Method for Total Inhibitor Content (TBC) of Light Hydrocarbons
9. Procedure
9.1 Preparation of Sample - Measure 100 +/- 1 mL of liquid sample (Warning - Extremely flammable gas under pressure. May form explosive peroxides upon exposure to air. Harmful if inhaled. Irritating to eyes, skin, and mucous membranes.) into a graduate that has been cooled to below -20°C. Pour the sample into a 250-mL Erlenmeyer flask and allow the liquid to evaporate at room temperature behind a shield in a well-ventilated hood. A steam bath may be used to complete the evaporation. Add 30 mL of water to the flask, stopper, shake, and filter through a rapid, hardened, low-ash paper that has previously been moistened. Repeat with two more 30-mL portions of water. Combine all filtrates, add from a pipet 5.0 +/- 0.1 mL of standard FeCl3 solution, dilute to 100 mL, and mix well.
9.2 Measurement of Sample - After the addition of the FeCl3 reagent, allow the solution to stand for from 5 to 15 min, then measure the absorbance of the solution by means of a photoelectric photometer, using water as a reference standard.
NOTE 2 - Take care to have the comparison tubes clean and free from fingerprints and spilled solution. From time to time, the two tubes should be checked against each other with blank solution in both.
9.3 Measurement of Sample - Make a "blank" determination, following the same procedure, but omitting the addition of the sample. Subtract the absorbance of the "blank" from that of the sample and record the difference as the "net" absorbance.
NOTE 3 - A "blank" determination need be made only when first using a bottle of freshly prepared FeCl3 solution to ascertain that the reagent was made properly.
