60.01 g and express the concentration as mg KHP/g of
solution. Mix thoroughly to dissolve the solution.
18. Procedure
18.1 Standardization of the Titrant 0.01 M Alcoholic KOH:
18.1.1 Weigh 2 g of KHP solution into a 125 mL or suitable
size beaker and record the weight to the nearest 0.0001 g if
using weight-based standard or pipette 2 mL of KHP solution
into a vessel and add approximately 50 mL of CO2 free water.
Titrate the solution to determine the titer of 0.01M KOH. This
volume of KHP solution will use approximately 2 mL of the
0.01 M KOH.
18.1.2 Prepare two additional KHP solutions to standardize
the titrant as in 18.1.
18.1.3 Use the three determinations to calculate the average
concentration (mol/L) of the KOH. The average of the titrant
mol/L determinations should agree 60.0005 M.
18.2 Determination of the Solvent Blank—Adjust the apparatus
in accordance with the manufacturer’s instructions to
provide a dynamic mode of titration. Addition of titrant volume
increments should not be greater than 0.2 mL. Measure
precisely 50 mL of propan-2-ol using a graduated cylinder,
pipet or automated dispensing device capable of dispensing 50
6 0.5 mL into a 125 mL or suitable size beaker. Stir the
solution and titrate. Record the volume (mL) of KOH to 60.01
mL used to titrate to the inflection point.
18.3 Analysis of the Sample:
18.3.1 Adjust the apparatus in accordance with the manufacturer’s
instructions to provide a dynamic mode of titrant
addition.
18.3.2 Weigh 5 g of biodiesel into a 125 mL or suitable size
beaker on an analytical balance and record the weight to the
nearest 0.0001 g. Measure 50 6 0.50 mL of IPA using a pipet
or automated dispensing device into a suitable beaker. Prepare
the electrodes as directed in 8.1. Place the beaker or titration
vessel on the titration stand and adjust its position so that the
electrodes are about half immersed. Start the stirrer, and stir
throughout the determination at a rate sufficient to produce
vigorous agitation without spattering and without stirring air
into the solution.
NOTE 19—It is important that the same volume of titration solvent 60.5
mL is used for the blank and samples or inconsistent results can occur.
18.3.3 Select the right burette, fill with 0.01-mol/L alcoholic
KOH solution, and place the burette in position on the titration
assembly, ensuring that the tip is immersed about 25 mm in
titration vessel liquid and titrate.
18.3.4 On completion of the titration, rinse the electrodes
and burette tip with propan-2-ol, followed by water. Immerse
the electrodes in water for at least 2 min before starting another
titration to restore the aqueous gel layer of the glass electrode.
Rinse the electrodes with propan-2-ol prior to running the next
sample. If electrodes are found dirty and contaminated, proceed
as in 8.1. Store electrodes according to 8.3.3.
18.3.5 Multiple titration inflection points are often found
during the analysis associated with organic acids which form
over time due to the oxidation of biodiesel over prolonged