Apparatus:
Use a suitable double-beam infrared spectrophotometer and matched 0.4
mm liquid sample cells with calcium fluoride windows.
Reagents and Solutions:Standard preparation:
Transfer about 10 mg of mono-tertiary-butyl-p-benzoquinone Reference Standard
(available from US Pharmacopeial Convention, Inc., 12601 Twinbrook Parkway,
Rockville, MD 20852, USA), accurately weighed, into a 10-ml volumetric
flask, dissolve in chloroform, dilute to volume with the same solvent
and mix.Sample preparation: Transfer about 1 g of the sample, previously
ground to a fine powder in a high-speed blender and accurately weighed,
into a 10-ml volumetric flask, dissolve in chloroform, dilute to volume
with the same solvent, and mix. Filter through a Millipore filter (UHWPO1300),
or equivalent, before use in the Procedure below.
Procedure:
Fill the reference cell with chloroform and the sample cell with the Standard
preparation. Place the cells in the respective reference and sample beam
of the spectrophotometer, and record the infrared spectrum from 1600 to
1775 cm-1. On the spectrum draw a background line from 1612
to 1750 cm-1, and determine the net absorbence (AS)
of the Standard preparation at 1659 cm-1.Similarly, obtain
the spectrum of the sample preparation, and determine its net absorbence
(AU) at 1659 cm-1.
Calculation:
Calculate the percent of t-butyl-p-benzoquinone in the sample by the formula:100
¡Á AU/AS ¡Á WS/WU whereWS
= the exact weight, in mg, of the mono-tertiary-butyl-p-benzoquinone Reference
Standard takenWU = the exact weight, in mg, of the sample taken.
Apparatus:
Use a suitable gas chromatograph equipped with a thermal conductivity
detector (F and M Model 810 or equivalent), containing a 0.61-m (2 ft)
¡Á 6.35-mm (outside diameter) stainless steel column packed with 20% Silicone
SE-30, by weight and 80% Diatoport S (60/80-mesh), or equivalent materials.
Operating conditions:
The operating parameters may vary, depending upon the particular instrument
used, but a suitable chromatogram may be obtained using the following
conditions:- Column temperature: programmed from 100 to 270¡ã, at 15¡ã per
min- Injection port temperature: 300¡ã- Carrier gas: helium, flowing at
a rate of 100 ml per min- Bridge current: 140 mA- Sensitivity: 1 ¡Á for
integrator (InfotronicsCRS 100), 2 ¡Á for recorder
Reagents and Solutions:
Stock solution: Weigh accurately about 50 mg each of hydroquinone (HQ),
2,5-di-t-butylhydroquinone (DTBHQ), and methyl benzoate (internal standard),
transfer into separate 50-ml volumetric flasks, dilute to volume with
pyridine, and mix.Calibration standards: Into separate 10-ml volumetric
flasks add 0.50, 1.0, 2.0 and 3.0 ml of the HQ stock solution, then to
each flask add 2 ml of the methyl benzoate (internal standard) stock solution,
dilute each to volume with pyridine, and mix. In the same manner prepare
four DTBHQ calibrating solutions. Prepare the trimethylsilyl derivative
of each solution as follows. Add 9 drops of calibration solution to a
2-ml gas syringe, add 250 ¦Ìl of N,O-bistrimethylsilylacetamide, and heat
at about 80¡ã for 10 min Chromato- graph 10-¦Ìl portions of each standard
in duplicate, and plot the concentration ratio of HQ to internal standard
(X-axis) against the response ratio of HQ to internal standard (Y-axis).
Plot the same relationships between DTBHQ and the internal standard.
Procedure:
Transfer about 1 g of the sample, accurately weighed, into a 10-ml volumetric
flask, add 2 ml of the methyl benzoate internal standard stock solution,
dilute to volume with pyridine, and mix. Prepare the trimethylsilyl derivative
as described above under Calibration standards, and then chromatograph
duplicate 10-¦Ìl portions to obtain the chromatogram. The approximate peak
times, in minutes, are: methyl benzoate, 2.5; TMS derivative of HQ, 5.5;
TMS derivative of tert-butylhydroquinone, 7.3; TMS derivative of DTBHQ,
8.4.
Calculation:
Determine the peak areas (response) of interest by automatic integration
or manual triangulation. Calculate the response ratio of HQ and DTBHQ
to internal standard. From the calibration curves determine the concentration
ratio of HQ and DTBHQ to internal standard, and calculate the % HQ and
% DTBHQ in the sample by the formula:A = Y ¡Á I ¡Á 10/SwhereA = the % HQ
or % DTBHQ in the sampleY = the concentration ratio (X-axis on calibration
curve)I = the percentage (w/v) of internal standard in the Sample preparationS
= the weight of sample taken, in g.
Apparatus:
Use a suitable gas chromatograph equipped with a flame ionization detector
(F and M Model 810 or equivalent), containing a 3.66-m (12-ft) ¡Á 3.18-mm
(outside diameter) stainless steel column packed with 10% Silicone SE-30,
by weight, and 90% Diatoport S (60/80 mesh), or equivalent materials.
Operating conditions:
The operating parameters may vary, depending upon the particular instrument
used, but a suitable chromatogram may be obtained using the following
conditions:- Column temperature: programmed from 70 to 280¡ã at 15¡ã per
minute and held- Injection port temperature: 275¡ã- Cell temperature: 300¡ã-
H2 and O2 (or air) settings: 1.4 atm (20 psi) each
Reagents and solutions:
Standard solution: Prepare a solution of toluene in octanol containing
approximately 50 ¦Ìg per ml, and calculate the exact concentration (CR)
in percent (w/v).Sample solution: Transfer about 2 g of the sample, accurately
weighed, into a 10-ml volumetric flask, dissolve in octanol, dilute to
volume with the same solvent, and mix. Calculate the exact concentration
of the solution (CS) in percent (w/v).
Procedure:
Inject a 5-¦Ìl portion of the Standard solution into the chromatograph,
and measure the height of the toluene peak (HR) on the chromatogram.
The toluene retention time is 3.3 min; other peaks are of no interest
in this analysis. Similarly, obtain the chromatogram on a 5-¦Ìl portion
of the Sample solution and of a blank consisting of octanol, and measure
the height of the toluene peak (HS).
Calculation
:Calculate the mg/kg of toluene in the sample by the formula:HS
/CR ¡Á CR/CS ¡Á 106