ASTM D5837 Standard Test Method for Furanic Compounds in Electrical Insulating Liquids by High-Performance Liquid Chromatography (HPLC)
10. Preparation of Extraction Standards in Solvent
10.1 Prepare the extraction standards by dilution of a weighed standard compound to a standard volume or by volumetric addition of a standard compound to a standard volume in accordance with either of the procedures described in 10.1.1 or 10.1.2.
10.1.1 Weight Procedure - Weigh out 0.100 g +/- 5 % ofeach of the five furanic compounds listed in this test method and record the weight to the nearest 0.1 mg. Dissolve weighed portions into 100 mL of acetonitrile or methanol. Take 1 mL of this solution and add to a clean 1-L volumetric flask. Add 199 mLofeither acetonitrile or methanol, using the same solvent as was used earlier to dissolve the weighed portions ofthe furanic compounds. Bring the solution in the volumetric flask to 1 L with water. Other ratios of solvent to water may be used such as to match that ofthe initial mobile phase. This solution yields a concentration of about 1 mg/L (1000 µg/L) of each of the furanic compounds. Use the actual mass of each compound to calculate the concentration. Store in a clean, dark plastic container. Do not store in glass.
10.1.2 Volumetric Addition - Furanic compounds that are not liquid at ambient temperature should be heated to 35°C where all of the compounds are in a liquid state. Use a 1-µL syringe to add the indicated volumes of furanic compounds to 10 mL ofacetonitrile or methanol. The volumes to be added are as follows:
0.83 µL +/- 1 % of 5-hydroxymethyl-2-furaldehyde
0.88 µL +/- 1 % of furfuryl alcohol
0.86 µL +/- 1 % of 2-furaldehyde
0.91 µL +/- 1 % of 2-acetylfuran
0.90 µL +/- 1 % of 5-methyl-2-furaldehyde
10.1.2.1 These volumes represent a mass of1000 µg ofeach of the five furanic compounds. Add 10 mL of acetonitrile or methanol containing the dissolved volumes of furanic compounds to 190 mL of the same solvent in a 1-L volumetric flask. Bring this solution to 1 L with water. Other ratios of solvent to water can be used such as to match that of the initial mobile phase. The resulting concentration is 1 mg/L (1000 µg/L) for each of the five furanic compounds. Store as indicated in 10.1.1.
11. Preparation of Calibration Standards in Oil
11.1 Prepare standards of furanic compounds in new dielectric liquid which has been tested and shown to have a flat baseline for the range of retention times for the compounds of interest. Mineral oil shall otherwise conform to Specification D3487. Other dielectric liquids should conform with applicable ASTM specifications.
NOTE 2 - The same type ofdielectric liquid should be used for standard preparation as the dielectric liquid found in the test specimen(s). This test method has been developed for mineral oil, but has been found to be applicable to other dielectric fluids.
11.2 Volumetric Preparation:
11.2.1 Use a graduated 1-µL syringe to inject volumes ofthe five furanic compounds as listed in 10.1.2 into 8 mL oftoluene. Dissolve the compounds and add quantitatively to a 1-L volumetric flask. Make sure all compounds are thoroughly mixed.
11.2.2 Dilute the 8 mL of toluene containing furanic compounds to a total volume of 1 L with electrical insulating oil of mineral origin. The solution yields a concentration of 1 mg/L (1000 µg/L) of each of the five furanic compounds. Store as described in 10.1.1.
11.3 Gravimetric Preparation:
11.3.1 Weigh out 0.100 g +/- 5 % of each of the five furanic compounds and record the weight to the nearest 0.1 mg. Dissolve the weighed portion in toluene and dilute volumetrically to 100 mL in toluene. Mix thoroughly so that all five furanic compounds are dissolved completely.
11.3.2 Volumetrically dilute 1 mL of the toluene solution from 11.3.1 to 1 L using electrical insulating oil of mineral origin. This solution of furanic compounds in oil yields a concentration of about 1 mg/L (1000 µg/L) for each of the furanic compounds. Use the actual mass of each compound recorded in 11.3.1 to calculate the exact concentration in the resulting solution. Store as described in 10.1.1.
