ASTM D5837 Standard Test Method for Furanic Compounds in Electrical Insulating Liquids by High-Performance Liquid Chromatography (HPLC)
12. Liquid/Liquid Extraction Procedure - Method A
12.1 Measure 1 to 2 mL ofthe extraction solvent (methanol, acetonitrile, or methanol/acetonitrile) into 10 mL of the test specimen in a test tube and cap securely. Mix using a vortex mixer for 3 min for acetonitrile or acetonitrile/methanol extractions or for 1 to 5 min for methanol extractions. Other ratios of solvent to oil can be used as long as it is verified that the extraction efficiencies are unchanged.
12.2 Allow the two phases to separate. The top phase is the extract, while the bottom phase consists ofthe nonpolar portion of the test specimen. Separation may be enhanced by centrifugation.
12.3 The extract may be run as is or may be diluted with water so that the resulting ratio of solvent to water is the same as that of the mobile phase used at the start of the HPLC run.
NOTE 3 - It has been found that filtering the extract prior to analysis by HPLC prolongs column life. Another effective method of cleanup is to pass the extract through a precolumn. If a precolumn is used, the laboratory needs to verify by experimentation that there is no significant loss of furanic compounds.
13. Solid Phase Extraction (SPE) - Method B
13.1 Insert SPE column(s) into the vacuum manifold and pass 3 to 5 mL of hexane through each SPE column under vacuum. Do not dry the column.
13.2 Mix 10 mL oftest specimen with 10 mL of hexane and pass through SPE column at a rate no faster than 3 mL/min. Other quantities of oil can be used as long as it is verified that the extraction efficiencies are unchanged.
13.3 Pass 10 to 20 mL hexane through the SPE column to rinse out residual oil and dry the column under vacuum for 5 min. Discard all eluates.
13.4 Elute retained compounds from the SPE column using an acetonitrile/water mixture composed of the same proportions as in the HPLC system’s mobile phase. (20 % acetonitrile:80 % water has been found to be satisfactory.) Elute no faster than 3 mL/min.
13.5 Collect the first 2.0 to 2.5 mL of eluate from the SPE column. Record the volume of eluate collected.
13.6 If the eluate is cloudy, filter the eluate with a 0.5-µm or smaller polytetrafluoroethylene or other inert material micro syringe filter or filter vial prior to insertion for analysis in the HPLC system. Whatever material is used, the laboratory needs to verify that no alternation and no significant loss of furanic compounds occur. Discard the spent SPE cartridge.
