Page:NIOSH Manual of Analytical Methods - 5524.pdf/8
METALWORKING FLUIDS (MWF) ALL CATEGORIES: METHOD 5524, Issue 2, dated 29 December 2014 - Page 8 of 10
Appendix 1. Procedure to remove PTFE filter contaminants that are soluble in and extracted with the ternary blend. Use this procedure to prevent high blanks from being obtained following extraction of PTFE filters. The filters are rinsed with ternary solvent (1:1:1 dichloromethane:methanol:toluene) described in NMAM Method 5524. The filters are air-dried and protected from airborne contamination prior to weighing and assembly into cassettes for field sampling. See evaluation of procedure which follows these instructions. EQUIPMENT, SUPPLIES, REAGENTS AND STANDARDS 1. 250 mL glass beaker(s) 2. 500 mL of ternary solvent 1:1:1 ratio of dichloromethane:methanol:toluene in a stoppered container 3. A fume hood 4. Watch glasses to fit the beakers 5. Glass stir rod 6. One box (or as many as required) of 2 micron PTFE filters to be cleaned; recommend cleaning no more than 1 package of 50 filters per 100 mL of solvent 7. Stainless steel forceps to manipulate filters 8. Large, lint-free paper towels 9. Clean, stainless steel metal trays or screen approximately 45 cm x 60 cm (18 inch x 24 inch) 10. Nitrile gloves 11. Clean, wide mouth glass container e.g., ointment jar with Teflon cap or French square bottle PROCEDURE Perform all of the following tasks inside a fume hood! 1. Wear nitrile gloves throughout this procedure to protect yourself from the solvent and to protect the filters from skin oil during handling. 2. Pour approximately 100 mL of ternary solvent into a 250 mL glass beaker. 3. Remove the PTFE filters from the package and remove the plastic spacers from between the filters. Place the filters individually (sample side up) into the beaker filled with ternary solvent. Be careful that the filters stay separated from each other and do not clump together. 4. Carefully stir the filters with the glass stir rod; do not allow the filters to turn over. Cover the beaker with the watchglass. Allow the filters to extract in the solvent in the beaker for 10 minutes. 5. Decant the ternary solvent out of the beaker and into a waste bottle. Use the stirring rod to compress and retain the filters in the beaker as the solvent is slowly decanted off. 6. Refill the beaker with 100 mL of fresh ternary solvent after decanting following step 5. Repeat steps 4 and 5, two times for a total of three solvent washes. 7. After the three rinses are complete, drain off as much solvent as possible. Remove the filters from the beaker using forceps and place them onto a clean stainless steel metal tray that has been covered with a large, lint-free paper towel. Alternatively, place them on a clean stainless steel screen. Place them onto the tray or screen, sampling side up. Allow the filters to dry overnight. Warning: Keep the hood sash approximately at or below the sash height level as marked on the
hood. If the sash is pushed lower, the higher air flow may blow the filters off the drying
tray or screen. Place a sign on the sash indicating that it is to be left at this height
overnight and not to be moved. 8. Place the dried filters in a clean French square glass bottle or a wide-mouthed Teflon™ capped ointment jar. Label the container “PTFE 2-µm filters rinsed with MWF solution,” giving the date, initials, and number of filters. Do not store filters in plastic containers. Filters are now ready to be used for sampling. Since the filters are not separated by spacers, use care to remove them from the storage container for use. NIOSH Manual of Analytical Methods (NMAM), Fifth Edition