FORMALDEHYDE: METHOD 2541, Issue 2, dated 15 August 1994 - Page 4 of 5 humidity in the study was 49% at 24 °C. A storage study was done by NIOSH/MRSB [1] by spiking samplers at two concentrations, 10.0 and 61.0 µg/sample [1]. Three spikes at each concentration were stored at different temperatures for seven days. The storage conditions were as follows: Sample set no.
Storage temp.
1 2 (a) (b) 3
20 °C 20 ° and 40 ° C 20 ° C 4 ° C (refrigeration)
Storage time 7 days 1 day 6 days 7 days
The recovery of formaldehyde was essentially 100% for all of the storage temperatures. REFERENCES: [1] [2]
[3] [4] [5]
[6]
Williams, K. J. Methods Development Efforts, NIOSH/MRSB, (NIOSH, Unpublished, 1989). "OSHA Analytical Methods Manual, method #52", U. S. Department of Labor, Occupational Safety and Health Administration, OSHA Analytical Laboratory, Salt Lake City, UT, March, 1985. User Check, DataChem Inc., NIOSH Seq. #6701-J (unpublished, June 1, 1989). NIOSH testimony on the OSHA Proposed Rules on Air Contaminants, Docket #H-020, August 1, 1988. NIOSH/OSHA Occupational Health Guidelines for Occupational Hazards, U. S. Department of Health and Human Services, Publ. (NIOSH) 81-123 (1981), available as GPO Stock #017-033-00337-8 from Superintendent of Documents, Washington, DC 20402. Kennedy, E.R., Ashley, K. Appl. Spectrosc ., 46, 266-272 (1992).
METHOD WRITTEN BY: Eugene R. Kennedy, Ph.D., and Karen J. Williams, NIOSH/DPSE. APPENDIX A: PREPARATION AND STANDARDIZATION OF FORMALDEHYDE STOCK SOLUTION (ca. 1 mg/mL) Dilute 2.7 mL 37% aqueous formalin solution to 1 L with distilled, deionized water. This solution is stable for at least three months. Standardize by placing 5.0 mL of freshly prepared 1.13 M sodium sulfite solution in a 50-mL beaker and stir magnetically. Adjust pH to between 8.5 and 10 with base or acid. Record the pH. Add 10.0 mL formaldehyde stock solution. The pH should now be greater than 11. Titrate the solution back to its original pH with 0.02 N sulfuric acid (1 mL acid = 0.600 mg HCHO; about 17 mL acid needed). If the endpoint pH is overrun, back-titrate to the endpoint with 0.01 N sodium hydroxide. Calculate the concentration, C s (mg/mL), of the formaldehyde stock solution:
where 30.0 = 30.0 g/equivalent of formaldehyde Na = normality of sulfuric acid (0.02 N) Va = volume of sulfuric acid (mL) used for titration Nb = normality of NaOH (0.01 N) Vb = volume of NaOH (mL) used for back-titration Vs = volume of formaldehyde stock solution (10.0 mL)
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
