FORMALDEHYDE H2 C=O METHOD:
OSHA : NIOSH: ACGIH:
MW:
30.03
2016, Issue 2
CAS: 50-00-0 EVALUATION: FULL
0.75 ppm; 2 ppm STEL 0.016 ppm; C 0.1 ppm; carcinogen C 0.3 ppm; suspected human carcinogen (1 ppm = 1.23 mg/m3 @ NTP)
PROPERTIES:
2016 RTECS: LP8925000 Issue 1: 15 January 1998 Issue 2: 15 March 2003
Gas; BP -19.5 o C; specific gravity 1.067 (air = 1); explosive range 7 to 73% (v/v) in air
NAMES & SYNONYMS: methanal; formalin (aqueous 30 to 60% w/v formaldehyde); methylene oxide
SAMPLING SAMPLER:
CARTRIDGE (Cartridge containing silica gel coated with 2,4-dinitrophenylhydrazine)
MEASUREMENT TECHNIQUE:
HPLC, UV DETECTION
ANALYTE:
2,4-dinitrophenylhydrazone of formaldehyde
EXTRACTION:
Elution with 10 mL of carbonyl-free acetonitrile
FLOW RATE: 0.03 to 1.5 L/min VOL-MIN: -MAX:
1 L @ 0.25 mg/m3 15 L @ 2.5 mg/m3
SHIPMENT:
Place caps onto cartridge. Ship on ice.
SAMPLE STABILITY:
34 days @ 5 °C [1]
BLANKS:
2 to 10 field blanks per set 6 to 10 media blanks per set
ACCURACY RANGE STUDIED:
0.025 to 2.45 mg/m3 (22-L samples) [2]
BIAS:
+4.4%
OVERALL PRECISION ( Ö r T ):
0.057 [1,2]
ACCURACY:
±19.0%
INJECTION VOLUME:
20 µL
MOBILE PHASE:
45% acetonitrile/55% water (v/v), 1.3 mL/min
COLUMN:
3.9 x 150-mm, stainless steel, packed with 5-µm C-18, SymmetryT M or equivalent
DETECTOR:
UV @ 360 nm
CALIBRATION:
Samplers fortified with standard solutions of formaldehyde in water
RANGE:
0.23 to 37 µg per sample [1,2]
ESTIMATED LOD: 0.07 µg/sample [1] PRECISION ( þ r ):
0.032 @ 1.0 to 20.0 µg/sample [1]
APPLICABILITY: The working range is 0.015 to 2.5 mg/m3 (0.012 to 2.0 ppm) for a 15-L sample. This method can be used for the determination of formaldehyde for both STEL and TWA exposures [1,2]. INTERFERENCES: Ozone has been observed to consume the 2,4-dinitrophenylhydrazine (2,4-DNPH) reagent and to degrade the formaldehyde derivative [3]. Ketones and other aldehydes can react with 2,4-DNPH; the derivatives produced, however, are separated chromatographically from the formaldehyde derivative. OTHER METHODS: NIOSH methods 2541 [4] and 3500 [5] and OSHA method 52 [6] are other methods for determination of formaldehyde in air. NIOSH method 5700 employs 2,4-DNPH and HPLC for determination of formaldehyde on textile or wood dust [7]. A journal method employs the same procedure for formaldehyde in automobile exhaust [8].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition FO RM ALD EHY DE: M ETH OD 2016, Issue 2, dated 1 5 Ma rch 2003 - Page 2 of 7 REAGENTS:
EQUIPMENT:
1. Form aldehyde stoc k solution,* aqu eou s, standardized, 1 m g/m L (see AP PEN DIX A ). Alternatively, standardized formaldehyde solution, aqueous, 4 m g/m L, is available commercially from Hach Co., Loveland, CO. 2. Ac eto nitrile,* distilled in glass, low c arbonyl conte nt.** 3. W ater, deionized and distilled. 4. Sulfuric acid, 0.02 N (pH standardization procedu re) or 0.1 N (colorime tric procedure). 5. Sodium hydroxide, 0.01 N. 6. Sodium sulfite (Na2SO 3), 1.13 M (pH proc edu re) or 0.1 M (colorim etric procedu re). Prepare fresh imm ediately before use. 7. Thymophthalein indicator solution, 0.04% (w/v) in 50:50 ethanol:water.
1. Sam pler: Plastic holder containing 0.35 g of 150-250 µm (60-100 mesh) silica gel coated with 1.0 mg of acidified 2,4dinitrophenylhydrazine. Pressure drop across sampler should be less than 28 inches of water (7 kP a) at 1.5 L/min. Sam plers are comm ercially available, [Supelco S10 LpDN PH c artridge, cat. No. 2-101 4; W aters Corp. Sep -Pak X PoSu re Aldehyde Sam pler, part No.W ATO 47205; see APPEND IX B for SKC sam pler]. 2. Pe rsonal sam pling pum p, 0.03 to 1.5 L/m in with flexible connecting tubing. 3. Vials, 4-mL, glass with PTFE-lined rubber septa caps. 4. Vials, 20-mL, glass. NOTE: Do not use vials with “polycone” liners (sources of high formaldehyde blanks)[5,9]. 5. Liquid chrom atograph with UV detector, recorder, integrator, and column (page 2016-1). 6. Syringes, 100-µL, 500-µL and 10-mL. 7. Volumetric flasks, 10-mL, 25-mL, and 1-L. 8. Burets, 50-mL. 9. pH m eter. 10. Mag netic stirrer. 11. Beaker, 50-mL. 12. Flask, Erlenmeyer, 250-mL. 13. Ozone scrubbe r (W aters Corp.)(optional). 14. Aluminum foil or black electrical tape (optional).
See SPECIAL PRECAUTIONS.
Carbonyl content of acetonitrile can be determined by passing 10 mL of the solvent through a cartridge of DNPH-coated silica gel and analyzing by HPLC. Formaldehyde content should be below the LOD.
SPECIAL PRECAUTIONS: Form aldehyde is a suspect ca rcinogen and a proven hum an sensitizer; it sho uld be han dled in a fum e ho od [10-12 ]. Acetonitrile is toxic and is a fire hazard (flash point = 12.8 oC).
SAMPLING: 1. Calibrate each personal sam pling pum p with a rep resenta tive sam pler (and ozo ne scrubber, if used) in line. 2. Open sam pler packet and remove end caps. 3. Attac h sa m pler to the sampling pump with flexible tubing. The W aters sampler is bi-directional and can be connected at either end. NOTE: The sampler does not have a backup section for determination of br ea kt hr ou gh . If h igh concentrations of aldehydes and ketones are a nticipated, conn ect tw o sa m plers in series. The back pressure of the sampling train will be higher and a lower flow rate may be required. 4. Sam ple 1 to 15 L of air at 0.03 to 1.5 L/min. NOTE: To protect from intense light, such as bright sunlight, the sampler can be wrapped with aluminum foil or electrical tape. 5. Plac e en d ca ps o nto the sa m pler and s eal sa m pler in an en velop e. Pro tect sam ples from hea t. 6. Ship sam ples on ice (0 °C ).
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition FO RM ALD EHY DE: M ETH OD 2016, Issue 2, dated 1 5 Ma rch 2003 - Page 3 of 7 SAMPLE PREPARATION: NOTE: Check acetonitrile for form aldehyde content by elution and analysis of a blank cartridge; the formaldehyde level sh ould be below the detec tion lim it. Since background levels of formaldehyde on the samplers may change during storage, compare samples with sampler blanks from the same lot. Samples and blanks should be stored under the same conditions. 7. Elute the formaldehyde derivative from the cartridge samplers with 10-mL quantities of acetonitrile. a. Collect effluent from each sampler in a 10-mL volumetric flask. b. Add ac eton itrile to the m ark for ea ch s am pler. NOTE: The silica gel bed of the sampler will retain approximately 0.5 mL of the original 10 mL.
CALIBRATION AND QUALITY CONTRO L: 8. Ca librate daily with at leas t six m edia working standard s over the rang e of interes t. a. Prepare a series of aqueou s form aldehyde solutions for the fortification of samplers. Suggested concentrations include 1, 4, and 20 µg/mL. See APPEND IX A for standardization of formaldehyde in water. b. Co nne ct the outlet of a ca rtridge sam pler to a personal sam pling pum p with flexible tubing. Turn on the pum p and m ake s ure there is a flow of air through the sa m pler. c. Load a 100-µL syringe with a selected volume of aqueous formaldehyde solution in the range of 30 to 90 µL. Suggested quantities of formaldehyde for spiking include 0.04, 0.10, 0.20, 0.30, 0.40, 0.80, 1.0 and 2.0 µg/sample. d. Place the tip of the syringe needle against the frit in the inlet of the sampler and eject the formaldehyde solution. e. Prepare the m edia working stand ard (steps 7.a and 7.b). f. Prepare a dditional working standards (steps 8.b. through 8.e.). g. Trans fer 3-m L aliquots of working standa rds to 4-m L vials, and analyze (steps 10, 12 an d 13). h. Prepare calibration graph, peak area or height vs. µg formaldehyde per sample. 9. Fortify and analyze three quality control spikes and three analyst spikes to ensure that calibration graph is in control.
MEASUREMENT: 10. Set liquid ch rom atog raph acc ording to manufacturer’s recomm endations and to conditions given on page 2016-1. 11. Transfer a 3 -m L aliquot of the sam ple solution from ste p 7 to a 4-m L vial. C ap the vial. 12. Injec t a 20-µL sam ple aliqu ot. 13. Me asu re pe ak area or pe ak heigh t. NOT E 1: If sample peak is larger than the largest standard peak, dilute an aliquot of the rem ain ing sample solution, reanalyze, and apply appropriate dilution factor in the calculations. NOT E 2: To ensure validity of the samples, identify those samples which contain more than 37 µg of form aldehyde. The ca pacity of the sam plers before breakthroug h m ay have been exceeded for these samples, and collection of smaller samples would be warranted. NOTE 3: The size of the 2,4-DNPH peak should be about 2.7 times the size of the formaldehyde-DNPH peak or larger. Otherwise, breakthrough from the sampler may have occurred.
CALCULATIONS: 14. Determine m ass , µg, of form aldehyde, W , found in the sample and the average media blank, B, from the calibration graph.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition FO RM ALD EHY DE: M ETH OD 2016, Issue 2, dated 1 5 Ma rch 2003 - Page 4 of 7 15. Calculate conce ntration, C, of formaldehyde in the air volume s am pled, V (L).
NOT E: µg/L / m g/m 3
EVALUATION OF METHOD: Issue 1 This m eth od was originally evaluated with W aters Sep-Pak XPoSure Aldehyde samplers using data produced at NIOSH and at W aters Corporation [2]. Test atm osphe res of form aldehyde were gen erated at W aters Corp. [2]. Overall measurem ent precision, Ö rT, was 0.057 based on NIOSH guidelines [13] including a 5% pum p error factor and estimated bias of +4.4%. Sample storage stability was evaluated over the ra nge of 0.5 to 55 µg formaldehyde/sample. Losses for W aters samplers were 4 to 8% when stored up to 14 days at 4 °C. An add itional study with W aters samplers found that losses were 5% or less after 4 days of storage at ambient temperature. All calibration standards used at W aters Corporation were liquid standard solutions of form aldehyde-DN PH deriva tive in ac eton itrile [2,14]. The capacity of DNPH -coated silica gel samplers was found to vary with relative hum idity (RH ) in add ition to concentration of formaldehyde. At a formaldehyde concentration of 1.2 m g/m 3 and at 5% breakthrough, the W aters sampler had a capacity at <10% RH of 55 µg, and at >85% RH a capac ity of 77 µg. At 2.4 m g/m 3 and <10% RH , the 5% breakthrough capacity of the W aters sampler was 59 µg of form aldehyde. At 2.6 m g/m 3 and >85% RH , the 5% brea kthroug h ca pac ity was 106 µ g. Thus, the smallest capacity at 5% breakthrough was 55 µ g of form aldehyde; the upper limit of the range of the method is two thirds of 55 µg, or 37 µg. Ca pac ity information for the W aters sampler is applicable to the Supelco sampler because (a) the W aters and Supelco samplers contain 0.9 and 1 mg of DNPH, respectively, and (b) each sampler contains 350 mg of silica gel. Issue 2 In subsequent work on this method, additional formaldehyde samplers were evaluated, Supelco S10 LpDNPH cartridges and SKC, In c. Aldehyde samplers (DNPH-coated silica gel tubes No.226-119) [1]. The sorbent beds of Supelco and W aters cartridges and front sections of SKC sam plers were treated with acetonitrile. Formaldehyde was not detected on any blank sampler (LOD = 0.01 µg/mL). The SKC sampler for aldehydes may be used for form aldehyde with m odifica tions o f this m etho d (See A PPEN DIX B). However, evaluation of the SKC sam pler at NIOSH has been limited. Supelco samplers were fortified with known quantities of free formaldehyde in water, and ca libration was performed with me dia standards prepared from Supelco samplers fortified with known quantities of free formaldehyde in water; average recoveries ranged from 96.3% to 99.3% for five levels at 1.00 to 20 :g of formaldehyde per sampler (pooled S r = 0.0316; n = 6 at each level). In a storage study, six Supelco samplers were fortified with 4-µg quantities of free formaldehyde in water. Sam plers were stored 34 days at 5 °C in the dark; the average recovery based on media standards was 99% (S r = 0.014). Eight media standards were prepared by fortification of Supelco samplers with solutions of free formaldehyde in water. The solutions were drawn through the DNPH-coated silica gel beds with an air pump. The resulting LOD and LOQ were 0.07 and 0.23 µg/sample, respectively, according to a least squares calibration graph. Standard solutions of formaldehyde-DNPH at 0.10 and 1.0 µg/mL (formaldehyde equivalent concentrations) were stored in airtight vials at 5 °C in the dark and were analyzed periodically. The standard so lutions we re found to be sta ble (with no dete cta ble loss) for at least 10 week s and at least 12 week s, respectively. It is suggested that the reader see the Back up Da ta Report for a com parison of m edia stan dards with liquid standards for calibration [1]. Air sampling for a 24-hour period can be performed with a single Supelco sampler. Thus, background levels at <1 ppb can be determined. NIOSH Manual of Analytical Methods (NMAM), Fourth Edition FO RM ALD EHY DE: M ETH OD 2016, Issue 2, dated 1 5 Ma rch 2003 - Page 5 of 7
REFERENCES: [1]
[2]
[3]
[4]
[5]
[6] [7]
[8] [9] [10] [11]
[12]
[13]
[14] [15]
Tu ck er SP [20 02]. Formaldehyde Backup Data Report for method 2016 Issue 2, National Institute for Occupational Safety and Health, DAR T, C incinn ati, OH . Unpublished report for evaluation of method mainly with Supelco S10 LpDNPH sam plers. Irane ta PC , Collam ati RA ., Costello DN, Crowley RJ, Fernandes RL, Hopkins MR, Knowles CE , Martin DM [1995]. A Validation Study of a Ne w Active Sampler for the Analysis of Formaldehyde in W orkplace and Indoor Air, W aters Corp., Milford, MA. Unpublished report for evaluation of method with W aters Sep-Pak XPoSure Aldehyde samplers. Kleindienst TE, Corse EW , Blanchard FT [1998]. Evaluation of the Performance of DNPH -coated Silica Gel and C 18 Cartridges in the Measurement of Formaldehyde in the Presence and Absence of Ozone. Environmental Science & Technology 32(1):124-130. NIOSH [1994]. Formaldehyde by GC: Method 2541. In: Eller PM, Cassinelli ME, eds. NIOSH M anual of Analytical Me thod s, 4 th ed. Cincinnati, OH: U.S. De partm ent of He alth and H um an Servic es, Pu blic He alth Service, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health. DHHS (NIOSH) Publication No. 94-113. NIOSH [1994]. Formaldehyde by VIS: Method 3500. In: Eller PM, Cassinelli ME, eds. NIOSH M anual of Ana lytical Method s, 4 th ed. Cincinnati, OH: U.S. De partm ent of He alth and H um an Servic es, Pu blic He alth Service, Centers for Disease Control and Prevention, National Institute for O cup ationa l Saerty and Health. DHHS (NIOSH) Publication No. 94-113. OSHA [1985]. Formaldehyde: Method 52. In: OSHA A nalytical Methods Manual, Salt Lake City, UT: U.S. Department of Labor, Occupational Safety and Health Administration, OSHA Analytical Laboratory. NIOSH [1994}. Formaldehyde on Dust (Textile or W ood): Method 5700. In: Eller PM, Cassinelli ME, eds. NIO SH Ma nua l of Analytical Metho ds, 4 th ed. Cincinnati, OH: U.S. Department of Health and Hum an Services, Public Health Service, Centers for Disease Control and Prevention, Nationa l Institute for Occupational Safety and Health. DHHS (NIOSH) Publication No. 94-113. Lipari F, Swarin S [1982]. Determination of Formaldehyde and Other Aldehydes in Automobile Exhaust with an Improved 2,4-Dinitrophenylhydrazine Method. J. Chromatogr. 247: 297-306. Dollberg DD, Smith DL, Tharr DG [1986]. Lab/Field Coordination. Appl. Ind. Hyg. 1:F44-F46. AC GIH [2001]. 2001 Threshold Limit Values® and Biological Exposure Indices. American Conference of Governmental Industrial Hygienists, Inc., Cincinnati, OH. AC GIH [1991]. Docum entation of Threshold Limit Values and Biological Exposure Indices, Sixth ed. Formaldehyde, pp. 664-688. American Conferenc e of G overnm enta l Indus trial Hygien ists, Inc ., Cincinnati, OH. Code of Federal Regulatons [1999]. Title 29, Part 1910.10 48, 29 CFR Chapte r XV II (7-1-99 Edition). Formaldehyde, pp. 354-378. O ccupa tional Safety and He alth Adm inistration, Labor. U.S. Government Printing Office, W ashington, D.C. Kennedy ER, Fischbach TJ, Song R, Eller PE, Shulman SA [1995]. Guidelines for Air Sampling and Analytical Method Development and Evaluation, Cincinnati, OH: National Institute for Occupational Safety and Health. DHHS (NIOSH) Publication No. 95-117. W aters Corp. [1994]. W aters Sep-P ak X PoSu re Aldehyde Sam pler Care and U se M anual, W aters Corp., Milford, MA, p. 31. W alker JF [1964]. Form aldehyde, Third Ed ., Cha pter 1 8, p. 48 6. Am erican Chem ical So ciety Monograph Series, Reinhold Publishing Corporation, New York.
METHOD REVISED BY: Samuel P. Tucker, Ph.D., NIOSH/DART. Method originally written by P Iraneta, W aters Corp., MJ Seymour and ER Kennedy, Ph.D., NIOSH/DART.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition FO RM ALD EHY DE: M ETH OD 2016, Issue 2, dated 1 5 Ma rch 2003 - Page 6 of 7 APPE ND IX A -
PREPA RA TIO N AND STANDARDIZATION OF FORMALDEHYDE STOCK SOLUTION (ca. 1 mg/mL)
Preparation. Dilute 2.7 mL 37% aqueous form alin solution to 1 L with distilled, deionized water. This solution is stab le for at least three m onth s wh en s tored at room tem pera ture. Standardization by pH Titration. Place 5.0 m L of freshly prepared 1.13 M sodium sulfite solution in a 50-mL beake r and stir magn etically. Adjust pH to between 8.5 and 10 with base or acid. Record the pH. Add 3.0 to 1 2.0 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 formaldehyde; about 17 mL acid needed). If the endpoint pH is overrun, bac k-titrate to the e ndp oint with 0.01 N sodium hydroxide. Calculate the co nce ntration , C s (mg/mL), of the form aldehyde stoc k solution:
W here :
30.0 = 30.0 g/equivalent of formaldehyde N a = normality of sulfuric acid (0.02 N) V a = volume of sulfuric acid (mL) used for titration N b = normality of NaOH (0.01 N) V b = volume of NaO H (mL) used for back-titration V s = volume of formaldehyde stock solution (mL)
Standardization by Colorimetric Titration. Place 50 mL of freshly prepared 0.1 M sodium sulfite and 3 drops of 0.04% thymoph thalein indicator (w/v) in 50:50 ethanol:water into a 250-m L Erlenm eyer flas k. Titrate the contents of the flask to a colorless endpoint with 0.1 N sulfuric acid (usually 1 or 2 drops is sufficient). The indicator is blue at pH values above the endpoint and is colorless at pH values below the en dp oin t. Transfer 3.0 to 12.0 mL of the formaldehyde solution to the same flask and titrate the m ixture with 0.1 N sulfuric acid to a colorless end point. Calculate the concentration, C (mg/mL), of formaldehyde in solution.
W here:
30.0 Na Va Vs
= = = =
g/equivalent of formaldehyde normality of sulfuric acid (0.1 N) volume of sulfuric acid used for titration (mL) volume of formaldehyde stock solution (mL)
NOTE: Sulfuric acid (0.1 N) is substituted for 0.1 N hydrochloric acid, which is specified in OSHA Method 52, in order to prevent possible formation of bis(chloromethyl)ether, a potent carcinogen , by reac tion of form aldehyde with hydrochloric a cid [12 ]. This colorimetric titration was adapted from OSHA Method 52 [5], which was based on the procedure of W alke r [15].
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition FO RM ALD EHY DE: M ETH OD 2016, Issue 2, dated 1 5 Ma rch 2003 - Page 7 of 7
APPENDIX B -
USE OF SKC SAMPLER FOR FORMALDEHYDE
The SKC, Inc. sampler for aldehydes (DNPH -coated silica gel tube, catalogue No. 226-119) may be used for sampling formaldehyde with modifications of this method. These modifications include the following: (a) Th e m axim um reco m m end ed a ir volum e sh ould be les s than 15 L at an air conce ntration of 2.5 m g/m 3 (indicated on page 2016-1), because the upper limit of the method for the SKC sam pler is probably less than 37 µg. (b) The procedure for recovery of analyte from the sorbent would be modified, i.e., placement of the sorbent sections in vials, addition of solvent, and possible use of an ultrasonic bath. (c) A volume of solvent much less than 10 mL can be used for recovery. However, the minimum volum e should be tes ted for adequate recovery. (d) Consequences of using a much sm aller volume of solvent for recovery include a lower LOD and LOQ, the need for a different range of calibration standards, and the need for a different range of fortification levels (step 8). (e) The m aximum volume of solution for fortification of the front sorbent bed must be less than 90 µL an d should be d eterm ined (step 8).
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition