Page:NIOSH Manual of Analytical Methods - 3500.pdf/1

 FORMALDEHYDE by VIS H2C=O

MW: 30.03

METHOD: 3500, Issue 2

CAS: 50-00-0

3500 RTECS: LP8925000

EVALUATION: FULL

OSHA : 0.75 ppm; 2ppm STEL NIOSH: 0.016 ppm; C 0.1 ppm; carcinogen; ACGIH: C 0.3 ppm; suspected human carcinogen (1 ppm = 1.23 mg/m 3 @ NTP)

Issue 1: 15 May 1989 Issue 2: 15 August 1994

PROPERTIES: gas; BP -19.5 °C; vapor density 1.067 (air = 1.00); explosive range 7 to 73 % v/v in air

SYNONYMS: methanal; formalin (aqueous 30 to 60 % w/v HCHO); methylene oxide

SAMPLING SAMPLER:

MEASUREMENT

FILTER + IMPINGERS (1-µm PTFE membrane and 2 impingers, each with 20 mL 1% sodium bisulfite solution)

TECHNIQUE:

V I S I B L E A B S O R P T I O N SPECTROMETRY

ANALYTE:

formaldehyde

FLOW RATE:

0.2 to 1 L/min

SAMPLE WORKUP:

note liquid volume; remove 4-mL aliquot

VOL-MIN: -MAX:

1 L @ 3 ppm 100 L

SHIPMENT:

transfer samples to low-density polyethylene bottles before shipping

COLOR DEVELOPMENT:

SAMPLE STABILITY:

30 day @ 25 °C [1]

BLANKS:

2 to 10 field blanks per set

chromotropic acid + absorbance @ 580 nm

sulfuric

acid;

CALIBRATION:

standard solutions of formaldehyde in distilled water

RANGE:

2 to 40 µg per sample [1,2]

ESTIMATED LOD: 0.5 µg per sample [2,3] PRECISION (Sr):

0.03 @ 1 to 20 µg per sample [3]

ACCURACY RANGE STUDIED:

1.25 to 7.5 mg/m 3 [2] (80-L samples)

BIAS:

none identified

ˆ ): 0.09 [2] OVERALL PRECISION (S rT ACCURACY:

± 18%

APPLICABILITY: The working range is 0.02 to 4 ppm (0.025 to 4.6 mg/m 3) for an 80-L air sample. This is the most sensitive formaldehyde method in the NIOSH Manual of Analytical Methods and is able to measure ceiling levels as low as 0.1 ppm (1 5-L sample). It is best suited for the determination of formaldehyde in area samples.

INTERFERENCES: Oxidizable organic materials may give a positive interference [2]. Phenol to formaldehyde ratios as low as 0.3 produce a - 15% bias [4]. A method for the removal of the phenol interference has been reported by Hakes et. al. [5]. Ethanol and higher M.W. alcohols, olefins, aromatic hydrocarbons [6] and cyclohexanone also produce small negative interferences [7]. Little interference is seen from other aldehydes [7].

OTHER METHODS: This method was originally adapted from the Intersociety Committee [8] and designated P&CAM 125 [4]. For personal samples or where interferences to this method are present, use Method 2541. Ref [9] is a recent review of formaldehyde methods.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94