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
