ASTM_D_5221_-_92_scan.pdf

ASTM D5223 92 O759530 0508274 237 m(#Designation:D 5221-92 AMERICAN SOCIETY FOR TESTING AND MATERIALS 191 6 Race St Philadelphia,Pa 191 03 Reprinted from the Annual Book of ASTM Standards.Copyright ASTM If not listed in the current combinad index,will appear in the nexi edition.Standard Test Method for Continuous Measurement of Formaldehyde in Air This standard i s issued under the fixed designation D 5221;the number immediately following the designation indicates the year of original adoption or,in the case of revision.the year of last revision.A number in parentheses indicates the year of last reapproval.A suprscript epsilon(t)indicaies an editorial change since the last revision or reapproval.1.Scope 1.I This test method covers the continuous measurement of formaldehyde vapor in indoor or outdoor atmospheres.I.2 This test method employs an automated wet-chemical colorimetric analyzer with a continuous signal output.I.3 The commercial analyzer has been modified such that formaldehyde vapor is absorbed in acidified(HCl)pararosaniline with subsequent addition of dilute sodium sulfite.,The resulting colored product has a strong absorption band in the visible region(530 to 600 nm).1.4 This test method is applicable to concentrations of formaldehyde from 10 to 500 pg/m3.Detection limits are dependent on sample airflow rate(maximum 1.0 L/min).1.5 The values stated in S I units are to be regarded as the standard.The inch-pound units given in parentheses are for information only.1.6 This standard does not purport to address all o f the safety problems,if any,associated with its use.It is the responsibility o f the user o f this standard to establish appro-priate safety and health practices and determine the applica-bility o f regulatory limitations prior to use.Specific precau-tionary statements are given in Note 1.2.Referenced Documents 2.1 ASTM Standards:D I193 Specification for Reagent Wate9 D I356 Terminology Relating to Atmospheric Sampling D 1605 Practices for Sampling Atmospheres for Analysis D3249 Practice for General Ambient Air Analyzer D 3609 Practice for Calibration Techniques Using Perme-and Analysis2 of Gases and Vapors2 Procedures2 ation Tubesz 3.Terminology 3.1 DeJinilions:3.1.1 For definitions of terms used in this test method,3.2 Descriptions o f Terms Specific to This Standard:3.2.I analyzer signal response-the magnitude of the sample response recorded by the analyzer,minus the re-sponse recorded in the absence of the analyte(that is,baseline condition).3.2.2 liquid equivalent standard-the concentration of a refer to Terminology D 1356.This test method is under jurisdiction of ASTM Committee P 2 2 on Sampling and Analysis of Atmospheres and is the direct responsibility of Subcommiitee D22.05 on Indoor Air.Current edition approved Jan.15.1992.Published March 1992.Aiiitrd UJJ ofASTM Siundurds,Vol 1 1.0 3.dilute formaldehyde solution expressed in terms of its equivalent vapor concentration(in air,by volume)that would produce an identical signal response if measured by the analyzer.4.Summary of Test Method 4.1 A modified commercial analyzer is used to continu-ously monitor concentrations of formaldehyde vapor in air.The analyzer incorporates the modified pararosaniline colonmetric procedure that is described in Ref 4.2 The complex chemistry of reactions involving pararosaniline and formaldehyde have been studied exten-sively during the 35 years since West and Gaeke published their procedure for the colorimetric determination of sulfur dioxide(2).Although there remains some disagreement concerning the mechanism involving the formation of the final product,it is generally agreed that the chromophore is an aikylsulfonic acid(1).4.3 The analyzer consists of a portable unit that contains a small diaphragm pump,an analytical module,a colonmeter w i t h glass flow cells,a peristaltic pump and tubing,and a 1 2-V rechargeable battery for optional DC power operation.4.4 An acidified pararosaniline scrubber solution is pumped through the reference cell in the colorimeter and is then diluted 1+1 with a liquid flow stream containing water.The diluted solution then passes into an air scrubber coil,where formaldehyde is quantitatively absorbed from the air sample stream.After the liquid and air are separated,the sample solution is mixed 1+1 with a dilute aqueous Na2S03 reagent.A series of time delay coils allow 16 min for color development of the chromophore.The absorbance of the sample solution is continuously measured as it passes through the sample cell,resulting in a O-to 4.0-V output signal generated by the microprocessor.A schematic repre-sentation of the major components and the liquid flow scheme of the instrument is shown in Fig.1.4.5 The analyzer baseline is established by introducing a source of zero air at the sample inlet.The monitor is calibrated by introducing one or more liquid equivalent formaldehyde standard solutions into the reagent flow se-quence while zero air is sampled.The baseline is then