Method IO-4.1

Determination of the Strong Acidity of Atmospheric Fine Particulates (<2.5 um)

This method is from EPA's Inorganic Compendium of methods and is for the determination of strong acidity of fine particulates (<2.5um) collected  from ambient air sources. Acidity is determined using pH meter.  Note that this is a draft method.

A 47mm, 2um pore size Teflon┬« filter is needed for sample collection.  The sample is collected by using a Annular Denuder System (ADS) per IO-4.1.  The ADS consists of an inlet with an impactor or cyclone pre-separator to remove all particles with an aerodynamic diameter greater than 2.5um, an annular denuder to remove ammonia and a filter.  Air is drawn through the sampler at 10 L/min. usually for a collection period of 24 hours.  The placement of the ADS varies according to the site location.  Please see Section 12.1.4 of the method for specifics.

After sample collection, the ends of the ADS are capped with a polyethylene cap and sent to the laboratory for extraction and analysis.  The filter must be unloaded in an ammonia-free atmosphere so use of a glove box is required.  The method states that the samples should be analyzed as soon as possible after extraction.  The pH meter is calibrated using sulfuric acid standards which should be prepared on the day of analysis.  The acidity of the sample extract is measured using a pH meter.

(EPA 625/R-96/010A)


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Method Data

Hold Times, Preservatives, Preps, Collection, Analytical & Documentation
Holding Time:   Analyze samples as soon as possible after collection per the method.
Preservatives:   None specified in the method.
Required Preps:   47mm Teflon filter
Collection Method:   Annular Denuder system per Compendium Method IO-4.1 procedures.
Analytical Methodology:   pH meter
Documentation:   IO-4.1

Analyte List*

Analyte Formula CAS Number Detection Limit
 pH unit

* The analytes and detection limits listed for each method represent the typical detection limits and analytes reported for that particular method. Keep in mind that analyte lists may vary from laboratory to laboratory. Detection limits may also vary from lab to lab and are dependent upon the sample size, matrix, and any interferences that may be present in the sample.