Method IO-3.4

Determination of Metals in Ambient Particulate Matter Using Inductively Coupled Plasma (ICP) Spectroscopy

This method is from EPA's Inorganic Compendium of methods and is for the determination of metals (and particulate matter (PM) if needed) from ambient air sources using inductively coupled plasma spectroscopy (ICP).

A pre-weighed, tared filter is needed for sample collection.  Method IO-3.1 outlines some of the various filters that may be used for this method, however, the most commonly used filter is a quartz filter.  The filter size for use in the ambient air methods is 8"x10".

The sample is collected by using a TSP (total suspended particulate matter) sampler per IO-2.1.  Air is drawn through the sampler and the filter that allows through suspended particles that are less than 100um.  An average flow rate of 1.70 m³/min. (60ft³/min.) over a period of 24 hours is typical. Typical collection volumes are 1600-2400m³.  Shorter sampling times may be needed if the filter clogs due particulate matter.  A general guideline is the sample is suspect if the final flow rate is less than 1/2 of the intial flow rate.  This would indicate that air did not pass through the filter constantly during sampling and the calculation of the sampled air volume would be inaccurate.

Note that the TSP sampler can be configured as per normal or fitted with a size-selective inlet impactor or cyclone to sample PM₁₀ (particles less than 10um).

After sample collection, the filter is removed, folded in half with the particulate catch on the inside of the fold and placed in an envelope for shipment to the laboratory.  Filters should be stored at 15-30 degrees C until analysis.  The labortory determines the amount of PM by weighing the filter to a constant weight (to the nearest 0.05mg).  The filter is then cut into 9 equivalent strips.  A representative sample is taken and used for digestion.  The method cites that nitric acid digestion or microwave digestion using hydrochloric acid/nitric acid are acceptable but that microwave digestion is preferred.  Once digested, the sample is analyzed for metals using ICP.  A variety of metals can be analyzed using ICP including others that are not shown below.