02/11/2012
09:35:19 am, by Bill Walsh CIH | 208 views
Side-Wall Deposits Affecting Gravimetric Results
Over the past ten years, the amount of material that may collect on the side walls of a cassette has become more broadly recognized as a significant contributor to the total amount of material collected during sampling. Both NIOSH and OSHA have issued guidelines stating that these deposits should be included with the analysis prep whenever possible. Galson has followed these guidelines, for example we wipe out the inner walls of the cassette and add the wipe to the digestion tube for metals analysis.
However, we cannot do this with filters collected for gravimetric analysis. The filters must be handled delicately and while loose material may be placed on the filter prior to weighing, there is no way to add the wall deposits. Recently the problems this might cause were highlighted when a client collected calcium carbonate samples using a matched weight MCE filter. The calcium carbonate results were up to 60% higher than the gravimetric results due to the high amount of material deposited on the side walls of the cassette. The problem was aggravated by the pure and electrostatic nature of the material sampled, but can be a problem whenever gravimetric analysis is followed by another technique that allows for side-wall material to be included.
We plan on footnoting analyses where this problem is observed and are also investigating alternative solutions. IOM samplers for example are weighed as a unit, which means that deposits on the side wall are included in the gravimetric results. The filter in the IOM head can be varied according to the subsequent analysis desired, which makes this a potential solution, although only the inhalable fraction of the sample will be collected. There is also a product called ACCU-CAP which also is weighed as a unit, but we have to do some studies to see if this type of filters is acceptable for further analyses.
The limitations of NIOSH 0500 and 0600 are becoming more and more in focus. Galson recognizes the problem, is taking action, and wants you also to be aware. Here is a link to some NIOSH guidance on the subject: http://www.cdc.gov/niosh/docs/2003-154/cassetteguidance.html
However, we cannot do this with filters collected for gravimetric analysis. The filters must be handled delicately and while loose material may be placed on the filter prior to weighing, there is no way to add the wall deposits. Recently the problems this might cause were highlighted when a client collected calcium carbonate samples using a matched weight MCE filter. The calcium carbonate results were up to 60% higher than the gravimetric results due to the high amount of material deposited on the side walls of the cassette. The problem was aggravated by the pure and electrostatic nature of the material sampled, but can be a problem whenever gravimetric analysis is followed by another technique that allows for side-wall material to be included.
We plan on footnoting analyses where this problem is observed and are also investigating alternative solutions. IOM samplers for example are weighed as a unit, which means that deposits on the side wall are included in the gravimetric results. The filter in the IOM head can be varied according to the subsequent analysis desired, which makes this a potential solution, although only the inhalable fraction of the sample will be collected. There is also a product called ACCU-CAP which also is weighed as a unit, but we have to do some studies to see if this type of filters is acceptable for further analyses.
The limitations of NIOSH 0500 and 0600 are becoming more and more in focus. Galson recognizes the problem, is taking action, and wants you also to be aware. Here is a link to some NIOSH guidance on the subject: http://www.cdc.gov/niosh/docs/2003-154/cassetteguidance.html
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