Ask the Expert Question:Under the Department of Defense (DOD) Quality Systems Manual 4, the language has changed from Minimum Detection Limit (MDL) to Limit of Detection (LOD) (and Limit of Quantitation (LOQ)). Is the LOD the same thing as MDL? What is TestAmerica's plan on becoming consistent with this new language?
Expert Response:The DOD is using all of these designations at this time.
The MDL definition has not changed and is essentially the lowest level at which a result can be reliably distinguished from a blank.
The LOD is higher than the MDL, and is supposed to be the level at which a true concentration in the sample will reliably give a result that is greater than the MDL.
LOQ definition has not changed and is the lowest quantitative level for the sample.
When reporting data, the LOD is used as the Non-Detect (ND) value, for example, NDs will be reported as < LOD.
Detects, however, are reported down to the MDL, with J flags if below the LOQ.
TestAmerica is reporting data for DOD projects using these conventions. We are not reporting this way to non DOD projects to be consistent with non DOD quality programs.
View Dr. Richard Burrows expert profile
Monday, March 28, 2011
Monday, March 21, 2011
Follow up to Benefits and Alternatives of the Various Methods for Metals Speciation for Chromium in Soils
Ask the Expert Question:
How do you overcome the redox interferences of 7196A/3060A?
Expert Response:
When using Methods 3060A/7196A it is common to also test for several other general chemistry parameters that relate to the reduction / oxidation conditions present in site soil samples. These auxiliary results are then used to help interpret the Cr(VI) results. Including client specified matrix spike samples is also an excellent way to assess matrix interferences.
In reducing soil conditions Cr(VI) is converted to Cr(III). This is a common remediation process. However, in some instances the reducing agent is not evenly distributed and unreacted pockets of Cr(VI) remain. When the sample is brought to the lab and run through the 3060A alkaline leaching process, both the reducing agent and the Cr(VI) are solubilized and complete the reaction. It makes it look as if there was no Cr(VI) in the sample, even though there really was. Matrix spike recoveries usually alert the data user when this situation has occurred. Using the method of standard additions (MSA) with Methods 3060A/7196A to calculate the Cr(VI) concentration can compensate for moderate reduction/oxidation interferences. Both the auxiliary general chemistry tests and MSA options are available at TestAmerica.
Colorimetric interferences are also possible in 7196A. When these occur, the ion chromatographic Method 7199 is the best and most cost effective way to minimize these interferences. This is about 2-4X more expensive than method 7196A. Method 7199 doesn’t resolve the reduction / oxidation interferences described above.
Method 6800 is capable of resolving most reduction / oxidation interferences as well as the colorimetric interferences that Method 7196A experiences. Method 6800 testing is about 10X more expensive than Method 7199. It is usually quoted by project.
View Dr. Mark Bruce's expert profile
How do you overcome the redox interferences of 7196A/3060A?
Expert Response:
When using Methods 3060A/7196A it is common to also test for several other general chemistry parameters that relate to the reduction / oxidation conditions present in site soil samples. These auxiliary results are then used to help interpret the Cr(VI) results. Including client specified matrix spike samples is also an excellent way to assess matrix interferences.
In reducing soil conditions Cr(VI) is converted to Cr(III). This is a common remediation process. However, in some instances the reducing agent is not evenly distributed and unreacted pockets of Cr(VI) remain. When the sample is brought to the lab and run through the 3060A alkaline leaching process, both the reducing agent and the Cr(VI) are solubilized and complete the reaction. It makes it look as if there was no Cr(VI) in the sample, even though there really was. Matrix spike recoveries usually alert the data user when this situation has occurred. Using the method of standard additions (MSA) with Methods 3060A/7196A to calculate the Cr(VI) concentration can compensate for moderate reduction/oxidation interferences. Both the auxiliary general chemistry tests and MSA options are available at TestAmerica.
Colorimetric interferences are also possible in 7196A. When these occur, the ion chromatographic Method 7199 is the best and most cost effective way to minimize these interferences. This is about 2-4X more expensive than method 7196A. Method 7199 doesn’t resolve the reduction / oxidation interferences described above.
Method 6800 is capable of resolving most reduction / oxidation interferences as well as the colorimetric interferences that Method 7196A experiences. Method 6800 testing is about 10X more expensive than Method 7199. It is usually quoted by project.
View Dr. Mark Bruce's expert profile
Tuesday, March 15, 2011
Benefits and Alternatives of the Various Methods for Metals Speciation for Chromium in Soils
Ask the Expert Question:Can you summarize the benefits and alternatives of the various methods for metals speciation for chromium in soils?
Expert Repsonse:
Method 3060A is the primary sample preparation method used to extract the hexavalent chromium (Cr(VI)) from a soil matrix. This sample preparation method must then be followed with an analysis method to determine the Cr(VI) concentration. There are three analytical technique options.
The most common is colorimetry as described in Method 7196A. This test is widely available and low cost. It can suffer from color based and reduction / oxidation chemistry (redox) matrix interferences.
Ion chromatography with colorimetric detection is used in Method 7199. Method 7199 is available from many labs, though it is less common than 7196A and is a bit more expensive. This method resists the color based interferences, but is still affected by the redox chemistry of the soil matrix.
The most sophisticated technique uses ion chromatography coupled with ICP/MS detection and uses isotopically labeled chromium species. This is described in Method 6800. There are only a few labs in the United States with this capability, TestAmerica being one of them. It is much more expensive than either 7196A or 7199. This method compensates for both color based and redox interferences in most samples.
All of the Cr(VI) analysis options are available from TestAmerica. For additional information on these methods, please submit at question at this link: http://www.testamericainc.com/contactus/contactform.aspx.
View Dr. Mark Bruce's expert profile
Expert Repsonse:
Method 3060A is the primary sample preparation method used to extract the hexavalent chromium (Cr(VI)) from a soil matrix. This sample preparation method must then be followed with an analysis method to determine the Cr(VI) concentration. There are three analytical technique options.
The most common is colorimetry as described in Method 7196A. This test is widely available and low cost. It can suffer from color based and reduction / oxidation chemistry (redox) matrix interferences.
Ion chromatography with colorimetric detection is used in Method 7199. Method 7199 is available from many labs, though it is less common than 7196A and is a bit more expensive. This method resists the color based interferences, but is still affected by the redox chemistry of the soil matrix.
The most sophisticated technique uses ion chromatography coupled with ICP/MS detection and uses isotopically labeled chromium species. This is described in Method 6800. There are only a few labs in the United States with this capability, TestAmerica being one of them. It is much more expensive than either 7196A or 7199. This method compensates for both color based and redox interferences in most samples.
All of the Cr(VI) analysis options are available from TestAmerica. For additional information on these methods, please submit at question at this link: http://www.testamericainc.com/contactus/contactform.aspx.
View Dr. Mark Bruce's expert profile
Monday, March 7, 2011
Ask the Expert Webinar Series launched!
The first webinar is March 24th and will feature Dr. Mark Bruce, Technical Director at the TestAmerica North Canton Laboratory, presenting on Incremental Sampling Methodologies (ISM). Future webinar topics will include endocrine disruptors, chemical issues related to natural gas fracking, and speciated metals, among others.
“TestAmerica has a long tradition of being the technical leaders within the environmental laboratory industry. We are very excited to expand our Ask the Experts program by sharing their expertise with the environmental community. The webinar series will mark a new chapter for TestAmerica as the LEADER in Environmental Testing,” added Rachel Brydon Jannetta, President and CEO.
Go to TestAmerica’s website to learn more about the upcoming webinars and register.
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