Ask the Expert Question:
We have had a need to analyze diesel fuel samples for sulfur and heat content analysis utilizing SW-846 Method 5050 and 9056 as the analytical procedure used to determine sulfate percent. Some of the samples may be analyzed for air permit compliance. The permits require us to have the sulfur content analyzed by ASTM D4294 or equivalent method.
I have read through the documentation on ASTM D4294, SW-846 Method 5050, and SW-846 Method 9056. It appears to me that the methods get to the same end point - sulfur content. However, I would like a second opinion from one of your content experts that confirms what I have concluded.
Experts Response:
The ASTM D4294 (energy dispersive X ray fluorescence technique) is widely used for measurement of sulfur in oils.
The EPA Methods 5050 and 9056 (determination of sulfate ion concentration) is a complete oxidation using a bomb calorimeter followed by analysis of the resulting sulfate. This technique is used for sulfur in oil and waste products and has been used for decades. This is a highly reliable method for determination of sulfur in oils.
Both techniques should give similar results.
View Dr. Charlie Carter's Experts profile
Monday, February 28, 2011
Monday, February 21, 2011
Source Types for Benzene Concentration Without Similar Elevated TEX Concentrations
Ask the Expert Question:
At a remediation site we are working on, there is a monitoring well that had soil samples taken during the drilling process and analyzed for BTEX. All concentrations were below 1 part per million. However, the groundwater analysis is presenting an extremely elevated level of benzene with comparable levels of the TEX components. Other wells in the area are either non-detect or have low concentrations for benzene. The data has been verified and is accurate.
We do not understand the elevated Benzene constituent. What type of source would yield such a high Benzene concentration without similar elevated TEX concentrations?
Experts Response:
When benzene is present in environmental samples it is typically an indication of contamination by gasoline or some type of hydrocarbon based fuel. In those cases, however, other aromatics such as toluene, ethyl benzene, and xylenes are present along with numerous alkanes and alkenes. In this sample, the volatiles analysis did not indicate the presence of the other gasoline constituents that we would normally expect.
Benzene was used in various commercial products up until the late 1970’s. These included Liquid Wrench, model cement, paint strippers, rubber cements, and degreasers. It was available commercially in hardware stores for various applications, much like mineral spirits and turpentine are today. Given the presence of benzene in this sample and the absence of other gasoline related constituents, it seems likely that the contamination resulted from a relatively pure source of benzene used for one of these applications.
View Dr. Charlie Carter's Experts profile
At a remediation site we are working on, there is a monitoring well that had soil samples taken during the drilling process and analyzed for BTEX. All concentrations were below 1 part per million. However, the groundwater analysis is presenting an extremely elevated level of benzene with comparable levels of the TEX components. Other wells in the area are either non-detect or have low concentrations for benzene. The data has been verified and is accurate.
We do not understand the elevated Benzene constituent. What type of source would yield such a high Benzene concentration without similar elevated TEX concentrations?
Experts Response:
When benzene is present in environmental samples it is typically an indication of contamination by gasoline or some type of hydrocarbon based fuel. In those cases, however, other aromatics such as toluene, ethyl benzene, and xylenes are present along with numerous alkanes and alkenes. In this sample, the volatiles analysis did not indicate the presence of the other gasoline constituents that we would normally expect.
Benzene was used in various commercial products up until the late 1970’s. These included Liquid Wrench, model cement, paint strippers, rubber cements, and degreasers. It was available commercially in hardware stores for various applications, much like mineral spirits and turpentine are today. Given the presence of benzene in this sample and the absence of other gasoline related constituents, it seems likely that the contamination resulted from a relatively pure source of benzene used for one of these applications.
View Dr. Charlie Carter's Experts profile
Monday, February 14, 2011
Volatile versus a Semi-Volatile Compounds
Ask the Expert Question:
What makes a compound a volatile versus a semi-volatile?
Expert Response:
There is no hard and fast rule to determine what is called a volatile compound and what is called semi-volatile. There are a variety of chemical characteristics that influence volatility, but for the most part the definitions that are used in environmental analysis are operational definitions.
The operational definition is whether a compound will purge from aqueous solution in a purge and trap device. If a compound will do so at a high enough rate to be detected and quantified, then it is considered to be volatile. If an analyte is only found in a semi-volatile analysis and is not present in the volatiles analysis, then almost by definition it is not volatile.
There are also, however, some physical chemical characteristics of volatile compounds. The key characteristics are (1) vapor pressure or boiling point, and (2) aqueous solubility. As the vapor pressure increases, a compound’s volatility increases. As its aqueous solubility decreases, it also becomes more volatile from an aqueous solution.
For example, 1,2,4-trichlorobenzene is about the highest boiling compound routinely included in a volatiles analysis. Its boiling point is listed as 214.4 degrees Celsius, and it is quite water insoluble. Nitrobenzene’s boiling point is 210.9 degrees Celsius, but it is more soluble in water due to the polar nature of the nitro group. It does not purge with sufficient efficiency, so it is not considered a volatile.
View Dr. Charlie Carter Experts profile
What makes a compound a volatile versus a semi-volatile?
Expert Response:
There is no hard and fast rule to determine what is called a volatile compound and what is called semi-volatile. There are a variety of chemical characteristics that influence volatility, but for the most part the definitions that are used in environmental analysis are operational definitions.
The operational definition is whether a compound will purge from aqueous solution in a purge and trap device. If a compound will do so at a high enough rate to be detected and quantified, then it is considered to be volatile. If an analyte is only found in a semi-volatile analysis and is not present in the volatiles analysis, then almost by definition it is not volatile.
There are also, however, some physical chemical characteristics of volatile compounds. The key characteristics are (1) vapor pressure or boiling point, and (2) aqueous solubility. As the vapor pressure increases, a compound’s volatility increases. As its aqueous solubility decreases, it also becomes more volatile from an aqueous solution.
For example, 1,2,4-trichlorobenzene is about the highest boiling compound routinely included in a volatiles analysis. Its boiling point is listed as 214.4 degrees Celsius, and it is quite water insoluble. Nitrobenzene’s boiling point is 210.9 degrees Celsius, but it is more soluble in water due to the polar nature of the nitro group. It does not purge with sufficient efficiency, so it is not considered a volatile.
View Dr. Charlie Carter Experts profile
Wednesday, February 9, 2011
Dust Sampling Methods and Equipment
Ask the Expert Question:
There are abandoned mine land sites in our area that are often used for recreational activities. These activities generate a great deal of dust. The sediments and mine wastes in these areas are potentially contaminated with heavy metals and could put people using these public areas at risk. Can you provide any information on methods to sample the dust? Also, where can I obtain the equipment to do the sampling?
Experts Response:
There are several considerations for deciding upon how to approach monitoring the dust.
The first consideration is: what will you compare your data to with regard to health standards or risk criteria? The answer will help to define how you will collect the samples. For example, it may make sense to compare your results to the National Air Quality Standard for the particular heavy metals contamination present, and/or the PM10 standard for Total Particulate. Some counties in the US even have their own ambient air quality criteria.
Your choice of criteria will dictate how the samples should be collected; the detection levels required and for what time period the samples must be collected. As an example, the National Air Quality Standard for Lead requires that a sample be collected for a 24 hour period.
A second consideration is: do you have a source of electrical power, or will it be necessary to use sampling equipment that is battery powered? Battery powered equipment may pose a problem if your sampling period must cover 24 hours.
TestAmerica does have air sampling pumps available for clients depending upon your sampling criteria. Click here to contact our expert, Mike McGee to inquire about the equipment and methods available.
View Mike McGee's Experts profile
There are abandoned mine land sites in our area that are often used for recreational activities. These activities generate a great deal of dust. The sediments and mine wastes in these areas are potentially contaminated with heavy metals and could put people using these public areas at risk. Can you provide any information on methods to sample the dust? Also, where can I obtain the equipment to do the sampling?
Experts Response:
There are several considerations for deciding upon how to approach monitoring the dust.
The first consideration is: what will you compare your data to with regard to health standards or risk criteria? The answer will help to define how you will collect the samples. For example, it may make sense to compare your results to the National Air Quality Standard for the particular heavy metals contamination present, and/or the PM10 standard for Total Particulate. Some counties in the US even have their own ambient air quality criteria.
Your choice of criteria will dictate how the samples should be collected; the detection levels required and for what time period the samples must be collected. As an example, the National Air Quality Standard for Lead requires that a sample be collected for a 24 hour period.
A second consideration is: do you have a source of electrical power, or will it be necessary to use sampling equipment that is battery powered? Battery powered equipment may pose a problem if your sampling period must cover 24 hours.
TestAmerica does have air sampling pumps available for clients depending upon your sampling criteria. Click here to contact our expert, Mike McGee to inquire about the equipment and methods available.
View Mike McGee's Experts profile
Monday, January 31, 2011
Sampling time for Method TO-9a
Ask the Expert Question:
We have procured several PUF sample trains from TestAmerica to test for dioxins and furans using EPA Method TO-9a. The method specifies a usual sampling time of 24 hours to obtain a sample air volume of between 325 to 400 m^3. We will probably run our sampler no longer than 60 minutes with a total sample volume collected of about 20 m^3. The 60 minute sample time bounds the time frame of the emissions we are trying to measure. Any additional time could introduce the potential for confounding sources to be captured in the sampler. Is this a concern of running the sampler less than the "usual" 24 hours from a MDC perspective or is the 24 hours just a convention specified in the method?
Experts Response:
The time recommendations cited in the Method are for relative reference purposes only, and are called out to show the volumes collected over that period of time as examples. There should be no deleterious effects to smaller sample volumes aside from higher reporting limits. If reporting limits are an important issue to your project, and they cannot be obtained by your 60 minute duty cycle, then you should consider more sampling during operational times when correct conditions are regained. That’s how incinerators are tested after a malfunction. Nothing should logically prevent multiple-sampling cycles of your test conditions when they occur. Your custom sampling implementation could take into consideration startup and shutdown, as needed.
Please also note that we often prepare a different apparatus of sampling media for much smaller air volumes than collected on a standard Hi-Volume sampler. The ORBO (click here to see attached picture) is prepared for battery operated pumps, and could be put much closer to your sources. They are very easy to handle.
Tuesday, January 25, 2011
What is the difference between total metals vs. dissolved metals analysis and what form the metal is being analyzed
Ask the Expert Question:
Can you explain the difference between total metals versus dissolved metals analysis and what form of the metal is being analyzed?
Expert Repsonse:
Total metals analysis for water samples include the metals content both dissolved in the water and present in the particulates in the water. Typically a dissolved metals analysis of a water sample is performed by removing the particulates with a filter, then analyzing the filtered water for metals. The most common filters used for this purpose have a 0.45 um pore size.
Total metals analysis results should always be greater than or equal to dissolved metals analysis results, because dissolved metals is a subset of total metals. Dissolved metals are generally considered more mobile and biologically available. Thus, the dissolved metals results are useful for risk assessment and fate & transport studies.
The specific metal species (or form) present in the dissolved fraction is highly dependent on the metal of interest. Most of the dissolved species are solvated metal cations such as Na(I) or Cr(VI). Some metals species are present as oxy anions such as arsenite.
Water solubility of the elemental metals (i.e. neutral valence state) is generally quite low. For example this website states elemental mercury [Hg(0)] has a water solubility limit of 56 ug/L at 25C (http://www.inchem.org/documents/cicads/cicads/cicad50.htm#2.1).
Most regulations use total metals results because it is often considered more conservative and protective, however, depending on the purpose of the regulation it might be based on dissolved or total metal concentrations.
View Dr. Mark Bruce's Experts profile.
Monday, January 17, 2011
What are the differances and applications of HRGC/HRMS and GC-MS/MS instruments
Ask the Expert Question:
What is the difference between the HRGC/HRMS and GC-MS/MS instruments?
What are its major applications?
What are its major applications?
Experts Response:
By definition HRGC/HRMS stands for “High Resolution Gas Chromatography/High Resolution Mass Spectrometry” and GC-MS/MS stands for “Gas Chromatography/Tandem Mass Spectrometry”.
Starting with the GC-MS/MS, this equipment is fitted with what can be described as a dual mass spectrometry and are generally triple quads (or 3 quadrupoles). Using a triple quad versus a standard GCMS give greater sensitivity (i.e. allows for lower detection limits from sub part per billion to sub part per trillion) and give greater resolution than a standard GCMS. For example a standard GCMS can resolve masses 1 atomic mass unit apart. A triple quad can resolve masses ~1000 atomic mass units apart. Using GC-MS/MS resolution increase allows for much greater selectivity than standard GCMS. Another feature of the GC-MS/MS is the dynamic range is much greater than a normal GCMS.
HRGC/HRMS is a completely different type of instrument for very specific applications. This instrument is fitted with a huge magnet and has electric sectors, lens and a 6 to 8 foot flight tube. Using this type of configuration jumps the resolution to 10,000 atomic mass resolutions. You can separate molecules that may have the same retention time but different masses 0.0001 amu apart. Also the HRGM/HRMS allows for sensitivity to sub parts per quadrillion level and below and you can easily see 0.5fg on column of 2,3,7,8-TCDD (which is difficult to impossible for a standard GCMS or GC-MS/MS to see). The dynamic range for the HRGC/HRMS is greater than 2000 times the low point so there is a lot of room to see the low end and the high end without saturating the detector.
There are many methods written for both types of instruments and you can use them for specific needs. If you are looking for gross contamination then a GCMS is the way to go for general screening and for analytes with little public health risk. GC-MS/MS is perfect for confirmation of low level GCMS results. If you are looking to confirm low level results of analytes with high public heath risk then the HRGC/HRMS may be a better option.
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