Accuracy and Precision of Various Mercury Vapor Analyzers
Abstract No:
1696
Abstract Type:
Student Poster
Authors:
S Prasertphong1, S Que Hee2
Institutions:
1UCLA, 90095, CA, 2University of California, Los Angeles, Los Angeles, CA
Presenter:
Supasara Prasertphong
UCLA
UCLA
Faculty Advisor:
Dr Shane Que Hee, PhD, FAIHA
University of California, Los Angeles
University of California, Los Angeles
Description:
Mercury exists in various states of matter, with the vapor form as the most hazardous among workers compared to the solid and liquid form. Various mercury vapor analyzers were studied and tested for accuracy and precision in a laboratory setting. The Jerome® J505, Nippon® EMP-3, and the Picoyune which utilized the atomic fluorescence spectroscopy, atomic absorbance spectroscopy, and the localized surface plasmon resonance were tested, respectively.
Situation/Problem:
Different devices provide accuracy at different concentrations, it is significant to test the accuracy and precision of the devices to ensure that mercury concentrations are accurate, in order to take appropriate action when out in the field.
Methods:
In the first experiment, the Nippon® EMP-3 and the Jerome® J505 were compared to the pre-determined mercury concentrations of 5, 25, and 250 µg/m3 and then the concentrations of the devices were compared to the reference of the Lumex RA-915+. In the second experiment, the PSA 10.534 was paired with the PSA CavkitCalc Software, an automated system to generate specific mercury concentrations through a mercury reservoir and set air flow. The Picoyune was tested alongside the Jerome® J505; the concentrations were tested at 4.5, 54, 106, 286, 468, 737, 828, and 1238 µg/m3.
The pre-determined mercury concentrations of 5, 25, and 250 µg/m3 were calculated by determining how much nitrogen was needed to be filled into separate 5 liter Tedlar bags using the Agilent ADM 1000 to monitor flow rate. Teflon tubing was connected to the air source to the bag and the sampling probe, in order to fill the bags with nitrogen. The flow rate was set at 0.950 L/min and the run time varied among the different concentrations. Initially, the concentration of 14,000 µg/m3 was given, thus all the calculations of the dilutions were done with this concentration. Calculations had to be re-calculated to obtain the actual concentrations of the mercury vapor once the vapor pressure was referenced.
According to the National Institute of Standards and Technology (NIST), the vapor pressure of mercury of 2.6 x 10-7 MPa provides the saturated headspace over liquid mercury at 25 degrees Celsius of 21,146 μg/m3 (Huber, Laesecke, & Friend). The mercury vapor pressure used by Huber, Laesecke, and Friend in MPa equates to 0.002 mmHg, also the standard vapor pressure used at 25 degrees Celsius quoted by Budavari, 1996. The vapor pressure of 0.002 mmHg was used to calculate the actual concentration, which the saturated headspace liquid mercury at 25 degrees Celsius is 21,588 μg/m3, approximately 3% from the literature value of 21,146 μg/m3; the literature value was used for all calculations. The liquid mercury was contained in a ~40 mL vial, equipped with a Teflon-lined septum. A 10 mL gas-tight syringe was used to sample the headspace. Once the mercury vapor was injected, the bag was scrunched to allow mixing. The average temperature during the process was 24.5 degrees Celsius.
The limitations of this methodology involve the use of Tedlar bags. Mercury vapor is likely to adhere to the bag, preventing the generation of proper concentrations. It would also be beneficial if the headspace of the mercury vapor was tested for each device to compare to the literature value. A major issue that was reoccurring was the size of the Tedlar bags, it would be more efficient if the bags were about 10 liters since the devices sampled large amounts of air as the same concentrations had to be re-generated a few times, which can also affect the accuracy of the concentration. After purging the bags with nitrogen the bags should have been tested with the different devices to ensure that the reading was 0.
The pre-determined mercury concentrations of 5, 25, and 250 µg/m3 were calculated by determining how much nitrogen was needed to be filled into separate 5 liter Tedlar bags using the Agilent ADM 1000 to monitor flow rate. Teflon tubing was connected to the air source to the bag and the sampling probe, in order to fill the bags with nitrogen. The flow rate was set at 0.950 L/min and the run time varied among the different concentrations. Initially, the concentration of 14,000 µg/m3 was given, thus all the calculations of the dilutions were done with this concentration. Calculations had to be re-calculated to obtain the actual concentrations of the mercury vapor once the vapor pressure was referenced.
According to the National Institute of Standards and Technology (NIST), the vapor pressure of mercury of 2.6 x 10-7 MPa provides the saturated headspace over liquid mercury at 25 degrees Celsius of 21,146 μg/m3 (Huber, Laesecke, & Friend). The mercury vapor pressure used by Huber, Laesecke, and Friend in MPa equates to 0.002 mmHg, also the standard vapor pressure used at 25 degrees Celsius quoted by Budavari, 1996. The vapor pressure of 0.002 mmHg was used to calculate the actual concentration, which the saturated headspace liquid mercury at 25 degrees Celsius is 21,588 μg/m3, approximately 3% from the literature value of 21,146 μg/m3; the literature value was used for all calculations. The liquid mercury was contained in a ~40 mL vial, equipped with a Teflon-lined septum. A 10 mL gas-tight syringe was used to sample the headspace. Once the mercury vapor was injected, the bag was scrunched to allow mixing. The average temperature during the process was 24.5 degrees Celsius.
The limitations of this methodology involve the use of Tedlar bags. Mercury vapor is likely to adhere to the bag, preventing the generation of proper concentrations. It would also be beneficial if the headspace of the mercury vapor was tested for each device to compare to the literature value. A major issue that was reoccurring was the size of the Tedlar bags, it would be more efficient if the bags were about 10 liters since the devices sampled large amounts of air as the same concentrations had to be re-generated a few times, which can also affect the accuracy of the concentration. After purging the bags with nitrogen the bags should have been tested with the different devices to ensure that the reading was 0.
Results / Conclusions:
The accuracy was calculated to ensure that the concentrations that were obtained by the Nippon® EMP-3 and the Jerome® J505 were near the expected concentration and or near the Lumex RA-915+ readings, which is considered the reference for the laboratory. In the first experiment, the relative error of the Jerome®J505 was -8% at the expected concentration of 5 µg/m3. Additionally, the Jerome J505 was more accurate at lower concentrations of 4.5, 54, and 106 µg/m3, with a maximum of -25% relative error at 54 µg/m3. Collectively for Jerome® J505, the relative standard deviation had the precision range of 44% to 154% (Table 1.8), being highest in the first experiment, along with a relative error (accuracy) of -62% to -20% in the second experiment. In comparison to the Lumex RA-915+, the relative errors were from -82% to -72%, unacceptable accuracy, but the highest precision were at 19%, 0%, and 0% for 5, 25, and 250 µg/m3, respectively. On the other hand, the Nippon EMP-3 had a high accuracy of 7% at 25 µg/m3 but the precision was high at all concentrations tested at 5, 25, and 250 µg/m3 with relative standard deviations at 25%, 12%, and 8%, respectively.
When the Jerome® J505 was compared to the Picoyune, it had a higher accuracy at lower concentrations of 4.5, 54, and 106 µg/m3, with a low relative standard deviation for all concentrations, but had low accuracy at concentrations 468 µg/m3 and up.
Even though the Jerome® J505 has a relatively high accuracy, especially at lower concentrations the precision was higher for the Nippon® EMP-3. The Jerome® J505 had a higher accuracy at concentration 5 µg/m3 to the expected compared to the Nippon® EMP-3, but the precision (i.e. % relative standard deviation) of the Nippon® EMP-3 was more precise as the relative standard deviation is less than or equal to 25%. Since the Nippon® EMP-3 was precise and had an accuracy similar to the Jerome® J505, it was recommended to be taken into the field. It is significant to ensure that the devices that are used in the field are precise and accurate to initiate a proper response to a critical situation.
When the Jerome® J505 was compared to the Picoyune, it had a higher accuracy at lower concentrations of 4.5, 54, and 106 µg/m3, with a low relative standard deviation for all concentrations, but had low accuracy at concentrations 468 µg/m3 and up.
Even though the Jerome® J505 has a relatively high accuracy, especially at lower concentrations the precision was higher for the Nippon® EMP-3. The Jerome® J505 had a higher accuracy at concentration 5 µg/m3 to the expected compared to the Nippon® EMP-3, but the precision (i.e. % relative standard deviation) of the Nippon® EMP-3 was more precise as the relative standard deviation is less than or equal to 25%. Since the Nippon® EMP-3 was precise and had an accuracy similar to the Jerome® J505, it was recommended to be taken into the field. It is significant to ensure that the devices that are used in the field are precise and accurate to initiate a proper response to a critical situation.
Primary Topic:
Technology
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Acknowledgements and References
List any additional people who worked on the project or provided guidance and support along with details on the role they played in the research. (Please include first name, last name, organization, city, state and country).
Claudia Alvarado - provided guidance and support on the potential obstacles that may occur during the experiment and how mercury vapor should be tested
Tracey Bence - provided guidance and support on preliminary details about the instruments before developing laboratory protocols for the experiment
Nga Malekzadeh - provided guidance and support on laboratory experiment by preparing all the instruments in the laboratory and feasibility of the experiment
Evan Hatakeyama - provided guidance and support on the feasibility of the experiment and recommendations on what could and could not be done