Overcoming Interferences Impacting Heavy Metals Analyses by Standards ICP-MS In Seawater
Handling Interferences in Complex Matrices for Metals, Nutrients, and COD
Oral Presentation
Prepared by R. Burnette
Eurofins Frontier Global Sciences, 11720 North Creek Parkway North, Suite 400, Bothell, Washington, 98011, United States
Contact Information: RobertBrunette@EurofinsUS.com; 206 660 7307
ABSTRACT
Overcoming Interferences Impacting Heavy Metals Analyses by Standards ICP-MS In Seawater
Robert Brunette (RobertBrunette@EurofinsUS.com)
Michael Flournoy (MichaelFlournoy@eurofinsus.com)
Eurofins Frontier Global Sciences, 11720 North Creek Parkway North, Suite 400, Bothell, WA 98011
Background
Because of natural interferences present in seawater, EPA nearly 25 years ago, supported the development of a seawater specific, trace metals analysis method (Reductive Precipitation EPA 1640). To this day, the subtlety between sea and freshwater metals analysis methods can be overlooked which can lead to inaccurate data, project delays and in some cases costly errors.
Seawater contains dissolved solids, such as chlorides and other salts that can cause spectral or non-spectral interferences when using standard ICP-MS instrumentation. The signal/peak from the salt can overlap or appear near the peak associated with the metal being measured, resulting potentially in an erroneously high metal concentration.
Although analysis methods such as EPA 6020 and EPA 200.8 were designed for metals analysis in fresh waters, these methods have been selected, in error, to support compliance monitoring projects such as NPDES seawater effluent discharge to ocean/brackish receiving waters. This error can be overlooked, if the laboratory does not specifically ask what type of matrix (fresh or seawater) was submitted for analysis.
Further, seawater analysis interferences are not always obvious when examining the performance of the metals analysis method (i.e. quality assurance samples do not always fail) and to the inexperienced eye, the affected chromatogram may not always be identified to be non-standard or have peak overlap. When these challenges are identified, some try to dilute the sample to minimize the interference which can potentially raise the reporting limit above the project regulatory limit.
The challenges described above were identified back in the late 1990s and lead to the development of EPA 1640 that can apply a Reductive Precipitation (RP) or Chelation Preconcentration step to selectively remove the salts present in the sample, while leaving the trace metals to then be measured interference free by ICP-MS. The Reductive Precipitation can be labor intensive and extend to longer Turn-Around-Times. The manual Reductive Precipitation EPA 1640 method as well as ICP-KED-MS systems equipped with Collision Cell technology have demonstrated to work very well to combat the interferences in seawater. More recently, Eurofins Frontier has invested in state of the art instrumentation (Mixed Resin Pre-concentration / HN03 Acid Elusion / ICP-MS detection) as well as ICP-QQQ (triple quadrapole) technology. These later methods will be compared and presented in a subsequent presentation.
Presentation:
This presentation includes a case narrative of data generated using a fresh water analysis method (standard ICP-MS) inadvertently used to measure trace metals in Seawater effluent. Seawater interferences overcame the instrument leading to instrument down time, multiple reruns and eventually attempts to use other instrumentation including ICP-AES and an ICP-MS equipped with a DRC (direct reaction chamber), leading to major project delays. Samples were then successfully analyzed the gold standard method EPA 1640 Reductive Precipitation followed by ICP-KED-MS (KED = collision cell) as well as Trace Metals version of EPA 200.8 also using an ICP-KED-MS instrument. A comparison of the data including results from standard ICP-MS, ICP-AES, ICP-DRC-MS, ICP-KED-MS and RP-EPA 1640 are presented.
Handling Interferences in Complex Matrices for Metals, Nutrients, and COD
Oral Presentation
Prepared by R. Burnette
Eurofins Frontier Global Sciences, 11720 North Creek Parkway North, Suite 400, Bothell, Washington, 98011, United States
Contact Information: RobertBrunette@EurofinsUS.com; 206 660 7307
ABSTRACT
Overcoming Interferences Impacting Heavy Metals Analyses by Standards ICP-MS In Seawater
Robert Brunette (RobertBrunette@EurofinsUS.com)
Michael Flournoy (MichaelFlournoy@eurofinsus.com)
Eurofins Frontier Global Sciences, 11720 North Creek Parkway North, Suite 400, Bothell, WA 98011
Background
Because of natural interferences present in seawater, EPA nearly 25 years ago, supported the development of a seawater specific, trace metals analysis method (Reductive Precipitation EPA 1640). To this day, the subtlety between sea and freshwater metals analysis methods can be overlooked which can lead to inaccurate data, project delays and in some cases costly errors.
Seawater contains dissolved solids, such as chlorides and other salts that can cause spectral or non-spectral interferences when using standard ICP-MS instrumentation. The signal/peak from the salt can overlap or appear near the peak associated with the metal being measured, resulting potentially in an erroneously high metal concentration.
Although analysis methods such as EPA 6020 and EPA 200.8 were designed for metals analysis in fresh waters, these methods have been selected, in error, to support compliance monitoring projects such as NPDES seawater effluent discharge to ocean/brackish receiving waters. This error can be overlooked, if the laboratory does not specifically ask what type of matrix (fresh or seawater) was submitted for analysis.
Further, seawater analysis interferences are not always obvious when examining the performance of the metals analysis method (i.e. quality assurance samples do not always fail) and to the inexperienced eye, the affected chromatogram may not always be identified to be non-standard or have peak overlap. When these challenges are identified, some try to dilute the sample to minimize the interference which can potentially raise the reporting limit above the project regulatory limit.
The challenges described above were identified back in the late 1990s and lead to the development of EPA 1640 that can apply a Reductive Precipitation (RP) or Chelation Preconcentration step to selectively remove the salts present in the sample, while leaving the trace metals to then be measured interference free by ICP-MS. The Reductive Precipitation can be labor intensive and extend to longer Turn-Around-Times. The manual Reductive Precipitation EPA 1640 method as well as ICP-KED-MS systems equipped with Collision Cell technology have demonstrated to work very well to combat the interferences in seawater. More recently, Eurofins Frontier has invested in state of the art instrumentation (Mixed Resin Pre-concentration / HN03 Acid Elusion / ICP-MS detection) as well as ICP-QQQ (triple quadrapole) technology. These later methods will be compared and presented in a subsequent presentation.
Presentation:
This presentation includes a case narrative of data generated using a fresh water analysis method (standard ICP-MS) inadvertently used to measure trace metals in Seawater effluent. Seawater interferences overcame the instrument leading to instrument down time, multiple reruns and eventually attempts to use other instrumentation including ICP-AES and an ICP-MS equipped with a DRC (direct reaction chamber), leading to major project delays. Samples were then successfully analyzed the gold standard method EPA 1640 Reductive Precipitation followed by ICP-KED-MS (KED = collision cell) as well as Trace Metals version of EPA 200.8 also using an ICP-KED-MS instrument. A comparison of the data including results from standard ICP-MS, ICP-AES, ICP-DRC-MS, ICP-KED-MS and RP-EPA 1640 are presented.
