perchlorate april 14, 2004 an integrated approach to ensure reliable perchlorate analytical results
TRANSCRIPT
Perchlorate
April 14, 2004
An Integrated Approach to Ensure Reliable Perchlorate Analytical Results
Agenda
Perchlorate Chemistry and Sources Current Methods for Testing Ion Chromatography LC/MS/MS An Integrated Approach A Success Story Summary and Conclusions
Perchlorate Ion
Perchlorate is a compound containing one chlorine atom and four oxygen atoms.
Perchlorate is an ion, meaning it carries an electrical charge, as indicated by the negative sign.
Natural Sources of Perchlorate
Chilean fertilizer deposits New Mexican potash Canadian potash Californian hanksite Bolivian playa crusts
Anthropogenic Sources of Perchlorate
Rocket Fuel Fireworks High explosives Flares Herbicides Automobile airbags Tracer munitions Detergents ?
How is perchlorate measured?
EPA Method 314.0Ion chromatography/conductivity detector
Enhanced (Modified) 314.0 Suppressed Conductivity Detector
SW-846 Method 9058 (draft)Ion Chromatography/conductivity detector
How is perchlorate measured? Other analytical methods that can detect perchlorate:
IC “Improved” Method 314.1 approved use of 2nd column confirmation and pre-concentration of samples.
IC/MS (ion chromatography/mass spectrometry) Proposed Method 330.0
LC/MS (liquid chromatography/mass spectrometry)
LC/MS/MS (liquid chromatography/mass spectrometry/mass spectrometry) Method 8321 Modified, Proposed Method 331.0
Ion Chromatography
Ion Chromatography An aqueous sample, comprised of
components A and B, is injected into the ion chromatograph.
The sample enters the analytical column which is packed with a material that can adsorb the components of the sample.
Some components are more strongly adsorbed.
Diagram from Fundamentals of Analytical Chemistry, Skoog, 1988.
Ion Chromatography
Fresh solvent is continuously injected into the instrument.
The solvent carries the sample components, A and B, through the column.
Component B is more strongly adsorbed onto the column and is moving thought the column at a slower rate.
The boundary between A and B is indistinct at this point.
Diagram from Fundamentals of Analytical Chemistry, Skoog, 1988.
Detector
Ion Chromatography
Component B is almost completely separated from component A.
The boundary between the two components is more distinct.
Diagram from Fundamentals of Analytical Chemistry, Skoog, 1988.
Detector
Ion Chromatography
Component B is completely separated from component A.
Component A exits the column through the detector at time t3.
The detector records component A as a peak (pictured below the column) in the sample chromatogram (graph).
Diagram from Fundamentals of Analytical Chemistry, Skoog, 1988.
Detector
Ion Chromatography Component B exits the
column through the detector at time t4.
The detector records component B as a peak (pictured below the column) in the sample chromatogram.
Diagram from Fundamentals of Analytical Chemistry, Skoog, 1988.
Detector
Solvent
Diagram from Fundamentals of Analytical Chemistry, Skoog, 1988.
Identification of Perchlorate by Ion Chromatography
11.2.4 The width of the retention time window used to make identifications should be based upon measurements of actual retention time variations of standards measured over several days. Three times the standard deviation of retention time may be used as a suggested window size but the retention time window should not extend beyond ± 5% of the retention time for perchlorate. The experience of the analyst should weigh heavily in the interpretation of these chromatograms.
EPA Method 314.0
IC Perchlorate Standard
High Conductivity
Carry Over
Matrix Spike Confirmation
Matrix Spike Non- Confirmation
Matrix Spike Non- Confirmation
Liquid Chromatography/MassSpectrometry/Mass
Spectrometry
LC/MS/MS
Leading edge technology
DoD Recommended
Pending Regulatory Approval
API MS/MS
Bowling Balls and Feathers: a simplification of mass spec separations
Identification By LC/MS/MS
Liquid chromatography separates perchlorate from other sample components in the same manner that ion chromatography does
Mass spectrometers (MS) are used as detectors in place of the conductivity detector used in IC.
Unlike conductivity detectors, an MS is a specific detector
Detection By LC/MS/MS The MS counts the number of ions that have a specific molecular
weight. Perchlorate has a characteristic molecular weight (MW). The first MS counts the number of ions that have the MW of
perchlorate: 1 Chlorine (35) + 4 Oxygens (16) = 99 The second MS removes one of the oxygen atoms and then counts the
number of “daughter” ions that have that MW: 1 Chlorine (35) + 3 Oxygens (16) = 83
Chlorine has a less abundant isotope (MW 37), so ions with MW 101 are also counted by the first MS and ions with MW 85 are counted by the second MS.
The retention time of the peak for MW 99 must be the same as the retention time of the peak for MW 83 for perchlorate to be confirmed. If the retention times are different, then the two molecular weight were detected from two different components and perchlorate is not confirmed.
Non-detect Analysis by LC/MS/MS
Analysis by LC/MS/MS
Reporting limit is 2 g/L.
Bottom chromatogram shows the counts of ions with molecular weight 83 (1 chlorine + 3 oxygens).
Top chromatogram shows the counts of ions with molecular weight (the isotope of chlorine).
Perchlorate is not detected.
Comparison of LC/MS/MSNon-Detect Detect
Reporting limit 2 g/L.
Bottom left shows MW 83 (1 chlorine + 3 oxygens).
Top left shows MW 85 (the isotope of chlorine).
Right chromatogram show the 18O internal standard (recovery 88%).
Perchlorate is detected.
Detect Analysis by LC/MS/MS
Perchlorate Decision Tree
Success Using the Perchlorate Decision Tree
Approximately 1000 samples were collected and analyzed for perchlorate from August 2003 through January 2004.
89 samples (about 9% of total) were pretreated and reanalyzed.
39 samples (about 3% of total) were reanalyzed by LC/MS/MS - 24 detects and 15 nondetects.
10 perchlorate detects (about 0.4% of total) were confirmed by LC/MS/MS – 58% false positive rate and a 0% false negative rate.
Summary Why use 314.0?
Cost CapacityAvailabilityPromulgated Methods
When to use LC/MS/MS?Definitive DataCritical SamplesSmall Projects
