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Low-Level Perchlorate Analysis in Groundwater by Improved IC & LC/MS/MS

March–April 2003

Presented by STL Denver


Presentation Outline

Background

Methods currently used for perchlorate

Methods & equipment for this study

Performance Characteristics: selectivity, sensitivity, precision, and accuracy

Plans for future work


Used in some consumer products

Primarily produced for solid rocket fuel and munitions

Found in groundwater near production, test facilities, and other places of use

Persistent and mobile in groundwater

Perchlorate Background


Perchlorate interferes with iodide uptake in the thyroid gland

Recent studies indicate developmental and growth effects at low concentrations, particularly to the development of the nervous system

Potential carcinogen Perchlorate has been found in 22 states,

including Colorado

What Is The Concern With Perchlorate?


Current Methods for Perchlorate

Technique Application• Ion-selective electrode (ISE) • Field screening

• Colorimetric • NIOSH air

• Capillary electrophoresis (CE) • FBI forensics

• Ion chromatography (IC) • EPA water, 314.0• Electrospray ionization • USAF & USEPA

mass spectrometry (ESI-MS) research labs•

Growing interest in DOD

and DOE


Evolution to Better Environmental Methods

Driven by need for: 1) Sensitivity

– Older “standard” 314.0 MDL = 1.5 ug/L– The action level for perchlorate in California and

Texas is 4 ug/L– The proposed Federal limit is 1 ug/L when

fetuses and newborns are of concern– Require quantitative limits < 1 ug/L– Require detection limits < 0.5 ug/L– Method 314.0 can meet these requirements


Evolution to Better Environmental Methods (Continued)

2) Selectivity / Ruggedness– Current IC methods approved for drinking

water– STL Denver’s LC/MS/MS method works

well in reagent water

3) How well do the methods work in groundwater / real-world field samples?


Methods for This Study

1. Ion Chromatography (IC)– Improved version of EPA Method 314.0,

Revision 1, Nov. 1999

– EPA approved method for drinking water only

– Data for this study was provided by STL Denver


What Is Improved IC?(Improved Method 314.0)

Large volume injector - 1,000 uL

Dionex AG11 guard column

Dionex AS11 separation column

Dionex AMMS (Anion Micro Membrane Suppressor) chemical suppressor in external mode─Biggest Improvement

Still within scope of Method 314.0


Methods for This Study (Continued)

2. Liquid Chromatography/Mass Spectrometry (LC/MS)

3. Liquid Chromatography/Tandem Mass Spectrometry (LC/MS/MS)– Magnunson et.al. (EPA National Risk

Management Research Laboratory), Analytical Chemistry, Vol. 72, No. 1; January 1, 2000

– E. Urbansky (EPA National Risk Management Research Laboratory), Critical Reviews in Analytical Chemistry, 2000, CRC

– Data for this study was provided by STL Denver


Groundwater (GW) Used for Validation Study

Groundwater from Missouri landfill

General water quality parameters:

pH = 8.0Conductivity = 1,600 uSTDS = 1,100 mg/LAlkalinity = 440 mg/L (as CaCO3)Sulfate = 460 mg/LChloride = 75 mg/L


Groundwater Spikes Prepared for Study

IC LC/MS/MS

0.1 ug/L: 8 replicates 8 replicates






Performance Characteristics

1. Selectivity


Equipment Configuration

Equipment IC LC/MS/MS

Eluent Reservoir

100 mM NaOH

10 mM NH4OH / 1:1 MeOH

Sample Injector 1,000 uL loop 50 uL loop

Guard Column AG11 N/A

Separation column

AS11 Alltech Ion Exchange

Interface to Detector

AMMS chemical suppressor

Electrospray ionization, neg. ion mode


Equipment Configuration(Continued)

Equipment IC LC/MS/MS

1st Stage Detector

Conductivity Cell

MS monitoring m/z 99 & 101

2nd Stage N/A Collision Cell

3rd Stage Detector N/A MS Monitoring m/z 83 & 85


Natural Isotopes of Chlorine Provide Confirmation for LC/MS/MS

Molecular ions analyzed in first stage:

ClO4- = Cl35+4O16 = m/z 99, 75.5% abundance

= Cl37+4O16 = m/z 101, 24.5% abundance

Daughter ions analyzed in third stage:

ClO3- = Cl35+3O16 = m/z 83

= Cl37+4O16 = m/z 85


Selectivity

By monitoring 4 ions and ion ratios, LC/MS/MS is more selective than IC

EPA Office of Drinking Water is working on Method 314.1, a dual column method, to avoid false positive results

What about IC/MS methodology?



2. Sensitivity


Working Range


1.0 ppb IC Standard in DI Water

Blow Up Signal:Noise 16

40CFR MDL = 0.2 ug/L


1.0 ppb IC Standard in Ground Water

Blow Up Signal:Noise (S:N) 12

40CFR136 MDL = 0.6


IC Detection Limit Near Max. Conductivity Threshold (MCT)

2 ppb not detected

5ppbS:N = 10


Effect of Ionic Strength on IC Background (20 ppb perchlorate)


0.1 ppb LC/MS/MS - m/z 83in DI Water

Signal:Noise = 11

40CFR136B MDL = 0.06 ug/L


0.1 ppb LC/MS/MS - m/z 85in DI Water

Similar sensitivity for confirmation ion


0.1 ppb LC/MS/MS Standard in Ground Water

Signal:Noise 7

40CFR136B MDL = 0.056 ug/L


Detection Limits in Groundwater (32% of MCT)

IC = 0.41 ug/L

LC/MS/MS = 0.056 ug/L


Sensitivity

LC/MS/MS is more sensitive than LC/MS LC/MS/MS sensitivity is little affected by

changes in ionic strength

IC sensitivity degrades by 10x over conductivity range prescribed by method

EPA Office of Drinking Water working on Method 314.1 to include pre-treatment options to remove interferences affecting IC sensitivity



3. Method Precision


LC/MS/MS Precision in Groundwater

Test No. * True Value (ug/L)

RSD (%)

1 0.1 11.9

2 0.4 12.3

3 1.0 13.9

4 2.5 9.2

5 5.0 6.4


IC Precision in Groundwater

Test No. * True Value (ug/L)

RSD (%)

1 0.1 0

2 0.4 0

3 1.0 16.5

4 2.5 10.3

5 5.0 5.9

* Includes Eight Replicates



4. Method Bias


Technique for Controlling Effect of Ionic Strength – Method 314.0

Determine maximum conductivity threshold (MCT), i.e., concentration that produces > 80% recovery

Dilute samples to conductance < MCT Significant problem remains Accuracy is controlled, but sensitivity is not Some labs evaporate samples to get lower

theoretical MDL ─ STL Denver does not


Effect of Ionic Strength on LC/MS/MS Analysis (5 ppb perchlorate)

0

20

40

60

80

100

120

0 200 400 600 800 1000 1200

MCT Value

% R

ec

ov

ery


Technique for Controlling Effect of Ionic Strength – LC/MS/MS

Standard addition for each sample High degree of linearity and precision allow

control of accuracy with standard additions (possible correction based on matrix spike recoveries)

High degree of precision ensures no significant loss of sensitivity

EPA is encouraging Cambridge Isotopes to make an O18 labeled perchlorate – Internal Standard


Recovery In Groundwater

0

20

40

60

80

100

120

Log Concentration (ug/L)

Re

co

ve

ry (

%)

IC

LC/MS/MS

0.1 0.4|

1.0|

2.5|

5.0


Summary of Method Performance in Groundwater

Improved IC LC/MS/MS

Working Range: 1-40 ug/L 0.1-10 ug/L

Linearity, r: >0.995 >0.995

MDL in GW: 0.61 ug/L 0.056 ug/L

RSD: 6-17 % 6-12 %

Recovery from: 0-108% 62-101%DI MDL to Mid-range


Conclusions

EPA approved 4x more sensitive than older 314.0 Accurate in samples with high ionic

strength But, sensitivity 1 / ionic strength

Improved Method 314.0 is method of choice where sensitivity and selectivity are adequate:


Conclusions

LC/MS/MS is a more powerful method Includes confirmation capability 10x more sensitive than improved 314.0 in

groundwater used for study Sensitivity less affected by ionic strength Because of ionization suppression,

requires standard addition per sample Good precision and linearity makes

method of additions practical


Future Method Improvements

Dual column IC

Precolumn cleanup techniques

– Barium columns

– Perchlorate-specific resins

Isotope dilution technique for LC/MS/MS

STL Denver to assist in EPA’s development of MS method

STL Denver is working with Dionex on Perchlorate by IC/MS/MS

leaders in environmental testing low-level perchlorate analysis in groundwater by improved ic &...

Documents

better environmental

perchlorate methods

current methods

ugl method

doe slide

improved method

stl denver slide

future work slide