matrix spike recoveries - us epasummary matrix spike recoveries with method 1623.1 should be more...

Matrix Spike Recoveries

Carrie Miller Cryptosporidium Lab Approval Program

Technical Support Center Standards and Risk Management Division Office of Ground Water and Drinking Water

November 15, 2012 U.S. Environmental Protection Agency 1

Matrix Spike vs Field Samples

• Procedure and limitations • Improved accuracy with Method 1623.1

in challenging water matrices • Observed matrix spike recovery with

Method 1623.1, n = 165

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Matrix Spike Procedure

• Mix sample continuously • Spike with pre-determined number of

Cryptosporidium oocysts • Perform Method 1623 or 1623.1 • Compare number detected with quantity added • Typically two matrix spikes for each source

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Matrix Spike Limitations

• Method variability • Matrix interference • Assumption

– spiked sample recovery = field sample recovery

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Method 1623 Variable in Reagent Water

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Blind Spike Average, Method 1623 ~50 Laboratories

Tennessee River Sediment Diatomaceous Earth

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MS Recoveries Round 1 Method 1623 n=3,335

November 15, 2012 U.S. Environmental Protection Agency

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Method 1623.1 Variable in Reagent Water

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Improved Accuracy in River Matrix

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Matrix Spike Results in Method Validations

Improved Recovery in Challenging Matrices

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Multi-Laboratory Improvement with Challenging Matrix

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Observed Matrix Spike Recovery With Method 1623.1 n=165

November 15, 2012 U.S. Environmental Protection Agency

Summary

Matrix spike recoveries with Method 1623.1 should be more accurate than recoveries with Method

1623 in challenging source waters.

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Miller.carrie@epa.gov

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