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TNI Standards Guidance

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Module: Radiochemistry


Subject: Matrix Spike Requirements

Question 1

Is a matrix spike required for all analyses?

A matrix spike is not specifically required, per se, but procedures are required for determining sample matrix effects.  The 2009 TNI Standard refers to method, compliance program, and client/project requirements.  Methods that are specific to the Clean Water Act are regulated by 40 CFR part 136.7 and the Safe Drinking Water Act methodology is governed 40 CFR Part 141 and 143. Part 136 requires matrix spikes and the majority of the USEPA methods and Standard Methods approved for use in drinking water require matrix spikes (laboratory fortified sample matrices). Where SW846 is concerned, most methods address matrix spiking and the laboratory should address their specific process in the individual analytical SOP.

Question 2

Can a surrogate be used instead of a matrix spike?
A surrogate is a compound/analyte which is similar to the target analyte(s) in chemical composition and behavior in the analytical process, but which is not normally found in environmental samples. 

Typically, a surrogate alone is not an adequate evaluation of sample matrix as the representation is too broad.  Where the method gives no other options and no matrix spiking requirements exist in the method, related compliance program governing documents (40 CFR xxx), or client project requirements a surrogate can be used to broadly assess matrix effects if the laboratory can show a proven relationship between the chosen surrogate analyte/compound and the analytes/compounds of interest or concern.  Long lists of analytes/compounds will require enough surrogates to represent all classes being analyzed.  Acceptance criteria must be established to evaluate performance and recovery to allow for the determination of matrix effect.  A surrogate cannot be used to replace a matrix spike if a matrix spike is specifically required by the regulation, method, or client requirements. 

A preferred alternative is to use the matrix spiking guidance given in V1M4 1.7.3.3.1 c.

Question 3

Can a tracer be used instead of a matrix spike?

Matrix spikes are required for Radiochemistry methods when that requirement is specified in the test method or specified by the client.  The use of the Tracer does not exempt the laboratory from having to perform the matrix spike when it is otherwise required.  The Tracer and/or Carrier enters into calculation formulas for chemical yield considerations for radioactivities, while sample matrix spikes assess possible sample matrix effects, as they do in other Chemistry test methods.  The Radiochemistry Technical Module correctly lists Matrix Spikes and Duplicates separately from, and in addition to, the requirements for Tracers and Carriers.



References:

TNI 2009 V1M2 Section 3.1

Matrix Spike (spiked sample or fortified sample): A sample prepared, taken through all sample preparation and analytical steps of the procedure unless otherwise noted in a referenced method, by adding a known amount of target analyte to a specified amount of sample for which an independent test result of target analyte concentration is available. Matrix spikes are used, for example, to determine the effect of the matrix on a method's recovery efficiency.

TNI 2009 V1M4 Section 1.7.3.3

Sample Specific Controls
The laboratory shall document procedures for determining the effect of the sample matrix on method performance. These procedures relate to the analyses of quality system matrix specific Quality Control (QC) samples and are designed as data quality indicators for a specific sample using the designated method. These controls alone are not used to judge laboratory performance.

TNI 2009
V1M6 Section 1.7.2.3c)

Tracer
For those methods that employ a tracer for yield determination, each sample result shall have an associated tracer yield calculated and reported. The tracer shall be added to the sample after subsampling, if required, but before any chemical treatment (e.g., chemical digestion, dissolution, separation, etc.) unless otherwise specified by the method. The tracer yield for each sample result shall be one of the quality control measures to be used to assess the associated sample result acceptance. The tracer yield shall be assessed against the specific acceptance criteria specified in the laboratory method SOP. When the specified tracer yield acceptance criteria are not met, the specified corrective action and contingencies shall be followed. The occurrence of a failed tracer yield and the actions taken shall be noted in the laboratory report to the client.

TNI 2009 V1M6 Section 1.7.2.3d)

Carrier

For those methods that utilize a carrier for yield determination, each sample shall have an associated carrier yield calculated and reported. The carrier shall be added to the sample after subsampling, if required, but before any chemical treatment (e.g., chemical digestion, dissolution, separation, etc.) unless otherwise specified by the method. The carrier yield for each sample shall be one of the quality control measures to be used to assess the associated sample result acceptance. The carrier yield shall be assessed against the specific acceptance criteria specified in the laboratory method SOP. When the specified carrier yield acceptance criteria are not met, the specified corrective action and contingencies shall be followed. The occurrence of a failed carrier yield and the actions taken shall be noted in the
laboratory report to the client.