EPA Method 8270D spiking question.

[MGD255]

I'm wondering where people are spiking for this method.

Typically in our lab we spike in the center of our calibration curve (but no more than 5x our PQL for SW 846 methods). One of our chemists noted that EPA method 8000 states that MS spiking concentrations should be no more than 50 x MDL.

If that's true than we've got a problem. That value is just about our PQL.

Are labs not using the Method 8000 rule? Where are your typical spiking concentrations for SW-846 methods.

Thanks.

[Bigbear]

We do EPA 525 which I think has about the same compound list. We calibrate from 0.1-10 ppb and spike @ 2.0 ppb.

[Steve Reimer]

If your PQL is ~ 10 times your MDL then your spike level is OK.
Note that the language is mostly suggestions because this is general guidance and the data use is not specified.

This is from method 8000C, (8000D is currently under construction)

Section 9.5...
The concentration of the matrix spike sample and/or the LCS should be determined as described in Secs. 9.5.1 and 9.5.2, and the spiking solutions should contain all of the target analytes of concern.
9.5.1 If, as in compliance monitoring, the concentration of a specific analyte in the sample is being checked against a regulatory concentration limit or action level, the spike should be at or below the limit, or 1 - 5 times the background concentration (if historical data are available), whichever concentration is higher.
If historical data are not available, it is suggested that a background sample of the same matrix from the site be submitted for matrix spiking purposes to ensure that high concentrations of target analytes and/or interferences will not prevent calculation of recoveries.
9.5.2 If the concentration of a specific analyte in a sample is not being checked against a limit specific to that analyte, then the analyst may spike the sample at the same concentration as the reference sample (Sec. 9.4.1), at 20 times the estimated limit of quantitation (LOQ) in the matrix of interest, or at a concentration near the middle of the calibration range. It is again suggested that a background sample of the same matrix from
the site be submitted as a sample for matrix spiking purposes.
9.5.3 To develop precision and accuracy data for each of the spiked compounds, the analyst has two choices: analyze the original sample, and an MS/MSD pair; or analyze the original sample, a duplicate sample, and one spiked sample. If samples are not expected to contain the target analytes of concern, then the laboratory may use a matrix spike and matrix
spike duplicate pair. If samples are expected to contain the target analytes of concern, then the laboratory may use one matrix spike and a duplicate analysis of an unspiked field sample as an alternative to the MS/MSD pair.