TNI Logo The NELAC Institute

TNI Standards Guidance

Disclaimer: This material represents the opinion of its authors. It is intended solely as guidance and does not include any mandatory requirements except where such requirements are referenced. This guidance does not establish expectations of being implemented universally, exclusively, in whole, or in part.

This guidance does not establish or affect legal rights or obligations and is not finally determinative of the issues it addresses. It does not create any rights enforceable by any party in litigation with TNI, its accreditation bodies, or affiliated institutions. Any decisions made by TNI regarding requirements addressed in this guidance will be made by applying the applicable standards, policies or procedures to the relevant facts.

 

Module: Quality Systems & Chemistry


Subject: Analytical Batch - Time Constraint

Question 1

Are there boundaries on "samples analyzed together as a group" in an analytical batch with regard to the requirements for continuing calibration verifications in TNI V1M4-1.7.2.c.i? Is there a time or another constraint on the maximum size of an analytical batch?

Note: This response is related only to analytical batch. It is important to note the difference between samples that are prepared together versus samples that are analyzed together.

There are boundaries to “samples analyzed together as a group” in an analytical batch, with regards to requirements for running a CCV; however, the usual constraints are found in mandated test methods, which apply as requirements more stringent than the TNI Standards as currently worded. Examples include “CCV/CCB every 10 samples” for EPA 200.7, 300.0, 351.2, et. al., CCV “each working day” for EPA 600-series methods, and CCV “every 12-hour work shift” for most EPA 8000-series methods. In the absence of any specific reference test method requirements, it is up to the laboratory to prove that, in the words of SM1020B, Section 10c, “the instrument performance has not changed significantly from the initial calibration.”

In a practical sense, one cannot justify analyzing samples intermittently over days, months, or years and say that those samples were “analyzed together as a group.” For example, if a typical GC sample run time is 30 minutes and over 2 hours elapses between one injection and the next injection, an analyst should not be claiming that these two samples were analyzed together unless it takes 90 minutes to prepare the GC system for the next injection. All samples in the group should have the same elapsed time difference between successive analysis start-times. The practical constraints would then be number of samples that can be loaded onto an auto-sampler tray or programmed into a computer program task-list and assigned one batch file-name.

If the analysis batch consists of a large number of samples and the CCV is run only at the beginning of the batch (and not at some points within the batch), the analyst may run the risk of generating a lot of unusable data if the instrument should fail or stop running in the middle of the batch, particularly if using an external-standard quantitation technique. If instrument shutdown happens in the middle of the batch, the TNI Standards in V1M2 Section 5.5.7 may require a CCV to be run to prove that the “overloaded and defective equipment” is still performing correctly. At a minimum, the laboratory would have to evaluate the effect of the instrument shutdown on samples analyzed prior to that time and implement its Control of Non-Conforming Environmental Testing Work procedures stipulated in V1M2 Section 4.9. Unless the samples analyzed prior to the shutdown are re-analyzed, there is a possibility that test results for these samples may need to be qualified, especially if the next CCV does not pass the acceptance criteria.

As another consideration (again assuming external-standard quantitation), theoretically, if the analytical batch is continuously running over a period of weeks and only one CCV was run at the beginning, test results for samples within that batch should not be reported to any clients until the weeks later, since the batch is still in progress and not yet concluded. If some samples were bracketed by a passing CCV within the batch, then it may be possible to report those test results as long as any LCS, method blank, matrix spikes, and matrix duplicates associated with the corresponding sample digestion, distillation, or extraction batches were also bracketed by that passing CCV.



References:

TNI 2009 V1M4-1.7.2.c.i

1.7.2 Continuing Calibration
c) Instrument calibration verification shall be performed:
i. at the beginning and end of each analytical batch. If an internal standard is used, only one verification needs to be performed at the beginning of the analytical batch;
ii. if the time period for calibration or the most recent calibration verification has expired;
or
iii. for analytical systems that contain a calibration verification requirement.

TNI 2009 V1M2 Section 5.5.7

5.5 Calibration Requirements
5.5.7 Equipment that has been subjected to overloading or mishandling, gives suspect results, or has been shown to be defective or outside specified limits, shall be taken out of service. It shall be isolated to prevent its use or clearly labelled or marked as being out of service until it has been repaired and shown by calibration or test to perform correctly. The laboratory shall examine the effect of the defect or departure from specified limits on previous tests and/or calibrations and shall institute the "Control of nonconforming work" procedure (see 4.9).