Inject blank in sequence.

[Alfred88]

Hi all:

Could you suggest the best approach to inject a blank (diluent) when you build a sequence of 2 or 3 standards (low conc, mid conc., and high conc), and sample extracts. The mid-conc. standard is the Continuing calibration verification (CCV), i.e. bracketing standard.
I saw a proposed sequence in a previous thread, with no blank injection.
viewtopic.php?t=7704

I am asking this, because some firms got cited for not injecting blanks between samples, to ensure there is no carry-over.

Also, anyone in pharma doing extra testing for each batch of samples, i.e. testing duplicate sample, spiked sample, control sample, sample blank. This extra testing is popular (required) in Environmental lab, because the results are not predictable. (BTW, we always do 2 injections for each sample, and run the bracketing standard between samples).

Thank you.

Alfred

[DR]

If your samples are so unpredictable, you should probably run a blank after each one, or at least each pair. If your method has been validated and shown no carry-over for standards, you should not need blanks. If you want some anyway, just do one after your initial set of standards.

Note - pharma background influenced opinions ^ Env. compendial requirements could be quite different...

[JGK]

I always included a carryover exercise as part of the method validatiom work removing the necessity of within run blanks.

[HW Mueller]

There is a new aspect of validation creeping up here which I never noticed or thought of before: You validate and then assume that this apparatus´performance will never change for all time??

[Alfred88]

Dear experts,
I am expecting a good advise from a "qualified person" with background in chromatography and regulatory affairs.

In the meantime, I am proposing this sequence. Please comment.

• Solvent blank
  solvent blank (optional)
  standard (1-5, or 1-6); this is the CCV (cont. calibration verification)
  standard (1), lower conc.
  standard (1), higher conc.
  CCV
  sample (1), may add duplicate
  CCV
  sample (1), duplicate
  CCV
  ---
  CCV
  solvent blank

Here is a justification for this sequence (QA plan for environ. samples):

One HPLC method blank before and after each sample batch

source: http://www.nwfsc.noaa.gov/assets/25/654 ... 7Final.pdf (see pp. 32)

Here is an extract from a latest FDA method for Melanine in formula:

The recommended sequence of injections is: solvent blank (Mobile Phase A), extracted matrix standards from 0.25 to 5 µg/g, solvent blank, control extracts, post-fortified extracts and solvent standards for calculation of recoveries and matrix effects, solvent blank, unknown samples, and continuous calibration standards (an extracted matrix standard as well as solvent standard at 7 ng/mL), to verify that instrument response was maintained during the run. For longer analysis runs, greater than ~10 hours, the calibration standards can be reanalyzed at the end.

Source: http://www.fda.gov/Food/ScienceResearch ... 071637.htm

Thank you for your comments
Alfred