Modified Griess test

[schoemanje]

Hi fellow Examiners

I would like to know if any validation has been performed by anyone one the Modiefied Griess test, Lead detection through sodium rhodizonate and copper detection through dithiooxamide tests?

The reason why I ask:

What would / can happen if one uses to much or too less of the required chemicals when conducting these tests?

Is there really a nedd to validate these tests?

I thank you for your assistance.

Best of regards.

Johan Schoeman
Ballistics Section
Pretoria
South Africa

[Ryan Larrison]

Johan,

Our lab system does require validation studies for new methods.  For instance, I wanted the option to use Bob Shem's alternative Griess test using Marshall's reagent.  Our lab system's quality manual required our unit to first validate and verify this method in a controlled experiment--even though Mr. Shem has done an outstanding job with researching and standardizing this method, and even though it is used commonly in the field by other laboratories.

Our quality manual seems to have just recently changed to make validation an optional requirement provided that the method in question has already been standardized, scientifically verified, and an accepted practice elsewhere.

Your question as to what would happen if an insufficient amount of reagent/chemical was used in a given test is a valid one which could best be discovered by actually testing it out in your lab.  You'll also get the benefit of experience and being able to use this experience as extra qualification in court.  For example, during our validation study with Marshall's reagent, we found that, as one would expect, too little Marshall's reagent (either through dilution with excess acetic acid or insufficient amounts of reagent) negatively impacted the sensitivity of the test.  (e.g.-not following Bob Shem's "recipe" to a T).

I guess in the end, I think performing validation testing can't hurt you or your lab.

Moderator's Note:  Here's a link to the Simplified Griess and Sodium Rhodizonate Test:  http://www.bobshem.com/smf/index.php?topic=101.0