New to this discussion group, but this may be of help.
We have been looking at a test for detecting materials of Forensic interest. The tests were to be printed on paper strips.
A proposed test which contained Ferric chloride was initially rejected as it was incredibly sensitive to lignin containing papers. Cotton linter papers (lignin free) show no reaction to the ferric chloride formulation.
We are looking at ways of quantifying this test, but it seems that even traces of lignin will produce a colour change.
As a colour test it is valuable to compare the paper to be tested against a cotton linter or lignin free paper (Such as a Whatman Filter). Familiarity with the colour change will not require this comparison on a routine basis.
This test will discolour the paper so may be regarded as destructive (but only 1mm diameter spot is required for detection) . If you are interested we can furnish you with details. We are working through papers with varying lignin concentrations to establish detection limits for lignin. But suffice to say that the test is extremely sensitive.
We can supply details (pre-publication) which would let you try it out.
Materials are all very inexpensive and more crucially safe.
Paul & Dymhna