Volume 17, Number 2
Sep 1993

That New Spot Test for Lignin is too Hazardous to Use, After All

Back to Phloroglucinol

A technical note in the last issue of this Newsletter reported a comparative test of two indicators for lignin in paper, carried out in the lab of the National Library of Australia. The indicators tested were phloroglucinol and aniline sulfate. They were found to be about equally accurate, but the aniline sulfate was recommended because it was cheaper. At the time of the original publication, the safety aspects of aniline sulfate were not investigated. Now it seems clear that it should not be recommended at all for use in preservation work.

Aniline sulfate readily dissociates in water into aniline and sulfuric acid. The American Conference of Governmental Industrial Hygienists (ACGIH) currently assigns a TLV (threshold limit value, the maximum safe exposure in an industrial setting) of 2 parts per million (ppm), and notes that skin absorption can be a significant source of exposure.

NIOSH's 1992 Occupational Safety and Health Guideline for Aniline says NIOSH has recommended that aniline be designated a potential occupational carcinogen and that exposure be limited to the lowest feasible concentration; contact with the worker's skin should be minimized. It says it causes the formation of methemoglobin, which results in a functional anemia that interferes with the ability of the blood to carry oxygen. Aniline, it says, is particularly dangerous because of the ease with which this substance is absorbed by the body after inhalation of the vapors or after contact of the skin with either the vapors or the liquid. Studies of chronic exposure to low concentrations connect it with anemia, digestive disturbances, lack of energy, and head-ache. To put the TLV into perspective, even carbon tetra-chloride has a higher TLV (5 ppm), indicating that it is less toxic than aniline.

The formula is (C₆H₇NH₂)₂.H₂SO₄, which is two aniline molecules bound weakly to sulfuric acid. The CAS number is 542-16-5. It comes in crystalline form. Brief instructions for use are in Chapter 10 of the Paper Conservation Catalog ("Spot Tests"), available from the American Institute for Conservation; directions for preparation and use are in Section F.1.3 in TAPPI T 401. Neither set of instructions includes safety precautions.