Use of magnetic circular dichroism spectroscopy for biologic monitoring of occupational exposures to toxicants.

Zinc protoporphyrin is the predominent fluorescent porphyrin accumulating in erythrocytes as a result of chronic lead absorption or iron-deficiency anemia. Although diagnostic concentrations or thresholds for it in erythrocytes have been inferred, normal adult averages have not been established. We quantitatively assessed average zinc protoporphyrin values during an investigation into the usefulness of magnetic circular dichroism spectroscopy as an analytical technique for biologic monitoring of industrial toxicant exposures. Blood samples drawn from 55 employees not exposed to lead were analyzed for blood lead, hematocrit, and zinc protoporphyrin. Average concentrations of zinc protoporphyrin determined with a hematofluorometer were compared with results obtained by magnetic circular dichroism spectroscopy. The latter results were comparable in kind but superior in quality to those of fluorometry. The magnetized spectroscopy followed Beer's Law at concentrations well below indigenous concentrations and was more sensitive than difference spectroscopy. Spectroscopic resolution of heme and zinc protoporphyrin moieties in a pyridine/NaOH mixture was complete.