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This study has demonstrated the feasibility of determining erythrocyte protoporphyrin concentration by the direct fluorimetric measurement of diluted whole blood. Excitation and emission wavelengths can be chosen to minimize heme (or hemoglobin) interference. Although results obtained by this method and an extraction method differed, the discrepancies were approximately constant and largely explainable on a basis of fluorescence quenching by heme. Nevertheless, several kinds of pathologic blood specimens having elevated protoporphyrin concentrations were easily detectable. Perhaps more important from a diagnostic sense, the method can be used to quantify directly the [PROTO]/[heme] ratio. This new approach to blood porphyrin assay should find extensive application in such public health problems as lead intoxication and iron deficiency.

Absorption and emission spectra and emission quantum yields are given for free-base (H/sub 2/), Zn, Cu, and Pd derivatives of tetrakis(perfluorophenyl)porphyrin (TFPP). The four-orbital model is used to rationalize differences in the optical properties among the derivatives of TFPP and the same derivatives of porphine (P), octaethylporphyrin (OEP), and tetraphenylporphyrin (TPP). It is concluded from absorption data that the energy difference between the two excited singlets, i.e., /sup 1/E(a/sub 2u/,e/sug g/) - /sup 1/E(a/sub 1u/,e/sub g/), decreases along the series Pd > Cu > Zn > H/sub 2/ and also along the series OEP > P > TFPP > TPP. The theory and date are reviewed, and it is concluded that the energy difference between the two excited triplets, i.e., /sup 3/E(a/sub 2u/,e/sub g/) - /sup 3/E(a/sub 1u/,e/sub g/), also decreases along these series. However the condition of degeneracy, e.g., /sup 1/E(a/sub 2u/,e/sub g/) - /sup 1/E(a/sub 1u/,e/sub g/) = 0, occurs for different molecules in the singlet and triplet cases. Theory also suggests that if /sup 3/E(a/sub 2u/,e/sub g/) > /sup 3/E(a/sub 1u/,e/sub g), the molecule should form a /sup 2/A/sub 1u/ cation radical and if /sup 3/E(a/sub 2u/,e/sub g/) < /sup 3/E(a/sub 1u/,e/sub g/) the molecule should formmore » a /sup 2/A/sub 2u/ radical. 4 figures, 2 tables.« less