204 LIGHT AND LIFE 



yield oi luminol in aqueous solution was measured in bicarbonate 

 buffer at pH 9.6, in 0.001 A^ NaOH (pH 11), 0.01 N NaOH (pH 12) , 

 0.1 N NaOH (pH 13), 1 A^ NaOH (pH 14), and 10 A^ NaOH. 

 These results are shown in Table 1. 



TABLE 1 

 Chemiluminescence Quantum Yield of Luminol for Various />H V^^LUES 



Chemiluminescence 

 Solution /»H Quantum Yield 



Bicarbonate Buffer 

 .001 A' NaOH 

 .01 A^NaOH 

 .1 A^NaOH 

 1 iVNaOH 

 10 iVNaOH 



Conclusions 



The data of Table 1 are significant in two respects. Firstly, they 

 indicate that with properly purified material and other proper ex- 

 perimental conditions a minimum of one light quantum is emitted 

 per approximately 50 luminol molecules oxidized, a much higher 

 efficiency than has been reported previously (2) . Secondly, the rapid 

 decrease in the chemiluminescence quantum yield with increasing 

 pH roughly parallels the decrease in the fluorescence quantum yield 

 of antinophthalic acid, as shown in Fig. 3. This, together with the 

 lack of concentration dependence of the chemiluminescence quantum 

 yield, the fact that aminophthalic acid is fluorescent in alkaline pH 

 whereas luminol is not, and the correspondence of the fluorescence 

 emission spectrum of aminophthalic acid with the chemiluminescence 

 emission spectrum of luminol would favor the former as the emitting 

 species over the neutral hmiinol molecide. It would be extremely 

 valuable to be able to correlate the chemical yield of aminophthalic 

 acid with the chemiluminescence quantinu yield. However, owing 

 to the low quantum yields observed in aqueous solution and also 

 owing to the possibility of finthcr dark reactions caused by the strong 

 oxidants used to initiate the chemiluminescence, the unambiguous 

 identification ol the excited oxidation product as the light-emitting 

 species cannot be made at this time, although it is strongly indicated. 



White (7) has loinul that the chemiluminescence of luminol in 

 organic solvents such as dimethyl sulfoxide appears to be even more 

 efficient. The emission spectrinn of this chemihnninescence is shifted, 

 peaking around IHO u\,,,. I*reliminary measurements of the chemi- 



