CHLOROPHYLLS a AND 6 607 



Table 21.1 — Continued 

 Chlorophyll b in ethj'l ether 



Observers (643 m/i) (453 m>i) (510 m^) 



Sprecher von Bernegg et al. 



(1935) 4.7 9.4 0.28 2.0 17 



Hagenbache^aZ. (1936).. 7.10 20.9 0.34 2.91 21 



Mackinney (1940) 5.00 13.6 0.26 2.72 19 



Zscheile and Comar (1941) 5.15 15.5 0.24 3.01 21 



Zscheile, Comar and Mac- 

 kinney (1942)^ 4.80 12.9 0.24 2.65 20 



Same'' 4.98 13.9 0.24 2.79 21 



Harris a nd Zscheile (1943) -- — — 2.98 — 



" Band "axes" — i. e., arithmetic means of the wave lengths of the hmits of blacken- 

 ing on a photographic plate (all other data in this table were obtained by photoelectric 

 photometry) . 



'' Zscheile and Comar's moist preparation measured by Mackinney. 



" Mackinney's dry preparation measured by Zscheile and Comar. 



<* Mackinney's dry preparation measured by Mackinney. 



The reproducibility of the red band encourages its use for the spectrophotometric 

 assay of the two chlorophylls. This method was developed by Ghosh and Sen-Gupta 

 (1931), Zscheile (1934, 1935), Sprecher von Bernegg, Heierle and Almasy (1935), Haskin 

 (1942), Comar and Zscheile (1942), Comar (1942) and Comar, Benne and Buteyn 

 (1943). Measurements at two different wave lengths are required to calculate the 

 concentrations of the two components. The use of the absorption maxima at 642.5 

 and 660 mix permits the most sensitive determination, but requires precise work, since 

 the extinction values in the sharp absorption peaks are very sensitive to variations in 

 the width of the spectrometer slit or to sUght errors in the adjustment of the monochro- 

 mator. Cross-checks at other wave lengths are therefore desirable. All errors could be 

 eliminated by the use of monochromatic Ught; but the spectrum of the mercury arc — 

 the usual source of monochromatic light in the laboratory — does not contain suitable 

 Unes in the red and orange regions. 



As pointed out once before, particularly wide discrepancies can be 

 noted between the different extinction curves in the blue-violet region {cf. 

 Table 21. IB). It was noted by Albers (1941) that the subsidiary violet 

 band (situated, in ethereal solution, at 410 mju in chlorophyll a and 430 

 m/i in chlorophyll b) sometimes appears as a slight hump on the main 

 band, and sometimes as a separate peak, almost as prominent as the main 

 one. The observed variations in the maximum height of the violet peak 

 may be caused by the more or less complete separation of this doublet 

 structure. 



Differences of this type cannot be attributed to the presence of caro- 

 tenoids, or other impurities. A renewed photometric study of this spectral 

 region is desirable. If the deviations will not disappear upon further puri- 

 fication of the material and improvement of the photoelectric methods, one 

 may have to consider, as a possible explanation, the existence of tautomers. 



