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274 REES AND ANDERSON September
Am = 0.071CElon + 0.082Chydroquinone .4290 = 0.010CElon + 0.226Chydroquinone.
The transformation of these equations is straightforward and yields the following equations:
CEIOD = 14.84^270 5.39^290 (2)
Chydroquinone = 4.66^290 ~ 0.66^270 (3)
It must be remembered that (2) and (3) are general equations. Any absorbancy correction due to the blank must be subtracted before the concentrations of Elon and hydroquinone are calculated.
PREPARATION AND USE OF CALIBRATION GRID
Choose the lowest combination of Elon and hydroquinone expected (such as point A in Fig. 2 where concentration of Elon is 2.00 grams per liter and concentration of hydroquinone is 1.00 gram per liter) and calculate the total absorbancy at each wavelength as follows using (1).
At 270 millimicrons:
Absorbancy of Elon = as3C = 0.071X2.00 = 0.142
Absorbancy of hydroquinone = as4C = 0 . 082 X 1 . 00 = 0.082
Total absorbancy at 270 millimicrons = 0 . 224 At 290 millimicrons:
Absorbancy of Elon = asiC = 0.010 X 2.00 = 0.020
Absorbancy of hydroquinone = a^C = 0.226 X 1.00 = 0.226
Total absorbancy at 290 millimicrons = 0.246
Plot the two total absorbancies (as point A in Fig. 2) which represent an Elon concentration of 2.00 grams per liter and a hydroquinone concentration of 1.00 gram per liter. Compute Points B, C, and D in a similar manner. Draw lines through these four points which represent the outer limits of the grid. To complete the grid, subdivide each side of the parallelogram into the number of parts represented by the range in concentration. Increments of 0.1 gram have been found practical.
It is thus possible to determine the concentration of both Elon and hydroquinone simultaneously when the absorbancy of a sample at each wavelength is known.
For example : Assume that the following absorbancies (each corrected by subtracting the absorbancy of the basic mix) were obtained during an analysis of a developer ; the absorbancy at 270 millimicrons was 0.280, and at 290 millimicrons was 0.360.