Chlorophyll content (a and b) was determined spectrophotometrically at the maxi­mum absorption wavelengths for each chlorophyll. DR 5000 UV-vis spectropho­tometer from Hach, USA, was used for all analyses. The wavelength maxima, A, for chlorophyll a and chlorophyll b are, respectively, 664 and 647 nm in 90% ace­tone and 665 and 652 nm in 90% methanol. One milligram of either chlorophyll a or chlorophyll b standard was dissolved in either a mixture of acetone (45 mL) and water (5 mL) or a mixture of methanol (45 mL) and water (5 mL) to form stock solutions. All of the stock solutions were then diluted with their respective solvent mixtures (either 90% acetone or 90% methanol) to form standard solutions with five different concentrations (0.004, 0.008,0.0012, 0.0016, and 0.02 mg/mL). Calibration curves of each chlorophyll type in a particular solvent mixture were created by plot­ting the absorbance of its standard solutions (at the maxima of both chlorophyll a and chlorophyll b) against concentration. In accordance to Lambert-Beer law, specific absorbance coefficient, a (in mL/mg/cm), is the gradient of the linear por­tion of the calibration curve [26]. Table 5 summarizes the wavelength maximas,

Amax, and the specific absorbance coefficents, a, of chlorophyll a and chlorophyll b in 90% acetone and 90% methanol. Concentrations of chlorophyll a and chlorophyll b in a pigment extract containing both chlorophylls can be simultaneously deter­mined using an extension of Lambert-Beer law which takes into account the contri­bution of chlorophyll b absorbance to the absorbance of chlorophyll a at chlorophyll a maxima and vice versa. Principles of this extended theorem and the derivation of its formulae can viewed elsewhere [26]. Based on the a values obtained in Table 5, concentration of chlorophyll a, Ca (mg/mL), and concentration of chlrorophyll b, Cb (mg/mL), in the diluted extract sample are calculated as follows:

For extracts in 90% acetone and 10% water,

Ca = 0.00964A664 — 0.00175Аб47 (1)

Cb = 0.01487A647 — 0.00410A664 (2)

where A664 and A647 are the absorbances of the diluted extract sample at 664 and 647 nm respectively.

For extracts in 90% methanol and 10% water,

Ca = 0.02215A665 — 0.01252A652 (3)

Cb = 0.01978A652 -0.00894A665 (4)

Where A665 and A652 are the absorbances of the diluted extract sample at 665 and 652 nm respectively.

The concentrations of chlorophyll in the original extract sample were obtained by multiplying the concentrations of chlorophyll in the diluted extract sample with a dilution factor of 24. Chlorophyll a yield (g chlorophyll a/g dried microalgae) was the product of concentration of chlorophyll a in the original extract sample and volume of acetone or methanol used in extraction (100 mL). Chlorophyll b yield was calculated in a similar manner, while chlorophyll yield was the sum of chloro­phyll a and chlorophyll b yields.