Turner fluorometer calibration

Chlorophyll concentrations were estimated from 40 ml subsamples following Suzuki and Ishimaru (1990). Samples were filtered on Whatman GF/F glass-fibre filters (pore size 0.45 pm). Chlorophyllous pigments were extracted by direct immersion of the filters in 5 ml of N,N-dimethylformamide, and actual extractions were made in the dark at 20°C. Concentrations of chlorophyll a in the extracts were determined following Strickland and Parsons (1972) using a Turner 450 fluorometer previously calibrated with chlorophyll a extracted from Anacystis nidulans (Sigma Chemicals, St Louis). 

Each sample to be analyzed was dissolved in tris(ethylenediamine)cadmium dihydroxide (1 mL) by stirring overnight, and then water (1 mL) was added. A 1-mL aliquot (concentration < 1.0%) was applied to the column, and elution proceeded with a pressure head of 100 cm and flow rate of 10 mL/h. A Turner 111 fluorometer (excitation filter 2A plus 47B and emission filter 8 plus 65A) fitted with a flow-through door allowed for automatic continuous monitoring of carbohydrates as they were eluted. Relative fluorescence was automatically recorded on a linear strip recorder. Fractions of 3 mL were collected on a FC-80K Gilson microfractionator. Typically, each sample was analyzed several times, usually at different concentrations, to ensure the reproducibility and accuracy of the data. A calibration run using the labeled dextrans was performed a minimum of one time per week. 

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