How to Check Algae Using a Spectrophotometer

Study algae up close with a spectrophotometer.
••• sea algae image by Svetlana Romanova from

A spectrophotometer is a tool used by scientists primarily in the fields of biology and chemistry to shine a beam of light through a sample and onto a light meter. The light beam can be filtered to a particular wavelength or narrow range of wavelengths. Since different types of algae grow at different depths in the ocean and fresh water bodies, scientists can check the algae's health and constitution by shining various wavelengths of light through algae samples with a spectrophotometer.

    Consider using a testing kit such as the Algaltoxkit F, which contains all the materials, including test specimen, needed to perform a test on algae samples with a spectrophotometer. Fill a 1 liter volumetric flask with 800 ml of deionized water and add nutrient stock from your test kit until 1,000 ml is reached. Cover and shake the vial to thoroughly mix the culturing medium in the vial.

    Empty the liquid from a glass tube containing algal beads (included in the test kit) and add 5 ml of the culturing medium you just made. Vigorously shake the glass tube by hand every two minutes until it's mixed or cap the tube and place it in a vortex shaker to speed up the process.

    Place the tube in a centrifuge for 10 minutes at 3,000 rotations per minute (rpm). Pour out the supernatant liquid at the top of the tube and add 10 ml of deionized water to the tube. Recap and place in the centrifuge again for another 10 minutes at 3,000 rpm. Pour off the supernatant again and add 10 ml cultural medium. Shake vigorously by hand for one minute.

    Pour the glass tube contents into a 25 ml calibrated flask and add culturing medium until the contents reach the 25 ml mark. Cap the flask and shake it by hand for one minute to mix the contents together. Pour 25 ml of the solution into an algal stock cell (included with the kit). Pour 25 ml of cultural medium into a calibration cell (included with the kit).

    Measure the optical density (OD) of the calibration cell by placing it beneath the spectrophotometer. The OD should measure 670 nano meters (nm). Turn the algal cell upside down and shake it gently for 10 seconds. Check the algae sample’s optical density by viewing the algal cell beneath the spectrophotometer and measuring the algal cell’s OD.

    Things You'll Need

    • Spectrophotometer
    • Algae specimen or test kit
    • Flasks
    • Glass tube
    • Deionized water
    • Centrifuge

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