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What Chlorophyll is and How to Measure it in Water

Chlorophyll is the green pigment found in plants, and it’s vital for photosynthesis. Measuring the chlorophyll concentration in water is important to estimate the abundance of phytoplankton. If a high level of chlorophyll is detected, it is an indication that a high level of phytoplankton is present in the water.

Aquaread Chlorophyll Sensor

Aquaread’s chlorophyll sensor is constructed from dense ABS/POM plastics and aluminium. It features robust sapphire lenses for the highest optical performance and scratch resistance.

It is a fixed response fluorometer, meaning it excites the chlorophyll in the water at a fixed wavelength (470nm) and then measures the subsequent emitted fluorescence (>630nm).

Chlorophyll

Key Features

  • Dense sapphire lenses are used on our chlorophyll sensor for their high clarity and scratch resistance.
  • Measurement range: 0 - 500µg/l.
  • Resolution: 0.01µg/l.
  • Accuracy: +/- 2% of reading.
  • Simple to install on a wide range of Aquaprobes.
  • Easy 2-point calibration using rhodamine dye.
  • Site specific calibration with grab sample calibration option.

Our Chlorophyll sensors can be installed into many of our probes, below are some examples. To see all of the probes that can house the chlorophyll sensor please visit the Products section.

AP-5000

AP-5000

Advanced portable multi-parameter Aquaprobe.

AP-LITE

AP-LITE

Single parameter Aquaprobe, for use with any of our sensors.

AP-7000

AP-7000

Long-term deployment multi-parameter Aquaprobe.

Simple installation

Installing the Chlorophyll sensor into an Aquaprobe is a straightforward process. First, unscrew the blanking plug from an appropriate aux socket. Then apply some of the provided silicon grease to the sensor thread and screw in the sensor. After installation, full calibration is required.

Simple calibration

Part of our ethos at Aquaread is “ease of use”, which is why we have simplified and automated the calibration process as much as possible. The chlorophyll sensor is calibrated at 2 points. A zero point and a 500µg/l rhodamine dye point. A stock solution of rhodamine dye is provided, and a small dilution of the stock is required to make the 500µg/l solution.

Once your solution is made, the calibration involves placing the probe into the solution and selecting the correct calibration option from the menu. A calibration report is saved when complete.

Grab sample factor

There can sometimes be a difference between measured values with the sensor and laboratory data when taking measurements at a particular site. These differences are caused by a number of factors.

It is possible to apply a multiplier to the data obtained from our sensor in order to make it better correlate with lab data for that particular site. To do this, we use a grab sample factor. We can calculate this factor by dividing the average grab sample value (measured in the lab) by the average value measured by our chlorophyll sensor.

This is a great addition to the software when trying to correlate new data with historic readings from the same site.

Limitations

Trying to accurately determine the number of cells present using fluorometric sensors is an indirect method of counting, thus not as accurate as direct cell counts that can be performed in a laboratory setting. Various external factors can affect the readings, for example, other microbiological species and compounds that fluoresce at similar wavelengths, differences in the fluorescent response between various species of phytoplankton, temperature, ambient light, and turbidity.

For these reasons, chlorophyll measurement taken directly in the field is intended for qualitative data collection over time to monitor changes in trend, not quantitative analysis.