FAQ bbe AlgaeLabAnalyser

Yes. The test cuvette must be calibrated to the specific AlgaeLabAnalyser (ALA) with which it will be used. Therefore, it is recommended to purchase the test cuvette together with a new ALA or after the ALA has been serviced. The test procedure compares the readings stored in the cuvette with the current measurement of the ALA. If the cuvette was calibrated to an older state of the ALA, the test cannot reliably determine the actual current condition of the instrument.

For this reason, the test cuvette should always be calibrated to the current state of the ALA.

No. Photosynthetic activity measurement is not a software-only upgrade.

The activity measurement requires additional hardware, including a laser diode and an additional excitation board. Only the calculation and evaluation of the measurements are performed by the software. Therefore, the required hardware must be installed in the instrument for photosynthetic activity measurements to be possible.

No. A dedicated software package for toxicity testing with the cuvette fluorometer is currently not available.

The measurement data can be exported to Microsoft Excel. By connecting the cuvette instrument to a PC, the data can be transferred to Excel, where different sample activities can be compared and statistical evaluations can be performed, as described in the brochure. The enhanced activity measurement is also not a software-only feature. Therefore, toxicity evaluation can be performed by analysing and comparing the exported measurement data, but there is currently no dedicated toxicity-testing software for the cuvette fluorometer.

Yes. The algae used for the toxicity tests is Chlorella vulgaris, the same algae used for the Algae-Toximeter.

The photosynthetic activity measurement can be used to assess the activity of the algae present and, indirectly, their potential contribution to oxygen production. However, the measurement does not represent the total oxygen concentration or oxygen availability in the upper water layer, as oxygen can also originate from other sources. The activity of the existing algae can be measured provided that the algae concentration is sufficiently high. A minimum concentration of approximately 3 µg/L chlorophyll is required for a reliable activity measurement. Below this concentration, activity measurements are not performed in order to avoid excessive measurement noise.

No. The AlgaeLabAnalyser (ALA) measures the concentration of cyanobacteria in the sample, but it cannot determine the concentration of cyanotoxins. A cyanobacteria concentration can potentially be used as an indicator or warning threshold. For example, a limit value for cyanobacteria concentration could be defined to alert the operator when the concentration exceeds a specified level. However, the ALA does not directly measure or quantify cyanotoxins.

No sample preparation is required. Samples can be measured directly with the Cuvette Fluorometer. However, the sample should not contain excessive amounts of humic substances or other strongly coloured yellow substances, as these can interfere with chlorophyll fluorescence and may lead to deviations in the chlorophyll determination.

The Cuvette Fluorometer have an automatic correction for yellow substances. If necessary, their influence can be compensated for by performing a new offset calibration too. In most cases, the resulting offset can then be used for subsequent measurements.

For samples from sludge or wastewater lagoons, particularly high levels of suspended solids or coloured degradation products may therefore affect the measurement accuracy.

The maximum recommended turbidity is approximately 150 FTU (Formazin Turbidity Units), the ISO-standard unit for turbidity measurement. The AlgaeLabAnalyser (ALA) measures turbidity for each LED using transmission measurements. The measured transmission values are then used to correct both the offset and the raw fluorescence data. This correction compensates for the influence of turbidity on the fluorescence measurement.

No. The AlgaeLabAnalyser cannot distinguish between living and dead algae based on its measurement. However, the ALA primarily detects living algal cells, because the chlorophyll-a fluorescence signal is rapidly lost or degraded after cell death. Therefore, dead algae contribute little or no measurable chlorophyll-a signal.

For a reliable spectral fingerprint calibration using the “Sp. Fingerprints” option, the recommended chlorophyll concentration is approximately 50–100 µg/L.

The chlorophyll concentration used for the fingerprint calibration should be determined using an independent reference method. It should not be determined using the same ALA for the purpose of calibrating the fingerprint. For our laboratory instrument, we recommend using the HPLC method to determine the reference chlorophyll concentration.

The Cuvette Instrument itself must not be used to determine the reference concentration for its own fingerprint calibration, as this would not provide an independent reference value.

Photosynthetic activity is calculated using the Genty parameter, which describes the photosynthetic efficiency of Photosystem II (PSII) after dark adaptation. The Genty parameter is calculated from the minimum and maximum fluorescence:

Genty = (Fm − F₀) / Fm × 100 [%]

The two fluorescence values are measured under different light conditions:

• F₀ (minimum fluorescence): measured at very low light intensity.
• Fm (maximum fluorescence): measured under high-intensity light.

A laser diode is used to excite the algae and induce maximum fluorescence (Fm).

The Genty parameter provides an indication of the photosynthetic efficiency and physiological condition of the algae. In general, a higher value indicates a healthier and more active photosynthetic system, while a value close to zero indicates strongly impaired photosynthetic activity or dead cells, even if a high fluorescence signal is still present. Environmental stressors such as heavy metals and herbicides can strongly affect the Genty value.

The Genty parameter is related to oxygen evolution and therefore to the electron transport rate (ETR). ETR describes the transfer of energy through the photosynthetic electron transport chain and links light absorption to the production of chemically stored energy. Typical activity values can vary considerably depending on the algae and measurement conditions. As general reference values:

• Green algae: approximately 60%
• Blue-green algae (cyanobacteria): approximately 50% or lower
• Diatoms and cryptophytes: approximately 30%, with considerable variation

Yes. Nusch described a correlation between chlorophyll-a concentration and algal cell numbers. In his work, chlorophyll-a was determined using an absorption-based method, and a correlation between chlorophyll-a concentration and fluorescence measurements was also demonstrated.

However, it is not generally advisable to estimate algal cell numbers from chlorophyll-a concentration alone, particularly in water samples containing different algae species.

The main reason is that algae can differ considerably in cell size and chlorophyll content. Therefore, the same chlorophyll-a concentration can correspond to very different cell numbers depending on the species or composition of the sample. Consequently, the correlation between chlorophyll-a concentration and cell count should be considered species- and sample-dependent rather than as a universal conversion.

The following components may require maintenance or replacement over time:

• Glass cuvette
• Magnetic stirrer
• Mains cable
• RS232 / USB cable
• Software updates – provided free of charge

Yes. A dedicated test cuvette is available for checking the performance of the instrument. The test cuvette can be used to verify whether the standard instrument settings are still within the expected range and to check whether the LEDs and photomultipliers are functioning correctly.