Frequently Asked Questions

Microplate Instrumentation

Question

What is the limit of detection of the Zenyth 200?

Answer

The limit of detection depends on the molar absorptivity of the sample at the measurement wavelength the volume of the sample. As an example, we have determined experimentally that for tartrazine (a yellow dye commonly used in food) that the limit of detection is 0.1 ng/µL at 472 nm in a 15 µL sample in a 384-well plate. The molar absorptivity of tartrazine at 472 nM is 20,330 L mol-1 cm-1. Absorbance measurements were obtained for more dilute solutions; however, the values were no longer in the linear range of the instrument (< +/- 0.7% and +/- 0.005 OD from 0.1 - 3.0 OD (400 - 750 nm).

The volume that can be measured in a 384-well plate is also dependent on a sample. In the example given above, the volume measured was 15 µL which was determined to be the smallest volume that could be measured accurately because of the plate type and solution. The volume used is dependent on the plate type and the composition of the solution because the solution should spread completely across the bottom of the well. If the plate used has a hydrophobic coating, then less volume might be used. Likewise, if the solution does not have a high surface tension, less volume can be used.


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