A Simple Technique to Increase Sensitivity for Fluorometric Determination of Chlorophyll-a in Oligotrophic Environments

Adequate fluorometer sensitivity is critical when investigating small changes in pigment concentration in oligotrophic environments, where chlorophyll-a levels can be near zero. Given the paucity of published methods for increasing fluorometer sensitivity, we present a simple technique for adjusting the basic operating level (BOL) of a 10-AU fluorometer (Turner Designs) to maximize pigment detection. The modified BOL setting presented here increases the signal response factor one order of magnitude over the conventional BOL setting, allowing near-zero chl-a concentrations to be measured with greater resolution. A 2x5 factorial block experiment was used to compare the sensitivity of the modified and conventional BOL settings at five chl-a concentration levels, ranging from 0.364 to 0.023 µg/L. The minimum detection limit was determined for each setting, based on the ability of the fluorometer to distinguish each concentration level from both zero and the four other concentration levels tested. A detection limit of 0.364 µg/L for chl-a was achieved with the conventional BOL setting, while a much lower detection limit of 0.023 µg/L for chl-a was achieved with the increased sensitivity and resolution of the modified BOL setting.