If they differ by more than 5 units, check a third time. Sample readings may drop if the tubes contained any residual acid and they may increase if solids settle out of suspension. Record all readings, gain and emissions window in chlorophyll book. Initial the page to identify the operator. 5. If samples read over 1000 on the 1x gain they should be diluted and reread.
Chlorophyll fluorescence can quench at high concentrations.
The dilution prepipette and 1 ml pipette are in the chlorophyll room. Rinse out all tubes 2X and drain upside down for the next user. If the tubes are dirty, wash in soap and water, rinse and dry. On the LTER project we use a fluorometric technique to measure chlorophyll concentration. The fluorometer is able to measure much lower concentrations than the alternative technique using the spectrophotometer.