Results from the first application FIFO–FlFFF (1
frit inlet/
frit outlet–
flow field-
flow fractionation) to the characterization of colored dissolved organic material (CDOM) in river and coastal waters are described. FlFFF separates compounds based on their diffusional characteristics. The
frit inlet/
frit outlet (FIFO) feature was recently developed to concentrate samples inside the FlFFF channel for improved stability, reproducibility and sensitivity. Our results show that FIFO increases sensitivity by an order of magnitude and the system has a linear response to molecular weight and concentration over a wide dynamic range. Errors for replicate analyses with a Caloosahatchee River sample from southwest Florida were <2.5 % for retention time and <4 % for peak areas, indicating good reproducibility and precision for the analysis of CDOM in natural water samples. However, recovery rates were low (35–65 % for fresh waters and 5.7–8.1 % for marine waters) and it will be necessary to test different membranes and lower molecular weight cut-off to improve recoveries in future studies. Molecular weights were calculated from the measured retention times and log-linear calibration curves generated with polystyrene sulfonate standards (1800–35,000Da). In river water,
98 % of CDOM occurred in a fraction centered around 2kDa and
2 % in a fraction with a maximum at 13kDa (based on maximum peak intensity for absorbance at 330nm and fluorescence at 350–450nm). This minor higher molecular weight fraction was completely gone in offshore coastal waters. This loss may be due to dilution of the river samples and/or biological and photochemical degradation of CDOM. Irradiating a river sample with sunlight produced a fractogram characteristic of marine waters, suggesting that photodegradation is an important mechanism in altering the molecular and optical characteristics of CDOM.
