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The main objectives of this research were to examine the effects of colloidal and particulatematter in fresh waters on dissolved organic carbon (DOC) and UVsub254/sub determinations, and to develop some guidelines for filteringfreshwater samples having widely varying turbidities. Over ninety percent of the organic matter in thenatural waters tested in this study was in the dissolved form and filter cake formation did not have asignificant impact on the DOC values of a sample. The experimental results showed that the level andcharacteristics of turbidity in a water sample, as well as the nature of pore structures and pore sizedistributions of a membrane filter selected for filtration play important roles in UVsub254/sub and SUVAsub254/subdeterminations. Measuring turbidity in the filtrate of a sample is a simple way to validate the UVsub254/sub, andthus SUVAsub254/sub, results. The results indicated that when filtrate turbidities were below 0.3 NTU, nosignificant impact of filtration volume, filter cake formation, and separation (or pretreatment) processesoccurred on DOC and UVsub254/sub determinations, and thus calculated SUVAsub254/sub values. However, when filtrateturbidities were higher than 0.5 NTU, UVsub254/sub results were affected by residual turbidity values, which alsoadversely impacted calculated SUVAsub254/sub values. These findings suggest that a conservative criterion forthe turbidity of a filtered UVsub254/sub sample, such as less than 0.3 NTU, can be adopted to minimizeinterferences on the results. Selection of small pore size filters (e.g., 0.2- or 0.1-m) and pretreatment ofsamples (e.g., prefiltration, settling) may be used to alleviate the problems caused by colloidal materials ina sample. It was also found that a minimum of 25-mL filter-to-waste volume (i.e., for hydrophilicpolyethersulfone filters or hydrophilic polypropylene filters of 47-mm disc size) would be applicable forvarious natural water samples with varying degree of turbidities prior to collecting samples for DOC andUVsub254/sub determinations. Includes 11 references, tables, figures.

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Edition: Vol. - No. Published: 11/15/2004 Number of Pages: 21File Size: 1 file , 2.7 MB