Elemental mercury is formed in aqueous solution by the chemical reduction of mercuric ion in the presence of humic acid. The reduction proceeds via first order kinetics (rate constant, 0.009 hour-(1)) and is depndent on pH. The reaction mechanism involves interaction of the ionic metal species with the free radical electrons of the humic acid.

We evaluated the suitability of N,N-dimethylformamide (DMF) for extraction and measurement of chlorophyll in phytoplankton and compared the extraction efficiencies of DMF, dimethyl sulfoxide (DMSO)–acetone, and 90% acetone. Absorbance spectra and specific absorption coefficients of chlorophylls a, b, and c in DMF and 90% acetone are similar. Acidification of 100% DMF extracts of pure chlorophyll a and healthy algal cultures produced acid ratios approximating 1.7. Thus, equations derived from the extinction coefficients of chlorophylls in 90% acetone can be applied to DMF extracts. DMF and DMSO–acetone each extract chlorophyll from green and blue-green algae more effectively than does 90% acetone. DMF is a better extractant than is DMSO–acetone for chlorococcalean species, especially when pigment concentrations are high, but the difference, although significant, is slight. The three solvents are equally efficient in extracting chlorophyll from samples composed of chrysophytes and flagellated chlorophytes. The lack of grinding when using either DMF or DMSO–acetone is a considerable convenience. The potential for destabilized spectrophotometer readings and contamination of the investigator due to the incomplete mixing of DMSO and acetone is eliminated when pure DMF is used.

No abstract

No abstract

No abstract