| Summary: | 碩士 === 國立高雄海洋科技大學 === 海洋環境工程研究所 === 105 === Estuary zone is between freshwater and seawater. The disturbance of salinity gradient will make ionic strength of estuary water unstable. Therefore, the measurements of pH by the glass electrode will become unpredictable and get poor results. Thus, in this experiment we choose spectrophotometric method to measure the pH of waters. Theoretically, an acid–base indicator dye is added to the sample, and the absorbances of the acid and base forms of the indicator are measured and used to calculate pH precisely.
Revealing the historic data, the pH of estuary waters range from 9 to 5 in Taiwan. We need the multi-indicators to better pH estimate in estuary. Accordingly, three sulfonephthalein indicators m-Cresol Purple (m-CP)、Phenol red (PR) and Bromocresol Purple (BCP) were selected, because these indicators are highly reproducible and calibration-free. To the higher pH waters, PR and m-CP are better choices, the performance comparison between two indicators show a precision about 0.0146±0.011 in seawater and0.0140±0.008 in freshwater respectively. Comparatively, to the lower pH waters, both BCP and PR serve well, the performance comparison between two indicators show a precision about 0.0139±0.0004 in seawater and 0.0127±0.011 in freshwater respectively.
Finally, we conduct a test between a universal pH indicator and sulfonephthalein indicators, the results show a precision about 0.22 in seawater and freshwater.
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