快速量測水體葉綠素a簡易儀器之設計與研究

水體優養化跟藻類多寡有很大關係，是因為水中營養物過多將導致藻類大量繁殖，而過多的藻類，相對會影響透明度變低，也正因為所有藻類皆含有葉綠素a(Chl-a)，所以葉綠素a濃度常被做為優養化程度高低的指標。而現今分析Chl-a濃度是到現地採取水樣後，帶回實驗室用環保署公布的水中Chl-a檢測方法－丙酮萃取法所分析出，這不但費時還費力，所以為了減少時間，有些會購買市面上量測Chl-a的分析儀器直接在現場量測，但市售的儀器單價較高在50,000～100,000不等，所以成本較高，故本研究想製作一個簡易儀器量測Chl-a濃度，不僅能降低分析所耗費的時間也能壓低成本，還能快速得到量測結果。所以先用光譜儀量測含有Chl-a的水樣後，發現在波段550~590nm、660~690nm、700~780nm的變化比較高，且在波段660~690nm會產生特有的光譜特徵，所以找出該波段的LED與PD製作成簡易儀器。本研究還根據LED與PD擺放位置的不同，分成穿透式、散射式及反射式三種量測法，再搭配不同的LED(綠光、黃光、紅光、近紅外光)，並用不同比例的Chl-a水樣相互做測試，最後是以穿透式量測法也就是LED在PD對面的擺放方式，以及波段650～710nm的紅光LED，來做最佳儀器設置，迴歸公式為 y=-24838x_T+11454，R²=0.93，建模平均誤差為20%，驗證平均誤差為13%。

關鍵字

光譜儀；葉綠素a ；發光二極體；光電二極體

並列摘要

The eutrophication has a lot to do with the amount of algae, because too much nutrients in the water is equals to algae proliferation, and too much algae will affect the transparency (SD) become low, and it is precisely because all algae contain chlorophyll-a (Chl-a), the concentration of chl-a is often used as an indicator of the degree of eutrophication. However, the current analysis of chl-a concentration is to take a water sample on site and bring it back to the laboratory to analyze it with the acetone extraction method, the chl-a detection method by the Environmental Protection Administration(EPA). This is not only time-consuming but also laborious, so in order to reduce time, someone will purchase a commercially available analytical instrument to measure chl-a and directly measurement it on site, but the unit price of the commercially available instrument ranges from 50,000 to 100,000, so the cost is too high. This research wants to make a simple instrument to measure chl-a, not only can reduce the time spent in analysis, but also reduce the cost, and can also immediately known measurement result. The first use a spectrometer to find the water sample containing chl-a. In the wavelength bands 550~590nm, 660~690nm, 700~780nm, the changes are relatively high, and in the wavelength band 660~690nm will produce unique spectral characteristics, so find out the combination of LED and PD in this light band to make the instrument. According to the different placement of LEDs and PDs, this study is divided into three measurement methods: transmission, scattering, reflecting, then match different LEDs (green, yellow, red, near-infrared), and use different proportions of chl-a water samples to test each other, and finally use the transmission measurement method, in other words, the LED is opposite the PD. To set the best instrument setting, the regression formula is y = -24838x_T + 11454, R²=0.93, the average modeling error is 20%, and the average verification error is 13%.