吸光度(absorbance)和透射率(transmittance)的區別

吸光率和透射率是兩個相關的，但在光譜分析中使用的量不同。吸光率和透射率之間的主要區別在於，吸光率測量入射光在材料中傳播時被吸收的程度，而透射率測量光被透射的程度。由於它們的定義方式，這兩個量不是互補的：也就是說，直接將透射率與吸光度相加並不能得到總的入射光。...

主要區別-吸光度與透射率

吸光率和透射率是兩個相關的，但在光譜分析中使用的量不同。吸光率和透射率之間的主要區別在於，吸光率測量入射光在材料中傳播時被吸收的程度，而透射率測量光被透射的程度。由於它們的定義方式，這兩個量不是互補的：也就是說，直接將透射率與吸光度相加並不能得到總的入射光。

當光透過一種材料時，它被材料中的分子吸收。因此，當光透過材料時，光的強度隨距離呈指數下降。透過測量入射光和透射光的強度，可以很容易地測量樣品溶液的透射率。利用透射率值，就可以計算樣品的吸光度。

什麼是透射率(tran**ittance)？

Tran**ittance ( ) is a measurement of how much light passes through a substance. The higher the amount of light that passes through, the larger the tran**ittance. Tran**ittance is defined as the ratio of the intensity of incident light: intensity of tran**itted light i.e. if the intensity of incident light is and the intensity of tran**itted light is , then

At times, this fraction may be represented as a percentage, where it is called the percentage tran**ittance ().

什麼是吸光度(absorbance)？

Absorbance () is defined as:

因此，還可以根據透射率百分比給出吸光度：

According to Beer-Lambert law, the absorbance of light, as it passes through a solution, is directly proportional to the path length of light through the material ( ) and the concentration ( ). So, we can write,

where is a c***tant called the molar absorptivity. This c***tant has a specific value for a given substance, provided the temperature of the substance and the wavelength of light passed through it are kept unchanged.

這是一個非常有用的關係，它允許透過測量樣品的光吸收率來發現未知溶液的濃度。

如果我們**一個溶液，讓光透過它，並繪製出當我們改變溶液的濃度時透射率是如何變化的（同時保持光透過的路徑長度不變），我們得到了透射率和濃度之間的指數關係：

Tran**ittance vs. Concentration

但是，如果我們計算相應的吸光度值，然後繪製吸光度與濃度的關係圖，我們將得到一條透過原點的直線，如比爾-朗伯定律所預測的：

Absorbance vs. Concentration

If the gradient of this graph is , then from Beer-Lambert law we have,

Then we can calculate the value of using the length through which light has travelled.

Once we have calculated , we can use it to measure concentrati*** of unknown soluti*** of the substance using the same setup (i.e., maintaining temperature, the wavelength of light and the path length of light the same).

在實驗室裡，分光光度計可以用來測量樣品對光的吸收率。