比色法的科學原理是什麼?What is the scientific principle of colorimetry?

Document ID :TE1598
Published Date : 08/04/2021
Source : Hach-UK

What is the scientific principle of colorimetry?

Colorimetry: Beer-Lambert Law

Colorimetric reactions can be measured on either a spectrophotometer or a colorimeter. Both of these instruments measure the intensity of light passing through the colored sample and convert this light intensity to a concentration based on a stored calibration curve. The instruments follow the principles of the Beer-Lambert Law. The Beer-Lambert law (referred to as Beer’s law) is the linear relationship between absorbance and concentration. 比色反應可藉由分光光度計或比色計測量。 這兩種儀器都測量穿過有色樣品的光強度,並根據儲存的校正曲線將此光強度轉換為濃度。 這些儀器遵循 Beer-Lambert 定律的原則。 Beer-Lambert 定律(比爾定律,又稱作比爾-朗伯定律)是吸光度與濃度的線性關係。

Generally Beer’s law is written as:
A = Ɛ x b x c
A is the measured absorbance
Ɛ is a wavelength-dependent absorptivity coefficient
b is the cell-path length
c is the analyte concentration
There is also a known relationship between absorbance and transmittance where:
A = -log T
A is absorbance
T is transmittance
Transmittance is defined as:
T = I / I0
I is the light intensity after it passes through the sample
I0 is the initial light intensity.
Combining the two equations above:
A = -log( I / I0 )

Instruments use the above equation to calculate the absorbance and display concentration based on the stored calibration curve. In short, the colorimetry reading is the light absorbed when passing through the sample.  儀器使用上述公式根據儲存的校正曲線計算吸光度和顯示濃度。 簡單來說,比色讀值是通過水樣時吸收的光。

In a spectrophotometer a lamp produces a spectrum of light and a single wavelength of light is selected using a monochromator (prism or diffraction grating) and a colored filter. The specific wavelength of light is focused through a lens and directed through the sample. The detector measures the amount of light absorbed (or transmitted) by the sample.  在分光光度計中,燈產生光譜,並使用單色器(棱鏡或繞射光柵)和彩色濾光片選擇單一波長的光。 特定波長的光通過透鏡聚焦並穿過水樣。 檢測器測量水樣吸收(或透射)的光量。

A basic colorimeter has a light emitting diode (LED) instead of a white light lamp and does not utilize a diffraction grating. A colorimeter is limited to performing analysis on parameters that fall within the wavelength of the individual filter, while spectrophotometers can analyze samples is a broad range of wavelengths determined by the diffraction grating.  基本的比色計使用發光二極管 (LED) 代替白光燈,並且不使用繞射光柵。 比色計僅限於對單個濾光片波長範圍內的參數進行分析,而分光光度計則可以分析由繞射光柵測定的寬廣波長範圍內的水樣。
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