用于样品分析的光谱法：技术概述

Several options exist for determining the composition, concentration, and purity of a laboratory sample. Among the most commonly used techniques are Ultraviolet/Visible (UV/Vis), Infrared (IR), and Atomic Absorption Spectrometry. Each technique is capable of providing some or all of these pieces of information you need. In addition, each of these instruments is capable of interrogated different types of samples, including air, industrial chemicals, biological fluids and foods. Therefore, selection of an appropriate technique for analysis of your sample is essential in obtaining the desired data.

UV/VIS光谱仪

Several types of UV/Vis spectrophotometers exist, however they all operate on the same basic principle. In short, discrete bandwidths of light are passed through a sample. “Visible” light energy can be seen by humans, while its close neighbor, ultraviolet, cannot. In the entire electromagnetic spectrum ranging from high-frequency, nano-width gamma rays to low-frequency, “long wavelengths” with no definitive size, light (colors) visible to humans makes up a very small percent.

PI电子根据其键合和结合程度，在不同的波长下吸收光。将发光的初始强度与通过样品传输到检测系统的光的强度进行了比较。使用啤酒定律，可以轻松确定样品的浓度。另外，由于化合物在独特的波长下吸收光，因此可以询问样品的组成。

UV/Vis spectrometers work well for investigating samples that contain transition metals, colored compounds (dyes or pigments), and organic compounds. Biological materials are especially well-suited to analysis by UV/Vis. This type of investigation will reveal wavelengths where the samples absorb light well, thus, if a full spectrum is read, one can determine not only concentration, but also the purity of a given sample. A drawback? UV/Vis does not indicate the exact wavelength being absorbed.

One benefit to this type of analysis is the relatively economical pricing of the instrumentation. The obvious limitation is that the sample must show itself in either the visible or UV bandwidths, which is not the reality for many organic compounds.

Infrared Spectrometers

IR spectroscopy examines samples using the infrared region of the electromagnetic spectrum, the group of frequencies making up visible light’s other close neighbor. In IR spectroscopy, infrared light is transmitted onto a sample. Different elemental bonding will vibrate at differing harmonic frequencies. The absorption of light at these frequencies is then detected and plotted across the IR spectrum. Based on the unique absorbance patterns, researchers are able to identify the particular bonds that occur in a sample. With this information, they can determine the molecules that are present.

IR spectrometry is particularly useful in identifying compounds in organic and inorganic chemistry. The principles of IR spectroscopy have also been applied in manufacturing scientific devices. For example, IR sensors are used for measuring CO₂levels in biological incubators.

红外光谱可以几乎以任何形式研究样品，这是一个值得注意的优势。因此，如果一个人有兴趣研究未知化合物的组成，那么红外光谱可能是一种非常强大的技术。该方法的一个缺点是它无法识别频谱是单个化合物还是多种化合物的结果。

Atomic Absorption Spectrometers

Atomic absorption spectroscopy is capable of determining 70 different elements in a sample. In AAS, the sample is first placed in an atomizer. Atomizers convert the sample into its elemental composition in a gaseous state. A source of radiation is then passed through the sample and measurements are taken. Based on the absorption of this radiation by each component, investigators are able to determine the composition of the sample, as each individual element will have a different (known) absorption rate.

There are numerous uses for AAS. In clinical laboratories, it detects the presence of metals in biological fluids or tissue samples. In the pharmaceutical industry, AAS may be used to determine if any catalyst remains from synthesis reactions in a manufactured compound. In environmental sciences, it can analyze the metal content in soil or water samples. The obvious benefit of AAS is its ability to determine elemental compositions. Drawbacks of AAS include the cost of the instrumentation and the limited number of compounds identified.

Thus, it is clear that UV/Vis, IR, and AA spectrometers are all powerful instruments that can examine unique properties within organic and inorganic samples. Selecting the appropriate instrument for your laboratory will depend on the characteristics, advantages, and drawbacks listed above. Lastly, one may consider using these techniques in concert for an extremely powerful line of investigation.

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