Chapter 18: Example Spectrometer | CHM 214 | 154

Jacob Stewart
16 Apr 202103:34
EducationalLearning
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TLDRThe script offers an insightful look into the practical application of a spectrometer, specifically an infrared spectrometer used in a research lab. It describes the setup, including a quantum cascade laser as the light source and a multi-pass cell for sample analysis. The process of measuring absorption by comparing pure nitrogen to a sample, in this case, isoprene, is explained. The resulting data is then converted into a spectrum of absorbance, highlighting the characteristic peaks that indicate the presence of isoprene. This real-world example effectively demonstrates how spectrometers are utilized to monitor specific compounds in samples.

Takeaways
  • 🌟 A spectrometer is a device used to measure the absorption of light, providing insights into the composition of samples.
  • 🔵 The speaker describes a setup with a quantum cascade laser as the light source, which is specific to infrared spectrometry.
  • 📏 A reference cell is used for calibrating the wavelength in the spectrometer, though its necessity depends on the specific setup.
  • 🚦 Lasers act as a built-in monochromator, producing light at a precise wavelength, which is crucial for accurate spectrometry.
  • 🔄 The multi-pass cell allows light to bounce back and forth multiple times, enhancing the interaction between the light and the sample.
  • 💡 Infrared light is used in the described setup, which is not visible to the naked eye.
  • 🌬️ The sample cell is filled with nitrogen as a 'blank' to measure the baseline amount of light reaching the detector.
  • 📈 The data from the spectrometer shows changes in light intensity at specific frequencies, which correspond to the absorption features of the sample.
  • 📊 Absorbance is calculated as the negative log of the ratio of transmitted light (p) to initial light (p naught), indicating the amount of light absorbed.
  • 🏹 The clear peaks in the absorption spectrum are indicative of the presence of specific molecules, such as isoprene in this case.
  • 📚 The real-world data presented was collected by students, demonstrating the practical application of spectrometry in measuring sample composition.
Q & A

  • What type of laser is used as a light source in the described spectrometer setup?

    -A quantum cascade laser is used as the light source in the described spectrometer setup.

  • What is the purpose of the reference cell in the spectrometer setup?

    -The reference cell is used for calibrating the wavelength of the sample in the spectrometer setup.

  • How does the multi-pass cell function in the spectrometer?

    -The multi-pass cell allows the light to bounce back and forth multiple times, increasing the path length and thus the sensitivity of the absorption measurements.

  • What is the role of nitrogen in the spectrometer experiment?

    -Nitrogen is used as a blank in the experiment, providing a baseline measurement of light transmission without the presence of the analyte.

  • What analyte is being measured in the provided example?

    -In the provided example, the analyte being measured is isoprene.

  • How is absorbance expressed in the context of the described spectrometer experiment?

    -Absorbance is expressed as the negative log of the ratio of transmission (p) to the initial transmission (p naught), which increases when the amount of light decreases.

  • What are the 'wiggles' observed in the detector signal while measuring pure nitrogen?

    -The 'wiggles' observed in the detector signal are due to fluctuations in the laser power as the frequency of the light changes.

  • What is the significance of the peaks observed in the absorption spectrum of isoprene?

    -The peaks in the absorption spectrum of isoprene are characteristic absorption features that indicate the presence and concentration of the analyte in the sample.

  • How does the quantum cascade laser's wavelength specificity affect the need for a monochromator in the setup?

    -Since the quantum cascade laser produces light at a very specific wavelength, it essentially acts as a built-in monochromator, reducing the need for an external monochromator in the setup.

  • What is the main application of the described spectrometer experiment?

    -The main application of the described spectrometer experiment is to measure the absorbance of specific analytes, such as isoprene, in a sample by comparing the light transmission with and without the analyte present.

Outlines
00:00
🌈 Introduction to Spectrometer and its Practical Application

This paragraph introduces the concept of a spectrometer and its practical application in an infrared spectrometer and hail lab. It describes the components of a spectrometer setup, including a quantum cascade laser as the light source, a reference cell for calibration, and a multi-pass cell for sample analysis. The paragraph explains the process of measuring absorption by comparing the light that reaches the detector with nitrogen as a blank and with the sample, in this case, isoprene. The concept of absorbance is introduced, which is calculated as the negative log of the ratio of transmitted light to the original light, and how it is used to identify the presence and quantity of isoprene in the samples.

Mindmap
Keywords
💡spectrometer
A spectrometer is an instrument used to measure the properties of light across different wavelengths. In the context of the video, it is used to analyze the absorption of light, specifically in the infrared range, which helps in identifying and quantifying certain compounds like isoprene. The script describes a practical setup of a spectrometer in an infrared spectrometer and hail lab, indicating its importance in scientific research and analysis.
💡absorption of light
The absorption of light refers to the process by which light is taken in by a material or substance, resulting in a decrease in the intensity of the light as it passes through. In the video, this concept is crucial for understanding how a spectrometer can detect and measure the presence of specific compounds by observing the light that is absorbed at particular wavelengths. The script provides a real-world example of measuring isoprene absorption, demonstrating how the technique can be applied in practice.
💡quantum cascade laser
A quantum cascade laser is a type of laser that emits light at specific wavelengths and is used as a light source in certain spectrometers. It is characterized by its ability to produce light at a very specific wavelength, effectively acting as a built-in monochromator. In the video, the quantum cascade laser is a key component of the spectrometer setup, highlighting its role in the accurate measurement of light absorption.
💡reference cell
A reference cell is used in spectrometry to calibrate the wavelength of the light being analyzed. It provides a baseline or 'blank' measurement against which the sample measurements can be compared. In the video, the reference cell is essential for ensuring the accuracy of the wavelength calibration, which is critical for the reliable detection and quantification of the target compound, such as isoprene.
💡monochromator
A monochromator is a device that selects a narrow band of wavelengths from a light source. In the context of the video, it is mentioned that lasers have a built-in monochromator function because they produce light at a very specific wavelength. This characteristic is important for spectrometry as it allows for precise analysis of light absorption at particular frequencies, which is crucial for identifying compounds through their absorption spectra.
💡multi-pass cell
A multi-pass cell is a component of a spectrometer that increases the path length of light through the sample, allowing for more light absorption to occur and thus enhancing the sensitivity of the measurement. In the video, the multi-pass cell is where the sample is placed, and the light bounces back and forth multiple times before reaching the detector. This setup enables the detection of smaller amounts of the target compound, such as isoprene, by amplifying the absorption signal.
💡detector
A detector in the context of a spectrometer is a device that measures the intensity of light after it has interacted with the sample. It converts the light signal into an electrical signal, which can then be analyzed to determine the absorption characteristics of the sample. In the video, the detector is crucial for capturing the absorption data that is used to identify and quantify compounds like isoprene.
💡absorbance
Absorbance is a measure of the amount of light absorbed by a substance, expressed as the negative logarithm of the ratio of transmitted light (p) to incident light (p naught). It is used in spectrometry to quantify the absorption characteristics of a sample and is directly related to the concentration of the absorbing species. In the video, absorbance is calculated to produce a spectrum that shows the specific wavelengths at which light is absorbed by isoprene, providing a means to identify and measure its presence in the sample.
💡isoprene
Isoprene is an organic compound that is the focus of the analysis in the video. It is a volatile organic compound commonly found in the atmosphere and is an important target for monitoring due to its role in atmospheric chemistry and its potential impact on air quality and climate. In the context of the video, isoprene is the analyte, and the spectrometer is used to measure its concentration by observing the characteristic absorption features in the resulting spectrum.
💡infrared light
Infrared light is a type of electromagnetic radiation with wavelengths longer than visible light but shorter than microwaves. It is not visible to the human eye. In the video, infrared light is the type of light being analyzed by the spectrometer, which is specifically designed for infrared spectroscopy. This allows for the detection and measurement of compounds like isoprene, which have characteristic absorption features in the infrared range.
💡calibration
Calibration is the process of adjusting an instrument or device to ensure that it provides accurate and consistent measurements. In the context of the video, the reference cell is used to calibrate the wavelength of the light source in the spectrometer, ensuring that the measurements taken are reliable and can be accurately compared to known standards. Proper calibration is essential for the accurate analysis of light absorption and the determination of compound concentrations.
Highlights

The introduction of a spectrometer in practical use, specifically an infrared spectrometer in a hail lab.

The use of a quantum cascade laser as a light source for the spectrometer, producing light at a very specific wavelength.

The presence of a reference cell for calibrating the wavelength of the sample in the spectrometer setup.

The absence of a monochromator in this setup due to the built-in monochromator feature of the laser.

The use of a multi-pass cell where light bounces back and forth multiple times before being detected.

Infrared light being used, which is not visible to the human eye.

Filling the multi-pass cell with nitrogen as a blank to measure the amount of light reaching the detector.

The process of taking absorption measurements by comparing the light transmission with and without the sample (isoprene).

The appearance of absorption features in the data as a result of specific frequencies having less light reaching the detector.

Expressing the data as absorbance by calculating the negative log of the ratio of transmission with and without the sample.

The increase in absorbance indicating a decrease in the amount of light in comparison to the original measurement.

Clear peaks in the absorption spectrum of isoprene, which are used to monitor its presence in samples.

The presentation of real-world data taken by students in the lab, demonstrating the practical application of the spectrometer.

The measurement of absorbance as a method to determine the amount of a specific substance (isoprene) in samples.

Transcripts

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SpectrometerLightAbsorptionQuantumCascadeLaserMulti-PassCellIsopreneInfraredSpectroscopyScienceLabDataAnalysisEducationalContentResearchMethodology