Instrumental analysis is used a lot within industry due to its ability to give us fast and accurate results. Within this article, we will explore what instrumental analysis is and its advantages. We will then look at an example of instrumental analysis called Flame Emission Spectroscopy. We will explore what it is used for and how to analyse the results.
What is instrumental analysis?
Instrumental analysis is a method of analysing different substances that relies on machines. Different methods of instrumental analysis work better at identifying different types of elements or compounds.
Principles of instrumental analysis
Instrumental analysis has many advantages compared to laboratory tests such as those discussed in the “Testing for Positive Ions”, “Testing for Negative Ions” and “Testing for Common Gases”.
The principles of instrumental analysis are:
Study Tip: When discussing the advantages of instrumental testing over laboratory tests, you must compare the sensitivity, speed and accuracy of both tests.
What are the types of instrumental methods of analysis?
Here we will see the flame emission spectroscopy, which is a very importqnt method of analysis.
Instrumental analysis example
A very important example of instrumental analysis is flame emission spectroscopy. Let's fins out what it is!
What is Flame Emission Spectroscopy?
Flame emission spectroscopy is a type of instrumental analysis. It is used to identify metal ions in a sample and their concentrations within the sample.
How Does Flame Emission Spectroscopy Work?
Within flame emission spectroscopy, the sample is heated up and vaporised. When substances are heated they emit radiation, often in the form of light (Electromagnetic Radiation). This is because electrons in the atoms become excited and jump up one or more energy levels. However, when they fall back down to their original energy level, they emit energy.
In flame emission spectroscopy, the intensity and the wavelength of the outputted light are measured and we receive an emission spectrum.
Below is an example of an emission spectrum. The coloured lines correspond to the wavelengths of light that have been emitted.
Fig. 1: Hydrogen Emission Spectrum | SaveMyExams
The intensity of the light produced by the sample is proportional to the number of ions that have been vaporised. This means we can measure the intensity of the light to determine the concentration of the metal ions that were in the sample solution.
Each ion produces its own unique emission spectrum. This means by comparing emission spectrums to reference spectrums, we can easily identify the ions that are present within the sample.
- Flame emission spectroscopy is useful as it allows us to use a sample with a mixture of different ions. The laboratory flame test, however, only allows us to use a sample that contains one type of metal ion.
- Shorter wavelengths have more energy. This means blue light will transfer more energy than red light.
How Do We Interpret the Results of Flame Emission Spectroscopy?
Using the data provided by the flame emission spectroscopy, we can determine the ions that were present in the sample and the concentrations of each of the ions.
Identifying Ions:
To determine the ions present in the sample, we need to look at the emission spectrum produced.
By comparing the output emission spectrum to other reference spectrums, we can identify the ions that were present in the sample.
Let’s say we have the reference spectrums:
Fig. 2: Reference emission spectrum | SaveMyExams
And our output flame emission spectrum looks like this:
Fig. 3: Output emission spectrum | SaveMyExams
By comparing our output emission spectrum to our reference spectrums, we can see that the output emission spectrum has a similar pattern to the reference spectrum of Mercury. This means that our sample must have contained Mercury ions.
Determining Concentrations
To determine the concentration of the ions present, we need to plot a calibration curve, before we carry out the flame emission spectroscopy on an unknown sample. A calibration curve is a graph with readings from the flame emission spectroscope plotted against known concentrations of a substance.
To plot the calibration curve, you will need to take readings of the flame emission spectroscope for different known concentrations of a particular metal ion.
Using the calibration curve we can then find out the concentration of a metal ion, using the readings we receive.
Let’s say we have a calibration curve for different concentrations of sodium, that we plotted before carrying out our spectroscopy:
Fig. 4: Calibration curve for different concentrations of sodium | BBC Bitesize
If during our flame emission spectroscopy, we identify that our sample contains sodium ions, we can measure the intensity of the wavelength to calculate the concentration of sodium ions in the sample. In the graph above, the flame photometer reading on the y-axis is a measure of the intensity of wavelength detected.
In our example, the photometer reading is 4, which corresponds to the intensity of electromagnetic radiation. Using our calibration curve, we know that the concentration of sodium ions in our sample is 0.02g·dm-3.
Remember to use a ruler to draw straight lines on a graph.
What are the advantages of instrumental methods of analysis?
Some of the advantages of instrumental methods of analysis are:
- The accuracy: Instrumental methods of analysis allow measurements to be much more precise than with more traditional methods.
- They are easy to use: instrumental methods of analysis are very easy to use, more than other methods.
- Possibility of measuring very small amounts of sample, as they are very accurate.
- They are very reliable.
Instrumental Analysis - Key takeaways
- Instrumental analysis is a method of analysing chemical substances using machines.
- Instrumental analysis is more accurate, faster and more sensitive than laboratory tests.
- Flame emission spectroscopy is an example of instrumental analysis and is used to identify metal ions within a sample and their concentrations.
- We can identify the metal ions within a sample by observing the output emission spectrum.
- We can calculate the concentration of a metal ion in a sample by measuring the wavelength of the light.
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