Atomic absorption spectrometry has been rapidly developed both at home and abroad since its inception in the mid-1950s. It has been widely used because of its advantages such as its sensitivity, accuracy, selectivity, and strong anti-interference ability. The various fields of chemical analysis were applied, and some were listed as standard analytical methods. In recent years, Atomic Absorption Spectroscopy has also received extensive attention and application in the field of water quality detection, and many grassroots water quality testing departments have equipped such instruments and have become a daily routine analysis method and method.
The analysis of samples by atomic absorption spectrometry is indeed a simple and easy to grasp analytical method, but it is by no means a high-precision analytical method. The main reason is that the atomic absorption spectrometer has many interference factors, such as the use of flame atoms. Absorption analysis, the fluctuation of the flame, the amount of solution lift, etc.; analysis by graphite furnace atomic absorption, graphite tube quality, spectral interference and other factors are not easy to control.
Based on my actual work experience, this article discusses several aspects that should be taken into account when performing quality control assessments using atomic absorption spectrometry:
First, for all kinds of samples have the most suitable analytical methods, to understand the scope of application of atomic absorption spectrometry, consider its adaptability
It is well known that the absolute detection limit of atomic absorption in graphite furnaces is very high. From this point of view, it was erroneously assumed that a sample with a high concentration can be measured by a graphite furnace atomic absorption method, or that graphite furnace atomic absorption is erroneously considered. The dynamic range of the method is very wide and has a high degree of accuracy.
For example, when a manufacturer purchases an instrument, he or she thinks that it is still a good instrument with a good detection limit indicator, and that a solution with a low concentration can certainly measure a solution with a high concentration. However, when the instrument is bought for use, it is understood that this judgment is wrong. For a solution with a high concentration, it must be diluted to an appropriate concentration range to be measured. Therefore, for the determination of high-concentration samples, the use of high-precision measurement methods, such as the use of spectrophotometry than the use of atomic absorption spectrometry is better. This is because the atomic absorption spectrometry measures the absorption of light, and the ratio of the half widths of the emission lines of the absorption line and the emission line of the hollow cathode lamp is only about 10, so that it is not possible to simultaneously measure a wide range of concentrations as in the emission spectroscopy.
Second, draw the correct working curve
Since the linear range of the atomic absorption method is narrow, it is particularly important to draw the correct working curve. When making the work curve, note the following points:
(1) Draw a working curve to take at least 5 to 7 points, and each point should be measured twice or more repeatedly until the measured value of the parallel sample meets the requirement, and then the next point is measured.
(2) The standard sample and the sample to be tested must use the same solvent system.
(3) The concentration range selected for the working curve should include the concentration of the sample to be tested. The ideal linear range of the atomic absorption method is within 0.1 to 0.5 of the absorbance. If the concentration is higher, the standard curve will be significantly curved. Therefore, the atomic absorption spectrophotometric method can only measure the narrower concentration range. As one of the remedy methods, various absorption lines with different sensitivities are used together to achieve a wide range of concentration. However, this method is not suitable for the alkali metal and alkaline earth metal elements with less absorption lines and can only be applied to such elements as lead, copper, iron, manganese, and platinum. As an alternative remedy, several points are measured at the point where the working curve begins to bend, in order to draw the correct working curve [1], or a one-member quadratic equation can be used to draw the working curve.
Second, the impact of sample dilution on the analysis results
Atomic Absorption In the field of water quality detection, two methods of flame atomic absorption and graphite furnace atomic absorption are commonly used. Since the sensitivity of the two methods is different, the corresponding analysis method should be selected according to the concentration range of the sample.
The scope of work of different instruments of the same project is different. Before making a sample, you should first understand the scope of work of your instrument. If the concentration range of the sample is not within the working range of your own instrument, consider diluting the sample so that the concentration range of the diluted sample is within the working range of the instrument. It is worth noting that the multiples of dilution are not too large, which is especially important when testing with graphite furnace atomic absorption. This is because the sensitivity of graphite furnace atomic absorption is very high, and the distilled water, deionized water and acid used must contain impurities, which will lead to measurement errors [1].
Third, the impact of acid on the determination
1, the impact of the blank value
A few years ago, the standard curve of lead in graphite furnace atomic absorption spectrometry was suddenly found to be much higher than the blank value. At the time, it was suspected that the container was contaminated, the container was washed again, and the blank solution was reconstituted (determination of 1% HNO3 deionized water for blank value). The result was still the same, and replacing the graphite tube again had no effect. After repeated experiments, the final discovery was interference with nitric acid [1]. The nitric acid used at the time was newly opened, and it was not a manufacturer that was used last time.
2, the impact on the sensitivity
Since some manufacturers produce nitric acid containing higher amounts of impurities than the label, the sensitivity of the assay is reduced when measured by graphite furnace atomic absorption spectrometry. If this happens, replace the nitric acid again, or use as little or no nitric acid as possible during the pre-treatment.
Due to the acid produced by different manufacturers, the content of impurities is not the same. Therefore, in the analysis of water samples with a graphite furnace, it must be noted that the acid added to the standard series and the acid added to the water sample must be the same batch of acid from the same manufacturer. Only in this way can the acid be determined in the standard series. The error in the determination of the water sample is controlled at the same level. This is particularly important in graphite furnace atomic absorption analysis.
In short, when using atomic absorption spectroscopy for sample analysis, on the one hand, we must have sufficient understanding of the performance of the instrument; on the other hand, we must continue to summarize experience and improve analytical techniques in practice. Only in this way can satisfactory results be obtained.
The analysis of samples by atomic absorption spectrometry is indeed a simple and easy to grasp analytical method, but it is by no means a high-precision analytical method. The main reason is that the atomic absorption spectrometer has many interference factors, such as the use of flame atoms. Absorption analysis, the fluctuation of the flame, the amount of solution lift, etc.; analysis by graphite furnace atomic absorption, graphite tube quality, spectral interference and other factors are not easy to control.
Based on my actual work experience, this article discusses several aspects that should be taken into account when performing quality control assessments using atomic absorption spectrometry:
First, for all kinds of samples have the most suitable analytical methods, to understand the scope of application of atomic absorption spectrometry, consider its adaptability
It is well known that the absolute detection limit of atomic absorption in graphite furnaces is very high. From this point of view, it was erroneously assumed that a sample with a high concentration can be measured by a graphite furnace atomic absorption method, or that graphite furnace atomic absorption is erroneously considered. The dynamic range of the method is very wide and has a high degree of accuracy.
For example, when a manufacturer purchases an instrument, he or she thinks that it is still a good instrument with a good detection limit indicator, and that a solution with a low concentration can certainly measure a solution with a high concentration. However, when the instrument is bought for use, it is understood that this judgment is wrong. For a solution with a high concentration, it must be diluted to an appropriate concentration range to be measured. Therefore, for the determination of high-concentration samples, the use of high-precision measurement methods, such as the use of spectrophotometry than the use of atomic absorption spectrometry is better. This is because the atomic absorption spectrometry measures the absorption of light, and the ratio of the half widths of the emission lines of the absorption line and the emission line of the hollow cathode lamp is only about 10, so that it is not possible to simultaneously measure a wide range of concentrations as in the emission spectroscopy.
Second, draw the correct working curve
Since the linear range of the atomic absorption method is narrow, it is particularly important to draw the correct working curve. When making the work curve, note the following points:
(1) Draw a working curve to take at least 5 to 7 points, and each point should be measured twice or more repeatedly until the measured value of the parallel sample meets the requirement, and then the next point is measured.
(2) The standard sample and the sample to be tested must use the same solvent system.
(3) The concentration range selected for the working curve should include the concentration of the sample to be tested. The ideal linear range of the atomic absorption method is within 0.1 to 0.5 of the absorbance. If the concentration is higher, the standard curve will be significantly curved. Therefore, the atomic absorption spectrophotometric method can only measure the narrower concentration range. As one of the remedy methods, various absorption lines with different sensitivities are used together to achieve a wide range of concentration. However, this method is not suitable for the alkali metal and alkaline earth metal elements with less absorption lines and can only be applied to such elements as lead, copper, iron, manganese, and platinum. As an alternative remedy, several points are measured at the point where the working curve begins to bend, in order to draw the correct working curve [1], or a one-member quadratic equation can be used to draw the working curve.
Second, the impact of sample dilution on the analysis results
Atomic Absorption In the field of water quality detection, two methods of flame atomic absorption and graphite furnace atomic absorption are commonly used. Since the sensitivity of the two methods is different, the corresponding analysis method should be selected according to the concentration range of the sample.
The scope of work of different instruments of the same project is different. Before making a sample, you should first understand the scope of work of your instrument. If the concentration range of the sample is not within the working range of your own instrument, consider diluting the sample so that the concentration range of the diluted sample is within the working range of the instrument. It is worth noting that the multiples of dilution are not too large, which is especially important when testing with graphite furnace atomic absorption. This is because the sensitivity of graphite furnace atomic absorption is very high, and the distilled water, deionized water and acid used must contain impurities, which will lead to measurement errors [1].
Third, the impact of acid on the determination
1, the impact of the blank value
A few years ago, the standard curve of lead in graphite furnace atomic absorption spectrometry was suddenly found to be much higher than the blank value. At the time, it was suspected that the container was contaminated, the container was washed again, and the blank solution was reconstituted (determination of 1% HNO3 deionized water for blank value). The result was still the same, and replacing the graphite tube again had no effect. After repeated experiments, the final discovery was interference with nitric acid [1]. The nitric acid used at the time was newly opened, and it was not a manufacturer that was used last time.
2, the impact on the sensitivity
Since some manufacturers produce nitric acid containing higher amounts of impurities than the label, the sensitivity of the assay is reduced when measured by graphite furnace atomic absorption spectrometry. If this happens, replace the nitric acid again, or use as little or no nitric acid as possible during the pre-treatment.
Due to the acid produced by different manufacturers, the content of impurities is not the same. Therefore, in the analysis of water samples with a graphite furnace, it must be noted that the acid added to the standard series and the acid added to the water sample must be the same batch of acid from the same manufacturer. Only in this way can the acid be determined in the standard series. The error in the determination of the water sample is controlled at the same level. This is particularly important in graphite furnace atomic absorption analysis.
In short, when using atomic absorption spectroscopy for sample analysis, on the one hand, we must have sufficient understanding of the performance of the instrument; on the other hand, we must continue to summarize experience and improve analytical techniques in practice. Only in this way can satisfactory results be obtained.