Why wasn't information about the mass of isotopes sufficient for identifying the isotopes? Provide an example to explain the answer.
Figure 2 shows 2.5 min averaged spectra of ambient aerosol
at nominal m/z 208 obtained with the HR-AMS located at T0. Panel A compares V- and W-mode open, closed and dif- ference (open minus closed) spectra, during a period with a high lead signal (marked in Fig. 6). The difference between the sensitivity and the resolution of V- and W-modes is evi- dent in the figure; W-mode spectra have more resolution but a noisier signal. Typically, the difference mass spectra cor- respond to the sampled aerosol, once the background gases in the detection region are accounted for by subtracting the closed from the open mass spectra (Canagaratna et al., 2007). However, in the case of lead ions, a closed signal of the same order of magnitude as the open signal was observed which, as it will be explained later, indicates that there is a residual sig- nal caused by aerosol components that evaporate slowly from the vaporizer due to their relatively low volatility (Huffman et al., 2009). Because of this slow evaporation, the difference signal cannot be interpreted as usual in the case of lead ions and will not be discussed further. Panel B in Fig. 2 shows the same open raw signals as Panel A together with spec- tral fits obtained assuming the presence of several individual ions whose signals have a modified Gaussian shape (DeCarlo et al., 2006). The atomic weight of the most abundant lead isotope (208Pb) is marked. The other fragments marked were selected in order to allow a more accurate fitting of the raw MS signal. They are most likely organic ions that contain C, H, O and/or N; however, their exact identification is be- yond the scope of this paper. Panel C in Fig. 2 is similar to panel B, but shows the spectra during a period with very low Pb signal (marked in Fig. 6). Signals corresponding to ions of the other main lead isotopes (207 Pb+ and 206 Pb+ ), as well as to the doubly charged ions of the three main lead isotopes (208 Pb++ , 207 Pb++ and 206 Pb++ ), were also observed (see Figs. S2 and S3). No signal for 204Pb+ was observed, as ex- pected due to its low abundance (0.027 relative to 208 Pb+ , (deLaeter et al., 2003)) and the limited signal-to-noise of our measurements.
igure 2 shows 2.5 min averaged spectra of ambient aerosol
at nominal m/z 208 obtained with the HR-AMS located at T0. Panel A compares V- and W-mode open, closed and dif- ference (open minus closed) spectra, during a period with a high lead signal (marked in Fig. 6). The difference between the sensitivity and the resolution of V- and W-modes is evi- dent in the figure; W-mode spectra have more resolution but a noisier signal. Typically, the difference mass spectra cor- respond to the sampled aerosol, once the background gases in the detection region are accounted for by subtracting the closed from the open mass spectra (Canagaratna et al., 2007). However, in the case of lead ions, a closed signal of the same order of magnitude as the open signal was observed which, as it will be explained later, indicates that there is a residual sig- nal caused by aerosol components that evaporate slowly from the vaporizer due to their relatively low volatility (Huffman et al., 2009). Because of this slow evaporation, the difference signal cannot be interpreted as usual in the case of lead ions and will not be discussed further. Panel B in Fig. 2 shows the same open raw signals as Panel A together with spec- tral fits obtained assuming the presence of several individual ions whose signals have a modified Gaussian shape (DeCarlo et al., 2006). The atomic weight of the most abundant lead isotope (208Pb) is marked. The other fragments marked were selected in order to allow a more accurate fitting of the raw MS signal. They are most likely organic ions that contain C, H, O and/or N; however, their exact identification is be- yond the scope of this paper. Panel C in Fig. 2 is similar to panel B, but shows the spectra during a period with very low Pb signal (marked in Fig. 6). Signals corresponding to ions of the other main lead isotopes (207 Pb+ and 206 Pb+ ), as well as to the doubly charged ions of the three main lead isotopes (208 Pb++ , 207 Pb++ and 206 Pb++ ), were also observed (see Figs. S2 and S3). No signal for 204Pb+ was observed, as ex- pected due to its low abundance (0.027 relative to 208 Pb+ , (deLaeter et al., 2003)) and the limited signal-to-noise of our measurements.
The information about the mass of isotopes is not sufficient for identifying the isotopes because there can be multiple isotopes with the same mass but different atomic numbers. Isotopes are atoms of the same element that have different numbers of neutrons in their nuclei.
For example, in the text provided, Figure 2 shows spectra obtained using a High-Resolution Aerosol Mass Spectrometer (HR-AMS) to analyze ambient aerosol. Panel B of Figure 2 shows the open raw signals and spectral fits obtained assuming the presence of several ions, including lead ions. The atomic weight of the most abundant lead isotope (208Pb) is marked. However, the other fragments marked in the spectrum are likely organic ions that contain C, H, O, and/or N. While the atomic weight (mass) of the lead isotopes is known, without additional information, it is not possible to determine the atomic number (the number of protons in the nucleus) of the isotopes. In this case, additional analysis and measurements are needed to accurately identify the specific isotopes present, such as using doubly charged ions (208Pb++, 207Pb++, 206Pb++) and observing the absence of certain isotopes (e.g., 204Pb+).
The mass of isotopes alone is not sufficient for identifying the isotopes because there can be multiple isotopes with the same mass. Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons, resulting in different masses. To fully identify an isotope, one needs to consider other properties such as its atomic number, which is the number of protons in the nucleus.
In the given example, the researchers are using a HR-AMS (High-Resolution Aerosol Mass Spectrometer) to analyze ambient aerosol samples. The spectra obtained at a specific mass-to-charge ratio (m/z) of 208 are discussed. The m/z refers to the ratio of the mass of the ion to its charge. Panel B of Figure 2 shows the open raw signals and spectral fits. The atomic weight of the most abundant lead isotope, which has an m/z of 208, is marked.
However, it is mentioned that there are other lead isotopes present as well, such as 207Pb+ and 206Pb+. These isotopes would have different masses but still have the same m/z value of 208. Therefore, simply knowing the mass or m/z value is not enough to identify the specific isotopes present. Further analysis and considerations of other properties, such as the presence of other isotopes and their relative abundances, are required for accurate identification.
In this case, the researchers are able to identify the isotopes by observing the signals corresponding to ions of different lead isotopes, including doubly charged ions. They compare the observed signals to known isotopic patterns and measure their relative abundances to confirm the presence of specific isotopes.
In summary, the mass of isotopes alone is not sufficient for identifying the isotopes because multiple isotopes can have the same mass. Further analysis of other properties, such as atomic number or isotopic patterns, is necessary for accurate identification.