Depending on the isotope, interferences can occur due to polyatomic ions or isobaric overlap. Therefore, use isotopes that do not have interferences but still have a sufficiently high isotopic abundance.
A longer integration time gives better precision but increases the required measurement time. Refer to "Limit of Detection".
The semiquantitative analysis is a method to get rough concentrations of unknown samples. Although the sensitivity coefficient of each element has already been registered in the MassHunter Workstation, since the coefficient can change due to the sensitivity of the instrument and tuning conditions, we recommend you correct the sensitivity coefficient every time. Typically, 10 ppb of tuning solution is typically used to correct the sensitivity coefficient.
When a semiquantitation is executed, after the isotope ratio and the interference of polyatomic ions are checked, the results are generated.
(When the background subtraction is specified. Otherwise, go to the next step.)
Check whether S after subtraction of the background signal is equal to or higher than 3% of the background signal. If it is smaller than 3%, the concentration is calculated, and only when the quantitation result output parameter is ON, the result is reported together with the possibility of error. Otherwise, go to the next step.
(When you analyze all isotopes of the target element. Otherwise, go to the next step.)
Check the difference between the isotope ratio of the target element and its natural isotope ratio. If it is equal to or less than ±10%, the concentration is calculated and reported. Otherwise, go to the next step.
If all signals in Check A are equal to or larger than 1% and all signals in Check B are equal to or larger than 0.1%, the concentration is calculated and reported. If any signal in Check A is equal to or less than 1% or any signal in Check B is equal to or less than 0.1%, the concentration is calculated, and only when the quantitation result output parameter is ON, the result is reported together with the possibility of interferences.
The output method is determined based on the setting of the quantitation result output parameter. If it is ON, all results are reported. If it is OFF, no results are reported. If AUTO is selected, the results for elements that might be interfered with are not reported.
The mass number used in a semiquantitative analysis can be changed in Edit SemiQuant Parameters. However, since the sensitivity coefficient cannot be changed accordingly, you must enter the sensitivity coefficient based on the isotopic abundance.
The semiquantitative analysis uses only the maximum signal for one mass. Therefore, the count in the semiquantitative report and the result in the Tabulate/Element in Spectrum are different from each other.
The following methods are available to verify whether quantitative results are correct:
Perform quantitative analysis on an unknown sample and another sample to which a known concentration of the measured elements has been added. The recovery is obtained from the concentration difference between them and the added concentration. Note that although the ideal value is 100%, if the added concentration is too small in comparison to the concentration of the original sample, the recovery may not be good.
Dilute the sample, then check that the quantitative results for the diluted and undiluted samples match. Typically, 5 to 10 times dilution is used.
Various reference materials are produced in many countries. The most general reference materials are produced by NIST (National Institute of Standard Technology) in the US. Those reference materials have certified values that were crosschecked by various analytical approaches. Analysis on a reference material allows you to check the reliability of the analysis with sample preparations
All these methods are used in USEPA Method 6020 (CLP-M).
The blank subtraction subtracts the quantitation result of a blank from the quantitation result of a sample. Therefore, the blank subtraction is used for the subtraction of the concentration in a quantitative or semiquantitative analysis.
The background subtraction executes the subtraction of spectra and is used in the analysis of the qualitative spectra.
If the background subtraction is used to calculate the data during replicated analyses, the average value of background is subtracted from each data in each repetition. Therefore, even if the background subtraction is done for the same data, the result may not be 0.