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Author:
Ed McCurdy, Agilent ICP-MS marketing expert
Glenn Woods, Agilent ICP-MS Application Specialist
Noriyuki Yamada, Agilent ICP-MS R & D expert
In January 2012, Agilent Technologies launched the world's first inductively coupled plasma tandem mass spectrometer, the 8800 ICP-MS / MS. As a follow-up report, this article compares the performance of the 8800 ICP-MS / MS with the existing quadrupole ICP-MS. It also details the hardware of the tandem mass spectrometer (MS) and its unique MS / MS mode Analyze the advantages.
Figure 1. Schematic diagram of the Agilent 8800 ICP-QQQ.
ICP triple quadrupole for MS / MS analysis
The 8800 tandem mass spectrometer is equipped with two quadrupoles: the first quadrupole (Q1) is located in front of the collision / reaction cell, and Q1 acts as the first-stage mass filter (MS / MS mode), which will exclude all except the target analytical ions ion. Therefore, the MS / MS mode ensures that ions entering the collision / reaction cell (CRC) are under control and are not affected by changes in the sample matrix. MS / MS provides a completely new way to eliminate the interference of mass spectrometry in ICP-MS through chemical reactions and ensure that changes in the matrix or other analytical elements will not affect the determination of target analytes.
For traditional quadrupole ICP-MS (ICP-QMS) equipped with CRC, the sample cannot be mass filtered before entering the reaction cell, so all ions in the sample enter the reaction cell. When measuring samples of different matrices, polyatomic ions caused by the matrix will cause new interference to the ions to be measured. Even if the sample matrix is ​​well processed and consistent (eg, using high-purity semiconductor grade reagents), the content of coexisting analytes may change, which will affect the polyatomic ions formed in the traditional ICP-QMS reaction cell. ICP-MS / MS will eliminate differences in results due to co-existing analyte content changes and variable matrices through the MS / MS mode.
Figure 2. Traditional ICP-QMS calculates the Ti content based on the determination of the polyatomic ion TiO formed in the reaction cell, and the results are completely consistent with the theoretical isotope abundance.
Figure 3. ICP-QMS spectrum of Ti (1 ppb) under 10 ppb Ni (blue), Cu (green) and Zn (pink) conditions. All the TiO polyatomic ions overlap with Ni, Cu or Zn.
Figure 4. Ni (blue), Cu (green), and Zn (pink) conditions of 10 ppb using the Agilent 8800 ICP-MS / MS in MS / MS mode for Ti (1 ppb).
Use ICP-MS / MS to reliably determine product ions formed in the reaction cell in MS / MS mode
In the reaction cell of the 8800 ICP-MS / MS, two different reaction modes can be used to separate analytes from interfering ions:
If the target analyte does not react with the selected reaction cell gas and the interfering ions can react with the reaction cell gas, the interfering ions can be neutralized or formed into new mass ions through the reaction, so that the analyte to be measured maintains its original Mass number, so as to eliminate interference.
If the target analyte can react with the selected reaction cell gas and the interfering ions do not react with the reaction cell gas, the new analyte polyatomic ion can be formed so that its mass can avoid the initial mass of the interference, This protects the analyte from interference.
These reaction mode methods can also be used for traditional quadrupole ICP-QMS. Figure 2 shows the results of measuring 1 ppb single element titanium standard using oxygen as the gas in the reaction cell. In the reaction cell, Ti will react with O2 to form TiO. Ti can be quantified by measuring the content of polyatomic ion TiO. For ordinary TiO, measurements are made at mass numbers 62, 63, 64, 65, and 66; for TiO generated from Ti isotopes, measurements are made at mass numbers 46, 47, 48, 49, and 50. The peak distribution of TiO is consistent with the theoretical abundance of Ti isotopes.
However, the overlapping spectrum in Figure 3 illustrates the problem faced when performing this analysis using traditional ICP-QMS: the polyatomic ion TiO is disturbed by the coexisting analytes Ni, Cu, and Zn (both at a concentration of 10 ppb). The natural masses of Ni, Cu, and Zn are 62 and 64 (Ni), 63 and 65 (Cu), and 64 and 66 (Zn) isotopes, respectively. When using ICP-QMS with a reaction cell for measurement, they will share Superimposed on all polyatomic ions Ti16O.
In contrast, when using the Agilent 8800 ICP-MS / MS to measure in MS / MS mode, Q1 will remove all mass ions except the target Ti ion, ensuring that the polyatomic ion TiO will not be measured with other substrates or Analyte elements are superimposed. The sample matrix of the superimposed spectrum shown in Figure 4 is the same as that in Figure 3, but Figure 4 uses the 8800 MS / MS measurement mode. All samples obtained a consistent TiO peak shape distribution (in line with the theoretical abundance of Ti isotopes), this result confirms that when using 8800 to measure Ti in MS / MS mode, even if there are coexisting analytes Ni, Cu, and Zn, Accurate results.
Agilent ICP-MS Journal
Are you interested in trace metal analysis and want to know the latest developments in ICP-MS? Then pay close attention to Agilent's special issue of ICP-MS. The special issue is published four times a year and is available in PDF format. To view the latest issue of the ICP-MS journal and all previous back issues, please visit the ICP-MS Journal Archive.
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