High-Resolution Quadrupole Mass Spectrometry Advantages

Integrated with a 19-mm tri-filter quadrupole and 2.9-MHz Quadrupole Power Supply (QPS), the MAX 50™ flange mounted quadrupole mass spectrometer and VeraSpec™ HRQ turnkey system from Extrel offer users the tools to deliver sensitive, speedy and reliable analysis. Realizing this level of performance with quadrupole mass spectrometry has shown to be an effective addition to high-resolution analysis.

Product Benefits:

• High resolution >4000 (M/ΔM–FWHM)
  • High resolution can be achieved when scanning the total mass range
• Rapid, high-resolution scans
  • Up to 5000 data points per amu in scans
• Variable resolution
  • User selectable resolution across total (50 amu) mass range
• High-abundance sensitivity
• Superior high-resolution mass stability
• Low detection limits
  • Approximately 10 ppm under high-resolution conditions

Figure 1. VeraSpec HRQ High-Resolution Quadrupole Mass Spectrometer.

Figure 2. MAX 50 Flange Mounted Quadrupole Probe and Control System.

High Resolution

The resolution capabilities are >4000 (M/ΔM–FWHM), measured with Argon at m/z 40. This facilitates the separation of species such as deuterium and helium, 4.028 and 4.002 amu, respectively. Figure 3 illustrates an example spectrum. This spectrum was captured with the aid of a scan speed of approximately 1 second per scan.

Figure 3. 3.98–4.04 amu Scan of 10% Helium, 10% Deuterium, Balance Argon

Variable Resolution—User Selected over Entire Mass Range

A common application of a quadrupole mass spectrometer needs a minimal resolution setting at 1 amu across the mass range, or unit-mass resolution. The Extrel system hardware is calibrated and fitted in the factory so as to create spectra with unit-mass resolution for all masses in range with zero (or near zero) software modifications. Calibration points, or software modifications, can be incorporated anywhere in the table within the mass range. This permits users to effortlessly change the settings to suit the requirements of their experiment.

Figure 4. Resolution Calibration Table.

Resolution points at m/z 4, 5, 18, 28, 32, and 40 were added to the table and fixed to 0.0. When the resolution at m/z 28 is changed, the resolution of the peaks between m/z 28 and the neighboring calibration point will get impacted. The relative modification is seen in the resolution calibration table and the changed resolution of m/z 28 and m/z 29 is displayed in Figure 5.

Figure 5. Resolution Calibration—Adjusted Table.

Total scans under high-resolution conditions, or total scans with unit-mass resolution, can be run if specified points are not incorporated in the table. Incorporating many points to the table develops a number of regions, each with diverse resolution settings across the scan.

Figure 6 shows an example of a full, 1-50 amu, scan with varied resolution. The spectrum was recorded with a two-second scan, high-resolution settings from m/z 3.9-4.1 amu, and nominal resolution elsewhere.

Figure 6. A mass spectrum of 1-50 amu showing a variable resolution. Sample consists of 10% helium, 10% deuterium, and balanced argon.

High Abundance Sensitivity

Abundance sensitivity is said to be an accurate value signifying the efficiency of how the mass spectrometer can measure neighboring peaks. This is essential for applications that deal with adjacent spectral signals with considerably different concentrations. Figures 7 and 8 illustrate the superior abundance sensitivity.

Figure 7. UHP helium scan for analysis of 3 He Isotope (1.4 ppm Relative Abundance). The Resolution was Set Appropriately for the Isotopic Analysis (Less than the maximum resolution for the scan).

High-resolution scan conditions are applied for observing this abundance sensitivity. In an analysis of helium and deuterium at changing relative concentrations, a high-abundance sensitivity removes any spectral interference between the two species. The dedicated overlay in Figure 8 signifies four such scans. The scans were captured using the following:

• UHP helium (saturating the detector)
• UHP helium mixed almost 50/50 with a helium/deuterium cylinder (10% helium, 10% deuterium, balance argon)
• UHP helium when added to the system (before saturating the detector)
• 10% helium, 10% deuterium, balance argon cylinder alone

Figure 8. High-resolution scans of varying relative concentrations of helium and deuterium collected using a one-second scan time, with 1500 Points/amu.

Fast High-Resolution Scans

Superior spectra are delivered without too much averaging of scan times. For experiments that necessitate a number of data points in every single scan, it is able to gather up to 5000 data points/amu.

Figure 9. High-resolution scan of helium and deuterium with maximum data points (points/amu) collected using one-second scan with the maximum amount of points/amu. The scan range of m/z 3.99–4.04 Resulted in 250 data points.

High-Resolution Mass Stability

A system’s long-standing stability is important for extended experiments or analyses, and to prevent unnecessary time checking and recalibrating mass position. Stability becomes progressively more visible and important under high-resolution settings. To observe the stability, a cylinder of 10% helium, 10% deuterium, balance argon was connected and tested for 24 hours. Spectra at six-hour time intervals, starting at t=0, were used to estimate the instrument’s stability. Spectra were collected using a 1-second scan having 5000 points/amu. Figure 10 illustrates a spectral overlay of the results found. The experiment shows almost no detectable mass spectral variations spanning a 24-hour time period.

Figure 10. Spectral overlay of high-resolution scans during 24-hour stability experiment.

Low Detection Limits

The resolution setting impacts a system’s detection limits. A sample dilution was used to experimentally establish low detection limits at high resolution. A cylinder of 10% helium, 10% deuterium, balance argon was diluted using UHP argon with two mass flow controllers. Approximately 50 cc/minute of dilution gas was used while the flow of sample was fixed to 8, 6, 4, 2, and 0 cc/minute. This data was used to develop a dilution curve and then calculate the low detection limits for both species. Figures 11 and 12 show the tabulated detection limit results for helium and deuterium, while the dilution curve is shown in Figure 13.

Figure 11. Low detection limit calculation for helium.

Figure 12. Low detection limit calculation for deuterium.

Figure 13. Dilution curve from helium-deuterium detection limit experiment.

This information has been sourced, reviewed and adapted from materials provided by Extrel CMS, LLC.

For more information on this source, please visit Extrel CMS, LLC.