Instrumentation and Technology

High Resolution Sector Field Inductively Coupled Plasma Mass Spectrometry*

*HR-SF-ICP-MS*

HR-SF-ICP-MS is The Gold Standard for analysis of Trace Elements in Biological Matrices.

• Interference free measurement of almost the whole periodic table and in almost all matrices
• From ultra-trace to matrix components
• Quantitative, Isotopic and Species Information

The Trace Elements Laboratory, at LHSC uses both the ELEMENT 1 (previously Finnigan MAT), and the Thermo Scientific ELEMENT 2 (both HR-SF-ICP-MS).

They outperform Low Resolution "Quadrupole" ICP-MS, in detection limits, sensitivity, interference elimination, and dynamic range (see below).

These 2 Instruments are both double focusing magnetic sector field ICP-Mass Spectrometers.
Both perform identically, using exactly the same technical principles.

Element

Click here to watch an ion flight demonstration movie

ICP-MS is the accepted and most powerful technique for the analysis and quantification of trace elements. Its applications range from the semiconductor industry to geological and environmental analyses, from biological research to material sciences. The most severe limitation of ICP-MS is polyatomic interferences on the elemental signals, originating from Argon and/or the sample matrix.. Elimination of interferences enables accurate and reliable quantitative multi-element analyses at trace levels, even without sample preparation.

The ELEMENT redefines high resolution ICP-MS by setting a new standard for productivity at the highest level of analytical performance. With the experience of more than 500 installed ELEMENT's, Thermo Fisher Scientific, the leader in high resolution ICP-MS, has rigorously optimized the ELEMENT for ease-of-use, stability and productivity. Autotuning of all parameters, including lenses, gas flows and the torch position ensures a reproducible and reliable system setup. Refined ion optics deliver high transmission at high resolution. The Thermo Scientific ELEMENT is the high resolution ICP-MS for routine productivity in your laboratory.

With the ELEMENT there is always access to the most powerful technique to solve a specific problem, combined with the highest sensitivity and the best signal-to-noise ratio. If there is a solution using
ICP-MS, the ELEMENT has it. No other ICP-MS system can make this claim: ultimate sensitivity at all resolution settings, ultimate selectivity through high mass resolution, 'hot' and 'cold' plasma conditions, high speed for transient signals, high stability for isotope ratios, full automation for routine productivity and full access to all instrumental parameters for method development.

• Multi-element analysis across the periodic table covering a mg/L to sub pg/L concentration range - Compatible with inorganic and organic solution matrices and solids
• High mass resolution to access spectrally interfered isotopes - Produces unambiguous elemental spectra
• A multi-elemental detector for transient signals - For example, CE, HPLC, GC, FFF and laser ablation
• High precision isotope ratios - On non-interfered or interfered isotopes
• Fully automated tuning and analysis - In conjunction with a comprehensive, customizable quality control system
• Reliability and robustness to serve as a 24/7 production control tool - Highest sample throughput
• Highest flexibility and accessibility to serve as an advanced research tool

HR-SF-ICP-MS*

• Argon gas passes through a quartz tube (Torch).
• The torch is surrounded at the end by a copper or silver coil (Load Coil), connected to a radio frequency generator (RF).
• As power is applied to the load coil from the RF, electrical and magnetic fields are established at the end of the torch.
• When a spark is applied to the argon flowing through the torch, electrons are stripped off the argon atoms, forming positive argon ions.
• These ions collide with other argon atoms, forming an argon discharge or Plasma (about 6000°C).

Sample Introduction

• Diluted samples are introduced through a peristaltic pump to a nebuliser, which produces a very fine aerosol within a spray chamber.
• The aerosol is carried by the argon gas into the torch, and then to the high temperature plasma, where the elements in the sample transported, are desolvated and vapourised.
• Dissociation occurs and most elements are fully ionized.

Plasma Interface and Transfer Optics

• Ions are then brought into the Mass Spectrometer via Interface Cones…metal disks with tiny apertures
• These apertures convert the ions into an ion beam, which is then focused using an electrostatic ion lens, under high vacuum.
• Photons are blocked from entering the interface.
• Once the ions enter the mass spectrometer, they are separated by their mass to charge ratio.
• Quadrupole instruments go no further than this before ion detection.
• Consequently they cannot eliminate mass overlap.

Double Focusing

• High Resolution instruments allow elimination or reduction of most interferences (Spectral and Polyatomic) by using both a Magnetic Sector Magnet and an Electric Sector Chamber.
• The Magnetic Sector disperses both ion energy and mass, and focuses all the ions with diverging angles of motion coming from the entrance slit, past the ion lens.
• The Electric Sector disperses only ion energy, and focuses the ions onto the exit slit, just before the detector (SEM).
• This arrangement is called Double Focusing.
• See internal view of instrument below

Resolution

• The Resolution can be changed by adjusting the width of the entrance and exit slits into the Spectrometer.
• These are called Low, Medium, and High Resolution.
• Some elements have overlapping interference masses, and require a narrower slit, thereby separating or resolving the interferences.
• ICP-MS (Inductively Coupled Plasma Mass Spectrometer) analysers have long been recognized as the most powerful technique for the analysis of trace elements.
• The most severe limitation with quadropole and collision-cell ICP-MS are the polyatomic interferences on the element signals, originating from the sample matrix and Argon.
• High Mass Resolution is the Gold Standard for the identification and elimination of these interferences.
• The resolved element ions are then detected or counted by a detector, which counts the number of ions, and amplifies them.
• The more ions of any particular element hitting the detector correspond to a higher concentration of element in that sample.
• By using Standard solutions and Control solutions, concentrations of unknown samples can be determined accurately.
  
  ICP-MS can also simultaneously determine up to 40 or more elements in 1 single sample.

Advantages of using High Resolution ICP-MS:

• Highest level of analytical performance
• Multi-element analysis across the periodic table covering mg/L to pg/L
• Variable Resolution: The resolving power from 300 for Low Resolution, 4000 for Medium Resolution and 10,000 for High Resolution allows the choice of resolution for each element to be analysed without any interferences and without over-resolving it.

Shown below is an example of the separation of Chromium in urine from the
interferences of ⁴⁰Ar¹²C and ³⁵Cl¹⁶O¹H in Medium Resolution.

Qudrupole Resolution	Low Resolution	Medium Resolution

Shown below is an example of that using the element Arsenic at m/z 75 separated
in High Resolution from the interference ⁴⁰Ar³⁵Cl.

Quadrupole	Low Resolution	Medium Resolution	High Resolution

• Do not have to apply ratio calculations due to interferences
• Ultimate sensitivity at all resolution settings, at Low Resolution Indium at 1 ppb will give a count greater than 1000,000 counts per second
• Ultimate selectivity through high mass resolution
• The combination of magnetic and electrostatic fields results in the double focusing high resolution properties of the Element. A magnetic field regulator with a high power stage controls the changing of the magnetic field. This results in the fastest scan speed possible using a magnet sector.
• Dual detection system. The element is equipped with a discrete dynode detector. The detector is linear from ppq to ppm. This allows for analysis of many elements in one single analysis. The Dynamic range is > 109 linear with automatic gain calibration.
• Use of Guard Electrode on torch decreases the ion spread, resulting in an increase in the ion transmission and much improved sensitivity.
• Guaranteed off-peak background noise of < 0.2 cps for all three resolutions, this allows for achieving the lowest detection limits
• Excellent signal stability:
  • <1% RSD over 10 minutes.
  • <2% RSD over 1 hour.

For further information see the ELEMENT2 Brochure by Thermo Scientific

Acknowledgements

Thanks to Thermo Fisher Scientific for the above documents.