AtomScopy

Techniques

Elemental Microscale Imaging / Solid sampling

Laser Ablation ICP-MS

Laser Ablation (LA) ICP-MS is a powerful elemental imaging technique which can visualize the spatial distribution of almost any element in solid samples with a resolution of 1-100 micrometer. The technique is highly sensitive with detection limits down to zeptogram levels (or ppb – parts per billion).

XRF Imaging

X-ray fluorescence imaging systems are a powerful tool to non-destructively visualize elements in solid samples. The technique is generally applicable to low mass elements and has low operating costs compared to other techniques. This is why this technique is a popular choice in routine labs.

Bulk Analysis

ICP-MS/OES

ICP-MS/OES is a versatile, powerful elemental analysis techniques which can handle almost any liquid sample. Extremely low (ppt) detection limits and very good linear dynamic range make this technique one of the most popular analysis techniques in the field of elemental analysis. This technique is often used in combination with sample digestion procedures, such as microwave digestion.

XRF Analyzer

XRF pellet analyzers provide a fast and reliable method of major element analysis, suitable for materials that can be pelletized using a pellet press and a binder material.

ICP-MS/OES

ICP-MS is the gold standard technique for elemental analysis of solutions. ICP-MS instruments can be conceptually broken up into 5 modules: (i) the sample introduction system, (ii) the ionization source: the inductively coupled plasma, an RF plasma source operating at > 4000K, (iii) the ion extraction system, (iv) the mass analyzer and (v) the ion detector. Samples are introducted into a nebulizer via a liquid introduction system consisting of peristaltic pumps, capillary systems, or syringe systems. The nebulizer creates an aerosol, which is run through a spray chamber. The aerosol is transported by a carrier gas to an Ar-based inductively coupled plasma source which will desolvate, atomize, and ionize the aerosol. The ions are extracted by the interface from the analytical zone in the central channel of the ICP operating at atmospheric pressure (β‰… 105 π‘ƒπ‘Ž) into the high vacuum environment (10βˆ’1 βˆ’ 10βˆ’6 π‘ƒπ‘Ž) maintained within the MS. Subsequently, ion optics guide the ion beam into a mass analyzer and filter away photons. The mass analyzer will either spread the ions temporal-spatially according to their π‘š/π‘ž, or filter ions with a specified π‘š/π‘ž prior to ion detection.Β 

Advantages/Disadvantages of ICP-MS

As an analytical tool, ICP-MS boasts distinct advantages such as a wide linear dynamic range, low LODs, high sample throughput, fast read-out, and full elemental mass spectrum coverage (enabling the detection of individual isotopes). Since its inception in the 1980’s the technique has been succesfully applied in countless applications. With the arrival of high-matrix tolerant ICP and specialist introduction systems, the direct analysis of organics, oils and high salt-containing solutions such as seawater has become possible.

The limitations of the technique include: (i) low tolerance for high total dissolved solids content solutions, (ii) spectral interferences, (iii) matrix effects, and (iv) considerable purchase and operating costs. Although full-spectrum capabilities are more
readily accessible in LA-ICP-OES (in terms of purchase cost), mass spectrometry is preferred due to significantly better LODs. Compared to TIMS and NAA, ICP-MS is characterized by superior ease-of-analysis; this is especially the case when an LA-system is used, as minimal sample preparation is required. The main application of ICP-MS today is the trace element and isotopic analysis of solutions in industry, the academia now represents only a minor fraction of the market.Β Β 

Laser Ablation ICP-MS

Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) is a powerful elemental and isotopic imaging technique based on a hyphenated setup of an ICP-MS instrument and a high-power laser used for sample introduction via laser ablation. The laser beam, impinged on the sample surface can remove material from the surface in the form of fine particles (an aerosol) through thermal and photon-dissociation processes (i.e. laser ablation). The aerosol is then transported to the plasma source of the ICP-MS instrument, which is capable of atomizing and ionizing the incoming particle stream. The positive excited ions are extracted into a mass analyzer of a mass spectrometer, after which a detector is used to characterize the position and/or time-of-arrival of individual ions into the detector.

Advantages/Disadvantages of LA-ICP-MS

The default sample introduction device for ICP-MS is a pneumatic nebulizer and a spray chamber, hence, solid materials have to be taken into solution prior to analysis. The direct in-situ analysis of solid material using laser ablation can however be preferable if the sample of interest is very hard to dissolve, such that an elaborate sample pre-treatment, increasing the risk of analyte losses or contamination, is required. In general, no sample preparation is required.

  • Solid sampling analysis is further characterized by a much higher sample throughput compared to liquid analysis. A characterization of the bulk contents of a solid material can be performed in a fraction of a second.
  • Full dissolution of a sample, or large scrapings of material are not needed. Despite being a destructive technique, the sample damage is microscopic, and can be made so small that is no longer visible by the human eye. The typical sample mass of sample removed is in the femtogram to zeptogram range
  • Improved absolute limits of detection. As the material that is introduced into the plasma is in a dry state, spectral interferences from hydroxides are heavily suppressed. In general, the dry plasma produces much cleaner/simpler spectra relative to solution ICP-MS. Compared to other elemental probes such as lab-scale XRF or LIBS, LA-ICP-MS is significantly more sensitive, with limits of detection in the ppb – parts per billion (and in some cases ppt) range.
  • The mass spectrometers used typically have a very wide linear dynamic range, from 10E6 to 10E9. This means that trace elements and major elements can be quantified simultaneously.
  • The mass spectrometer can monitor multiple elements. The information produced by LA-ICP-MS can cover a very large portion of the periodic table. Almost any element is accessible, with few exceptions (H, N, O, Ar and F). This also allows for trace element fingerprinting of solid samples, e.g. for provenance determination or forensic analysis.
  • The ability of the laser to sample the material at a well-defined location – the diameter of the laser beam can be varied from < 1 Β΅m to > 100 Β΅m, while the penetration depth per shot is 10-500 nm allows for spatially resolved analysis of the sample surface. LA-ICP-MS can produce a 2- or 3-dimensional image of the elemental and isotopic distribution of the sample surface, as well as depth profiles. Local inclusions or sample defects can also be specifically targeted.
  • A wide variety of samples can be analyzed, From conducting to non-conducting, inorganic to organic, almost any material is amendable to LA-ICP-MS. Even liquids are amendable in some cases. This is why the application field for the technique ranges from biology/medical/pharma, forensic, archaeology and geology to solid state. Furthermore, the analysis is performed under atmospheric pressures, so samples prone to outgassing are also amendable. Cryogenic options are also available.
  • LA-ICP-MS can detect multiple nuclides of most elements at high precision, enabling isotopic analysis of materials. This has many applications, e.g. for geochronology.
  • Laser ablation can be coupled to any type of ICP-MS. This can range from quadrupole-based systems, to sector-field MS, or even multi-collector ICP-MS, which is a dedicated tool for high-precision isotopic analysis.

XRF & Imaging

X-ray fluorescence spectroscopy is an excellent quantitative, sensitive elemental analysis technique, suitable for non-destructive and non-contact analysis. The technique is broadly applied in academia and industry in both lab-based systems and large accelerator installations. XRF is a fluorescence effect in the X-ray range. High energy photons of a wavelength of 0.01-10 nm (energy range of ca. 100eV-100keV), which is in the range of interatomic distances, can transfer their energy to electrons of the inner atomic orbitals upon photon-matter interaction, exciting these inner shell electrons towards higher orbitals, or ejecting them with an πΈπ‘˜ = β„Žπœˆ βˆ’ 𝐸𝑏𝑖𝑛𝑑𝑖𝑛𝑔 (the photoelectric effect) and creating inner shell vacancies. Relaxation of the electron cloud to the ground state can provoke: i) the emission of fluorescence photons (π‘π‘’π‘šπ‘–π‘ π‘ π‘–π‘œπ‘› = πœ”) with energies equivalent to the energy differences of electron transitions of the electron cascade and wavenumber πœˆΜƒ = π‘˜(𝑍 βˆ’ 𝜎) with 𝜎 a screening constant, and ii) internal conversion (radiationless transitions) with energy dissipation towards vibrational modes, and iii) Auger electron emission. As the energy differences between the shell levels are unique to each element, the energy of the X-ray photon can be used to identify the element. The detection of these X-ray photons take place by specialized detectors, such as silicon drift detectors, which can discriminate the energy and quantity of the incoming photons. With the use of standards, the number of collected photons can be linked to a concentration in a sample. By illuminating only small zones of a sample for each analysis, the elemental distribution of a sample can be mapped. Note that X-rays can penetrate dozens of mm into a sample, so the information revealed also pertains to the elemental distribution inside a sample.