PIES plasma cell in operation.

Lenterra is developing a miniature analytical instrument which combines the advantages of fast gas chromatography (GC) and specific gas detection, capable of sample identification independently from GC column retention time.

 This device relies on a new technology called Penning Ionization Electron Spectroscopy (PIES) in plasma. The patented PIES technique consists of the measurement of the energy of electrons liberated by Penning ionization collisions between helium metastable atoms and analyte molecules in the afterglow of a gas discharge. Since the energy of Penning electrons is specific to the species, the resultant data can be used to identify gas components and measure their concentrations.

Advantages of PIES Detection

Demand exists for gas analysis instruments that are small in size, cheap in price, and versatile in functionality. A combination of a short-column fast-chromatographic separation with a simple and rugged detector capable of identifying unknown species is an ideal instrument for modern analytical needs.
The analytical platform based on PIES technology is a combination of a miniature GC column and a PIES detector working in isothermal mode thus reducing the size of the GC element and providing the possibility of realizing the PIES gas analyzer in a miniaturized, portable form. PIES enables identification of coeluting gases based on unique spectral signatures, independently of GC retention time, which significantly reduces the requirements for accurate temperature and flow control in the GC column. No optics or high vacuum are required in PIES technology, and the spectra are recorded using a collector electrode placed inside a glow discharge cell.

Fundamental Principles

Selective detection of gases, in which both the concentration and type of gas can be determined, is possible through the measurement of a variety of fundamental quantities. These include molecular mass (as in mass spectrometry), resonant electromagnetic emission/absorption (as in photon spectroscopy), and column retention time (as in gas and liquid chromatography). A less common quantity that can be used is the energy of electrons produced through ionization.

Penning ionization is a phenomenon in which an excited atom or molecule collides with another atom or molecule resulting in ionization of that particle. The electron produced in such a collision possesses a kinetic energy equal to the energy originally stored in the excited particle, minus the energy required to ionize the second particle (and any excitation energy carried away by the new ion). Penning reactions involving particular species of particles result in specific electron energies which make up spectral “fingerprints” that can be used to identify gases (much like in the more conventional optical spectroscopy). Measurement of these electron energy spectra is called Penning ionization electron spectroscopy (PIES).

PIES can be performed by using a glow discharge plasma, in which electrical energy is used to ionize a gas, to form a population of excited particles necessary to produce Penning ionization. A commonly used atomic species for this is helium, which has a metastable state with sufficient energy to ionize the vast majority of molecular species. Helium acts as a carrier gas, with which small amounts of an analyte gas are mixed. The spectrum of electron energy produced through Penning ionization in the afterglow of this helium-analyte plasma is measured by an electrical probe, from which the identification and concentration of the analyte can be determined.

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