Development of medium pressure laser ionization, MPLI. Description of the MPLI ion source

Abstract

A novel pulsed valve/ion source combination capable of time-resolved sampling from atmospheric pressure has been developed for use with laser ionization time of flight mass spectrometry. The source allows ionization extremely close to the nozzle of the pulsed valve, enabling ultra-sensitive detection of a number of compounds, e.g., NO, at mixing ratios Ͻ1 pptV. Furthermore, at analyte mixing ratios in the ppbV range, the temporal resolution of the system is in the sub-second regime, allowing time-resolved monitoring of highly dynamic and complex mixtures, e.g., human breath or reacting chemical mixtures in atmospheric smog chamber experiments. Rotational temperatures of ϳ50 K have been observed for analytes seeded in the supersonic jet expansion at a distance of 1 mm downstream of the nozzle orifice. The refinement of the original ion source has drastically reduced the impact of reflected laser light and the resultant electron impact signals previously observed. The general applicability of this technique is demonstrated here by coupling the source to commercially available as well as home-built time-of-flight mass spectrometers. Finally, we discuss the MPLI technique in view of the very recently introduced atmospheric pressure laser ionization (APLI) as well as the traditional jet

Electrospray ionization/atmospheric pressure photoionization multimode source for low‐flow liquid chromatography/mass spectrometric analysis

“…Use of a repeller electrode has been previously demonstrated to enhance ion collection at reduced pressures with the photoionization technique of medium pressure laser ionization, either increasing ion intensity26 or ion selectivity;27 however, at atmospheric pressure, the resulting effects are influenced by solvent or solvent‐cluster interactions. As seen in Fig.…”

Simultaneous Measurement of Nitric Oxide (NO) and Nitrogen Dioxide (NO2) in Simulated Automobile Exhaust Using Medium Pressure Ionization—Mass Spectrometry

“…The application and benefits of using an MPLI source are described elsewhere. 36,37 Mass Spectrometer Used with Scheme 2. The mass spectrometer used with the narrow-bandwidth light system (Scheme 2) is a home-built, mobile TOF instrument equipped with a single-stage reflectron.…”

Atmospheric‐pressure laser ionization: a novel ionization method for liquid chromatography/mass spectrometry

“…In view of the presently described newly evolving laser ionization technique operating at ion source pressures around p = 1 atm , the acronym APLI becomes ambiguous. In order to describe the former technique more accurately, the term medium‐pressure laser ionization (MPLI) has been introduced49 with the intention of better distinguishing the three pressure regimes in which currently applied laser ionization techniques operate. The commonly used inlet systems for laser ionization mass spectrometry are shown in Fig.…”

“…The high analyte density allows for selective ultra‐sensitive measurements (see Refs. 46–49 for details). Employing APLI (Fig.…”

“…(d) MPLI approach as described in detail in Refs. 46–49. (e) APLI approach as introduced in this contribution.…”