JEOL Resources

Aperture Size Influences Oxidation in Positive-Ion Nitrogen Direct Analysis in Real Time Mass Spectrometry

Fri, 10 Jun 2022 09:31:31 GMT

Abstract

Direct Analysis in Real Time (DART) mass spectrometry commonly uses helium as the DART gas. With the looming helium shortage, other gases are being evaluated for DART. Nitrogen is inexpensive and readily available, making it a desirable alternative. However, NO⁺ reagent ions present in positive-ion nitrogen DART result in extensive oxidation for many compounds. The DART source uses a ceramic insulator cap to protect the operator from electrical shock. The most common cap has an aperture with a 2.5 mm inner diameter, through which the gas exits the DART source. By using a cap with a narrow (0.5 mm) ID, oxidation can be significantly reduced for nitrogen DART. The 0.5 mm cap is hypothesized to reduce back-diffusion of atmospheric oxygen into the DART source, with a reduction in the relative abundance of NO⁺ and increase in the relative abundance of [(H₂O)₂ + H]⁺ as the reactive species responsible for ionization of the analytes.

To access this article, please click here: https://doi.org/10.1021/jasms.2c00115

Detecting the color chemicals in autumn leaves by using The Ambient Ionization Toolbox™

Tue, 27 Oct 2020 13:06:12 GMT

The AccuTOF-DART Ambient Ionization Toolbox® provides multiple methods for chemical analysis with ambient ionization, without having to change ion sources. This makes it fast and easy to characterize chemical compounds with different polarities and chemical structures, such as the chemical compounds that produce the bright colors of autumn leaves.

For the leaf extracts, Argon DART with chlorobenzene dopant was highly selective for detecting conjugated nonpolar compounds such as phytosterols and carotenoids. PaperSpray and MAIV were effective for detecting charged and polar compounds such as chlorophyll and anthocyanins.

Identifying “Buried” Information in LC/MS Data

Wed, 04 Mar 2020 11:58:09 GMT

It is not always easy to identify minor unknown components in complex LC/MS datasets. The new DART™ ion source screened for components that were not immediately recognized in LC/MS analysis of tea samples. LC/TOFMS datasets can contain high-resolution, exact-mass data for all ionized components of a complex mixture. Even with concurrent UV detection and chromatographic enhancement software, it is not always easy to identify all of the components that are present in the dataset. Furthermore, suppression effects may mask important information. Here, a new technique known as Direct Analysis in Real Time (DART™) was used to screen tea samples and provide elemental compositions for minor components that were “buried” in LC/MS data collected for tea analysis. DART is a powerful new ionization method that permits direct analysis of solid, liquid, or gas samples at atmospheric pressure and ground potential. DART has been applied to rapid in-situ analysis of a very wide range of materials ranging from drugs to explosives, foods, and beverages.

GC/MS with a DART® Ion Source

Wed, 04 Mar 2020 11:40:51 GMT

Experimental Conditions

A JEOL AccuTOF-DART mass spectrometer was used as the detector. The GC/MS interface consisted of short piece of 1/8 inch OD copper tubing wrapped with heat tape. A thermocouple was used to check the interface temperature. The GC column extended about 1 cm from the tubing into the heated gas stream of the DART ion source and positioned directly in front of the sampling orifice for the mass spectrometer atmospheric pressure interface. The DART source was operated with helium gas with the gas heater set to 300 degrees C. The GC was operated with the standard GC column (30 m ID x 0.32 mm film thickness DB-5 column) used for GC/MS measurements in our laboratory. GC conditions for the Grob mix were: split injection, oven temperature ramped from 40 to 200 degrees at 6 degrees per minute.

Elemental Compositions from Exact Mass Measurements and Accurate Isotopic Abundances

Wed, 04 Mar 2020 10:34:44 GMT

Exact masses have been used for decades to calculate elemental compositions for known and unknown molecules. The traditional approach calculates all possible combinations of user-specified atoms that fall within a given error tolerance of a measured mass. The number of possible combinations increases dramatically with increasing mass and as more atoms are included in the search set. In many cases, it is not possible to determine a unique composition based on mass alone. A common source of error in measuring isotopic abundances with scanning mass spectrometers is related to fluctuations in ion current during measurement. The AccuTOF family of mass spectrometers overcomes this problem by analyzing all of the isotopes formed at the same instant. Combined with a high-dynamic-range detector, this provides highly accurate isotopic abundances. It has been shown that accurately measured isotopic abundances can be combined with measured exact masses to dramatically reduce the number of possible elemental compositions for an unknown. It is often possible to deduce a unique elemental composition, facilitating the identification of unknown substances.

DART Contamination Resistance: Analysis of Compounds in Saturated Salt and Buffer Solutions

Sun, 23 Feb 2020 15:22:40 GMT

50 ppm solutions of chlorpromazine were prepared in ultrapure deionized (DI) water, aqueous solutions of saturated sodium chloride and saturated potassium phosphate buffer, and raw urine. Two microliters of each solution were applied to glass melting point tubes and analyzed by DART.

The mass spectra are shown below. All spectra are characterized by [M+H]⁺ and there is no evidence of [M+Na]⁺ or [M+K]⁺. Sample suppression is not observed at this concentration.