Capabilities and limitations of direct analysis in real time orbitrap mass spectrometry and tandem mass spectrometry for the analysis of synthetic and natural polymers
Maxime C. Bridoux, Xavier Machuron-Mandard
CEA, DAM, DIF, Arpajon, FranceRATIONALE. Despite the widespread use of direct analysis in real time mass spectrometry (DART-MS), its capabilities in terms of accessible mass range and the types of polymers that can be analysed are not well known. The goal of this work was to evaluate the capabilities and limitations of this ionization technique combined with orbitrap mass spectrometry and tandem mass spectrometry, for the characterization (structural and polydispersity metrics) of various synthetic and natural polymers.
METHODS. The capabilities and limitations of DART-MS (and -MS2), using an orbitrap mass spectrometer, for polymer analysis were evaluated using various industrial synthetic polymers and biopolymers. Stainless steel mesh screens secured on a movable rail were used as the sampling surface, onto which 5 μL of various polymers dissolved in tetrahydrofuran were added. Assignment of spectral features and calculation of molecular weight and polydispersity metrics were performed using Polymerix™ software and the results were compared with those obtained by gel-permeation chromatography (GPC).
RESULTS. Protonated oligomers and ammonium adducts were instantaneously detected as the major ionisation products in positive ion mode. Only perfluoropolyethers (PFPEs) were ionised in negative mode and detected as [M]-. ions. Only singly charged molecular species were observed for all oligomers under study, allowing for a rapid determination of the molecular weight and polydispersity metrics of polymers. At elevated DART gas temperatures (400-500°C) the molecular weight and polydispersity metrics compared fairly well with those obtained by GPC, with polymers whose masses ranged from 200 g.mol-1 to 4000 g.mol-1.
CONCLUSIONS. DART-MS allowed the direct and rapid analysis (mass spectra and tandem mass spectra of all the polymers were acquired in seconds) based on the exact masses of their [M+H]+ and [M+NH4]+ ions (in the positive mode) or [M]-. ions (for polymers having a high sensitivity toward electron-capture ionisation such as PFPEs), as well as the exact masses of their product ions, for both synthetic and natural polymers under ambient conditions without any sample pre-treatment.
Joseph R. Swider
The McCrone Group, Westmont, IL
The use of a direct analysis in real time (DART) mass spectrometer (MS) instrument was optimized for 22 compounds of organic explosive residues to provide a guide for DART-MS users in rapid screening of explosive compounds. Samples were introduced as neat solutions and sequential dilutions to determine optimal instrument conditions and lowest concentration detectable. Most compounds were optimized to 250°C in the negative ion mode, and several compounds benefited from the addition of a chloride dopant from methylene chloride (amino-dinitrotoluenes, RDX, EGDN, and PETN). Few compounds were more sensitive in the positive ion mode (TEGDN, DEGDN, HNS, and DMNB). Mixtures of compounds were detected using clean room wipes, directly from their surfaces and from subsequent extractions. Compounds from the mixtures were also successfully detected in soil and from swipes of spiked surfaces. The instrument showed merit in detection of pg/μL solutions for most of the compounds and among the substrates tested.
Yang Wanga, Li Liua, Li Mab, Shuying Liua
Jilin Ginseng Academy, Changchun University of Chinese Medicine, Jilin, Changchun 130117, China, School of Environmental Air Security and Pollution Control Engineering, Jinan University, Guangzhou 510632, China
Direct analysis in real time (DART) coupled with quadrupole time-of-flight mass spectrometry (Q-TOF-MS) was applied to investigate the different types of saccharides including ginseng oligosaccharide extract with minimal sample pretreatment. Helium gas temperature into the DART ion source was adjusted to find optimal ionization temperature for glucose in increments of 50 °C from 50 °C to 450 °C. It was observed that gas temperature had a significant effect on signal intensity in DART mass spectra. The temperature for the glucose ionization should be at least 150 °C, and the signal intensity reached optimal ionization state at 250 °C. With the increase of a sugar chain, a higher gas temperature was needed for saccharide ionization. Interestingly, sugar cluster formation can be observed at 450 °C for disaccharides and trisaccharides. It is found that the [M+NH4]+ ions of trisaccharide and ginseng oligosaccharides can be rarely produced without any derivatization even at 450 °C. All the samples except five carbon monosaccharides can generate the m/z 198 ion, so it is difficult to determine whether a m/z 198 ion is the [M+NH4]+ ion of glucose or merely a sample fragment ion most likely an ammoniated monosaccharide fragment.