Quantitative Analysis of Nitrotoluene Isomer Mixtures Using Femtosecond Time-Resolved Mass Spectrometry

Abstract

Discrimination of isomers in a mixture is a subject of ongoing interest in biology, pharmacology, and forensics. We demonstrate that femtosecond time-resolved mass spectrometry (FTRMS) effectively quantifies mixtures of ortho-, para-, and meta-nitrotoluenes, the first two of which are common explosive degradation products. The key advantage of the FTRMS approach to mixture quantification lies in the ability of the pump–probe laser control scheme to capture distinct fragmentation dynamics of each nitrotoluene cation isomer on femtosecond timescales, thereby allowing for discrimination of the isomers using only the signal of the parent molecular ion at m/z 137. Upon measurement of reference dynamics of each individual isomer, the molar fractions of binary and ternary mixtures can be predicted to within ∼5 and ∼7% accuracy, respectively.

Quantitative Identification of Nonpolar Perfluoroalkyl Substances by Mass Spectrometry

“…The dominant mechanism of linear alkane fragmentation is σ-cleavage involving secondary carbons, followed by σ cleavage of CH 2 moieties . Based on projects by our group and others aimed at the identification and quantification of isomeric mixtures using femtosecond SFI MS, − we explore if a similar approach can be used to identify and quantify mixtures of PFAS. Quantitative mass spectrometric identification without chromatographic separation of isomeric mixtures by femtosecond laser pulse ionization was pioneered by Dela Cruz et al , Multidimensional MS was accomplished by using differently shaped laser pulses to improve the identification of warfare agents and the analysis of mixtures of isomers. , Advantages of SFI-MS include their speed, sensitivity, and minimal analyte usage.…”

“…The chirped pulses were used to analyze ternary mixtures of ortho -, meta -, and para -fluorotoluene . More recently, binary and ternary mixtures of ortho , meta , and para -nitrotoluene were analyzed by comparing the time-dependence of the parent molecular ion following 1300 nm pump and 650 nm probe pulses …”

“…33 More recently, binary and ternary mixtures of ortho, meta, and para-nitrotoluene were analyzed by comparing the time-dependence of the parent molecular ion following 1300 nm pump and 650 nm probe pulses. 34 The key for identifying between the two PFAS compounds is to capitalize on small differences in certain ion yields between the two compounds. To do this, the 16 largest peaks in the mass spectrum are chosen to represent the total ion yield.…”

Experimental and Theoretical Analysis of Tricyclic Antidepressants by Ultraviolet Picosecond Laser Desorption Post-Ionization Mass Spectrometry

“…Experimental application of single-photon ionization to pulsed laser or ion desorption (i.e., for laser secondary neutral mass spectrometry) remains largely confined to molecules with ionization energies below 8 eV due to the limited laboratory sources of pulsed vacuum ultraviolet radiation . However, ultraviolet, ∼30 ps-LD can be extended by coupling to multiphoton or strong field ionization. ,, Mid-infrared ultrashort pulse-LD vibrationally excites water , and is well developed for hydrated biological samples. 213 nm, 30 ps-LD will electronically excite a wide range of materials, but requires further study to determine any advantages over ns-LD at 213 nm .…”

“…Picosecond-LDPI-MS is conceptually similar to MALDI-MS with the substantial differences that there is no matrix, a picosecond-pulsed laser replaces the nanosecond-pulsed desorption laser, and time-delayed pulses from a second laser induce photoionization. Here, a 157 nm (7.9 eV) fluorine excimer laser is used for single-photon ionization, but other postionization lasers can be used in LDPI-MS to induce multiphoton ionization or strong field ionization. ,, Prior work has examined both ns- and fs-LDPI-MS, making the use of ps-LDPI-MS an obvious avenue for investigation. Picosecond-LDPI-MS with 213 nm (5.8 eV), ∼30 ps-LD is used here to detect imipramine and three other tricyclic antidepressants: clomipramine, desipramine, and amitriptyline.…”