Extractive-liquid sampling electron ionization-mass spectrometry (E-LEI-MS): a new powerful combination for direct analysis

Abstract

One of modern analytical chemistry main challenges is providing as fast as possible results in different application fields. In this view, real-time analysis techniques are experiencing ever-increasing success as they can provide data quickly, almost without sample preparation steps. Most of real-time approaches are based on direct mass spectrometry (DMS), a method of analyzing samples without the need for separation or pre-treatment steps. Instead, the sample is directly introduced into the mass spectrometer for analysis. In this context, ambient ionization mass spectrometry (AIMS) techniques are widely represented and successfully used. Extractive-liquid sampling electron ionization-mass spectrometry (E-LEI-MS) represents a different analytical strategy that allows coupling ambient sampling with electron ionization (EI), avoiding any sample preparation step and providing identification based on the comparison with the National Institute of Standards and Technology (NIST) library spectra. E-LEI-MS consists of a dispositive for solvent release and sampling at ambient conditions coupled with an EI source of a single quadrupole mass spectrometer. A micromanipulator allows fine (x,y,z) positioning of a sampling tip. MS can operate in scan or SIM modes depending on the application goals and requirements. Several preliminary successful results were already obtained due to the highly informative EI mass spectra generation. The system was applied to the analysis of active ingredients in pharmaceutical tablets, pesticides on fruit peel, a drug of abuse (cocaine) determination in banknotes, and analysis of unknown components on painting surfaces. Both forensic and artwork applications allowed determining the spatial distribution of the analytes. Here we present a proof-of-concept of E-LEI-MS for targeted/non-targeted analysis and semi-quantitative detection.

Figure 1

Configuration of the E-LEI-MS system.

Figure 2

(A) Analysis of a Surgamyl tablet: TIC; (B) NIST library spectrum matching: red, experimental spectrum; blue, library spectrum. The arrow indicates the sampling start.

Figure 3

(A) Analysis of a Brufen tablet: TIC; (B) NIST library spectrum matching: red, experimental spectrum; blue, library spectrum. The arrow indicates the sampling start.

Figure 4

(A) Analysis of a NeoNisidina tablet: TIC; (B) EI experimental full spectrum; (C) acetaminophen selected ions: SIM; (D) acetylsalicylic acid selected ions: SIM; (E) caffeine selected ions: SIM. The arrow indicates the sampling start.

Figure 5

(A) Analysis of an orange peel fortified with chlorpyrifos: TIC; (B) analysis of an orange peel fortified with imazalil: TIC; NIST library spectra matching: red, experimental spectra for chlorpyrifos (C) and imazalil (D); blue, library spectra. The arrows indicate the sampling start.

Figure 6

(A) Analysis of spots 1–3 (intact) and 4 (cocaine) on a banknote: TIC; (B) EI experimental full spectrum of a negative spot (matrix); (C) NIST library spectrum matching: red, experimental spectrum; blue, library spectrum. The arrow indicates the sampling start.

Figure 7

(A) Spectrum obtained from the analysis of the painting surface: TIC; (B) spectrum obtained from the analysis of the painting deeper layer: TIC. NIST library spectra matching: red, experimental spectra for isopropyl myristate (C) and isopropyl palmitate (D); blue, library spectra.