Article pubs.acs.org/ac
Simultaneous Detection of Polar and Nonpolar Compounds by Ambient Mass Spectrometry with a Dual Electrospray and Atmospheric Pressure Chemical Ionization Source Sy-Chyi Cheng,*,† Siou-Sian Jhang,† Min-Zong Huang,† and Jentaie Shiea*,†,‡ †
Department of Chemistry, National Sun Yat-Sen University, 70 Lienhai Road, Kaohsiung 80424, Taiwan Department of Medicinal and Applied Chemistry, Kaohsiung Medical University, 100 Shih-Chuan 1st Road, Kaohsiung 80780, Taiwan
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ABSTRACT: A dual ionization source combining electrospray ionization (ESI) and atmospheric pressure chemical ionization (APCI) was developed to simultaneously ionize both polar and nonpolar compounds. The source was constructed by inserting a fused silica capillary into a stainless steel column enclosed in a glass tube. A high dc voltage was applied to a methanol solution flowing in the fused silica capillary to generate an ESI plume at the capillary tip. A high ac voltage was applied to a ring electrode attached to the glass tube to generate plasma from the nitrogen gas flowing between the glass tube and the stainless steel column. The concentric arrangement of the ESI plume and the APCI plasma in the source ensured that analytes entering the ionization region interacted with both ESI and APCI primary ion species generated in the source. Because the high voltages required for ESI and APCI were independently applied and controlled, the dual ion source could be operated in ESI-only, APCI-only, or ESI+APCI modes. Analytes were introduced into the ESI and/or APCI plumes by irradiating sample surfaces with a continuous-wavelength laser or a pulsed laser beam. Analyte ions could also be produced by directing the dual ESI+APCI source toward sample surfaces for desorption and ionization. The ionization mechanisms involved in the dual ion source include Penning ionization, ion molecule reactions, and fused-droplet electrospray ionization. Standards of polycyclic aromatic hydrocarbons, angiotensin I, lidocaine, ferrocene, diesel, and rosemary oils were used for testing. Protonated analyte ions were detected in ESI-only mode, radical cations were detected in APCI-only mode, and both types of ions were detected in ESI+APCI mode.
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another study, a heated metal probe was positioned close to a thin-layer chromatography (TLC) plate to perform thermal desorption of analytes such as inks, drugs, explosives, and pesticides on the TLC plate.27,28 The gaseous analytes generated by thermal desorption then entered a source for ESI first followed by corona discharge APCI next. Because thermal desorption generates analytes with low molecular weights (
