Search

In response to Gulf of Mexico deepwater horizon oil spill, we have developed an atmospheric pressure photoionization (APPI) based ultra high performance liquid chromatography-mass spectrometry (UHPLC-MS) method for high-sensitivity analysis of United States Environmental Protection Agency (US EPA) 16 priority pollutant polynuclear aromatic hydrocarbons (PAHs) in oysters. Analyses were performed on an Agilent's Infinity 1290 UHPLC system coupled with a G6140A single quadrupole MS detector with Syagen's PhotoMate® APPI® source. Column separation was achieved using Zorbax Eclipse PAH column. Chlorobenzene was used as an APPI dopant for maximum overall sensitivity. Dynamic linear ranges were evaluated and found to cover 3.6-5.1 (Ave. 4.4) orders of magnitude with R² of at least 0.995. A quick, easy, cheap, effective, rugged, and safe (QuEChERS) extraction and cleanup procedure was used. The spike recoveries ranged from 77% to 110% with %RSD of 0.6-6.7 at spike concentrations below or substantially below the US Food and Drug Administration (FDA) level of concern in oysters. The on-column instrument detection limits (IDLs, 6σ S/N=3) ranged from 8 to 106 pg with an average of 23 pg for 16 PAHs. The method detection limits (MDLs, 6σ S/N=3) ranged from 0.013 to 0.129 ppm with an average of 0.040 ppm for all analytes. These MDLs were about 5 times to over 4 orders of magnitude lower than US FDA levels of concern in oysters., (Copyright © 2012 Elsevier B.V. All rights reserved.)

In this work, we evaluate the performance of liquid chromatography-atmospheric pressure photoionization-mass spectrometry (LC-APPI-MS) for non-aqueous reversed phase analysis of six triacylglycerol model compounds using six binary mobile phases including MeOH/iPrOH, MeOH/CHCl(3), MeOH/CH(2)Cl(2), CH(3)CN/iPrOH, CH(3)CN/CHCl(3), and CH(3)CN/CH(2)Cl(2). All mobile phases give comparably good separation performance on a Gemini C(18) column with carefully adjusted gradient elution programs. APPI sensitivity varies from one mobile phase to the other without dopants; however use of dopants brings sensitivity to comparable levels for all mobile phases. MeOH/iPrOH offers high sensitivity without dopants due to self-doping effect and dopants are not necessary for this mobile phase. Dopants enhance analyte sensitivity to a varying degree for each of the mobile phases tested. Photo-induced chemical ionization (PCI) of solvent may play a significant role in achieving high sensitivity. Two critical parameters affecting sensitivity are photoabsorption cross-sections and ionization potentials of mobile phase solvents. How these mobile phase solvents affect APPI sensitivity and their dependency on dopant use are discussed. All six mobile phases offer comparable overall limits of detection for the analytes tested. These results indicate that LC-APPI-MS is a successful tool for neutral lipid analysis, giving high sensitivity with a variety of non-aqueous mobile phases.

In this work, we optimize parameters and conditions for analysis of fatty acid ester and acylglycerol lipids by atmospheric pressure photoionization-mass spectrometry (APPI-MS). The investigated parameters include atmospheric pressure chemical ionization (APCI) nebulizer/vaporizer physical orientation and APPI lamp face position, solvent selections, mobile phase compositions and flow rates, cone voltages and probe temperatures. APPI sensitivity is found to be highly dependent on mobile phase compositions. Normal phase solvents offer much higher sensitivity and better peak shape than reversed phase for nonpolar lipids. Hexane and isooctane are found to be two solvents generating highest S/N for eicosapentaenoic acid (EPA) methyl ester. The effects of mobile phase flow rates on sensitivity are found to be target analytes and target ions specific. However, the flow rate changes do not significantly affect the sensitivity of three out of four tested analytes under normal phase conditions over tested flow rates of 50-500muL/min. Cone voltage is found to be one of key parameters affecting sensitivity. Optimum probe temperature is found to be more dependent on mobile phase compositions than on the specific target analytes. Aqueous reversed-phase mobile phase requires higher probe temperature than normal phase for better sensitivity. More volatile mobile phase solvents require lower probe temperature for analyte desolvation. APPI offers four to five decades of linear ranges under normal phase condition. Full scan mass spectra of individual lipid standards, custom lipid mixtures and natural fish oil show that APPI spectra are clean and very easy to interpret. APPI also gives stable, reproducible peak responses with good peak shape. Limits of detection (LODs) by FIA (S/N=3) are estimated to be 12pg for EPA methyl ester and monoarachidin, 19pg for diarachidin and 7pg for trielaidin. LODs on-column are estimated to be 94pg for EPA methyl ester, 90pg for monoarachidin and diarachidin and 24pg for trielaidin.