Thin layer chromatography/desorption flame-induced atmospheric pressure chemical ionization/mass spectrometry for the analysis of volatile and semi-volatile mixtures.

Flame-induced atmospheric pressure chemical ionization (FAPCI) has been used to directly characterize chemical compounds on a glass rod and drug tablet surfaces. In this study, FAPCI was further applied to interface thin layer chromatography (TLC) and mass spectrometry (MS) for mixture analysis. METHODS: A micro-sized oxyacetylene flame was generated using a small concentric tube system. Hot gas flow and primary reactive species from the micro-flame were directed toward a developed TLC gel plate to thermally desorb and ionize analytes on the gel surface. The resulting analyte ions subsequently entered the MS inlet for detection. RESULTS: A 1-1.5-mm-wide light-brown line was observed on the TLC plate after the desorption FAPCI/MS (DFAPCI/MS) analysis, revealing that the gel surface withstood a high temperature from the impact of the micro-flame. Volatile and semi-volatile chemical compounds, including amine and amide standards, drugs, and aromatherapy oils, were successfully desorbed, ionized, and detected using this TLC/DFAPCI/MS. The limit of detection of TLC-DFAPCI/MS was determined to be 5 ng/spot for dibenzylamine and ethenzamide. CONCLUSIONS: TLC/DFAPCI/MS is one of the simplest TLC-MS interfaces showing the advantages such as low costs and an easy set up. The technique is useful for characterizing thermally stable volatile and semi-volatile compounds in a mixture.

Efficiency of a Novel Light-Emitting Diode (LED) Trap for Trapping Rhyzopertha dominica (Coleoptera: Bostrichidae) in Paddy Rice Storehouses.

The lesser grain borer Rhyzopertha dominica is the major pest of stored paddy rice globally, including in Taiwan. It has strong phototaxis and is good at flying, suitable for developing a light-trapping method to monitor and control it. In the present study, a wavelength of light-emitting diodes (LEDs), i.e., 373 nm, was determined to be the most efficient to trap R. dominica using a dodecagon maze. Accordingly, an LED trap, named the Taiwan Agricultural Research Institute-LED (TARI-LED) trap, was invented, which comprised LEDs of two distinct wavelengths (373 and 408 nm), a wavelength switch, a suction fan, and an insect collector. The trapping efficiency was assessed in a 4-m3 laboratory arena and two paddy rice storehouses. An initial assessment was performed in the laboratory arena and showed that the TARI-LED trap with 373-nm wavelength for R. dominica rapidly increased in the first 30 min, reaching the highest trapping rate (68.5%) after 3 h. In addition, no significant difference was observed between the suction fan turned on or off. The field tests showed that the 373-nm wavelength had the highest effectiveness for trapping R. dominica in the two paddy rice storehouses, and no significant difference was observed in the number of R. dominica trapped by the 373-nm TARI-LED trap or the CDC-UV light trap. In conclusion, our TARI-LED trap 373 nm exhibited high efficiency in trapping R. dominica in paddy rice storehouses. Moreover, a suction fan-free design should benefit long-term and safe use in paddy rice storehouses trapping R. dominica.

Gas chromatography combined with flame-induced atmospheric pressure chemical ionization mass spectrometry for the analysis of fatty acid methyl esters and saturated hydrocarbons.

A simple flame-induced atmospheric pressure chemical ionization (FAPCI) source was developed to couple a gas chromatograph (GC) with a mass spectrometer (MS). The interface consisted of a heated transfer line and a high voltage-free ambient FAPCI source. Nitrogen gas flowing through the heated transfer line was utilized to deliver the analytes eluted from a GC column to the ionization region. A micro oxyacetylene flame was positioned under the exit of heated transfer line, which generated primary charged species in the ionization region. Since the temperature at the ionization region was below 200 °C, the analytes were not thermally decomposed. Protonated analytes were formed by reacting the analytes with flame-induced charged species through ion-molecule reactions (IMRs). The simple GC-FAPCI/MS was used to characterize a series of fatty acid methyl esters (FAMEs) and long-chain normal alkanes, which showed protonated FAME and oxidized n-alkane ions on the mass spectra. The limits of detection (LODs) for C15:0 to C25:0 FAMEs were 1-2.5 pg. A calibration curve ranging from 2.5 to 500 pg, with a R2 value of 0.9821, was obtained.

A SCAR-based method for rapid identification of four major lepidopterous stored-product pests.

Since Taiwan became a World Trade Organization member in 2002, large quantities of grain have been imported from different countries, and insect pests are frequently intercepted from these imported commodities in quarantine inspection. Because most insects are intercepted as immature forms, morphological identification is problematic; therefore, we developed a DNA identification method based on a sequence-characterized amplified region- polymerase chain reaction (SCAR-PCR). Three sets of multiplex SCAR-PCR mixtures, namely SCAR-I, -II, and -III, were developed with each set composed of four species-specific primer pairs derived from the genomic DNA of four major lepidopterous stored-product pests: Corcyra cephalonica (Stainton), Cadra cautella (Walker), Sitotroga cerealella Oliver, and Plodia interpunctella (Hübner). The SCAR-I amplicons of C. cephalonica, C. cautella, S. cerealella, and P. interpunctella were 205, 550, 324, 382 bp, respectively, while those of SCAR-II were 341, 565, 261, and 170 bp, and those of SCAR-III were 514, 555, 445, and 299 bp. These multiplex PCR mixtures could sensitively and unambiguously detect and identify in approximately 5 h individuals among the four lepidopterous pests intercepted in imported stored-products. In summary, the SCAR-PCR method we developed represents a rapid, sensitive and accurate technique for identifying insect species of stored products in plant quarantine operation.

Electrospray-assisted laser desorption/ionization mass spectrometry for direct ambient analysis of solids.

A new method of electrospray-assisted laser desorption/ionization (ELDI) mass spectrometry, which combines laser desorption with post-ionization by electrospray, was applied to rapid analysis of solid materials under ambient conditions. Analytes were desorbed from solid metallic and insulating substrata using a pulsed nitrogen laser. Post-ionization produced high-quality mass spectra characteristic of electrospray, including protein multiple charging. For the first time, mass spectra of intact proteins were obtained using laser desorption without adding a matrix. Bovine cytochrome c and an illicit drug containing methaqualone were chosen in this study to demonstrate the applicability of ELDI to the analysis of proteins and synthetic organic compounds.

Eliminating the interferences from TRIS buffer and SDS in protein analysis by fused-droplet electrospray ionization mass spectrometry.

Multiply charged protein ions were detected from the solutions containing a high concentration of tris(hydroxymethyl) aminomethane buffer (TRIS) and sodium dodecyl sulfate (SDS) using fused-droplet electrospray ionization mass spectrometry (FD-ESI/MS). The sample aerosols were generated at ambient temperature with a pneumatic nebulizer commonly used to produce sample aerosols in an atmospheric pressure chemical ionization (APCI) source. The aerosols were carried by nitrogen gas to the tip of a capillary where charged methanol droplets had been continuously generated by electrospraying an acidic methanol solution. The neutral sample aerosols then fused with the charged methanol droplets and electrospray ionization proceeded from the newly formed fused droplets to generate multiply charged protein ions. Because of its low solubility in methanol, TRIS molecules (concentration as high as 1 M) were efficiently excluded from the newly formed droplets and the protein ion signals were detected and observed in the mass spectra. To remove the interferences from SDS, equal moles of positively charged cetyltrimethylammonium bromide (CTAB) was added into the SDS containing sample solution to form the dodecyl sulfate-cetyltrimethylammonium ion pair (DS-CTA). The DS-CTA ion pair has a low polarity and solubility in methanol and is excluded from the fused droplet. Protein ions were still detected from the solution containing 10(-2) M of SDS.