We have developed a novel spray ionization method for interfaces in capillary electrophoresis/mass spectrometry and liquid chromatography/mass spectrometry. This method is called "sonic spray" ionization. In this method it is not necessary to apply an electric field to the capillary of the ion source, which operates at room temperature. A solution in methanol and water from a fused-silica capillary is sprayed under atmospheric pressure with nitrogen gas flow coaxial to the capillary. Gaseous ions as well as droplets are produced from the solution by the spray, and the positive ions are analyzed with a doublefocusing mass spectrometer. We found that the detected ion intensity depends on the Mach number or the gas velocity. Ions are detected at a gas velocity higher than a certain value, and the ion intensity has a maximum at a Mach number of about 1, i.e., the sonic velocity. Preliminary results for solutions of dopamine, lysine, and gramicidin S are presented.Spray ionization methods such as atmospheric pressure chemical ionization (APCI),1 thermospray (TS),2 electrospray (ES),3 ion spray (IS),4 and atmospheric pressure spray (APS)5 have been developed for use as an interface in liquid chromatography/mass spectrometry (LC/MS). However, the use of these ionization methods is limited by restrictions in solvent composition, solution flow rate, and chemical species being analyzed. Capillary electrophoresis (CE) has recently been recognized as a powerful method for solution separation.6 Also, combined CE/MS with ES interface has been developed.7In these interfaces, ions or molecules in a solution are effectively converted to gaseous ions. Charged droplets are produced by spraying the solution, and the gaseous ions are emitted from the droplets. For example, in TS and APS, charged

We have developed a sonic spray ionization method, in which a methanol and water solution is sprayed from a fused-silica capillary with gas flow coaxial to the capillary. Ions as well as charged droplets are produced under atmospheric pressure, and their intensities depend on the gas flow rate (gas velocity). Positive ions produced from dilute solutions of molecules regarded as neurotransmitters, such as catecholamine, by this ionization method have been analyzed with a quadrupole mass spectrometer. The protonated dopamine molecule is detected in the spray of the 10 nM solution, and the mass spectrum is compared with that obtained by the ion spray ionization method. A comparison between the mass-analyzed ion intensity and the ion current, which represents the sum of ions and charged droplets, shows that most ions are produced from the charged droplets after spraying. Furthermore, we found that the charged droplet formation cannot be ascribed to the traditional models of friction electrification, electrical double layer, or statistical charging. An explanation is proposed based on the ion concentration distribution in a small droplet.

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Anodizing of Ta-Al bilayers ͑aluminum deposited on tantalum͒ was performed in 0.2 M H 2 C 2 O 4 solution to transform the aluminum metal into its nanoporous oxide followed by pore widening and reanodizing to different voltages in the range of 100-600 V. The anodic films consist of an upper layer of nano-sized tantala columns penetrating into the pores and a lower layer of continuous tantalum oxide under the porous alumina film. The columns are mainly composed of tantalum pentoxide and tantalum sub-oxides TaO 2 , Ta 2 O 3 , and TaO while the lower film layer is tantalum monoxide. At the boundary between the columns and alumina cells, a region of mixed ͑composite͒ Ta 2 O 5 and Al 2 O 3 is formed due to channeling of the ionic current through the outer part of the alumina cell walls. The relationship between the layers and the ionic transport during oxide growth depend on pore size and formation voltage. The dielectric properties of the anodic films are close to those of an ideal capacitor. Voltage-independent apparent dielectric constant of 12.6 was determined for the films formed by normal reanodizing. The relatively higher dielectric constant for the films formed by reanodizing through the widened pores rises from 17.6 to 24.0 in the voltage range of 270-400 V, which is due to the change in morphology, relative amount and chemical composition of anodic tantala in the complex film structure. The nanocomposite anodic films can be used as dielectrics for high-voltage low-leakage current electrolytic capacitors.

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