Conceptual Demonstration of Ambient Desorption-Optical Emission Spectroscopy Using a Liquid Sampling-Atmospheric Pressure Glow Discharge Microplasma Source.

The concept of ambient desorption-optical emission spectroscopy (AD-OES) is demonstrated using a liquid sampling-atmospheric pressure glow discharge (LS-APGD) microplasma as the desorption/excitation source. The LS-APGD has previously been employed for elemental analysis of solution samples and particulates introduced via laser ablation in both the optical emission and mass spectrometries (OES, MS) modes. In addition, the device has been shown to be effective for the analysis of elemental and molecular species operating in an ambient desorption/ionization mass spectrometry (ADI-MS) mode. Proof-of-concept is presented here in the use of the LS-APGD to volatilize three very diverse sample forms (metallic thin films, dry solution residues, and bulk materials), with the liberated material excited within the microplasma and detected via OES, i.e., AD-OES. While the demonstration is principally qualitative at this point, it is believed that the basic approach may find application across a broad spectrum of analytical challenges requiring elemental analysis, including metals, soils, and volume-limited solutions, analogous to what has been seen in the development of the field of ADI-MS for molecular species determinations.

Parallel, open-channel lateral flow (immuno) assay substrate based on capillary-channeled polymer films.

Presented here is a novel implementation of polypropylene capillary-channeled polymer (C-CP) films, functionalized for bioaffinity separations and implemented as a platform for lateral flow (immuno) assays. The parallel ∼80 µm × 80 µm channels pass test solutions down the 30 mm film length via spontaneous wicking action, setting up the possibility for immobilizing different capture agents in the respective channels. The base-film modification process is divided into two steps: ultraviolet light treatment to improve hydrophillicity of the polypropylene substrate and the physical adsorption of a functionalized lipid tethered ligand (LTL) as a selective capture agent. The entire modification procedure is performed under ambient conditions in an aqueous solution without extreme pH conditions. In this demonstration, physical adsorption of a biotinylated-LTL onto the UV-treated PP surface selectively captures Texas Red-labeled streptavidin (SAv-TR) in the presence of enhanced green fluorescence protein (EGFP), which passes without retention in less than 5 s. In addition to the fluorescence imaging of the protein solutes, matrix assisted laser desorption/ionization-mass spectrometry (MALDI-MS) was used to confirm the formation of the LTL-SAv conjugates on the channel surface as well as to demonstrate an alternative means of probing the capture step. The present effort sets the groundwork for further development of C-CP films as a parallel, multi-analyte LFA platform; a format that to-date has not been described.

Determination of Isoflavone Content in SRM 3238 Using Liquid Chromatography-Particle Beam/Electron Ionization Mass Spectrometry.

The characterization of marker components in botanical materials is a challenging task, and the increased consumption of botanicals and dietary supplements demands a greater understanding of the associated health benefits and risks. In order to successfully acquire and compare clinical results and correlate health trends, accurate, precise, and validated methods of analysis must be developed. Presented here is the development of a quantitative method for the determination of soy isoflavones (daidzin, glycitin, genistin, daidzein, and genistein) using LC-particle beam/electron ionization-MS (LC-PB/EIMS). An internal standard (IS) approach for quantitation with 7-hydroxy-4- chromone as the IS compound was used, with response factors for each individual isoflavone obtained from calibrant solutions. The results from this method were compared with the certified and reference values for National Institute of Standards and Technology (NIST) SRM 3238 Soy-Containing Solid Oral Dosage Form to demonstrate that the method was in control. Results obtained using LC-PB/EIMS were consistent with the NIST certified or reference values and their uncertainties for all five isoflavones, demonstrating that the LC-PB/EIMS approach is both accurate and precise when used for the determination of the target isoflavones in soy-containing dietary supplement finished products while simultaneously providing structural information.

Preliminary Assessment of Potential for Metal-Ligand Speciation in Aqueous Solution via the Liquid Sampling-Atmospheric Pressure Glow Discharge (LS-APGD) Ionization Source: Uranyl Acetate.

The determination of metals, including the generation of metal-ligand speciation information, is essential across a myriad of biochemical, environmental, and industrial systems. Metal speciation is generally affected by the combination of some form of chromatographic separation (reflective of the metal-ligand chemistry) with element-specific detection for the quantification of the metal composing the chromatographic eluent. Thus, the identity of the metal-ligand is assigned by inference. Presented here, the liquid sampling-atmospheric pressure glow discharge (LS-APGD) is assessed as an ionization source for metal speciation, with the uranyl ion-acetate system used as a test system. Molecular mass spectra can be obtained from the same source by simple modification of the sustaining electrolyte solution. Specifically, chemical information pertaining to the degree of acetate complexation of uranyl ion (UO2(2+)) is assessed as a function of pH in the spectral abundance of three metallic species: inorganic (nonligated) uranyl, UO2Ac(H2O)n(MeOH)m(+), and UO2Ac2(H2O)n(MeOH)(m)H(+) (n = 1, 2, 3, ...; m = 1, 2, 3, ...). The product mass spectra are different from what are obtained from electrospray ionization sources that have been applied to this system. The resulting relationships between the speciation and pH values have been compared to calculated concentrations of the corresponding uranyl species: UO2(2+), UO2Ac(+), UO2Ac2. The capacity for the LS-APGD to affect both atomic mass spectra and structurally significant spectra for organometallic complexes is a unique and potentially powerful combination.

Evaluation of synthesized lipid tethered ligands for surface functionalization of polypropylene capillary-channeled polymer fiber stationary phases.

Polypropylene (PP) capillary-channeled polymer (C-CP) fibers have been used in this laboratory as stationary phases for high performance liquid chromatography and solid phase extraction of proteins. Greater selectivity has been realized through the functionalization of the PP fibers through the physical adsorption of commercially available head group-modified poly(ethylene glycol) lipids (PEG-lipids), where the head group is chosen to affect affinity separations. We refer to this general surface modification methodology as lipid tethered ligands (LTLs). In this study, LTLs were synthesized by solid phase synthesis. In comparison to the commercial PEG-lipids, the synthesized LTLs contain no chemically labile phosphate groups. Instead of an ester linkage in the commercial lipids, amide functionality was used in the synthesized LTLs to attach the lipids and ligands. By use of fluorescence imaging of FITC-labeled LTLs, the synthesized LTL was shown to be superior to the commercial LTL in terms of the adsorption efficiency to PP C-CP fibers, the resistance to solvent wash from the PP C-CP fibers, and their chemical stability under acidic, neutral and basic conditions. The PP C-CP fibers functionalized with a synthesized LTL that was biotinylated at the head group are shown to be capable of capturing streptavidin from E. coli cell lysate more efficiently than the PP C-CP fibers functionalized with the commercial biotinylated PEG-lipid. The functionalization of PP C-CP fibers with the synthesized LTLs is a simple, but highly efficient, method to generate novel stationary phases with a variety of functionalities for solid phase extraction and liquid chromatography.

Evaluation of the operating parameters of the liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source for elemental mass spectrometry.

The liquid sampling-atmospheric pressure glow discharge (LS-APGD) has been assessed as an ionization source for elemental analysis with an interdependent, parametric evaluation regarding sheath/cooling gas flow rate, discharge current, liquid flow rate, and the distance between the plasma and the sampling cone of the mass spectrometer. In order to better understand plasma processes (and different from previous reports), no form of collision/reaction processing was performed to remove molecular interferents. The evaluation was performed employing five test elements: cesium, silver, lead, lanthanum and nickel (10(-4) mol L(-1) in 1 mol L(-1) HNO3). The intensity of the atomic ions, levels of spectral background, the signal-to-background ratios, and the atomic-to-oxide/hydroxide adduct ratios were monitored in order to obtain fundamental understanding with regards to not only how each parameter effects the performance of this LS-APGD source, but also the inter-parametric effects. The results indicate that the discharge current and the liquid sampling flow rates are the key aspects that control the spectral composition. A compromise set of operating conditions was determined: sheath gas flow rate = 0.9 L min(-1), discharge current = 10 mA, solution flow rate = 10 µL min(-1), and sampling distance = 1 cm. Limits of detection (LODs) were calculated using the SBR-RSDB (signal-to-background ratio/relative standard deviation of the background) approach under the optimized condition. The LODs for the test elementals ranged from 15 to 400 ng mL(-1) for 10 µL injections, with absolute mass values from 0.2 to 4 ng.

Ambient desorption/ionization mass spectrometry using a liquid sampling-atmospheric glow discharge (LS-APGD) ionization source.

A novel approach to ambient desorption/ionization mass spectrometry (ADI-MS) is described, based on a recently developed liquid sampling-atmospheric pressure glow discharge (LS-APGD) ionization source. The device is essentially unmodified relative to its implementation in elemental mass spectrometry, where the operational space is characterized by low operation power (<10 W) and low solution delivery rates (<50 µL min(-1)). In this implementation, the plasma is produced between a Ni anode and an electrolytic liquid (1 M HNO3) cathode flowing through a glass capillary that is angled towards the sample surface, at a distance of ~2 mm away. Analyte species can be desorbed/ionized from neat solution residues and complex solid samples. The ADI-LS-APGD source is mounted onto the source interface of a Thermo Finnigan LCQ Advantage Max quadrupole ion trap mass spectrometer without modifications to the instrument faceplate or ion optics. Described here is the initial evaluation of the roles of source geometry and working parameters, including electrolytic solution composition and plasma current, on the response of caffeine residues, with preliminary limits of detection based on the relative standard deviation of the spectral background suggested to be on the 10-pg level. Demonstrative spectra are presented for green tea extracts and raw leaves, coffee beans, a dried (raw) tobacco leaf, an analgesic tablet, and paper currency. Versatility is further revealed through the determination of components in common cigarette smoke. In each case, the spectra are characterized by (M + H)(+) species of the expected constituents. The capacity for a single source to perform both in solution and particulate elemental analysis (as shown previously) and ADI of molecular species is unique in the realm of mass spectrometry.