Analytical characterization of microfabricated SU-8 emitters for electrospray ionization mass spectrometry

We present a detailed optimization and characterization of the analytical performance of SU-8-based emitters for electrospray ionization mass spectrometry (ESI/MS). The improved SU-8 fabrication process presented here enhances patterning accuracy and reduces the time and cost of fabrication. All emitters are freestanding and enable sample delivery by both pressure-driven and spontaneous flows. The optimized emitter design incorporates a sharp, double-cantilevered tip implemented to the outlet of an SU-8 microchannel and provides highly sensitive ESI/MS detection. Moreover, the optimized design allows the use of relatively large microchannel dimensions (up to 200 x 50 microm(2), w x h) without sacrificing the detection sensitivity. This is advantageous with a view of preventing emitter clogging and enabling reproducible analysis. The measured limits of detection for the optimized emitter design were 1 nM for verapamil and 4 nM for Glu-fibrinopeptide B with good quantitative linearities between 1 nM and 10 microM (R(2) = 0.9998) for verapamil and between 4 nM and 3 microM (R(2) = 0.9992) for Glu-fibrinopeptide B. The measured tip-to-tip repeatability for signal intensity was 14% relative standard deviation (RSD) (n = 3; 5 microM verapamil) and run-to-run repeatability 4-11% RSD (n = 4; 5 microM verapamil) for all individual emitters tested. In addition, long-term stability of < 2% RSD was maintained for timescales of 30 min even under free flow conditions. SU-8 polymer was also shown to be chemically stable against most of the tested electrospray solvents.     

Carbohydrate and steroid analysis by desorption electrospray ionization mass spectrometry

Desorption electrospray ionization mass spectrometry (DESI-MS) is applied to the analysis of carbohydrates and steroids; the detection limits are significantly improved by the addition of low concentrations of salts to the spray solvent.     

Vibrational characterization of the 1:1 iodine-benzene complex isolated in solid krypton

The structure and properties of a 1:1 iodine-benzene complex isolated in an inert krypton matrix at low temperature have been studied with infrared and resonance Raman spectroscopy and with MP2 calculations. The structure of the ground-state complex is found to be unsymmetric, and the I-I vibrational frequency is found to be red-shifted by 3.94 cm(-1) upon complexation. The experimental data agree well with computational results, leading to the conclusion that the I2-Bz complex structure is not axial but of above-bond type, identically with other halogen-benzene complexes.     

Ionspray microchip

An ionspray microchip is introduced. The chip is based on the earlier presented nebulizer microchip that consists of glass and silicon plates bonded together. A liquid inlet channel, nebulizer gas inlet, and nozzle are etched on the silicon plate and a platinum heater is integrated on the glass plate. The nebulizer microchip has been previously used in atmospheric pressure chemical ionization, atmospheric pressure photoionization, sonic spray ionization, and thermospray ionization modes. In this work we show that the microchip can be operated also in ionspray mode by introducing high voltage to the silicon plate of the microchip. The effects of operation parameters (voltage, nebulizer gas pressure, sample solution flow rate, solvent composition, and analyte concentration) on the performance of the ion spray microchip were studied. Under optimized conditions the microchip provides efficient ionization of small and large compounds and good quantitative performance. The feasibility of the ion spray microchip in liquid chromatography/mass spectrometry (LC/MS) was demonstrated by the analysis of tryptic peptides of bovine serum albumin. Copyright © 2010 John Wiley & Sons, Ltd.     

Analysis of lipids with desorption atmospheric pressure photoionization‐mass spectrometry (DAPPI‐MS) and desorption electrospray ionization‐mass spectrometry (DESI‐MS)

In this article, the effect of spray solvent on the analysis of selected lipids including fatty acids, fat‐soluble vitamins, triacylglycerols, steroids, phospholipids, and sphingolipids has been studied by two different ambient mass spectrometry (MS) methods, desorption electrospray ionization‐MS (DESI‐MS) and desorption atmospheric pressure photoionization‐MS (DAPPI‐MS). The ionization of the lipids with DESI and DAPPI was strongly dependent on the spray solvent. In most cases, the lipids were detected as protonated or deprotonated molecules; however, other ions were also formed, such as adduct ions (in DESI), [M‐H]⁺ ions (in DESI and DAPPI), radical ions (in DAPPI), and abundant oxidation products (in DESI and DAPPI). DAPPI provided efficient desorption and ionization for neutral and less polar as well as for ionic lipids but caused extensive fragmentation for larger and more labile compounds because of a thermal desorption process. DESI was more suitable for the analysis of the large and labile lipids, but the ionization efficiency for less polar lipids was poor. Both methods were successfully applied to the direct analysis of lipids from pharmaceutical and food products. Although DESI and DAPPI provide efficient analysis of lipids, the multiple and largely unpredictable ionization reactions may set challenges for routine lipid analysis with these methods. Copyright © 2012 John Wiley & Sons, Ltd.     

Rapid LC-UV Analysis of Iohexol in Canine Plasma for Glomerular Filtration Rate Determination

A rapid high-performance liquid chromatography UV method and a simple sample preparation for analyzing iohexol in canine plasma, for evaluating glomerular filtration rate (GFR) and intestinal permeability, were developed and validated. Trifluoroacetic acid (TFA) was used for protein precipitation and iohexol extraction from plasma, followed by vortex mixing and centrifugation. As an internal standard, 4-aminobenzoic acid (para-aminobenzoic acid, PABA) was added. The supernatant (5 μL) was injected into a Zorbax SB-C18 LC column maintained at 50 °C. The mobile phase of the LC method was a water–methanol gradient at pH 3.0 adjusted with TFA. Fast LC measurement was achieved by using a rapid-resolution LC technique. Total run time was 13 min, and UV wavelength was set at 246 nm. Precision of the method was 0.2–9.0%, depending on the iohexol concentration in plasma. Recovery of iohexol from plasma was over 90%, and recovery of the internal standard 99.1 ± 1.4%. The calibration curve was linear (r = 0.9997) over iohexol concentrations of 2.5–150 μg mL^?1 (n = 5). This method is fast, simple, reliable and applicable in clinical settings.     

Modification of polypropylene surfaces with micropits and hierarchical micropits/nanodepressions

Micropit surfaces and hierarchically structured micropit/nanodepression surfaces were fabricated in polypropylene by injection moulding. The first step in the process was the microstructuring of aluminium foils with a micro-working robot to obtain a pattern of micropits. Dimensions of the micropits could be controlled by adjusting the working parameters of the robot. The microstructured faces of some of the foils were anodized to aluminium oxide giving a surface in which both micropits and the smooth areas between were covered with nanopores. Mould inserts for the injection moulding were obtained by cold mounting of an epoxy resin mixture on the foils. After the epoxy resin had hardened, the foils were etched away. Dimensions of the micropillars and micropillars/nanobumps on the epoxy related to the dimensions of the structures on the foils. Finally, structures were replicated in polypropylene as micropits and hierarchical micropits/nanodepressions by injection moulding. The dimensions of these hollow structures corresponded well with those of the epoxy pillars and the original micropits.Static and dynamic contact angles on the micropit-structured polypropylene surfaces were elevated from the slightly hydrophobic values of smooth polypropylene. With hierarchical micropit/nanodepression structures, the contact angles approached the superhydrophobic limit of 150°. The work demonstrates an inexpensive and reproducible technique to fabricate hollow structures of various dimensions and scales on polypropylene and modify the surface properties of the polymer.     

Critical evaluation of adsorption-based sampling of vaporized metal species in flue gases

Diffusion-controlled sampling techniques, i.e. diffusion screens and diffusion tubes (= denuders), can be used in the collection of several vaporized heavy metal species in clean gases (pure N₂ atmosphere) at elevated temperatures. Collection efficiencies obtained for Hg, HgCl₂, Cd, CdCl₂ and ZnCl₂ were over 90% using adsorption on Au-coated diffusion screens and Ag-coated denuders. However, the collection efficiencies for Zn and PbCl₂ were significantly lower. In field measurements performed at a hazardous waste incineration plant and in a power plant equipped with a circulating fluidized-bed boiler, collection efficiencies seemed to vary noticeably depending on the sampling conditions and metal species to be sampled. Best collection efficiencies were obtained for mercury with both Ag coated denuders and Au coated screens whereas cadmium showed significantly poorer results in field measurements than in the laboratory. Sampling of zinc and lead species seemed to be problematic in all cases. Of the two sampling techniques, the denuder technique is more recommendable than the screen technique for sampling in relatively clean gases. However, neither of these techniques should be used in flue gases without further understanding of the collection mechanisms. Received: 6 November 1996 / Revised: 3 July 1996 / Accepted: 14 July 1996     

Determination of triacylglycerols in donkey milk by using high performance liquid chromatography coupled with atmospheric pressure chemical ionization mass spectrometry

The separation and determination of triacylglycerols (TAGs), which are the main components of naturally occurring fats and oils, in milk fat is a challenging task due to the very complex nature of this matrix. In the present study the TAG fraction of donkey milk lipids has been characterized by using high performance liquid chromatography-atmospheric pressure chemical ionization mass spectrometry (HPLC-APCI-MS). HPLC in reversed phase mode has been used for TAG separation and silver ion (Ag+) HPLC has been used as a second dimension to clarify and confirm the identification. The RP-HPLC eluate was fractionated and the fractions of interest were injected onto the Ag+-HPLC column. In both cases peak assignment was carried out by combining retention data with APCI-MS spectra information. In total, 55 TAGs in donkey milk fat were identified (without considering the positional isomers) and quantified on the basis of percentage peak areas in the RP-HPLC chromatogram (without the use of correction factors). Amongst the identified triacylglycerols, POLn, POO, PPO, CaPO, POL, and PPoO proved to be the main components of the TAG fraction of donkey milk.     

Use of bioluminescent bacterial sensors as an alternative method for measuring heavy metals in soil extracts

The luminescence based bacterial sensor strains Pseudomonas fluorescens OS8 (pTPT11) for mercury detection and Pseudomonas fluorescens OS8 (pTPT31) for arsenite detection were used in testing their application in detecting heavy metals in soil extracts. Three different soil types (humus, mineral and clay) were spiked with 1, 100 or 500 μg g⁻¹ Hg²⁺ or As³⁺. Samples were taken 1, 14 and 30 days and extracted with water, ammonium acetate, hydrogen peroxide and nitric acid to represent water soluble, bioavailable, organic matter bound and residual fractions, respectively. The lowest mercury-concentration measured using biosensor (0.003 μg kg⁻¹) was considerably lower than by chemical method (0.05 μg kg⁻¹). The sensor strain with pTPT31 appeared to have a useful detection range similar to that of chemical methods. Concentration results with chemical and biosensor analysis were very similar in the case of mercury-spiked samples. Although some of the arsenite samples showed higher variation between methods, it is concluded that the bacteria can be used as an alternative traditional methods for different types of samples.