Laura Luosujärvi

Rapid fabrication of high aspect ratio silicon nanopillars for chemical analysis

In this study, a method for fabrication of high aspect ratio silicon nanopillars is presented. The method combines liquid flame spray production of silica nanoparticle agglomerates with cryogenic deep reactive ion etching. First, the nanoparticle agglomerates, having a diameter of about 100 nm, are deposited on a silicon wafer. Then, during the subsequent cryogenic deep reactive ion etching process, the particle agglomerates act as etch masks and silicon nanopillars are formed. Aspect ratios of up to 20:1 are demonstrated. The masking process is rapid, cheap and has the potential to be scaled up for large areas. Three other structured silicon surfaces were fabricated for comparison. All four surfaces were utilized as desorption/ionization on silicon (DIOS) sample plates. The mass spectrometry results indicate that nanopillar surfaces masked with the liquid flame spray technique are well suited as DIOS sample plates.

Desorption and ionization mechanisms in desorption atmospheric pressure photoionization.

The factors influencing desorption and ionization in newly developed desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS) were studied. Redirecting the DAPPI spray was observed to further improve the versatility of the technique: for dilute samples, parallel spray with increased analyte signal was found to be the best suited, while for more concentrated samples, the orthogonal spray with less risk for contamination is recommended. The suitability of various spray solvents and sampling surface materials was tested for a variety of analytes with different polarities and molecular weights. As in atmospheric pressure photoionization, the analytes formed [M + H](+), [M - H](-), M(+*), M(-*), [M - H + O](-), or [M - 2H + 2O](-) ions depending on the analyte, spray solvent, and ionization mode. In positive ion mode, anisole and toluene as spray solvents promoted the formation of M(+*) ions and were therefore best suited for the analysis of nonpolar compounds (anthracene, benzo[a]pyrene, and tetracyclone). Acetone and hexane were optimal spray solvents for polar compounds (MDMA, testosterone, and verapamil) since they produced intensive [M + H](+) ion peaks of the analytes. In negative ion mode, the type of spray solvent affected the signal intensity, but not the ion composition. M(-*) ions were formed from 1,4-dinitrobenzene, and [M - H + O](-) and [M - 2H + 2O](-) ions from 1,4-naphthoquinone, whereas acidic compounds (naphthoic acid and paracetamol) formed [M - H](-) ions. The tested sampling surfaces included various materials with different thermal conductivities. The materials with low thermal conductivity, i.e., polymers like poly(methyl methacrylate) and poly(tetrafluoroethylene) (Teflon) were found to be the best, since they enable localized heating of the sampling surface, which was found to be essential for efficient analyte desorption. Nevertheless, the sampling surface material did not affect the ionization mechanisms.

Environmental and food analysis by desorption atmospheric pressure photoionization‐mass spectrometry

Desorption atmospheric pressure photoionization-mass spectrometry (DAPPI-MS) is a versatile surface analysis technique for a wide range of analytes, especially for neutral and non-polar analytes. Here, a set of analytes typically found in environmental or food samples was analyzed by DAPPI-MS. The set included five polyaromatic hydrocarbons (PAHs), one N-PAH, one brominated flame retardant, and nine pesticides, which were studied with three different spray solvents: acetone and toluene in positive ion mode, and anisole in negative ion mode. The analytes showed [M + H](+), M(+*), and [M-H](-) ions as well as fragmentation and substitution products. Detection limits for the studied compounds ranged from 30 pg to 1 ng (from 0.14 to 5.6 pmol). To demonstrate the feasibility of the use of DAPPI-MS two authentic samples - a circuit board and orange peel - and a spiked soil sample were analyzed. Tetrabromobisphenol A, imazalil, and PAHs were observed from the three above-mentioned samples, respectively. The method is best suited for rapid screening analysis of environmental or food samples.

Gas chromatography/mass spectrometry of polychlorinated biphenyls using atmospheric pressure chemical ionization and atmospheric pressure photoionization microchips.

Gas chromatography (GC) and ion trap mass spectrometry (MS) were combined with microchip atmospheric pressure chemical ionization (microAPCI) and microchip atmospheric pressure photoionization (microAPPI) sources. Selected polychlorinated biphenyls (PCBs, IUPAC Nos. 28, 52, 101, 118, 138, 153 and 180) were analyzed by GC/microAPCI-MS and GC/microAPPI-MS to demonstrate the applicability of the miniaturized ion sources in negative ion mode analysis. The microAPCI and microAPPI methods were evaluated in respect of detection limit, linearity and repeatability. The detection limits for the PCB congeners were somewhat lower with microAPCI than with microAPPI, whereas microAPPI showed slightly wider linear range and better repeatability. With both methods, the best results were obtained for highly chlorinated or non-ortho-chlorinated PCBs, which possess the highest electron affinities. Finally, the suitability of the GC/microAPPI-MS method for the analysis of PCBs in environmental samples was demonstrated by analyzing soil extracts, and by comparing the results with those obtained by gas chromatography with electron capture detection (GC/ECD).

Analysis of street market confiscated drugs by desorption atmospheric pressure photoionization and desorption electrospray ionization coupled with mass spectrometry

The rapid screening analysis of drugs has a wide range of applications in the field of forensics and toxicology. Since the introduction of ambient desorption/ ionization techniques, rapid screening of drugs bymass spectrometry (MS) has become possible. Desorption electrospray ionization (DESI), direct analysis in real time (DART), atmospheric solids analysis probe (ASAP), and desorption sonic spray ionization (DeSSI) have all been used in the analysis of commercial and illicit drugs. In DESI, charged solvent droplets, generated by a high gas flow and an electric potential between the sprayer and the mass spectrometer, desorb the analytes from a solid surface as a result of electrostatic and pneumatic forces, and in positive ion mode mainly [MþH]þ ions are produced. Another recently reported desorption/ionization method feasible for drug analysis is desorption atmospheric pressure photoionization (DAPPI). DAPPI is a thermal desorption/ionization method, in which the heated jet, produced by a microchip nebulizer and consisting of nitrogen and spray solvent vapor, is directed towards the sample in order to desorb the analytes from the sampling surface. Desorbed species are then photoionized in the gas phase and ions are analyzed with a mass spectrometer. In the positive ion mode DAPPI produces Mþ . or [MþH]þ ions depending on the analyte and the spray solvent used. Tablets and cream formulations can be analyzed as such by DESI-MS or DAPPI-MS but, due to the nature of desorption/ionization methods, powdered samples need to be compressed to prevent puffing of the powder. In this letter we describe rapid screening applications for powdered samples of drugs of abuse. Instead of being compressed, the drug samples were dissolved in solvent prior to analysis, and analyzed by both DAPPI-MS and DESI-MS. Both methods were observed to be feasible for the rapid detection of drug compounds. The methods are faster than conventional infusion studies with atmospheric pressure photoionization mass spectrometry (APPI-MS) or electrospray ionization mass spectrometry (ESI-MS) and, in addition, both are feasible for very small amounts of sample. The sensitivity of the analysis and the ions generated depended on the analyte, the ionization method, and desorption/ionization conditions. The confiscated drug samples included powders of amphetamine, cocaine, heroin, methamphetamine, and methylenedioxymethamphetamine (MDMA) (Table 1). The samples also contained cutting agents. The powdered drug samples were dissolved in methanol, after which the stock solutions (0.5mg/mL) were further diluted with water/methanol (50:50) to working solutions of 10mg/ mL. For the analysis, 1mL of the sample solution per one sampling spot was pipetted on the sampling surface (poly(methyl methacrylate), PMMA) and left to dry. The actual amount of the analyte in one sample spot was then 2.5–7.8 ng depending on the purity of the drug sample (Table 1). Dried droplets of the samples were desorbed from the PMMA sampling surface, ionized, and analyzed by an ion trap mass spectrometer equipped with a capillary extension (Esquire 3000þ, Bruker Daltonics, Bremen, Germany) operating in positive ion mode. Custom-made DAPPI and DESI sources were used in the analysis. The DAPPI source consisted of a nebulizer microchip, which produced a heated plume to desorb the analytes from the sampling surface into the gas phase, and of a krypton discharge lamp (Cathodeon, Cambridge, UK), which produced photons for photoionization. terscience.wiley.com) DOI: 10.1002/rcm.4005 The heating power of the microchip was 4.5W, which corresponds to a plume temperature of approximately 2208C at 10mm distance, or approximately 3008C on the sampling surface at 4mm distance. The spray solvents used in DAPPI were HPLC grade acetone (Mallinckrodt Baker B.V., Deventer, The Netherlands) and toluene (Labscan, Dublin, Ireland). The DAPPI spray solvent flow rate was 10mL/min. A description of the detailed structure of the ion source is presented elsewhere. In the DESI source, spray solvent was introduced using a silica capillary and spray gas was introduced coaxially at approx. 10 bar pressure. The DESI spray solvent line was grounded and a voltage of 4 kV was applied to the capillary extension of the mass spectrometer. The DESI spray solvent consisted of water (purified with a Milli-Q purifying system, Millipore, Molsheim, France) and methanol (Mallinckrodt Baker B.V.) in the ratio 50:50 with 0.1 vol-% addition of formic acid (99%, Acros Organics, Geel, Belgium). The DESI spray solvent flow rate was 3mL/ min. In both ion sources the plumewas directed onto the sampling surface at 458 angle. The sample spot was placed at a distance of 3mm from the tip of the capillary extension of the mass spectrometer, and the distance between the spray and the sampling surface was 3mm. Nitrogen was used as the spray gas in both techniques. The same powder samples were also identified by gas chromatography/mass spectrometry (GC/MS; HP 6890 gas chromatograph/HP 5973 MSD quadrupole mass spectrometer; Agilent Technologies, Waldbronn, Germany) and quantified by liquid chromatography with UV detection (LC/UV; HP 1100, Agilent Technologies, Santa Clara, CA, USA) (amphetamine and metamphetamine) or gas chromatography with flame ionization detection (GC/FID; HP 6890, Agilent Technologies, Waldbronn, Germany) (cocaine and heroin) to obtain reference data from the samples and the analyte mass percentages reported in Table 1. All the active compounds found by GC/MS analysis were also observed in the analysis by DAPPI-MS and DESI-MS (Table 1). The identities of

Surface assisted laser desorption/ionization on two-layered amorphous silicon coated hybrid nanostructures

Matrix-free laser desorption/ionization was studied on two-layered sample plates consisting of a substrate and a thin film coating. The effect of the substrate material was studied by depositing thin films of amorphous silicon on top of silicon, silica, polymeric photoresist SU-8, and an inorganic-organic hybrid. Des-arg9-bradykinin signal intensity was used to evaluate the sample plates. Silica and hybrid substrates were found to give superior signals compared with silicon and SU-8 because of thermal insulation and compatibility with amorphous silicon deposition process. The effect of surface topography was studied by growing amorphous silicon on hybrid micro- and nanostructures, as well as planar hybrid. Compared with planar sample plates, micro- and nanostructures gave weaker and stronger signals, respectively. Different coating materials were tested by growing different thin film coatings on the same substrate. Good signals were obtained from titania and amorphous silicon coated sample plates, but not from alumina coated, silicon nitride coated, or uncoated sample plates. Overall, the strongest signals were obtained from oxygen plasma treated and amorphous silicon coated inorganic-organic hybrid, which was tested for peptide-, protein-, and drug molecule analysis. Peptides and drugs were analyzed with little interference at low masses, subfemtomole detection levels were achieved for des-arg9-bradykinin, and the sample plates were also suitable for ionization of small proteins.

Analysis of selective androgen receptor modulators by gas chromatography-microchip atmospheric pressure photoionization-mass spectrometry

A gas chromatography-microchip atmospheric pressure photoionization-mass spectrometric (GC-μAPPI-MS) method was developed and used for the analysis of three 2-quinolinone-derived selective androgen receptor modulators (SARMs). SARMs were analyzed from spiked urine samples, which were hydrolyzed and derivatized with N-methyl-N-(trimethylsilyl)trifluoroacetamide before analysis. Trimethylsilyl derivatives of SARMs formed both radical cations (M+•) and protonated molecules ([M + H]+) in photoionization. Better signal-to-noise ratios (S/N) were obtained in MS/MS analysis using the M+• ions as precursor ions than using the [M + H]+ ions, and therefore the M+• ions were selected for the precursor ions in selected reaction monitoring (SRM) analysis. Limits of detection (LODs) with the method ranged from 0.01 to 1 ng/mL, which correspond to instrumental LODs of 0.2–20 pg. Limits of quantitation ranged from 0.03 to 3 ng/mL. The mass spectrometric response to the analytes was linear (R ≥ 0.995) from the LOQ concentration level up to 100 ng/mL concentration, and intra-day repeatabilities were 5%–9%. In addition to the GC-μAPPI-MS study, the proof-of-principle of gas chromatography-microchip atmospheric pressure chemical ionization-Orbitrap MS (GC-μAPCI-Orbitrap MS) was demonstrated.