Age-related changes in the lateral lipid distribution in a human lens described by mass spectrometry imaging.

The lateral lipid distribution in eye lenses of three human donors were studied by matrix-assisted laser desorption ionization imaging mass spectrometry using a high mass resolution. By using exact mass measurements this study shows the relationship between the aging process and the number of lipids detected as well as between aging and the abundance of products derived from sphingomyelins by hydrolysis. Variable lipid composition was also observed in the nuclear, barrier, or cortex regions of the lens samples. This is the first study that suggests the distribution of lysolipids as a potential biomarker panel for the aging of human lens tissue.

Hydrophilic interaction liquid chromatography in food analysis.

The use of hydrophilic interaction liquid chromatography (HILIC) in food analysis in the last decade is reviewed. The HILIC mechanism is briefly discussed, but main emphasis is put on the use of HILIC for separation of different food matrices. The food matrices are divided into food of animal origin and related products, vegetables, fruits and related compounds, and other food-related matrices. A list on important applications is provided for each category including experimental conditions and a brief summary of the results. The 100 references included will provide the reader a comprehensive overview and insight into HILIC applications to food analysis.

Spatial distribution of glycerophospholipids in the ocular lens.

Knowledge of the spatial distribution of lipids in the intraocular lens is important for understanding the physiology and biochemistry of this unique tissue and for gaining a better insight into the mechanisms underlying diseases of the lens. Following our previous study showing the spatial distribution of sphingolipids in the porcine lens, the current study used ultra performance liquid chromatography quadrupole time-of-flight mass spectrometry (UPLC-QTOFMS) to provide the whole lipidome of porcine lens and these studies were supplemented by matrix-assisted laser desorption ionization mass spectrometry imaging (MALDI MSI) of the lens using ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FTICR MS) to determine the spatial distribution of glycerophospholipids. Altogether 172 lipid species were identified with high confidence and their concentration was determined. Sphingomyelins, phosphatidylcholines, and phosphatidylethanolamines were the most abundant lipid classes. We then determined the spatial and concentration-dependent distributions of 20 phosphatidylcholines, 6 phosphatidylethanolamines, and 4 phosphatidic acids. Based on the planar molecular images of the lipids, we report the organization of fiber cell membranes within the ocular lens and suggest roles for these lipids in normal and diseased lenses.

Molecular mass spectrometry imaging in biomedical and life science research.

This review describes the current state of mass spectrometry imaging (MSI) in life sciences. A brief overview of mass spectrometry principles is presented followed by a thorough introduction to the MSI workflows, principles and areas of application. Three major desorption-ionization techniques used in MSI, namely, secondary ion mass spectrometry (SIMS), matrix-assisted laser desorption ionization (MALDI), and desorption electrospray ionization (DESI) are described, and biomedical and life science imaging applications of each ionization technique are reviewed. A separate section is devoted to data handling and current challenges and future perspectives are briefly discussed at the end.

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.

Laser desorption-ionization of lipid transfers: tissue mass spectrometry imaging without MALDI matrix.

Mass spectrometry imaging of tissue-lipid transfers without MALDI matrix is demonstrated. Commercially available nanostructured surfaces (nano-assisted laser desorption-ionization or NALDI) are used as substrates for imprinting of tissue sections. The lithographic transfers are then washed and the two-dimensional distribution of the lipids is imaged by laser desorption-ionization mass spectrometry. The NALDI imaging of lipid transfers is compared with standard MALDI imaging of matrix-coated tissue sections. The obtained images are of the same quality, and no spatial information is lost due to the imprinting process. NALDI imaging is faster due to the absence of the time-consuming matrix deposition step, and the NALDI mass spectra are less complex and easier to interpret than standard MALDI. In this particular application example, NALDI mass spectrometry is able to identify the same lipid species as MALDI mass spectrometry and provides better distinction between kidney and adrenal gland tissues based on the lipid analysis.

Visualizing spatial lipid distribution in porcine lens by MALDI imaging high-resolution mass spectrometry.

The intraocular lens contains high levels of both cholesterol and sphingolipids, which are believed to be functionally important for normal lens physiology. The aim of this study was to explore the spatial distribution of sphingolipids in the ocular lens using mass spectrometry imaging (MSI). Matrix-assisted laser desorption/ionization (MALDI) imaging with ultra high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) was used to visualize the lipid spatial distribution. Equatorially-cryosectioned, 12 microm thick slices of tissue were thaw-mounted to an indium-tin oxide (ITO) glass slide by soft-landing to an ethanol layer. This procedure maintained the tissue integrity. After the automated MALDI matrix deposition, the entire lens section was examined by MALDI MSI in a 150 microm raster. We obtained spatial- and concentration-dependent distributions of seven lens sphingomyelins (SM) and two ceramide-1-phosphates (CerP), which are important lipid second messengers. Glycosylated sphingolipids or sphingolipid breakdown products were not observed. Owing to ultra high resolution MS, all lipids were identified with high confidence, and distinct distribution patterns for each of them are presented. The distribution patterns of SMs provide an understanding of the physiological functioning of these lipids in clear lenses and offer a novel pathophysiological means for understanding diseases of the lens.

Integrated liquid chromatography-heated nebulizer microchip for mass spectrometry.

A new integrated microchip for liquid chromatography-mass spectrometry (LC-MS) is presented. The chip is made from bonded silicon and glass wafers with structures for a packed LC column channel, a micropillar frit, a channel for optional optical detection, and a heated vaporizer section etched in silicon and platinum heater elements on the glass cover. LC eluent is vaporized and mixed with nebulizer gas in the vaporizer section and the vapor is sprayed out from the chip. Nonpolar and polar analytes can be efficiently ionized in the gas phase by atmospheric pressure photoionization (APPI) as demonstrated with polycyclic aromatic hydrocarbons (PAHs) and selective androgen receptor modulators (SARMs). This is not achievable with present LC-MS chips, since they are based on electrospray ionization, which is not able to ionize nonpolar compounds efficiently. The preliminary quantitative performance of the new chip was evaluated in terms of limit of detection (down to 5 ng mL(-1)), linearity (r>0.999), and repeatability of signal response (RSD=2.6-4.0%) and retention time (RSD=0.3-0.5%) using APPI for ionization and PAHs as standard compounds. Determination of fluorescent compounds is demonstrated by using laser-induced fluorescence (LIF) for detection in the optical detection channel before the vaporizer section.

Automated ambient desorption-ionization platform for surface imaging integrated with a commercial Fourier transform ion cyclotron resonance mass spectrometer.

A fully automated atmospheric pressure ionization platform has been built and coupled with a commercial high-resolution Fourier transform ion cyclotron resonance mass spectrometer (FTICR-MS) instrument. The outstanding performance of this instrument allowed screening on the basis of exact masses in imaging mode. The main novel aspect was in the integration of the atmospheric pressure ionization imaging into the current software for matrix-assisted laser desorption ionization (MALDI) imaging, which allows the user of this commercial dual-source mass spectrometer to perform MALDI-MS and different ambient MS imaging from the same user interface and to utilize the same software tools. Desorption electrospray ionization (DESI) and desorption atmospheric pressure photoionization (DAPPI) were chosen to test the ambient surface imaging capabilities of this new ionization platform. Results of DESI imaging experiments performed on brain tissue sections are in agreement with previous MS imaging reports obtained by DESI imaging, but due to the high resolution and mass accuracy of the FTICR instrument it was possible to resolve several ions at the same nominal mass in the DESI-MS spectra of brain tissue. These isobaric interferences at low resolution are due to the overlap of ions from different lipid classes with different biological relevance. It was demonstrated that with the use of high-resolution MS fast imaging screening of lipids can be achieved without any preseparation steps. DAPPI, which is a relatively new and less developed ambient ionization technique compared to DESI, was used in imaging mode for the first time ever. It showed promise in imaging of phytocompounds from plant leaves, and selective ionization of a sterol lipid was achieved by DAPPI from a brain tissue sample.

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.

Direct analysis of illicit drugs by desorption atmospheric pressure photoionization.

The feasibility of desorption atmospheric pressure photoionization (DAPPI) in the direct analysis of illicit drugs was demonstrated by the analysis of confiscated drug samples of various forms such as tablets, blotter paper, and plant resin and bloom. 3,4-Methylenedioxymethamphetamine (MDMA), amphetamine, phenazepam, and buprenorphine were detected from the analyzed tablets, lysergic acid diethylamide (LSD) and bromobenzodifuranylisopropylamine (bromo-Dragonfly, ABDF) from blotter paper, and Delta(9)-tetrahydrocannabinol (THC) and cannabinol from Cannabis Sativa bloom and resin. The amphetamines, phenazepam and ABDF showed protonated molecules independent of the solvent used, whereas buprenorphine, LSD and the cannabinoids showed molecular ions with toluene and protonated molecules with acetone as the solvent.

Comprehensive two-dimensional liquid chromatography coupled with mass spectrometry.

In this review, instrumental aspects of comprehensive two-dimensional liquid chromatography coupled with mass spectrometry are presented. The milestones of LCxLC are briefly summarized. Instrument configuration, selection of experimental conditions, the different interfaces used in the system and the current applications of LCxLC-MS systems are described.

Application of silicon nanowires and indium tin oxide surfaces in desorption electrospray ionization.

Two nanostructured surfaces are introduced as advantageous substrates for desorption electrospray ionization mass spectrometry (DESI-MS). Nano-assisted laser desorption/ionization (NALDI) plates coated with silicon nanowires (SiNWs) and indium tin oxide (ITO) layers on glass are both conductive non-polar surfaces that were originally designed as superior substrates for matrix-free laser desorption/ionization. In this study, NALDI/SiNWs and ITO were tested as potentially useful DESI substrates for selected model analytes (cyclosporine, beauverolide, surfactin and nystatin). Both nanostructured surfaces produced more intense and longer-lasting signals than other tested surfaces (polytetrafluoroethylene, glass, polymethylmethacrylate and chromatography paper).

Desorption atmospheric pressure photoionization.

An ambient ionization technique for mass spectrometry, desorption atmospheric pressure photoionization (DAPPI), is presented, and its application to the rapid analysis of compounds of various polarities on surfaces is demonstrated. The DAPPI technique relies on a heated nebulizer microchip delivering a heated jet of vaporized solvent, e.g., toluene, and a photoionization lamp emitting 10-eV photons. The solvent jet is directed toward sample spots on a surface, causing the desorption of analytes from the surface. The photons emitted by the lamp ionize the analytes, which are then directed into the mass spectrometer. The limits of detection obtained with DAPPI were in the range of 56-670 fmol. Also, the direct analysis of pharmaceuticals from a tablet surface was successfully demonstrated. A comparison of the performance of DAPPI with that of the popular desorption electrospray ionization method was done with four standard compounds. DAPPI was shown to be equally or more sensitive especially in the case of less polar analytes.

Comparison of two different solvents employed for pressurised fluid extraction of stevioside from Stevia rebaudiana: methanol versus water.

Pressurised fluid extraction using water or methanol was employed for the extraction of stevioside from Stevia rebaudiana Bertoni. The extraction method was optimised in terms of temperature and duration of the static or the dynamic step. Extracts were analysed by liquid chromatography followed by UV and mass-spectrometric (MS) detections. Thermal degradation of stevioside was the same in both solvents within the range 70-160 degrees C. Methanol showed better extraction ability for isolation of stevioside from Stevia rebaudiana leaves than water within the range 110-160 degrees C. However, water represents the green alternative to methanol. The limit of detection of stevioside in the extract analysed was 30 ng for UV detection and 2 ng for MS detection.

Microchip sonic spray ionization.

The first microchip version of sonic spray ionization (SSI) as an atmospheric pressure ionization source for mass spectrometry (MS) is presented. The microchip used for SSI has recently been developed in our laboratory, and it has been used before as an atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI) source. Now the ionization is achieved simply by applying high (sonic) speed nebulizer gas, without heat, corona discharge, or high voltage. The microchip SSI was applied to the analysis of tetra-N-butylammonium, verapamil, testosterone, angiotensin I, and ibuprofen. The limits of detection were in the range of 15 nM to 4 microM. The technique was found to be highly dependent on the position of the chip toward the mass spectrometer inlet, and on the gas and the sample solution flow rates. The microchip SSI provided dynamic linearity following a pattern similar to that used with electrospray, good quantitative repeatability (RSD=16%), and long-term signal stability.

Characterisation of Stevia rebaudiana by comprehensive two-dimensional liquid chromatography time-of-flight mass spectrometry.

Comprehensive two-dimensional liquid chromatography (LC x LC) connected on-line to electrospray ionisation time-of-flight mass spectrometry (ESI-TOF-MS) was employed for analysis of aqueous extract of Stevia rebaudiana. Different combinations of strong cation-exchange (SCX), amino (NH2), and octadecyl siloxane (C18) stationary phases were tested in the separation of all nine known sweet Stevia glycosides. A combination of C18 as the first-dimension column and NH2 as the second-dimension column fully separated all the glycosides from the matrix. The method proved to be quantitative and repeatable. The limit of detection (S/N=3) for stevioside, a widely used natural sweetener, was 43.4 ng/g in dry leaves. The RSD for retention times was <0.1% and that of peak areas 4.5%.

Comprehensive two-dimensional liquid chromatography-time-of-flight mass spectrometry in the analysis of acidic compounds in atmospheric aerosols.

A novel method utilising comprehensive two-dimensional liquid chromatography interfaced to electrospray ionisation time-of-flight mass spectrometry was developed for the determination of organic acids in atmospheric aerosols. The system was applied to the analysis of methanolic extracts of filters from a high volume sampler. The enhanced separation power of two-dimensional separation was demonstrated in the analysis of both rural and urban samples. Quantification was performed for compounds for which standards were available. Limit of detection was 2-200 ng/ml. Average reproducibility of retention times in each dimensions was 0.1%, and average reproducibility of peak areas was 8% (10 microg/ml, n=3).

Determination of lycopene in food by on-line SFE coupled to HPLC using a single monolithic column for trapping and separation.

A method that would eliminate the degradation of lycopene during analysis was developed. Supercritical fluid extraction (SFE) with carbon dioxide as the extraction medium was connected on-line to high performance liquid chromatography (HPLC) where a single monolithic column was used for trapping and the subsequent separation of analytes. The method was linear over the studied range (0.1-2.5 microg), and it was repeatable (R.S.D. 3.9%), sensitive (LOD = 0.5 ng) and fast (35 min). Lycopene was determined in tomatoes, fruit and several food products. Because of the on-line construction, lycopene was not in contact with air or light during the whole procedure and the amount analysed should therefore correspond to the real amount in the sample.

Direct on-line continuous supercritical fluid extraction and HPLC of aqueous pyrethrins solutions.

A new method, employing supercritical fluid extraction (SFE) connected on-line with high-performance liquid chromatography, was developed for the determination of pyrethrins and piperonyl butoxide in aqueous solutions. The principle of the laboratory-made device for SFE is based on the low mutual solubility of water and supercritical (liquid) CO2. This device works in continuous mode that offers extraction of unlimited sample volumes. Different extraction temperatures and pressures were tested to find optimum extraction conditions. The addition of organic modifier and inorganic salt to the water sample to increase extraction recovery was investigated. The method was evaluated, and it was applied for the extraction of aqueous samples spiked with commercial insecticides. The working concentration range of the method was from the limit of quantification (0.1 microg L(-1)) to the solubility of the analytes in water.