Molecular Mapping of Sebaceous Squalene by Ambient Mass Spectrometry.

Squalene (SQ), a highly unsaturated sebaceous lipid, plays an important role in protecting human skin. To better understand the role of SQ in clinical medicine, an efficient analytical approach is needed to comprehensively study the distribution of SQ on different parts of the skin. In this study, sebaceous lipids were collected from different epidermal areas of a volunteer with sampling probes. Thermal desorption-electrospray ionization/mass spectrometry (TD-ESI/MS) was then used to characterize the lipid species on the probes, and each TD-ESI/MS analysis was completed within a few seconds without any sample pretreatment. The molecular mapping of epidermal squalene on whole-body skin was rendered by scaling the peak area of the extracted ion current (EIC) of SQ based on a temperature color gradient, where colors were assigned to the 1357 sampling locations on a 3D map of the volunteer. The image showed a higher SQ distribution on the face than any other area of the body, indicating the role of SQ in protecting facial skin. The results were in agreement with previous studies using SQ as a marker to explore sebaceous activity. The novelty and significance of this work are concluded as two points: (1) direct and rapid detection of all major classes of sebaceous lipids, including the unsaturated hydrocarbons (SQ) and nonpolar lipids (e.g., cholesterol). The results are unique compared to other conventional and ambient ionization mass spectrometry methods and (2) this is the first study to analyze SQ distribution on the whole-body skin by a high-throughput approach.

Using thermal desorption electrospray ionization mass spectrometry to rapidly determine antimicrobial preservatives in cosmetics.

RATIONALE: Characterization and quantification of permitted preservatives are important inspections to prevent the overuse of preservatives in authentic formulations. However, the complexity of sample matrices makes preservative determination in cosmetics a tedious process. A rapid analytical strategy to identify preservatives would insure large numbers of products are in compliance with government regulations. METHODS: Thermal desorption electrospray ionization mass spectrometry (TD-ESI-MS) was used to directly detect preservative compounds in authentic formulations without sample pretreatment. The technique employs a metal probe, which was configured for sampling cosmetics in their original states and was inserted in a closed preheated oven to thermally desorb analytes. The desorbed analytes were then carried by a nitrogen gas stream into an ESI plume, where the formed ions were subsequently detected by the mass analyzer. RESULTS: The TD-ESI mass and tandem mass spectra of different classes of preservative standards were rapidly obtained, and the limits of detection were far below the legal limit of their respective concentrations. The preservatives were also directly detected in different types of authentic formulations in the absence of sample preparation, and within a few seconds per sample. Calibration curves for preservatives in four common formulations yielded good linearity in the regulation-allowed range. CONCLUSIONS: Due to its sensitivity, short analysis time, repeatability, and quantitative ability, TD-ESI-MS may serve as a suitable tool for large-scale screening of cosmetic preservatives to assure product safety. Copyright © 2016 John Wiley & Sons, Ltd.

Using electrospray laser desorption ionization mass spectrometry to rapidly examine the integrity of proteins stored in various solutions.

Electrospray laser desorption ionization mass spectrometry (ELDI/MS) allows the rapid desorption and ionization of proteins from solutions under ambient conditions. In this study, we have demonstrated the use of ELDI/MS to efficiently examine the integrity of the proteins stored in various solutions before they were further used for other biochemical tests. The protein standards were prepared in the solutions containing buffers, organic salts, inorganic salts, strong acid, strong base, and organic solvents, respectively, to simulate those collected from solvent extraction, filtration, dialysis, or chromatographic separation. Other than the deposit of a drop of the sample solution on the metallic sample plate in an ELDI source, no additional sample pretreatment is needed. The sample drop was then irradiated with a pulsed laser; this led to desorption of the analyte molecules, which subsequently entered the ESI plume to undergo post-ionization. Because adjustment of the composition of the sample solution is unnecessary, this technique appears to be useful for rapidly evaluating the integrity of proteins after storage or prior to further biochemical treatment. In addition, when using acid-free and low-organic-solvent ESI solutions for ELDI/MS analysis, the native conformations of the proteins in solution could be detected.

Molecular cartography of residue pesticides on grape surface in 3D by ambient ionization tandem mass spectrometry.

Thermal desorption-electrospray ionization tandem mass spectrometry (TD-ESI/MS/MS) was used to characterize the residual pesticides that were collectedfromthe surface of a grapewithmetallic sampling probes. Fungicides, insecticides, and miticides were detected, where results were validated by simple solvent extraction followed by gas chromatography tandem mass spectrometry and liquid chromatography tandem mass spectrometry analyses. To explore the distribution of pesticide residues on grape surfaces, 149 locations of a grape surface were collected and followed by TD-ESI/MS/MS analysis. The molecular cartography was then generated from analysis of residual pesticides on the grape surface in 3D.

Obtaining molecular imagings of pesticide residues on strawberry surfaces with probe sampling followed by ambient ionization mass spectrometric analysis.

Thermal desorption-electrospray ionization tandem mass spectrometry (TD-ESI/MS/MS) was used to rapidly characterize the residual pesticides collected on the surface of a strawberry with a metallic probe. Twelve pesticides, including nine fungicides and three miticides, were detected; the results were validated by comparison with results that used solvent extraction followed by gas chromatography/mass spectrometry and liquid chromatography/tandem mass spectrometry analyses. The distribution of pesticide residues on a strawberry's surface was explored by collecting multiple samples using probes from 40 positions on the strawberry, with the collected samples being analyzed with TD-ESI/MS/MS. The obtained molecular information was used to construct mass spectrometry imaging of the strawberry's pesticide residues.

High-throughput screening of phthalate-containing objects in the kindergartens by ambient mass spectrometry.

High-throughput screening of plastic products in children's living environment is necessary to identify phthalate-containing objects for the concern of public health and safety. A novel strategy of probe collecting technique combined with ambient mass spectrometry was developed to carry out the large-scale sample analysis. Analytes from the surface of approximately 500 objects each in two kindergartens in Taiwan were collected using the same number of the metallic probes. After being delivered to laboratory, the analytes on the probes were analyzed with thermal desorption-electrospray ionization/mass spectrometry (TD-ESI/MS). As sample pretreatment was unnecessary, the analysis of phthalates on a probe was completed within 30 s enabling high-throughput screening of a large number of objects. All procedure including sampling and TD-ESI/MS analysis together with report writing for a kindergarten was completed in one day. A reasonable relative standard deviation (<15.6%) was obtained from replicate analyses of phthalate standards. Single-point calibration was used to perform semi-quantitative analysis, and results were validated by liquid chromatography/mass spectrometry (LC/MS). It was found that 20-40% of the objects in two kindergartens contained greater than low-level (>2 ng) of phthalates and 40-60% of the objects in the kindergartens contained more than one kind of phthalate.

Fine Needle Aspiration Combined With Matrix-assisted Laser Desorption Ionization Time-of-Flight/Mass Spectrometry to Characterize Lipid Biomarkers for Diagnosing Accuracy of Breast Cancer.

BACKGROUND: Fine needle aspiration (FNA) cytology has been widely used for pathologic assessment of breast lesions. However, the examination suffers a risk of false-negative results owing to insufficient sample volumes, inaccurate sampling positions, nondefinitive cytologic features, or suboptimal cell preservation. One approach to improve its accuracy is using modern mass spectrometry to detect disease biomarkers, of which the tissue samples are collected through FNA. METHODS: The biological compounds in the FNA tissue samples were extracted and characterized by matrix-assisted laser desorption ionization time-of-flight/mass spectrometry (MALDI-TOF/MS). The results were further analyzed by principal component analysis. Distribution of lipid biomarkers on tissues was explored by imaging mass spectrometry. RESULTS: Lipid profiles of the tissue samples collected by FNA were rapidly obtained through MALDI-TOF/MS analysis. Phosphatidylcholines and triacylglycerols were detected as the predominant compounds in cancerous and normal regions, respectively. The samples were clearly classified by principal component analysis, based on the differences in their lipid profiles. Different lipid patterns were clearly viewed through the molecular imaging of normal and tumorous regions of breast tissue samples. CONCLUSION: The FNA-MALDI-TOF/MS approach can provide complementary information for pathological examinations and improve the accuracy of breast cancer diagnoses. Owing to the ease of operation and automation, it is possible to efficiently screen the lipid biomarkers in a large number of tissue samples by means of MALDI-TOF/MS.

Biomarker Characterization by MALDI-TOF/MS.

Mass spectrometric techniques frequently used in clinical diagnosis, such as gas chromatography-mass spectrometry, liquid chromatography-mass spectrometry, ambient ionization mass spectrometry, and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI-TOF/MS), are discussed. Due to its ability to rapidly detect large biomolecules in trace amounts, MALDI-TOF/MS is an ideal tool for characterizing disease biomarkers in biologic samples. Clinical applications of MS for the identification and characterization of microorganisms, DNA fragments, tissues, and biofluids are introduced. Approaches for using MALDI-TOF/MS to detect various disease biomarkers including peptides, proteins, and lipids in biological fluids are further discussed. Finally, various sample pretreatment methods which improve the detection efficiency of disease biomarkers are introduced.

Principle component analysis combined with matrix-assisted laser desorption ionization mass spectrometry for rapid diagnosing the sera of patients with major depression.

BACKGROUND: Previously, we demonstrated that 6M HCl hydrolysis followed by matrix-assisted laser desorption/ionization (MALDI-TOF) mass spectrometry is a useful technique to detect potential protein biomarkers in the sera collected from major depression (MD) patients and from healthy controls. METHODS: In this study, the effects of various organic acids in hydrolyzing proteins in serum were first examined. The organic matrixes commonly used in MALDI analysis were also examined for characterizing the hydrolyzed peptides. Finally, principle component analysis (PCA) was used to analyze the MALDI mass spectra of acid-hydrolyzed serum samples. RESULTS: It was found that 20% TFA and sinapinic acid were the optimal reagents for hydrolysis and MALDI matrix. Samples collected from MD patients and healthy controls were readily classified through PCA analysis. A receiver operating characteristic (ROC) curve based on the ratio of the intensities of the two fragment ions (m/z 8606 and 9287) indicated by PCA plot was also constructed. The area under the curve was 0.845; the sensitivity and specificity were both 80%. CONCLUSIONS: An analytical platform employing trifluoroacetic acid to hydrolyze serum proteins followed by MALDI-TOF/MS and PCA analysis was developed to rapidly differentiate the sera between MD patients and healthy controls.

Diagnosis of albuminuria by tryptic digestion and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry.

BACKGROUND: Matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometry has been successfully used to detect trace albumin in urine for the diagnosis of albuminuria. However, only the monomeric form of albumin was detected with this approach. METHODS: Trypsin was used to digest urinary albumin and its related compounds in urine to produce characteristic peptides. The digest solution was subsequently analyzed by MALDI-TOF MS to obtain peptide ion signals which were used as diagnostic biomarkers for albuminuria. RESULTS: The analytical protocol was optimized for efficient digestion and high-performance MALDI-TOF MS analysis. The limit of detection (LOD) of albumin in urine was about 5×10(-7)M. CONCLUSIONS: Trypsin digestion combined with MALDI-TOF MS analysis is an efficient and simple approach for rapidly diagnosing albuminuria.

Matrix-assisted laser desorption ionization/time-of-flight mass spectrometry for clinical diagnosis.

BACKGROUND: Matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometry is known as an extremely sensitive analytical tool for characterizing different types of biological compounds including proteins, peptides and lipids. Since MALDI-TOF analysis requires very simple sample pretreatment, the technique can be used for rapidly detecting biochemical compounds serving as disease biomarkers. RESULTS: This mini-review focuses on the applications of MALDI-TOF in the detection of potential disease biomarkers in various biological samples. CONCLUSIONS: The potential disease biomarkers are mostly abundant proteins, peptides, or lipids including: albumin; hemoglobin; α-defensins; trimethylamine; phospholipids; and glycated α- and ß-globin, which are indicators of albuminuria; fecal occult blood and ischemic stroke; dry eye disease and/or aging; trimethylaniuria; breast cancer; and diabetes, respectively.

Differentiation of virulence of Helicobacter pylori by matrix-assisted laser desorption/ionization mass spectrometry and multivariate analyses.

BACKGROUND: The ability to determine the virulence of a Helicobacter pylori strain would be helpful for predicting the development of gastrointestinal disease and suggesting medical treatment. METHODS: A protocol based on matrix-assisted laser desorption ionization/time-of-flight mass spectrometry (MALDI-TOF MS) was established for the efficient detection of peptides and proteins in extracts of H. pylori cells. Two multivariate statistical methods-principal component analysis (PCA) and hierarchical clustering analysis-were used to analyze the resulting MALDI mass spectra of reference strains and clinical isolated/inoculated strains. RESULTS: Based on differences in their peptide and protein profiles, H. pylori strains having similar virulence genotypes were grouped together on the PCA score plot. Hierarchical cluster analysis revealed high conformity between the protein profiles and the respective virulence genotypes. The inoculated H. pylori strain, which was clustered in the same group with the high-virulence reference strains, also resulted in severe histopathological lesions in gerbils. CONCLUSIONS: MALDI-TOF MS combined with multivariate analyses shows the ability to rapidly differentiate H. pylori strains in terms of their virulence.

The study of interferences for diagnosing albuminuria by matrix-assisted laser desorption ionization/time-of-flight mass spectrometry.

BACKGROUND: Matrix-assisted laser desorption ionization/time-of-flight (MALDI-TOF) mass spectrometric analysis of albumin (ALB) biomarkers is an alternative approach toward the rapid diagnosis of proteinuria for screening a large number of samples. The aim of this study is to reveal if interfering factors in urinary dipstick approach would affect the results of diagnosing albuminuria by MALDI-TOF MS. METHODS: The effects of various interfering chemicals on the diagnosis of albumin in urine were examined using both MALDI-TOF mass spectrometric and dipstick approaches. Semi-quantification of albumin was performed by using MALDI-TOF MS. RESULTS: Interferences from various drugs, detergents, vitamins and their metabolites, alkaline, and blood, which often cause false-positive and false-negative results in conventional urinary dipstick analysis, are avoided when using this MALDI-TOF MS approach. It was found that the intensity of +1 and +2 albumin ions varies with the albumin concentration. A log/log plot of the intensity ratio vs. albumin concentration is then used as a calibration curve for semi-quantifying the albumin in urines. CONCLUSIONS: MALDI-TOF MS is an effective approach toward avoiding interferences caused by various chemical compounds during the rapid diagnosis of albumin in urine. Semi-quantification of albuminuria is also achieved by this MALDI-TOF MS approach.

Detection of melamine in a human renal uric acid stone by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS).

BACKGROUND: The link between melamine-contaminated daily foodstuffs and urolithiasis formation has drawn an international concern. However, detection of melamine levels in urine may not completely represent external melamine exposure. Thus, finding an additional analytical method for the study of environmental melamine exposure and its adverse effect in humans is crucial. METHODS: Eleven adult patients diagnosed with uric acid urolithiasis were retrospectively analyzed. Melamine levels in their overnight one-spot urine samples were measured by a triple quadrupole liquid chromatography tandem mass spectrometry (LC-MS/MS). The compositions of stone samples were analyzed by the Fourier transform infrared (FTIR) spectrophotometer and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). RESULTS: Seven (63.6%) out of 11 patients had detectable melamine levels in their urine specimens (method of detection limit: 0.8 ng/ml). Three patients (27.3%) were highly suspected of having melamine-containing urolithiasis in FTIR spectra. In one of those three cases who still had available stored stone specimens, MALDI-TOF MS further confirmed melamine components in this male patient's stone specimens. In contrast, his urinary melamine level was below the detection limit by LC-MS/MS. CONCLUSIONS: Direct analysis of melamine in the composition of urolithiasis by MALDI-TOF MS can be an additional analytical method to evaluate for external melamine exposure.

Ambient ionization mass spectrometry: a tutorial.

Ambient ionization is a set of mass spectrometric ionization techniques performed under ambient conditions that allows the direct analysis of sample surfaces with little or no sample pretreatment. Using combinations of different types of sample introduction systems and ionization methods, several novel techniques have been developed over the last few years with many applications (e.g., food safety screening; detection of pharmaceuticals and drug abuse; monitoring of environmental pollutants; detection of explosives for antiterrorism and forensics; characterization of biological compounds for proteomics and metabolomics; molecular imaging analysis; and monitoring chemical and biochemical reactions). Electrospray ionization and atmospheric pressure chemical ionization are the two main ionization principles most commonly used in ambient ionization mass spectrometry. This tutorial paper provides a review of the publications related to ambient ionization techniques. We describe and compare the underlying principles of operation, ionization processes, detecting mass ranges, sensitivity, and representative applications of these techniques.

Ambient ionization mass spectrometry.

Mass spectrometric ionization methods that operate under ambient conditions and require minimal or no sample pretreatment have attracted much attention in such fields as biomedicine, food safety, antiterrorism, pharmaceuticals, and environmental pollution. These technologies usually involve separate ionization and sample-introduction events, allowing independent control over each set of conditions. Ionization is typically performed under ambient conditions through use of existing electrospray ionization (ESI) or atmospheric pressure chemical ionization (APCI) techniques. Rapid analyses of gas, liquid, and solid samples are possible with the adoption of various sample-introduction methods. This review sorts different ambient ionization techniques into two main subcategories, primarily on the basis of the ionization processes, that are further differentiated in terms of the approach used for sampling.

Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry to rapidly screen for albuminuria.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is used as an alternative method for the rapid diagnosis of albuminuria. This technique requires no further sample pretreatment than simply mixing the urine sample with a MALDI matrix and drying under ambient conditions. The resulting MALDI mass spectra reveal albumin ions having charges ranging from +1 to +5. The detection of albumin is possible using any of the three most common MALDI matrices - sinapinic acid (SA), 2,5-dihydroxybenzoic acid (2,5-DHB), or 4-hydroxy-alpha-cyanocinnamic acid (alpha-CHC). Using this analytical approach, the limit of detection for albumin in urine is 10(-6) M, approximately 5 to 10 times lower than that detectable through conventional chemical testing.