An activated carbon substrate surface for laser desorption mass spectrometry

A method to obtain laser desorption/ionization mass spectra of organic compounds by depositing sample solutions onto a carbon substrate surface is demonstrated. The substrate consists of a thin layer of activated carbon particles immobilized on an aluminum support. In common with the porous carbon suspension samples used in previous “surface-assisted laser desorption/ionization” (SALDI) work, the mass spectra contain only a few “matrix” background ion peaks, minimizing interference with analyte ion peaks. The presence of glycerol ensured that the ion signals were stable over hundreds of laser shots. In addition, the carbon substrate surface has several advantages over the suspension samples. The use of a very thin layer of carbon significantly improves the sensitivity. Detection limits range from attomoles for crystal violet to femtomoles for bradykinin. Very little sample preparation is required as the analyte solution is simply pipetted onto the substrate surface and glycerol added. When using an alternate sample deposition method, a mass resolution for bradykinin of 1800 is achieved in linear time-of-flight mode. This is close to the resolution limit set by the detector system and above instrument specification for matrix-assisted laser desorption/ionization mass spectra.     

Determination of arsenic in water samples by Total Reflection X-Ray Fluorescence using pre-concentration with alumina

The determination of arsenic in water samples requires techniques of high sensitivity. Total Reflection X-Ray Fluorescence (TXRF) allows the determination but a prior separation and pre-concentration procedure is necessary. Alumina is a suitable substrate for the selective separation of the analytes. A method for separation and pre-concentration in alumina, followed by direct analysis of the alumina is evaluated. Quantification was performed using the Al–Kα and Co–Kα lines as internal standard in samples prepared on an alumina matrix, and compared to a calibration with aqueous standards. Artificial water samples of As (III) and As (V) were analyzed after the treatment. Fifty milliliters of the sample at ppb concentration levels were mixed with 10 mg of alumina. The pH, time and temperature were controlled. The alumina was separated from the slurry by centrifugation, washed with de-ionized water and analyzed directly on the sample holder. A pre-concentration factor of 100 was found, with detection limit of 0.7 μgL⁻¹. The percentage of recovery was 98% for As (III) and 95% for As (V) demonstrating the suitability of the procedure.     

On the mechanism of ion formation from the aqueous solutions irradiated with 3 microm IR laser pulses under atmospheric pressure

The mechanism of atmospheric pressure (AP) laser ionization of water and water/glycerol liquid samples at a 3-microm wavelength is studied experimentally. For the ion desorption, an in-house built Yb : YAG-pumped optical parametric oscillator (OPO) infrared (IR) laser has been coupled with AP MALDI ion source interfaced to an ion trap mass spectrometer (MS). It has been shown that water is primarily responsible for ion generation in water/glycerol samples, while glycerol increases the solution viscosity and decreases the water evaporation rate and sample losses. In contrast to AP UV-MALDI, the electric field in the case of AP IR-MALDI does not assist in ion production. It was found that the absence of the electrical field provides the optimum ionization condition both for water and water/glycerol liquid samples at the 3-microm laser irradiation. A two-stage ion formation mechanism, which includes the initial emission of microdroplets and release of molecular ions at the second stage, can explain the experimentally observed ion signal dependencies upon the voltage applied between MS inlet and the MALDI sample plate. Postionization using additional corona discharge APCI increases the observed signal by approximately 50%, which indicates that some portion of the analyte is desorbed in the form of neutral molecules.     

Forensic identification of spilled biodiesel and its blends with petroleum oil based on fingerprinting information

A case study is presented for the forensic identification of several spilled biodiesels and its blends with petroleum oil using integrated forensic oil fingerprinting techniques. The integrated fingerprinting techniques combined SPE with GC/MS for obtaining individual petroleum hydrocarbons (aliphatic hydrocarbons, polyaromatic hydrocarbons and their alkylated derivatives and biomarkers), and biodiesel hydrocarbons (fatty acid methyl esters, free fatty acids, glycerol, monoacylglycerides, and free sterols). HPLC equipped with evaporative scattering laser detector was also used for identifying the compounds that conventional GC/MS could not finish. The three environmental samples (E1, E2, and E3) and one suspected source sample (S2) were dominant with vegetable oil with high acid values and low concentration of fatty acid methyl ester. The suspected source sample S2 was responsible for the three spilled samples although E1 was slightly contaminated by petroleum oil with light hydrocarbons. The suspected source sample S1 exhibited with the high content of glycerol, low content of glycerides, and high polarity, indicating its difference from the other samples. These samples may be the separated byproducts in producing biodiesel. Canola oil source is the most possible feedstock for the three environmental samples and the suspected source sample S2.     

Quantitative analysis of urinary glycerol levels for doping control purposes using gas chromatography-mass spectrometry

The administration of glycerol to endurance athletes results in an increased fluid retention and improved performance, particularly under hot and humid conditions. Consequently, glycerol is considered relevant for sports drug testing and methods for its detection in urine specimens are required. A major issue in this regard is the natural occurrence of trace amounts of glycerol in human urine, which necessitates a quantitative analysis and the determination of normal urinary glycerol levels under various sporting conditions. A quantitative method was established using a gas chromatography/isotope-dilution mass spectrometry-based approach that was validated with regard to lower limit of detection (0.3 microg mL(-1)), lower limit of quantification (0.9 microg mL(-1)), specificity, linearity (1.0-98.0 microg mL(-1)), intraday and interday precision (<20% at 2.4, 24.1 and 48.2 microg mL(-1)) as well as accuracy (92-110%). Sample aliquots of 20 microL were enriched with five-fold deuterated glycerol, dried and derivatised using N-methyl-trimethylsilyltrifluoroacetamide (MSTFA) before analysis. The established method was applied to a total of 1039 doping control samples covering various sport disciplines (349 endurance samples, 286 strength sport samples, 325 game sport samples and 79 other samples) in- and out-of-competition, which provided quantitative information about the glycerol content commonly observed in elite athletes' urine samples. About 85% of all specimens yielded glycerol concentrations < 20.0 microg mL(-1) and few reached values up to 132.6 microg mL(-1). One further sample, however, was found to contain 2690 microg mL(-1), which might indicate the misuse of glycerol, but no threshold for urinary glycerol concentrations has been established yet due to the lack of substantial data. Based on the results obtained from the studied reference population, a threshold for glycerol levels in urine set at 200 microg mL(-1) is suggested, which provides a tool to doping control laboratories to test for the misuse of this agent in elite and amateur sport.     

A binary matrix of 2,5-dihydroxybenzoic acid and glycerol produces homogenous sample preparations for matrix-assisted laser desorption/ionization mass spectrometry

We introduce a two-component matrix for ultraviolet matrix-assisted laser desorption/ionization mass spectrometry (UV-MALDI-MS) that consists of 2,5-dihydroxybenzoic acid (DHB) and glycerol. Upon slow evaporation of residual water/methanol solvents in a pre-vacuum chamber sample preparations are obtained that exhibit a homogeneous morphology with analyte-matrix crystals evenly distributed over the whole sample spot. At a molar DHB/glycerol ratio of approximately 1:5, the crystals range in length from approximately 100 to 300 microm and are about 15-30 microm wide. Mass spectra of peptides, proteins, and an oligosaccharide are presented and compared with those recorded from standard dried-droplet DHB matrix. The ion signals show a reproducibility of the order of 10-15% when scanning the surface of an individual sample or even different samples that contain the same amount of peptide, A close to linear relationship between peptide concentration and the corresponding peptide ion signal is found over three orders of magnitude of sample prepared. However, when a fixed position is irradiated with a large number of laser pulses, a monotonous decay of peptide ion signal with time is observed. Potentially, the binary matrix will be especially useful for the analysis of samples that are stabilized in buffered aqueous glycerol solution and preliminary results addressing this aspect are shown.     

Charge state distribution shifting of protein ions observed in matrix-assisted laser desorption ionization mass spectrometry

By using a new sample preparation method for matrix-assisted laser desorption ionization, a significant shift to lower mass-to-charge values can be obtained for many protein samples. The sample preparation technique involves the creation of a thin film of protein-doped -cyano-4-hydroxycinnamic acid (CHCA) matrix formed in the presence of glycerol on top of a previously deposited pad of CHCA matrix. The higher charge states were not observed if the laser power was significantly above the threshold needed to produce protein molecular ions. Similar spectra were observed when samples were prepared in the presence of urea. The phenomenon was specific for the CHCA matrix because no effects were observed when sinapinic acid (3,5-dimethoxy-4-hydroxy-trans-cinnamic acid) and 2-(4-hydroxyphenylazo) benzoic acid matrices were used with the new sample preparation method.     

Quantitative distribution analysis of alumina inclusion particles in ferritic stainless steels by using laser‐induced breakdown optical emission spectrometry

This paper describes an analytical method for determining the spatial distribution of alumina inclusion particles in several ferritic stainless steels by laser‐induced breakdown optical emission spectrometry with a single‐shot laser scanned on the sample surface. For this purpose, an irradiation system, which comprised a Q‐switched Nd:YAG laser with an average energy of 50 mJ/pulse and a precisely driven X‐Y‐Z sample stage, was prepared. A Czerny–Turner‐mounting spectrograph equipped with an ICCD detector was employed for a time‐resolved measurement of the laser‐induced breakdown optical emission spectrometry signal. The intensity ratio of Al I 396.152 nm to Cr I 396.368 nm was measured each for the single shot, while the irradiation positions were step‐wise moved in the X‐Y direction and then the same sampling area was repeatedly irradiated by subsequent laser shots in the Z direction. The number of alumina particles was mapped from the intensity ratio of Al/Cr each for the irradiation points in both the lateral and in‐depth directions, enabling the distribution of alumina particles to be presented. The resolution of our measuring system was 40 μm in the lateral position and 6–7 μm in the depth direction, which were mainly determined by the crater size of a laser shot. A typical size of the alumina particles (several μm) was smaller than their resolutions; nevertheless, the suggested method would be still more effective to give the distribution of alumina particles, especially the coarse ones, because of its rapid response for the analytical result. Copyright © 2017 John Wiley & Sons, Ltd.     

Infrared laser post-ionization of large biomolecules from an IR-MALD(I) plume

A two-infrared laser desorption/ionization method is described. A first laser, which was either an Er:YAG laser or an optical parametric oscillator (OPO), served for ablation/vaporization of small volumes of analyte/matrix sample at fluences below the ion detection threshold for direct matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A second IR-laser, whose beam intersected the expanding ablation plume at a variable distance and time delay, was used to generate biomolecular ions out of the matrix-assisted laser desorption (MALD) plume. Either one of the two above lasers or an Er:YSGG laser was used for post-ionization. Glycerol was used as IR-MALDI matrix, and mass spectra of peptides, proteins, as well as nucleic acids, some of which in excess of 10(5) u in molecular weight, were recorded with a time-of-flight mass spectrometer. A mass spectrum of cytochrome c from a water ice matrix is also presented. The MALD plume expansion was investigated by varying the position of the post-ionization laser beam above the glycerol sample surface and its delay time relative to the desorption laser. Comparison between the OPO (pulse duration, tau(L) = 6 ns) and the Er:YAG laser (tau(L) approximately 120 ns) as primary excitation laser demonstrates a significant effect of the laser pulse duration on the MALD process.     

Improved method for determination of abamectin and ivermectin in cattle plasma.

A liquid chromatographic (LC) method was developed for determination of abamectin (ABM) and ivermectin (IVM) in cattle plasma. The sample was extracted with acetonitrile and cleaned up on an alumina column. After conversion to stable fluorescent derivative with trifluoroacetic anhydride and N-methylimidazole, the sample was analyzed by LC with fluorescence detection (Ex 365 nm and Em 475 nm). Doramectin was used as an internal standard. Recoveries ranged from 91.2 to 100.7% for IVM and from 87.0 to 98.7% for ABM, with 1-50 ng/mL fortified samples. The coefficients of variation were <10.1%. The limit of detection was 0.02 ng/mL for ABM and IVM in 1.0 mL samples.     

Utilisation of enzymatic reactions in Al2O3 powder moulding process

Direct Coagulation Casting (DCC) method was applied for an alumina powder molding. In the paper the results of studies on the application of the reaction of acetic acid generation from glycerol triacetate catalyzed by lipase PPL for the flocculation of ceramic slips are presented. The ceramic samples obtained according this method were homogenous of a low content of organic binder (below 0.5 mass%), high tensile strength in the green state (>1 MPa) and high uniformity of thickening and a uniform structure. This revised version was published online in July 2006 with corrections to the Cover Date.     

X射线荧光光谱法测定氧化铝中杂质元素

应用X-射线荧光光谱法测定了氧化铝中11种杂质成分（SiO2，Fe2O3，Na2O，K2O，CaO，TiO2，P2O5，ZnO，V2O5，Ga2O3，Cr2O3）。试样用四硼酸锂和偏硼酸锂作混合熔剂融熔制成玻璃状片形熔块。通过在高纯氧化铝中加入一定量的上述11种元素的纯氧化物配制成中间标准样品，并用此中间标准样品和纯氧化铝作为空白试样组成高、低标，制备了校正曲线。又用此中间标准样品与纯氧化铝按一定比例配制控制样品对分析过程进行质量控制。对所提出方法的精密度进行了考核，结果表明以上11种杂质成分测定结果的RSD值均小于10％。用4种标样对此方法的准确度进行验证，结果表明所得测定值与已知值之间的误差均符合标准规定。     

离子阱串联质谱法检测鱼肉中指示性多氯联苯

建立了使用离子阱串联质谱技术和同位素稀释技术准确测定鱼肉中的7种指示性多氯联苯（PCB）单体的方法。方法的检出限为0．025—0．068ng／g,6个加标鱼样（添加水平1ng／g）中7个单体的回收率为87.2％～103.7％,RSD为3．2％-8．7％（n=6）。本方法定量准确可靠,可用于食品中指示性PCB的测定。     

A novel laser desorption/ionization method using through hole porous alumina membranes

Rationale

A novel matrix‐free laser desorption/ionization method based on porous alumina membranes was developed. The porous alumina membranes have a two‐dimensional (2D) ordered structure consisting of closely aligned straight through holes of sub‐micron in diameter that are amenable to mass production by industrial fabrication processes.

Methods

Considering a balance between the ion generating efficiency and the mechanical strength of the membranes, the typical values for the hole diameter, open aperture ratio and membrane thickness were set to 200 nm, 50% and 5 μm, respectively. The membranes were coated with platinum on a single side that was exposed to the laser. Evaluation experiments were conducted on the feasibility of this membrane structure for an ionization method using a single peptide and mixed peptides and polyethylene glycol samples and a commercial matrix‐assisted laser desorption/ionization (MALDI) time‐of‐flight mass spectrometer in the positive ion mode.

Results

Results showed a softness of ionization and no sweet spot nature. The capillary action of the through holes with very high aspect ratio enables several loading protocols including sample impregnation from the surface opposite to the laser exposure side.

Conclusions

The feasibility study indicates that the through hole porous alumina membranes have several advantages in terms of usefulness over the conventional surface‐assisted laser desorption ionization (SALDI) methods. The proposed novel ionization method is termed Desorption Ionization Using Through Hole Alumina Membrane (DIUTHAME).

     

Decreased molybdenum emission in a carbon arc caused by zirconium carbide formation on the sample electrode

The presence of about 10% zirconium (as oxide) in alumina samples obtained by the ignition of aluminum 8-quinolinolate (precipitated as a trace-element collector) greatly dereased the intensity of molybdenum emission when the alumina was analysed by means of a cathode-layer carbon arc. Retention of the molybdenum on the sample electrode was confirmed with radioactive molybdenum-99. A prominent crystalline residue on the cathode, identified as ZrC by x-ray powder diffraction, was probably responsible for the decreased emission. Thus, zirconium crucibles cannot be used for the sodium carbonate fusion of samples in a spectrochemical procedure for determining traces of molybdenum in soils and plants.     

Use of aqueous slurry sampling for the determination of lead in human hair samples by electrothermal atomic absorption spectrometry

A method for the determination of lead in human hair slurries by electrothermal atomic absorption spectrometry was optimized. Particle size reduction was achieved with a vibrational mill ball equipped with zirconia cups, 20 min being sufficient grinding time to achieve an adequate particle diameter (<1 mum). The use of different thickening agents, namely glycerol, Triton X-100 and Viscalex HV30, was studied and glycerol was found to be the best. The use of Pd and Mg(NO(3))(2) at optimum concentrations of 20 and 25 mg l(-1) respectively was found to be satisfactory for stabilizing lead at 1100 degrees C. A limit of detection of 0.21 mg kg(-1) was obtained. The limit of detection can be reduced to 0.05 mg kg(-1) without loss of analytical performance by increasing four-fold the amount of hair sample. Accuracy was studied by analysis of a CRM 397 human hair reference material with a certified lead content of 33.0 +/- 1.2 mg Pb kg(-1). The standard addition method was used for the determination of lead in hair samples from healthy people, the levels being between 2.3 and 35.5 mg kg(-1).     

Hydride generation atomic absorption spectrometric determination of bismuth after separation and preconcentration with modified alumina

A simple and sensitive method has been developed for the trace determination of bismuth in aqueous samples by a combination of solid‐phase extraction and hydride generation atomic absorption spectrometry. The method is based on the use of a column packed with 2‐mercaptobenzothiazole immobilized on sodium dodecyl sulfate coated alumina. Different parameters influencing the separation and preconcentration of bismuth such as pH, sample volume, type, and concentration of eluent, and the flow rate of sample and eluent were studied. A sample volume of 500.0 mL resulted in a preconcentration factor of 100. The precision (relative standard deviation, N = 10) at the 300 ng/L level and the limit of detection (3s) were found to be 2.3% and 12 ng/L, respectively. The developed method was successfully applied to the determination of bismuth in natural water samples and two certified reference materials.     

Analysis of native milk oligosaccharides directly from thin-layer chromatography plates by matrix-assisted laser desorption/ionization orthogonal-time-of-flight mass spectrometry with a glycerol matrix

We have recently presented a new method for direct coupling of high-performance thin-layer chromatography (HPTLC) with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS), illustrated by the analysis of a complex ganglioside mixture. In the current communication, an adaptation of this procedure to mixtures of native oligosaccharides from human and from elephant milk is described. The key features in this method are (1) glycerol as a liquid matrix, to provide a homogeneous wetting of the silica gel and a simple and fast MALDI preparation protocol, (2) an infrared (IR) laser for volume material ablation and particular soft desorption/ionization conditions, and (3) an orthogonal time-of-flight mass spectrometer for a high mass accuracy, independent of any irregularity of the silica gel surface. Chromatographic "mobility profiles" were determined by scanning the laser beam across the analyte bands. The current limit of detection for the MS analysis was determined to approximately 10 pmol of individual oligosaccharides spotted for chromatography. A liquid composite matrix, containing glycerol and the ultraviolet (UV-)MALDI matrix alpha-cyano-4-hydroxycinnamic acid, allows a direct HPTLC-MALDI-MS analysis with a 337 nm-UV laser as well. Compared to the IR-MALDI mode, the analytical sensitivity in UV-MALDI was found to be lower by one order of magnitude, whereas unspecific analyte ion fragmentation as well as adduct formation was found to be more extensive.     

Optimization of a matrix solid-phase dispersion method with subsequent clean-up for the determination of ethylene bisdithiocarbamate residues in almond samples

A matrix solid-phase dispersion (MSPD) method with subsequent clean-up has been developed to isolate the ethylene bisdithiocarbamate (EBDC) main metabolites (ethylenethiourea, ETU, and ethylenebis [isothiocyanate] sulphide, EBIS) in almond samples. The optimized experimental set-up configuration involved 0.2 g of almond sample, washed sand as MSPD support and NaOH as defatting agent. A subsequent purification step on alumina using acetonitrile as extraction solvent was enough to remove all interferent matrix components, including the fatty material, and provide clean extracts. Quantitative analysis was performed by reversed phase liquid chromatography (RPLC) with diode-array ultraviolet absorbance (DAD UV) detector. Analytes recoveries were between 76 and 85% with relative standard deviations ranging from 3 to 12%. The low limits of quantification of 0.05 and 0.07 mg kg(-1) achieved for ETU and EBIS, respectively, make the method useful for the determination of EBDC residues on almond samples.     

Determination of natural levels of lithium and strontium in human blood serum by discrete injection and atomic emission spectrometry with a nitrous oxide—acetylene flame

A sensitive technique is described for the rapid, direct determination of normal levels of lithium and strontium in 100-μl samples of human blood serum without separation or preconcentration. Nitrous oxide—acetylene flame emission spectrometry, using conventional atomic absorption apparatus is used, with discrete sample injection. Lithium and strontium standards were prepared in 21% (v/v) glycerol which approximates the viscosity of serum. It is recommended that serum samples be analyzed by either calibration with artificial serum and glycerol standards or by immediate standard microaddition procedures. Results for pooled human serum indicate accuracy and precision of better than 6% at the 10 ng ml^-1 level. The method is free from nebulizer clogging and matrix interferences and should be useful as a routine clinical laboratory procedure.