Liquid extraction surface analysis in-line coupled with capillary electrophoresis for direct analysis of a solid surface sample

A surface-sampling technique of liquid extraction surface analysis (LESA) was in-line coupled with capillary electrophoresis (CE) to expand the specimen types for CE to solid surfaces. The new direct surface analysis method of LESA–CE was applied to the determination of organophosphorus pesticides, including glufosinate-ammonium, aminomethylphosphonic acid, and glyphosate on the external surface of a fruit such as apple. Without any sample pretreatment, the analytes sprayed on the surface of a half apple were directly extracted into a liquid microjunction formed by dispensing the extractant from the inlet tip of a separation capillary. After extraction, the analytes were derivatized in-capillary with a fluorophore 4-fluoro-7-nitro-2,1,3-benzoxadiazole and analyzed with CE-laser induced fluorescence (LIF). The limits of detection for glufosinate-ammonium, aminomethylphosphonic acid, and glyphosate were 2.5, 1, and 10 ppb, respectively, which are at least 20 times lower than the tolerance limits established by the U.S. Environmental Protection Agency. Thus, we demonstrated that LESA–CE is a quite sensitive and convenient method to determine analytes on a solid surface avoiding the dilution from sample pretreatment procedures including homogenization of a bulk sample.     

Laser-induced ablation of a steel sample in different ambient gases by use of collinear multiple laser pulses

The sensitivity of laser-induced breakdown spectroscopy of solid samples depends on the number of ablated and excited analytes. Laser ablation of solid samples can be enhanced by using collinear multiple laser pulses, for example double or triple pulses, rather than single laser pulses with the same total laser pulse energy. The ablation rates and the plasma conditions are affected by the ambient gas. In this study laser ablation was examined by varying the interpulse separation of the multiple pulses, within double and triple-pulse bursts, and the gas mass density at constant gas pressure. Different ambient gases and gas mixtures consisting of argon, oxygen, and nitrogen were used to study their effect on ablation rates. In a pure argon atmosphere (99.999% v/v Ar) the ablation burst number required to penetrate a steel plate of thickness 100 μm is reduced by a factor of approximately six by use of triple-pulse bursts with a symmetric interpulse separation of 15 μs rather than single pulses with the same total burst energy of 105 mJ. For double and single pulses the factors are 1.6 for Ar and 2.8 for synthetic air. Analyte lines are 4 to 8 times more intense if an argon atmosphere, rather than air, is used.     

Comparison of the effect of excimer laser irradiation and RF plasma treatment on polystyrene surface

Polystyrene (PS) samples were treated with excimer laser, argon and oxygen plasmas. The surface of PS was irradiated using ArF excimer pulsed laser (λ=193 nm). Radio frequency glow discharge (RF) was used to generate the argon and oxygen plasmas. The samples were processed at different number of pulses and treatment times. The changes were characterized by atomic force microscopy (AFM), attenuated total reflectance Fourier transform infrared (ATR-FTIR), scanning electron microscopy (SEM) and contact angle measurements. The data from ATR-FTIR spectra showed the induction process of oxygen-based functional group in both PS samples treated with RF plasma and laser. AFM and SEM observations demonstrated that a specific nanostructure was created on the laser-treated PS surface. Contact angle measurement indicated higher wettability of the treated PS with both argon and oxygen plasmas and lesser wettability of laser-treated samples. The data from in vitro assays showed the significant cell attachment and growth onto plasma-treated surfaces in comparison with laser treated samples.     

Stabilization of cellulosolytic enzymes by sorption on the plant raw materials surface

Russian Chemical Bulletin - The influence of a cellulosolytic complex sorbed on the plant raw materials surface on the stabilization of enzymes during the subsequent mechanical treatment was shown....     

Activation effects of a platinum electrode by laser pulse irradiation on the electro-oxidation of glucose in alkaline solution.

In order to demonstrate the activation effects of a Pt electrode by laser pulse irradiation, the electro-oxidation of glucose was tested at an activated Pt electrode by cyclic voltammetry. A fixed potential was applied to the electrode, and then the electrode was irradiated with laser pulses from a Nd:YAG laser at 20 Hz for 20 s. Activation by the laser pulse irradiation gave two remarkable effects on cyclic voltammograms from the electro-oxidation of glucose in a 0.1 mol dm(-3) NaOH solution, i.e., surface modulation and cleaning effects. Significant differences were found in the cyclic voltammograms at the activated and at the simply polished electrodes. Such differences in the oxidation waves are attributed to a crystallographic change of the electrode surface induced by a laser ablation, accompanied by laser pulse irradiation. Due to the cleaning effect, the activated Pt electrode gave a sharp oxidation wave at -0.3 V even in real samples containing various organic compounds that could foul the electrode, though the activated Pt electrode lacked selectivity to the electro-oxidation of glucose.     

Patterning of cells on a PVC film surface functionalized by ion irradiation

Micropatterns of cells on a poly(vinyl chloride) (PVC) film surface were created by using ion irradiation. A PVC film was irradiated with H⁺ ions through a pattern mask in order to create patterns of the hydrophilic/hydrophobic regions on the PVC surface. The effect of ion irradiation on the surface properties of the PVC film was characterized by using Fourier transform‐infrared spectroscopy (FT‐IR), water contact angle measurement, and X‐ray photoelectron spectroscopy (XPS). The results revealed that the chemical environment of the PVC film surface was effectively changed by ion irradiation due to dehydrochlorination and oxidation. The in vitro cell culture on the patterned PVC film surface showed selective adhesion and proliferation of the cells on the ion‐irradiated regions. Well‐defined 50 µm patterns of the cells were obtained on the PVC film surface irradiated to 1 × 10¹⁵ ions/cm². Copyright © 2009 John Wiley & Sons, Ltd.     

Effect of surface tension on the relaxation of a viscoelastic half-space perturbed by a point load

We study the effect of surface tension on the flattening of a surface perturbed by a point load subsequent to its removal. The surface bounds an infinite isotropic linear viscoelastic incompressible half space. The point load is initially applied for a sufficiently long time so that the half space is fully relaxed before the load removal. An exact solution is obtained assuming small deformation. We then specialize our theory to the case of a standard viscoelastic solid. There is an initial reduction of the surface displacement immediately after load removal that is found to be directly proportional to the ratio of applied load to surface tension. This is followed by a temporal decay of the surface profile that depends only on the relaxation time and the long and short time moduli of the viscoelastic solid. Our work also provides the Green's function for a suddenly applied point load on the surface of a viscoelastic half space. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 274–280     

AES investigations of the iron surface composition after laser irradiation under atmospheric conditions

The laser induced modification of iron surfaces with atmospheric species was investigated by means of Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). Different laser systems were used for irradiating iron samples in a wide range of the laser processing parameters up to small foci and ultra short pulses.A nitriding of iron connected with an oxidation of the near surface region was observed in the wavelength range between 193 nm and 10.6 m using large foci (0.1 cm²) and short pulses (10...1400ns). In case of small foci (7·10^–6cm²) with ns-pulses (50 ns) an enrichment of the iron melt with nitrogen and an advanced oxidation of the surrounding area of the laser spot were detected. When using shorter pulses (200 fs, 40 ps) no indications for a nitriding were found.     

Surface grafting of polyethylene by mutual irradiation in methyl acrylate vapor. III. Quantitative surface analysis by x-ray photoelectron spectroscopy

X-ray photoelectron spectroscopy (ESCA) has been used for quantitative surface analysis of surface grafts prepared by mutual irradiation of polyethylene (PE) in methyl acrylate (MA) vapor with γ rays and high-energy electrons. The binding-energy shift between the C_1s electrons in the ester group of poly(methyl acrylate) (PMA) and in PE is large enough (ca. 3.6 eV) to distinguish the PMA and PE components. The C_1s peak-area ratio of ester carbon to other carbons is related quantitatively to graft composition by constructing a calibration curve for a given instrument and excitation source, with a series of homogeneous grafts of known composition used as the calibration standards. Using the calibration curve and the measured peak ratio, the surface composition of the surface grafts is determined. The relations between surface compositions according to ESCA and attenuated total reflection (ATR) infrared spectroscopy and between adhesive bond strength and ESCA composition are discussed. In the electron-induced grafts, the grafted surface reaches maximum adhesive bondability with attainment of 100 mole % MA in the surface detected by ESCA; i.e., with formation of a homopolymer layer. The ESCA composition can be used as an indicator of the presence of the homopolymer layer or as a criterion for predicting adhesive bond strength.     

A comparative study on methods of optimal sample preparation for the analysis of oligonucleotides by matrix-assisted laser desorption/ionization mass spectrometry

Metal adducts (e.g., Na+ and K+) significantly hinder the analysis of oligonucleotides by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Although a number of sample purification methods exist, to date no comparative study exists to determine the most efficient method for purifying oligonucleotides. The objective of this work was to perform such a study. Several different oligonucleotide samples were synthesized. Aliquots of these samples were then purposely contaminated with sodium acetate to generate representative contaminated (salted) oligonucleotide samples. A number of popular oligonucleotide purification techniques were then tested as to their effectiveness at removing Na+ from the salted samples. The effectiveness of Na+ removal was qualitatively assessed by comparing the MALDI mass spectra of the original sample, the salted sample, and the salted sample after purification. Micropipet tips packed with C18 reversed-phase packing material (e.g., Zip Tips) appear to be the most effective means of purifying the oligonucleotides investigated. Minidialysis was found to be an effective alternative for purifying higher molecular weight oligonucleotides (> 10,000 u).     

Calculation and optimization of sample identification by laser induced breakdown spectroscopy via correlation analysis

Linear correlation analysis may be used as a technique for the identification of samples with a very similar chemical composition by laser induced breakdown spectroscopy. The spectrum of the “unknown” sample is correlated with a library of reference spectra. The probability of identification by single shot analysis can be estimated by the method described in this paper. When a right identification is not obtained by single shot correlation analysis the accuracy can be increased by averaging spectra or by averaging the correlation coefficients. The number of spectra or correlation coefficients to be averaged to obtain a 99.9% right identification is evaluated. We found out that the number of spectra to be averaged is equal to the number of correlation coefficients to be averaged. The benefit of using averaged spectra over averaging correlation coefficients is a faster calculation.     

Investigation of solid sample microhomogeneity by laser microanalysis

Summary The microhomogeneity of the distribution of doped neodymium in YAG:Nd³⁺ single crystals and of impurities in an aluminium alloy standard are studied by means of laser emission microanalysis. The applied statistical methods are briefly described: one-way variance analysis, two-way variance analysis, calculation of regression models of the element concentration distribution in samples, gradient method and cluster analysis.

---

Untersuchung der Mikrohomogenität fester Proben durch Laser-Mikroanalyse

     

Nanoscale analysis of surface oxides on ZnMgAl hot-dip-coated steel sheets

In this work, the first few nanometres of the surface of ZnMgAl hot-dip-galvanised steel sheets were analysed by scanning Auger electron spectroscopy, angle-resolved X-ray photoelectron spectroscopy and atomic force microscopy. Although the ZnMgAl coating itself is exhibiting a complex micro-structure composed of several different phases, it is shown that the topmost surface is covered by a smooth, homogeneous oxide layer consisting of a mixture of magnesium oxide and aluminium oxide, exhibiting a higher amount of magnesium than aluminium and a total film thickness of 4.5 to 5 nm. Especially by the combined analytical approach of surface-sensitive methods, it is directly demonstrated for the first time that within surface imprints—created by industrial skin rolling of the steel sheet which ensures a smooth surface appearance as well as reduced yield-point phenomenon—the original, smooth oxide layer is partly removed and that a layer of native oxides, exactly corresponding to the chemical structure of the underlying metal phases, is formed.     

Comparison of different sample treatments for the analysis of quinolones in milk by capillary-liquid chromatography with laser induced fluorescence detection

A simple and very sensitive capillary-liquid chromatography method coupled with laser induced fluorescence detection has been developed for the simultaneous determination of seven quinolones of veterinary use in milk. Moreover, a comparison between two different sample treatments (QuEChERS and molecularly imprinted polymer, MIP) has been carried out in terms of efficiency of the extraction (number of analytes to be analysed and absence of interferences), throughput, linear dynamic range in matrix-matches calibrations, detection and quantification limits and accuracy (trueness and precision, by means of recovery assays). The results showed that the QuEChERS procedure was more efficient and faster, showing good recoveries, sensitivity and precision for all the studied compounds. Employing this proposed method, very low detection limits, between 0.4 μg/kg for danofloxacin, and 6 μg/kg for sarafloxacin, have been obtained.     

Photon activation analysis of environmental water: Studies of direct sample irradiation

During trace element analysis in water by photon activation analysis it has been shown that long time bremsstrahlung exposure of the water samples followed by a post-concentration step yielded the most reliable results. Higher specific activity and thus — to a certain extent — higher analytical sensitivities were obtained by pre-concentration on a sorption pellet thereafter activated. The particular problems of each technique investigated are discussed in detail.     

Development of a laser ablation-hollow cathode glow discharge emission source and the application to the analysis of steel samples.

A novel atomic emission spectrometry comprising laser ablation as a sampling source and hollow cathode plasma for the excitation of ablated sample atoms is proposed. In this arrangement, a conventional Grimm-type discharge lamp is employed, but the polarity of the power supply is reversed so that the cylindrical hollow tube acts as a cathode and the glow discharge plasma is produced within this tube. A laser is irradiated to introduce sample atoms into the discharge plasma. Ablated atoms are excited by collisions with electrons and gas species, and emit characteristic radiation upon de-excitation. The experiments were conducted only in an atmosphere of helium gas so as to avoid a rapid erosion of the cathode hollow tube. Phase-sensitive detection with a lock-in amplifier was utilized to reject the continuous background emission of the plasma gas and emissions of sputtered atoms from the tube material. The unique feature of this technique is that the sampling and excitation processes can be controlled independently. The proposed technique was employed for the determination of Cr, Mn, and Ni in low-alloyed steel samples. The obtained concentrations are in good agreement with the reported values. The relative standard deviation (RSD), a measure of the analytical precision, was estimated to be 2-9% for Cr, 3-4% for Mn, and 4-11% for Ni determination.     

Local damage of HT-materials by laser irradiation in the SEM

By using a pulsed Nd:YAG laser the high temperature materials zirconium oxide, fine grain graphite and silicon nitride were rapidly irradiated (heating thermal shock) and their damage behavior was investigated. The laser beam parameters at sample surface were detected by a laser beam analyzing system and correlated with the local damage mechanisms of the materials as erosion, crack formation and solid-solid phase transformation. For the investigations image analysis, localized x-ray analysis, and the ion beam slope cutting technique were applied. The temperature field in the material was simulated by using temperature dependent material parameters for different laser beam parameters. The results illustrate both the strong influence of the temporal and spatial laser energy profile and the materials properties to the material damage.Dedicated to Professor Dr. rer. nat. Dr. h.c. Hubertus Nickel on the occasion of his 65th birthday     

The analysis and attribution of the time-dependent neutron background resultant from sample irradiation in a SLOWPOKE-2 reactor

The Royal Military College of Canada (RMCC) has commissioned a Delayed Neutron Counting (DNC) system for the analysis of special nuclear materials. A significant, time-dependent neutron background with an initial maximum count rate, more than 50 times that of the time-independent background, was characterised during the validation of this system. This time-dependent background was found to be dependent on the presence of the polyethylene (PE) vials used to transport the fissile samples, yet was not an activation product of vial impurities. The magnitude of the time-dependent background was found to be irradiation site specific and independent of the mass of PE. The capability of RMCC’s DNC system to analyze the neutron count rates in time intervals <1 s facilitated a more detailed data analysis than that obtained in previous DNC systems recording cumulative neutron counts. An analysis of the time-dependent background behaviour suggested that an equivalent of 120 ng of ²³⁵U contamination was present on each irradiated vial. However, Inductively Coupled Plasma—Mass Spectroscopy measurements of material leached from the outer vial surfaces after their irradiations found only trace amounts of uranium, 0.118 ± 0.048 ng of ²³⁵U derived from natural uranium. These quantities are insufficient to account for the time-independent background, and in fact could not be discriminated from the noise associated with time-independent background. It is suggested that delayed neutron emitters are deposited in the vial surface following fission recoil, leaving the main body of uranium within the irradiation site. This hypothesis is supported by the physical cleaning of the site with materials soaked in distilled water and HNO₃, which lowered the background from a nominal ²³⁵U mass equivalent of 120 to 50 ng per vial.     

Manipulation of nucleation and polymorphism by laser irradiation

Recently, laser-induced nucleation (LIN) has been attracting significant attention because of its many advantages, including non-mechanical contact, spatiotemporal controllability, and high nucleation probability. Consequently, there is a high demand for precise control methods for polymorphism, particularly in the pharmaceutical industry. The precise control of nucleation and polymorphism, as well as the expansion of their versatility, is indispensable in elucidating the mechanism of nucleation and polymorphism. If LIN can be exploited to precisely control polymorphism, it will be possible to appropriately control the solubility, bioavailability, and stability of targets. Currently, numerous mechanisms for LIN involving targets, solvents, laser light sources, and additives have been proposed. In this review, the authors summarize the history and current state of the research on nucleation and LIN-controlled polymorphism reported over the past two decades while focusing on the different light sources (pulsed laser vs. continuous-wave laser). Furthermore, the authors introduce the classical nucleation and two-step nucleation models and discuss the similarities and differences in the mechanisms of nucleation and polymorphism control based on these two models.