Relative Sensitivity Coefficients Research Articles

Relative ion intensities of maltooligosaccharide ethers in electrospray ionization ion trap mass spectrometry: A quantitative evaluation

Electrospray ionization coupled with mass spectrometry (ESI-MS) is an important analytical technique for the analysis of polysaccharide derivatives. It can be used to analyze substitution patterns in mixtures of oligomers to recognize heterogeneities, bimodality or blocky sequences. Quantitative analysis is hampered, however, by the fact that compounds of different chemistry and molar mass usually show different ionization efficiencies. In order to study the parameters of influence and to understand whether relative ion intensities in MS follow certain patterns. We analyzed fully O-methylated and fully O-perdeuteriomethylated oligosaccharides as two extreme cases of possible mixed O-Me-/O-Me-d3 by ESI-MS under defined conditions. Binary and complex mixtures of maltooligosaccharide ethers from DP 1 to 7 by were prepared from partially hydrolyzed per-O-methyl-β-cyclodextrin (Me-β-CD) and per-O-deuteromethyl-β-cyclodextrin (Me-d3-β-CD). Reference data for their real compositions were obtained after reductive amination by HPLC–UV. Within the applicable concentration range and with properly adjusted instrumental parameters, relative sensitivities (Me-d3/Me) in ESI-MS remained constant for a respective DP. With increasing DP, the relative sensitivity coefficients decreased from 1.01 for DP 2 to 0.78 for DP 6 for the binary mixtures and showed similar behavior for complex mixtures. The decrease in relative sensitivity coefficients for corresponding Me-d3 and Me derivatives has been overcome by m-amino-benzoic acid labeling and ESI-MS in negative mode or by measuring the original mixtures in nano-ESI-MS. Thus, discrimination probably caused by differences in surface activity and electrophoretic mobility can be leveled by an appropriate tag or formation of smaller droplets as in nano-ESI.

Chemometrics and theoretical approaches for evaluation of matrix effect in laser ablation and ionization of metal samples

Matrix effect is one of the shortcomings of direct solid analysis which makes the quantitative analysis a great challenge. All of the physical properties of solid and laser parameters could make contributions to the matrix effect. For better understanding and controlling laser ablation process, it is of great importance to investigate how and to what extent these factors would affect matrix effect, through simulation and chemometrics works.In this study, twenty-three solid standards of six types of metal matrices were analyzed, including aluminum, copper, iron, nickel, tungsten and zinc. The influence of laser pulse duration was investigated by applying nanosecond (ns) and femtosecond (fs) lasers to a buffer-gas-assisted ionization source coupled with an orthogonal time-of-flight mass spectrometer. After relative sensitivity coefficients (RSCs) of each element in different matrices were calculated, they were combined with the physical property values of the matrices to form a dataset which was analyzed by the chemometrics tool of orthogonal partial least-squares (OPLSs). The S-plot result reveals that thermal properties of solid play vital roles in the matrix effect induced by ns-laser ablation, while fs-laser could significantly reduce the thermal effect. Additionally, a theoretical model was figured out to simulate the RSCs by combining the laser–solid interaction process and plasma expansion process. The model prediction shows a relatively close agreement with experimental result, revealing that the model could reasonably explain the process of matrix effect.

Toward the Selection of Control Parameters in Models of the Purposeful Weather and Climate Modification

A unified methodology for planning and implementation of weather and climate modification (geoengineering) can be apparently developed based on the ideas and methods of geophysical cybernetics in which the climate system and its processes represent a control object and the role of the controlling subsystem is given to the appropriate social structures and, in particular, to operators having the necessary resources. This problem can be solved based on the sensitivity theory of dynamical systems. In this paper, as an example, we study the impact of the main parameters that control the development of baroclinic instability in the atmosphere on the growth rate of unstable waves. Analytical expressions for the absolute and relative sensitivity coefficients are obtained, which allows estimating the model response to the control parameters and, therefore, drawing a conclusion about the hypothetical ability to control the large-scale wave dynamics in the atmosphere and ocean. Selecting the baroclinic instability as a subject of this study is due to the significant role of this physical mechanism in the formation of the general circulation of the atmosphere and ocean, and, consequently, the Earth's climate.

Hollow-Core Photonic Crystal Fiber Based on C<sub>2</sub>H<sub>2</sub> and NH<sub>3</sub> Gas Sensor

In this paper, we propose a new hollow-core photonic crystal fiber, which can be available for gas sensor. In addition, properties of the fiber are analyzed at the wavelength of C2H2and NH3absorption peak 1530nm and 1967nm, respectively. For both wavelengths, relative sensitivity coefficients are higher than 0.95, which makes sense in gas sensing. We also get relationship between relative sensitivity coefficient and radius of fiber core, as well as effective refractive index of the mode field.

Minimizing Matrix Effect by Femtosecond Laser Ablation and Ionization in Elemental Determination

Matrix effect is unavoidable in direct solid analysis, which usually is a leading cause of the nonstoichiometric effect in quantitative analysis. In this research, experiments were carried out to study the overall characteristics of atomization and ionization in laser-solid interaction. Both nanosecond (ns) and femtosecond (fs) lasers were applied in a buffer-gas-assisted ionization source coupled with an orthogonal time-of-flight mass spectrometer. Twenty-nine solid standards of ten different matrices, including six metals and four dielectrics, were analyzed. The results indicate that the fs-laser mode offers more stable relative sensitivity coefficients (RSCs) with irradiance higher than 7 × 10(13) W·cm(-2), which could be more reliable in the determination of element composition of solids. The matrix effect is reduced by half when the fs-laser is employed, owing to the fact that the fs-laser ablation and ionization (fs-LAI) incurs an almost heat-free ablation process and creates a dense plasma for the stable ionization.

Coupling of LMS with a fs-laser ablation ion source: elemental and isotope composition measurements

Mass spectrometric analysis of elemental and isotopic compositions of several NIST standards is performed by a miniature laser ablation/ionisation reflectron-type time-of-flight mass spectrometer (LMS) using a fs-laser ablation ion source (775 nm, 190 fs, 1 kHz). The results of the mass spectrometric studies indicate that in a defined range of laser irradiance (fluence) and for a certain number of accumulations of single laser shot spectra, the measurements of isotope abundances can be conducted with a measurement accuracy at the per mill level and at the per cent level for isotope concentrations higher and lower than 100 ppm, respectively. Also the elemental analysis can be performed with a good accuracy. The LMS instrument combined with a fs-laser ablation ion source exhibits similar detection efficiency for both metallic and non-metallic elements. Relative sensitivity coefficients were determined and found to be close to one, which is of considerable importance for the development of standard-less instruments. Negligible thermal effects, sample damage and excellent characteristics of the fs-laser beam are thought to be the main reason for substantial improvement of the instrumental performance compared to other laser ablation mass spectrometers.

Hydrogen-Rich Gas Production by Cogasification of Coal and Biomass in an Intermittent Fluidized Bed

This paper presents the experimental results of cogasification of coal and biomass in an intermittent fluidized bed reactor, aiming to investigate the influences of operation parameters such as gasification temperature (T), steam to biomass mass ratio (SBMR), and biomass to coal mass ratio (BCMR) on hydrogen-rich (H2-rich) gas production. The results show that H2-rich gas free of N2 dilution is produced and the H2 yield is in the range of 18.25~68.13 g/kg. The increases of T, SBMR, and BCMR are all favorable for promoting the H2 production. Higher temperature contributes to higher CO and H2 contents, as well as H2 yield. The BCMR has a weak influence on gas composition, but the yield and content of H2 increase with BCMR, reaching a peak at the BCMR of 4. The H2 content and yield in the product gas increase with SBMR, whilst the content of CO increases first and then decreases correspondingly. At a typical case, the relative linear sensitivity coefficients of H2 production efficiency to T, SBMR, and BCMR were calculated. The results reveal that the order of the influence of the operation parameters on H2 production efficiency is T > SBMR > BCMR.

Mass spectrometry of solid samples in open air using combined laser ionization and ambient metastable ionization

Mass spectrometry of solid samples in open air was carried out using combined laser ionization and metastable ionization time-of-flight mass spectrometry (LI-MI-TOFMS) in ambient environment for qualitative and semiquantitative (relative analyte information, not absolute information) analysis. Ambient metastable ionization using a direct analysis in realtime (DART) ion source was combined with laser ionization time-of-flight mass spectrometry (LI-TOFMS) to study the effects of combining metastable and laser ionization. A series of metallic samples from the National Institute of Standards and Technology (NIST 494, 495, 498, 499, and 500) and a pure carbon target were characterized using LI-TOFMS in open air. LI-MI-TOFMS was found to be superior to laser-induced breakdown spectroscopy (LIBS). Laser pulse energies between 10 and 200mJ at the second harmonic (532nm) of an Nd:YAG laser were applied in the experiment to obtain a high degree of ionization in plasmas. Higher laser pulse energy improves signal intensities of trace elements (such as Fe, Cr, Mn, Ni, Ca, Al, and Ag). Data were analyzed by numerically calculating relative sensitivity coefficients (RSCs) and limit of detections (LODs) from mass spectrometry (MS) and LIBS spectra. Different parameters, such as boiling point, ionization potential, RSC, LOD, and atomic weight, were shown to analyze the ionization and MS detection processes in open air.

Two-Dimensional Separation in Laser Ionization Orthogonal Time-of-Flight Mass Spectrometry

The capabilities of two-dimensional separation using a high irradiance laser ionization orthogonal time-of-flight mass spectrometer (LI-O-TOFMS) were demonstrated in this paper. Ions were separated via their initial kinetic energy in one dimension and their mass-to-charge ratios in the other dimension. Investigation of the transient ion profiles after laser pulses revealed that the separation of analyte ions from multiply charged ions and gas species ions was achieved. Comparison of mass spectra in the normal accumulation mode and in the two-dimensional separation mode indicated that the relative sensitivity coefficients are stable and close to their true values in the two-dimensional separation mode, especially for trace elements that are prone to interference.

Analysis of solids with different matrices by buffer-gas-assisted laser ionization orthogonal time-of-flight mass spectrometry

A laser ionization orthogonal time-of-flight mass spectrometer with a low-pressure source and high laser irradiance was used to analyze 27 solid samples with 9 different matrices, including aluminium, soil, copper sulfide, zinc sulfide, iron, nickel, copper, zinc, and tungsten. The influence of laser energy on non-stoichiometric effects, such as matrix effects and elemental fractionation, has been investigated. The results indicate that matrix effects can be alleviated to a great extent at high laser irradiance. Additionally, with the irradiance of 1010–1011 W cm−2, most elements presented relatively stable relative sensitivity coefficients (RSC), while W, Pb, and Bi demonstrated unusual characteristics that their RSCs increased along with increasing laser energy.

Sensitivity analysis of the evaporation module of the E-DiGOR model

Sensitivity analysis of the soil-water-evaporation module of the E-DiGOR (Evaporation and Drainage investigations at Ground of Ordinary Rainfed-areas) model is presented. The model outputs were generated using measured climatic data and soil properties. The first-order sensitivity formulas were derived to compute relative sensitivity coefficients. A change in the net solar radiation significantly affected potential evaporation from bare soils estimated by the Penman-Monteith equation. The sensitivity coefficients were positive, with a mean value of 0.82. The sensitivity of potential soil evaporation to soil heat flux was lower during the summer months and higher during the winter. The gradient of saturated vapour pressure–temperature curve increased or decreased the potential evaporation rates because of the occurrence of the gradient variable in both the numerator and denominator of the equation. Increases in the vapour pressure deficit increased the evaporation and its effect was more pronounced in the winter. In the case of aerodynamic resistance, the coefficients were constantly negative, and became more negative in the winter, which means a negative correlation between the input and output. In Aydın's equation, the dependent variable (actual soil evaporation) was initially very sensitive to a change in the water potential of a wet soil. The sensitivity decreased progressively during the drying period. The coefficients related to the absolute values of soil water potential were constantly negative, with a mean value of -0.19. The sensitivity of actual soil evaporation to air-dry water potential remained low in the wet soil and was higher in the drier soil. The sensitivity coefficient to measure the impact of potential evaporation on actual evaporation did not change during the study. According to Aydın and Uygur's equation, potential soil evaporation greatly affected the output (soil water potential) in the wet soils. In Kelvin's equation, increases in air temperature increased the absolute value of water potential at air-dryness. The sensitivity coefficients, owing to relative humidity, showed a great deal of fluctuation.

Femtogram Detection and Quantitation of Residues Using Laser Ionization Orthogonal Time-of-Flight Mass Spectrometry

A newly developed high irradiance laser ionization orthogonal time-of-flight mass spectrometer (LI-O-TOFMS) was employed for the elemental analysis of residues, which were prepared by evaporating mixed salt solutions. The residues were first characterized in terms of shape and elemental distribution. In TOFMS detection, all of the metal elements in the residue can be observed in the spectra. Relative sensitivity coefficients for different elements were within 1 order of magnitude, which meets semiquantitative analysis criteria. By calculating the individual masses from the ablated area due to a single laser shot, the absolute detection limit reached 7 x 10(-15) g for most metal elements. The results indicate that LI-O-TOFMS is capable of performing ultratrace elemental qualification and quantification, with an absolute limit of detection and an absolute limit of quantitation at the femtogram level.

Semiquantitative Multielemental Analysis of Biological Samples by a Laser Ionization Orthogonal Time-of-Flight Mass Spectrometer

Semiquantitative multielemental analyses of biological samples (tea leaf standard, Laminaria japonica, and pig skin) were demonstrated with a newly developed laser ionization orthogonal time-of-flight mass spectrometer (LI-O-TOFMS). The sample was directly ablated and ionized with high irradiance after simple sample preparation. Relative sensitivity coefficients (RSC) were calculated and evaluated for sensitivity differences. Due to the employment of a collisional cooling device and the orthogonal geometry of the TOF system, high resolving power can be obtained, such that elemental peaks and interferential peaks with the same nominal mass can be distinguished. The detection limit of microg g(-1) levels can be commonly achieved for elemental determination.

Influence of wavelength, irradiance, and the buffer gas pressure on high irradiance laser ablation and ionization source coupled with an orthogonal Time of Flight Mass Spectrometer

Influence of laser wavelength, laser irradiance and the buffer gas pressure were studied in high irradiance laser ablation and ionization source coupled with an orthogonal time-of-flight mass spectrometer. Collisional cooling effects of energetic plasma ions were proved to vary significantly with the elemental mass number. Effective dissociation of interferential polyatomic ions in the ion source, resulting from collision and from high laser irradiance, was verified. Investigation of relative sensitivity coefficients (RSC) of different elements performed on a steel standard GBW01396, which was ablated at 1064 nm, 532 nm, 355 nm, and 266 nm, has demonstrated that the thermal ablation mechanism could play a critical role with the first three wavelengths, while 266 nm induces non-thermal ablation principally. Experimental results also indicated that there is no evident discrepancy for most metal elements on RSCs and LODs among four wavelengths at high irradiance, except that high boiling point elements like Nb, Mo, and W have higher RSCs at higher irradiance regions of 1064 nm, 532 nm, and 355 nm due to thermal ablation. A geological standard and a garnet stone were also used in the experiment subsequently, and their RSCs and LODs for metal elements show nonsignificant dependence on wavelength at designated irradiances. All results reveal that relatively uniform sensitivity can be achieved at any wavelength for metal elements in the solids used in our experiments at an appropriate irradiance for the low pressure high irradiance laser ablation and ionization source.

A small high‐irradiance laser ionization time‐of‐flight mass spectrometer

A small high-irradiance laser ionization time-of-flight mass spectrometer (LI-TOFMS) with orthogonal sample introduction was described. High irradiance of 6 x 10(10) W/cm(2) at 532 nm from a Nd:YAG laser was applied in the experiment to get a high ionization degree in plasma and to dissociate the interferential polyatomic ions. Meanwhile, the interferential multiply charged ions resulted by high-irradiance were nearly eliminated in the spectrum by utilizing helium as the buffer gas in the ion source due to three-body recombination, which resulted in a relatively clean background. Improved signal stability was obtained by automated step moving of the sample stage in short time intervals. By using two sets of Einzel lens in transport system, nearly uniform relative sensitivity coefficients (RSCs) were achieved for most of metal elements including light ions which were detected in extremely low sensitivity in previous hexapole transportation instrument. The resolving power reaches 2200, and the detection limits (DLs) are 10(-6) g/g for metal elements in the steel standard.

Semi-quantitative analysis of geological samples using laser plasma time-of-flight mass spectrometry

A method has been developed that allows the direct measurement of the elemental composition of geological samples based on a newly developed laser plasma time-of-flight mass spectrometer with a collisional cooling system. This technique has the merits of small sample consumption and rapid elemental analysis. Four geological reference materials were used in the experiment. The system has shown a satisfactory resolving power with few interferences in the spectra. The limits of detection were about 10−6–10−7 g g−1 for most of the metal elements. The relative sensitivity coefficients (RSCs) of the elements with mass heavier than 30 amu could be used for direct semi-quantitative analysis.

Synthesis and electrical conductivity of films based on rare-earth oxides

A number of physicochemical properties of samples are investigated. Changes in the electrical resistance of films based on the yttrium, terbium, and praseodymium oxides in an air atmosphere and upon interaction with different gaseous media (ozone, argon, methanol, ethanol) are studied. The ranges of operating temperatures and the maximum relative sensitivity coefficients of the films under investigation are determined.

Parametric evaluation of laser ablation and ionization time-of-flight mass spectrometry with ion guide cooling cell

A novel laser ablation and ionization time-of-flight mass spectrometer has been used for direct elemental analysis of alloys. The system was incorporated with an ion guide cooling cell to reduce the kinetic energy distribution for the purpose of better resolution. Parametric studies have been conducted on the system with respect to the buffer gas pressure and the distance from sample to the nozzle to obtain the maximal signal intensities. In order to obtain satisfactory relative sensitivity coefficients (RSC) for different elements, the influence of the laser irradiance, nozzle voltage, rf frequency and voltage of the hexapole were also investigated. Under the optimized conditions, the RSC of different elements were available for direct semi-quantitative analysis. The mass resolving power (FWHM) of the spectrometer was approximately 7000 (m/Δm) and the limit of detection (LOD) was 10 − 6 g/g.

A hardware and software system for the laser time-of-flight mass spectrometer

The hardware and software system for a laser time-of-flight mass spectrometer is based on the double-level principle. At the upper level, the personal computer automatically controls online recording and processing of mass spectra with the highest priority. The monitoring and stabilization functions are fulfilled by controllers of the second control level. The exchange between the controllers and personal computer takes place in the periods between mass-spectrum recording and processing. The use of the hardware and software system has made it possible (i) to form short mass peaks with a half-height duration of up to 10 ns, (ii) to decrease a scatter of relative sensitivity coefficients from two or three down to one order of magnitude, and (iii) to increase a dynamic range of the recorded mass spectra up to 1−1 × 109.

Quantification of heavy metals in clays by dry plasma laser ablation-ICP-MS

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is applied for the analysis of powdered clays used for water filtration. For the quantitative determination of trace element concentrations in clays, three matrix dilutions of red clay (RAIP) and brick clay-679 (NBS) reference materials are used to perform calibration curve. A mixture of ultrapure graphite and powders of the samples and reference materials are homogenized by using a shaker. It is found that the ablation efficiency is better in case of raster mode than single point mode in laser ablation. Calibration curves for trace elements were measured without and with 13C as internal standard element. 13C is used to compensate for signal fluctuations caused by the variation of the ablated sample mass. The regression coefficients of the calibration curves are better than 0.98 with internal standardization. This quantification method provided analytical results with deviations of 5–12% from the recommended and proposed values in clay-679 (NBS). In order to compare two different approaches for the quantification of analytical results in LA-ICP-MS, relative sensitivity coefficients (RSCs) of trace elements is determined using 88Sr as internal standard in red clay (RAIP). The experimentally obtained RSCs are in the range of 0.3–4.9 for all elements of interest. Therefore, the measured concentrations are corrected with RSCs. The relative standard deviation (R.S.D.) of the determination of the trace element concentration is about 3–9%. Heavy metal concentrations obtained by the two quantification methods in LA-ICP-MS are compared with the concentrations obtained by graphite furnace-atomic absorption spectrometry (GF-AAS).