Instrument-specific Parameters Research Articles

Importance of powder diffraction raw data archival in a curated database for materials science applications.

In recent years, there is a significant interest from the crystallographic and materials science communities to have access to raw diffraction data. The effort in archiving raw data for access by the user community is spearheaded by the International Union of Crystallography (IUCr) Committee on Data. In materials science, where powder diffraction is extensively used, the challenge in archiving raw data is different to that from single crystal data, owing to the very nature of the contributions involved. Powder diffraction (X-ray or neutron) data consist of contributions from the material under study as well as instrument specific parameters. Having raw powder diffraction data can be essential in cases of analysing materials with poor crystallinity, disorder, micro structure (size/strain) etc. Here, the initiative and progress made by the International Centre for Diffraction Data (ICDDR) in archiving powder X-ray diffraction raw data in the Powder Diffraction FileTM (PDFR) database is outlined. The upcoming 2025 release of the PDF-5+ database will have more than 20 800 raw powder diffraction patterns that are available for reference.

Optimized combination of MALDI MSI and immunofluorescence for neuroimaging of lipids within cellular microenvironments.

Proper neurological function relies on the cellular and molecular microenvironment of the brain, with perturbations of this environment leading to neurological disorders. However, studying the microenvironments of neurological tissue has proven difficult because of its inherent complexity. Both the cell type and metabolomic underpinnings of the cell have crucial functional roles, thus making multimodal characterization methods key to acquiring a holistic view of the brain's microenvironment. This study investigates methods for combining matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI MSI) and immunofluorescence (IF) microscopy to enable the concurrent investigation of cell types and lipid profiles on the same sample. In brief, 1,5-diaminonaphthalene (DAN), α-cyano-4-hydroxy-cinnamic acid (CHCA), and 2,5-dihydroxybenzoic acid (DHB) were tested in addition to instrument-specific parameters for compatibility with IF. Alternatively, the effects of IF protocols on MALDI MSI were also tested, showing significant signal loss with all tested permutations. Ultimately, the use of CHCA for MALDI MSI resulted in the best IF images, while the use of DAN gave the lowest quality IF images. Overall, increasing the laser power and number of shots per laser burst resulted in the most tissue ablation. However, optimized parameter settings allowed for minimal tissue ablation while maintaining sufficient MALDI MSI signal.

Toward the General Mechanistic Model of Liquid Chromatographic Retention.

Large datasets of chromatographic retention times are relatively easy to collect. This statement is particularly true when mixtures of compounds are analyzed under a series of gradient conditions using chromatographic techniques coupled with mass spectrometry detection. Such datasets carry much information about chromatographic retention that, if extracted, can provide useful predictive information. In this work, we proposed a mechanistic model that jointly explains the relationship between pH, organic modifier type, temperature, gradient duration, and analyte retention based on liquid chromatography retention data collected for 187 small molecules. The model was built utilizing a Bayesian multilevel framework. The model assumes (i) a deterministic Neue equation that describes the relationship between retention time and analyte-specific and instrument-specific parameters, (ii) the relationship between analyte-specific descriptors (log P, pKa, and functional groups) and analyte-specific chromatographic parameters, and (iii) stochastic components of between-analyte and residual variability. The model utilizes prior knowledge about model parameters to regularize predictions which is important as there is ample information about the retention behavior of analytes in various stationary phases in the literature. The usefulness of the proposed model in providing interpretable summaries of complex data and in decision making is discussed.

Grating Spectrometry and Spatial Heterodyne Fourier Transform Spectrometry: Comparative Noise Analysis for Raman Measurements

The desire for portable Raman spectrometers is continuously driving the development of novel spectrometer architectures where miniaturisation can be achieved without the penalty of a poorer detection performance. Spatial heterodyne spectrometers are emerging as potential candidates for challenging the dominance of traditional grating spectrometers, thanks to their larger etendue and greater potential for miniaturisation. This paper provides a generic analytical model for estimating and comparing the detection performance of Raman spectrometers based on grating spectrometer and spatial heterodyne spectrometer designs by deriving the analytical expressions for the performance estimator (signal-to-noise ratio, SNR) for both types of spectrometers. The analysis shows that, depending on the spectral characteristics of the Raman light and on the values of some instrument-specific parameters, the ratio of the SNR estimates for the two spectrometers () can vary as much as by two orders of magnitude. Limit cases of these equations are presented for a subset of spectral regimes which are of practical importance in real-life applications of Raman spectroscopy. In particular, under the experimental conditions where the background signal is comparable or larger than the target Raman line and shot noise is the dominant noise contribution, the value of is, to a first order of approximation, dependent solely on the relative values of each spectrometer’s etendue and on the number of row pixels in the detector array. For typical values of the key instrument-specific parameters (e.g., etendue, number of pixels, spectral bandwidth), the analysis shows that spatial heterodyne spectrometer-based Raman spectrometers have the potential to compete with compact grating spectrometer designs for delivering in a much smaller footprint (10–30 times) levels of detection performance that are approximately only five to ten times poorer.

The Application of a Low-temperature Physical Plasma Device Operating Under Atmospheric Pressure Leads to the Production of Toxic NO2.

Physical plasma is a mixture of reactive particles and electromagnetic radiation. Due to the antimicrobial, immunomodulatory, anti-inflammatory, wound-healing promoting, and antineoplastic effects of body tempered physical plasma under atmospheric pressure (cold atmospheric plasma: CAP), CAP therapy is increasingly becoming the focus of surgical and oncological disciplines. However, when applied in practice, a potential emission of harmful noxae such as toxic nitrogen oxides must be taken into account, which was investigated in the following study. MiniJet-R Ar CAP device was characterized with respect to NOX-specific spectra, ultraviolet radiation C (UVC) intensity in the range of 200-275 nm and the formation of NOX gases. Instrument-specific parameters such as gas flow, energy setting of the high-frequency generator, and flow rate of the carrier gas Ar were varied. To test the toxic properties of the NO2 concentrations formed by CAP, SK-OV-3 human ovarian cancer cells were incubated with different NO2 concentrations and cell growth was monitored for 120 h. The operation of MiniJet-R led to the formation of NO2 in the proximity of the CAP effluent. Synthesis of NO led to a NO-specific spectrum in the range of 100-275 nm, whereby UVC radiation produced reached intensities of up to 90 mW/m2 NO gas itself, however, was not detectable, as it was converted to NO2 rapidly. Cell culture incubation experiments demonstrated that NO2 in these concentration ranges had no influence on the cell growth of human cancer cells. Although no limit values were exceeded in the present study, the emission of high-energy UVC radiation and toxic NO2 is a risk factor with regard to the legal regulations on workplace protection (operator hazard) and the approval of medical devices (patient hazard). This is important for considerations regarding treatment frequency and duration. The growth inhibitory effect of CAP treatment on human cancer cells principally suggests a medical application of the MiniJet-R device, although more extensive studies will have to follow.

A model framework to retrieve thermodynamic and kinetic properties of organic aerosol from composition-resolved thermal desorption measurements

Abstract. Chemical ionization mass spectrometer (CIMS) techniques have been developed that allow for quantitative and composition-resolved measurements of organic compounds as they desorb from secondary organic aerosol (SOA) particles, in particular during their heat-induced evaporation. One such technique employs the Filter Inlet for Gases and AEROsol (FIGAERO). Here, we present a newly developed model framework with the main aim of reproducing FIGAERO-CIMS thermograms: signal vs. ramped desorption temperature. The model simulates the desorption of organic compounds during controlled heating of filter-sampled SOA particles, plus the subsequent transport of these compounds through the FIGAERO manifold into an iodide-CIMS. Desorption is described by a modified Hertz–Knudsen equation and controlled chiefly by the temperature-dependent saturation concentration C*, mass accommodation (evaporation) coefficient, and particle surface area. Subsequent transport is governed by interactions with filter and manifold surfaces. Reversible accretion reactions (oligomer formation and decomposition) and thermal decomposition are formally described following the Arrhenius relation. We use calibration experiments to tune instrument-specific parameters and then apply the model to a test case: measurements of SOA generated from dark ozonolysis of α-pinene. We then discuss the ability of the model to describe thermograms from simple calibration experiments and from complex SOA, and the associated implications for the chemical and physical properties of the SOA. For major individual compositions observed in our SOA test case (#C=8 to 10), the thermogram peaks can typically be described by assigning C25∘C* values in the range 0.05 to 5 µg m−3, leaving the larger, high-temperature fractions (>50 %) of the thermograms to be described by thermal decomposition, with dissociation rates on the order of ∼1 h−1 at 25 ∘C. We conclude with specific experimental designs to better constrain instrumental model parameters and to aid in resolving remaining ambiguities in the interpretation of more complex SOA thermogram behaviors. The model allows retrieval of quantitative volatility and mass transport information from FIGAERO thermograms, and for examining the effects of various environmental or chemical conditions on such properties.

Analyzing chromatographic data using multilevel modeling.

It is relatively easy to collect chromatographic measurements for a large number of analytes, especially with gradient chromatographic methods coupled with mass spectrometry detection. Such data often have a hierarchical or clustered structure. For example, analytes with similar hydrophobicity and dissociation constant tend to be more alike in their retention than a randomly chosen set of analytes. Multilevel models recognize the existence of such data structures by assigning a model for each parameter, with its parameters also estimated from data. In this work, a multilevel model is proposed to describe retention time data obtained from a series of wide linear organic modifier gradients of different gradient duration and different mobile phase pH for a large set of acids and bases. The multilevel model consists of (1) the same deterministic equation describing the relationship between retention time and analyte-specific and instrument-specific parameters, (2) covariance relationships relating various physicochemical properties of the analyte to chromatographically specific parameters through quantitative structure-retention relationship based equations, and (3) stochastic components of intra-analyte and interanalyte variability. The model was implemented in Stan, which provides full Bayesian inference for continuous-variable models through Markov chain Monte Carlo methods. Graphical abstract Relationships between log k and MeOH content for acidic, basic, and neutral compounds with different log P. CI credible interval, PSA polar surface area.

Evaluation and Inter-Comparison of Oxygen-Based OC-EC Separation Methods for Radiocarbon Analysis of Ambient Aerosol Particle Samples

Radiocarbon analysis is a widely-used tool for source apportionment of aerosol particles. One of the big challenges of this method, addressed in this work, is to isolate elemental carbon (EC) for 14C analysis. In the first part of the study, we validate a two-step method (2stepCIO) to separate total carbon (TC) into organic carbon (OC) and EC against the EUSAAR_2 thermal-optical method regarding the recovered carbon concentrations. The 2stepCIO method is based on the combustion of OC in pure oxygen at two different temperature steps to isolate EC. It is normally used with a custom-built aerosol combustion system (ACS), but in this project, it was also implemented as a thermal protocol on a Sunset OC-EC analyzer. Results for the recovered EC mass concentration showed poor agreement between the 2stepCIO method on the ACS system and on the Sunset analyzer. This indicates that the EC recovery is sensitive not only to the temperature steps, but also to instrument-specific parameters, such as heating rates. We also found that the EUSAAR_2 protocol itself can underestimate the EC concentration on untreated samples compared to water-extracted samples. This is especially so for highly loaded filters, which are typical for 14C analysis. For untreated samples, the EC concentration on long-term filter samples (two to five days sampling time) was 20–45% lower than the sum of EC found on the corresponding 24-h filter samples. For water-extracted filter samples, there was no significant difference between long-term and the sum of daily filter samples. In the second part of this study, the 14C was measured on EC isolated by the 2stepCIO method and compared to methods from two other laboratories. The different methods agree well within their uncertainty estimates.

Effect of Various Operational Parameters on Drug Release from a 1% Hydrocortisone Semisolid Dosage Form Using the Vertical Diffusion Cell Apparatus

The purpose of this study was to identify operational parameters of the vertical diffusion cell (VDC) apparatus that have an influence on results of drug release testing from semisolid dosage forms, which are one of three types of topically applied products (see USP General Chapter Topical and Transdermal Drug Products—Product Quality Tests ). The VDC apparatus operates using a static diffusion cell, a synthetic membrane, and an appropriate receptor medium. A cream formulation containing 1% hydrocortisone was used for the current study. The operational parameters investigated were stirring rate, mixing helix, stirring while sampling, medium degassing, membrane wetting with Ethomeen (a surfactant), and membrane wetting time. Stat-Ease design of experiment software was used to create partial factorial experimental designs to evaluate these parameters. The effects of the operational parameters were evaluated using mean drug release rate (slope, μg/cm2/min1⁄2) and the standard deviation (SD) of six individual release rates for each experimental setup. Results of the study indicate that one parameter, the presence of Ethomeen for wetting the membrane, had a large and significant effect on both drug release rates and SD. Two parameters, stirring while sampling and mixing helix, had a significant impact on the drug release rate when Ethomeen was not used. Two parameters, medium degassing and stirring while sampling, had significant effects on the variability of the results (SD). Additionally, instrument-specific parameters (e.g., mixing helix) also contributed significantly to the variability of drug release rates. INTRODUCTION Topically applied drug products include ophthalmic, semisolid, and transdermal dosage forms (1). Drug products topically administered via the skin fall into two general categories, those applied for local action (e.g., semisolid dosage forms) and those intended for systemic effects (e.g., transdermal drug products). The drug substance in either category must be released from the carrier before it can contact the epidermal surface and be available for penetration into the stratum corneum and lower layers of the skin. A performance test for topical drug products therefore should be able to measure drug release from the dosage form. Although it is not an indicator of bioavailability, the drug release test should be capable of detecting changes in the finished product drug release characteristics that have the potential to alter the biological performance of the drug in the dosage form. The drug release test for semisolid dosage forms should be reproducible and reliable. The vertical diffusion cell (VDC) apparatus, which uses a static diffusion cell, a synthetic membrane, and an appropriate receptor medium, has emerged as one of the most widely used apparatus for testing the in vitro release of topical dosage forms (2, 3). The VDC apparatus is simple to operate and generally yields reliable and reproducible results when employed by properly trained laboratory personnel (4). The objective of the present study was to evaluate the influence of some operational parameters on the release of the drug from the semisolid dosage form. The authors evaluated individual or combined effects of stirring rate, mixing helix, membrane wetting with Ethomeen, membrane wetting time, stirring while sampling, and medium degassing on the release rate of a 1% hydrocortisone cream formulation using two VDC apparatus, each from a different vendor. The study evaluated the release rate (steady-state flux) and between-cell standard deviation (SD) of release rates of 1% hydrocortisone cream. MATERIALS AND METHODS Materials and Reagents Reagents used were a current and valid lot of USP Hydrocortisone Reference Standard, Milli-Q water, acetonitrile HPLC grade (Fisher Scientific, Waltham, MA), water HPLC grade, ethanol (Warner Graham, Cockeysville, MD), isopropyl myristate (IPM) (Alfa Aesar, Ward Hill, MA), Ethomeen-12 (AkzoNobel), and Tuffryn 0.45-μm mem*Corresponding author. e-mail: ess@usp.org dx.doi.org/10.14227/DT190312P6

Dielectric Reference Materials for Mathematically Modeling and Standardizing Grain Moisture Meters

Dielectric-type instruments are the most widely used technology for grain moisture measurement. Measuring fundamental dielectric parameters (dielectric constant and loss factor) rather than instrument-specific parameters is advantageous in terms of understanding the physical basis of the measurement and in transferring calibrations; however, few grain moisture meter models report such fundamental parameters. One reason for this is the difficulty in calibrating instruments to measure dielectric parameters. High molecular weight alcohols are commonly used as dielectric reference materials for calibrating research-type instruments. However, grain moisture meters are designed to handle grain rather than liquids, so performing meaningful tests on alcohols is very difficult. Suitable granular dielectric reference materials are needed. This article describes research assessing the suitability of three alcohols (1-pentanol, 1-hexanol, and 1-decanol) and low-loss dielectrics (glass beads, plastic beads, plastic pellets, and air) as dielectric reference materials for grain moisture meters. Complex reflection coefficient measurements were performed from 1 to 501 MHz with an HP-4291A material/impedance analyzer and a transmission-line dielectric test cell. Mathematical models based on ABCD matrix methods were created to predict complex permittivity from the measurements of complex reflection coefficient. The low-loss materials were used successfully for calibrating the system to measure permittivity in spite of the fact that their permittivity values were unknown. Two characteristics were assumed: constant dielectric constant over the frequency range, and constant (near zero) loss factor over the frequency range. These two constraints (along with electrical test cell parameters defined by finite element analysis and the test cell physical dimensions) permitted unambiguous determination of all parameters for the test cell mathematical model. The resulting test cell model accurately predicted dielectric characteristics of alcohols.

Problem of Applying Modern Uncertainty Concepts to the Measurement of Instrument-Specific Parameters

This paper presents a number of problems that occur when applying the Guide to the Expression of Uncertainty in Measurement (GUM) to modern instruments. These instruments are often automatic, which makes it complicated to evaluate the uncertainty components in each measurement step because it is difficult to control and analyze them. Many of these instruments try to quantify instrument-specific parameters, which are difficult to compare with others that have the same dimension but are measured using other techniques. Often, these parameters lack traceable calibration, which may result in a large uncertainty component. This paper also considers the human aspect of the measurement process

Validation of quantitative NMR

NMR is by definition a quantitative spectroscopic tool because the intensity of a resonance line is directly proportional to the number of resonant nuclei (spins). This fact enables, in principle, a precise determination of the amount of molecular structures and, hence, of substances in solids as well as liquids. With the increase of sensitivity due to stronger and stronger static magnetic fields including improved electronics the detection limits have been pushed down significantly. However, the lack of a precise protocol that considers and controls the aspects of both the measurement procedure as well as the spectra processing and evaluation is responsible for the fact that quantitative investigations of identical samples in various laboratories may differ severely (deviations up to 90% relative to gravimetric reference values). Here, a validated protocol for quantitative high resolution 1H-NMR using single pulse excitation is described that has been confirmed by national and international round robin tests. It considers all issues regarding linearity, robustness, specificity, selectivity and accuracy as well as influences of instrument specific parameters and the data processing and evaluation routines. This procedure was tested by the investigation of three different 5-model-compound mixtures. As a result of the round robin tests using the proposed protocol it was found that the maximum combined measurement uncertainty is 1.5% for a confidence interval of 95%. This applies both for the determination of molar ratios and of the amount fractions of the various components. Further, the validation was extended to purity determinations of substances as shown for 1,8-epoxy- p-menthane (cineole).

Determination of rare earth and refractory trace element abundances in early solar system objects by ion microprobe

Experimental and analytical procedures devised for measurement of rare earth element (REE) abundances using a secondary ion mass spectrometer (ion microprobe) are described. This approach is more versatile than the conventional techniques such as neutron activation analysis and isotope dilution mass spectrometry by virtue of its high spatial resolution that allows determination of REE abundances in small domains (10-20 micron) within individual mineral phases. The ion microprobe measurements are performed at a low mass-resolving power adopting the energy-filtering technique (Zinner and Crozaz 1986) for removal and suppression of unresolved complex molecular interferences in the REE masses of interest. Synthetic standards are used for determining various instrument specific parameters needed in the data deconvolution procedure adopted for obtaining REE abundances. Results obtained from analysis of standards show that our ion microprobe may be used for determining REE abundances down to ppm range with uncertainties of ∼ 10 to 15%. Abundances of rare earth and several other refractory trace elements in a set of early solar system objects isolated from two primitive carbonaceous chondrites were determined using the procedures devised by us. The results suggest that some of these objects could be high temperature nebular condensates, while others are products of melting and recrystallization of precursor nebular solids in a high temperature environment.

Description of a computer program for quantitative spectral analysis of ICP-AES spectra generated with a high resolution computer-controlled monochromator

A FORTRAN computer program is described performing automatic quantitative spectral analysis on spectral windows (approximately 15 experimental effective line widths wide) obtained with scans from a high resolution computer-controlled monochromator, using short integration times on each wavelength position (e.g. 250 ms). This program quantifies the net analyte signal from the measurements in the relevant spectral region, whereby all possible contributions from the background and/or interfering lines are considered. This artificial intelligence obviates all operator descisions with respect to background correction and spectral interference correction. The article gives a detailed description of how this program works and discusses the following topics: smoothing of raw data, peak detection, background correction, test for spectral interference and correction of most spectral interferences, and calculation of the final net signal and its standard deviation. The present program enables accurate analyses of samples without any prior knowledge of sample composition and requires the utmost minimum of operator-software interaction. The dependency on instrument specific parameters is limited to a single value, viz. the average experimental effective line width. As all essential spectral information is condensed in the final output and is accompanied by appropriate warning messages, a diagnosis can be easily made in the event of abnormalities. The combination of the proposed measurement mode and accompanying spectral analysis is evaluated and compared with the classical three point (longer integration time) measurement modes with respect to detection power, accuracy, speed and user-friendliness.