Analytical Signal Response Research Articles

An Analytical Antenna Modeling of Electromagnetic Wave Propagation in Inhomogeneous Media Using FDTD: A Comprehensive Study.

This paper discusses the challenges in characterizing electromagnetic (EM) waves propagating through inhomogeneous media, such as reinforced cement concrete and hot mix asphalt. Understanding the EM properties of materials, including their dielectric constant, conductivity, and magnetic permeability, is crucial to analyzing the behavior of these waves. The focus of this study is to develop a numerical model for EM antennas using the finite difference time domain (FDTD) method, and to gain a deeper understanding of various EM wave phenomena. Additionally, we verify the accuracy of our model by comparing its results with experimental data. We analyze several antenna models with different materials, including the absorber, high-density polyethylene and perfect electrical conductors, to obtain an analytical signal response that is verified against the experimental response. Furthermore, we model the inhomogeneous mixture of randomly distributed aggregates and voids within a medium. We verify the practicality and reliability of our inhomogeneous models using experimental radar responses on an inhomogeneous medium.

Supercritical Fluid Nanospray Mass Spectrometry.

Supercritical fluids are typically electrosprayed using an organic solvent makeup flow to facilitate continuous electrical connection and enhancement of electrospray stability. This results in sample dilution, loss in sensitivity, and potential phase separation. Premixing the supercritical fluid with organic solvent has shown substantial benefits to electrospray efficiency and increased analyte charge state. Presented here is a nanospray mass spectrometry system for supercritical fluids (nSF-MS). This split flow system used small i.d. capillaries, heated interface, inline frit, and submicron emitter tips to electrospray quaternary alkyl amines solvated in supercritical CO2 with a 10% methanol modifier. Analyte signal response was evaluated as a function of total system flow rate (0.5-1.5 mL/min) that is split to nanospray a supercritical fluid with linear flow rates between 0.07 and 0.42 cm/sec and pressure ranges (15-25 MPa). The nSF system showed mass-sensitive detection based on increased signal intensity for increasing capillary i.d. and analyte injection volume. These effects indicate efficient solvent evaporation for the analysis of quaternary amines. Carrier additives generally decreased signal intensity. Comparison of the nSF-MS system to the conventional SF makeup flow ESI showed 10-fold signal intensity enhancement across all the capillary i.d.s. The nSF-MS system likely achieves rapid solvent evaporation of the SF at the emitter point. The developed system combined the benefits of the nanoemitters, sCO2, and the low modifier percentage which gave rise to enhancement in MS detection sensitivity.

Diatom Biosilica in Targeted Drug Delivery and Biosensing Applications: Recent Studies

Diatoms are single-cell algae encased in a cell wall (named frustule) composed of transparent, biogenic (or opaline) silica with intricate and strikingly regular patterns. Over the past 30 years, these microorganisms have proven to be a valuable replacement for synthetic silica that satisfies numerous pharmaceutical requirements for the realization of drug delivery vectors, biosensing supports and photonic crystals. It is not only the structural features of the diatoms, but also the possibility of chemically modifying the frustule that permits the relatively straightforward transformation of the biosilica into potential devices for biomedical applications. In this short review, we explore the applications of diatoms-derived biosilica in the drug delivery and biosensing fields. Specifically, we consider the use of diatoms for the targeted delivery of anticancer and antibiotic drugs and how the same microalgae are employed in the fabrications of biosensors whose analyte signal response is evaluated via fluorescence and surface-enhanced Raman scattering techniques. We limit our discussion to studies published in the last seven years, with the intention of minimizing possible redundancy with respect to previously published contributions.

Spherical Sampler Probes Enhance the Robustness of Ambient Ionization Mass Spectrometry for Rapid Drugs Screening.

Ambient ionization mass spectrometry has become one of the most promising approaches for rapid and high-throughput screening of small molecules in complex biological matrices for emergency medicine, forensics, and food and agriculture applications. The simple procedures for sample collection and ionization without additional pretreatment are vital in these fields. Many efforts have been devoted to modifying various ambient ionization techniques to simplify the procedures and improve the robustness and sensitivity of the methods. Here, we demonstrate the implementation of rigid spherical sampler probes to improve the robustness of touch spray ionization mass spectrometry. The sphericity of the probes increases the stability of the cone-jet mode of electrospray, reduces the requirements for fine positioning of a sampler in the ion source, and decreases the possibility of corona discharge occurrence. The utilization of spherical sampler probes allows fast, non-invasive sampling, followed by rapid analysis for various drugs of different chemical classes in complex biological matrices, such as the whole blood or sebum collected from the skin surface. The linearity of the analytical signal response from drug concentration confirms the possibility of creating a simple semiquantitative method for small molecules monitoring using spherical sampler probes.

An SPRi Biosensor for Determination of the Ovarian Cancer Marker HE4 in Human Plasma.

Human epididymis protein 4 (HE4) is an ovarian cancer marker. Various cut-off values of the marker in blood are recommended, depending on the method used for its determination. An alternative biosensor for HE4 determination in blood plasma has been developed. It consists of rabbit polyclonal antibody against HE4, covalently attached to a gold chip via cysteamine linker. The biosensor is used with the non-fluidic array SPRi technique. The linear range of the analytical signal response was found to be 2–120 pM, and the biosensor can be used for the determination of the HE4 marker in the plasma of both healthy subjects and ovarian cancer patients after suitable dilution with a PBS buffer. Precision (6–10%) and recovery (101.8–103.5%) were found to be acceptable, and the LOD was equal to 2 pM. The biosensor was validated by the parallel determination of a series of plasma samples from ovarian cancer patients using the Elecsys HE4 test and the developed biosensor, with a good agreement of the results (a Pearson coefficient of 0.989). An example of the diagnostic application of the developed biosensor is given—the influence of ovarian tumor resection on the level of HE4 in blood serum.

Assessment of paper tip angular position, carryover, matrix effects and dried blood spot storage effect on paper spray mass spectrometry

Experimental and validation parameters of paper spray mass spectrometry.

Development of a quantitative method for the analysis of cocaine analogue impregnated into textiles by Raman spectroscopy.

Cocaine trafficking in the form of textile impregnation is routinely encountered as a concealment method. Raman spectroscopy has been a popular and successful testing method used for in situ screening of cocaine in textiles and other matrices. Quantitative analysis of cocaine in these matrices using Raman spectroscopy has not been reported to date. This study aimed to develop a simple Raman method for quantifying cocaine using atropine as the model analogue in various types of textiles. Textiles were impregnated with solutions of atropine in methanol. The impregnated atropine was extracted using less hazardous acidified water with the addition of potassium thiocyanate (KSCN) as an internal standard for Raman analysis. Despite the presence of background matrix signals arising from the textiles, the cocaine analogue could easily be identified by its characteristic Raman bands. The successful use of KSCN normalised the analyte signal response due to different textile matrix background interferences and thus removed the need for a matrix-matched calibration. The method was linear over a concentration range of 6.25-37.5mg/cm2 with a coefficient of determination (R2 ) at 0.975 and acceptable precision and accuracy. A simple and accurate Raman spectroscopy method for the analysis and quantification of a cocaine analogue impregnated in textiles has been developed and validated for the first time. This proof-of-concept study has demonstrated that atropine can act as an ideal model compound to study the problem of cocaine impregnation in textile. The method has the potential to be further developed and implemented in real world forensic cases.

Reverse-Polynomial Dilution Calibration Methodology Extends Lower Limit of Quantification and Reduces Relative Residual Error in Targeted Peptide Measurements in Blood Plasma

Matrix effect is the alteration of an analyte's concentration-signal response caused by co-existing ion components. With electrospray ionization (ESI), matrix effects are believed to be a function of the relative concentrations, ionization efficiency, and solvation energies of the analytes within the electrospray ionization droplet. For biological matrices such as plasma, the interactions between droplet components is immensely complex and the effect on analyte signal response not well elucidated. This study comprised of three sequential quantitative analyses: we investigated whether there is a generalizable correlation between the range of unique ions in a sample matrix (complexity); the amount of matrix components (concentration); and matrix effect, by comparing an E. coli digest matrix (∼2600 protein proteome) with phospholipid depleted human blood plasma, and unfractionated, nondepleted human plasma matrices (∼10(7) proteome) for six human plasma peptide multiple reaction monitoring assays. Our data set demonstrated analyte-specific interactions with matrix complexity and concentration properties resulting in significant ion suppression for all peptides (p < 0.01), with nonuniform effects on the ion signals of the analytes and their stable-isotope analogs. These matrix effects were then assessed for translation into relative residual error and precision effects in a low concentration (∼0-250 ng/ml) range across no-matrix, complex matrix, and highly complex matrix, when a standard addition stable isotope dilution calibration method was used. Relative residual error (%) and precision (CV%) by stable isotope dilution were within <20%; however, error in phospholipid-depleted and nondepleted plasma matrices were significantly higher compared with no-matrix (p = 0.006). Finally a novel reverse-polynomial dilution calibration method with and without phospholipid-depletion was compared with stable isotope dilution for relative residual error and precision. Reverse-polynomial dilution techniques extend the Lower Limit of Quantification and reduce error (p = 0.005) in low-concentration plasma peptide assays and is broadly applicable for verification phase Tier 2 multiplexed multiple reaction monitoring assay development within the FDA-National Cancer Institute (NCI) biomarker development pipeline.

Analytical determination of aliskiren in pharmaceutical formulations using boron-doped diamond electrodes

Electrooxidation of aliskiren on a BDD electrode.

Quantitative analysis of polysorbates 20 and 40 by matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry

Polysorbates are nonionic surfactants that consist primarily of fatty acid esters of polyethoxy sorbitan. This study proved that polysorbates can be quantitatively analyzed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Using MALDI-TOF MS, relative intensity and concentration ratios were correlated, and extensive research was conducted to understand the influencing factors. Polysorbate 20 and 40 were mixed in the desired ratios and irradiated with a N2 laser. MALDI-TOF mass spectra were recorded in positive ion mode to test the linearity. All commercial polysorbates were analyzed to determine the relative concentration of the components using the same method. The relative peak intensity ratio as a function of the relative concentration ratio was analyzed, and a reasonably good linearity (R(2) = 0.987 for polysorbate 20) was obtained. This study illustrates the process of converting the analyte signal response into the concentration, supporting the notion that quantitative MALDI-TOF MS can be used to analyze polymers. MALDI-TOF MS analysis of commercial polysorbate formulations revealed a complex mixture of oligomers that was related to the fatty acid composition. Polysorbates 20 and 40 were characterized, and the simultaneous quantitative analysis of polysorbate 20 was reported. This method requires no tedious sample pretreatment. Therefore, it is a promising method for the rapid simultaneous quantitation of polysorbates 20 and 40.

Mass Spectrometry Parameters Optimization for the 46 Multiclass Pesticides Determination in Strawberries with Gas Chromatography Ion-Trap Tandem Mass Spectrometry

Multiclass analysis method was optimized in order to analyze pesticides traces by gas chromatography with ion-trap and tandem mass spectrometry (GC-MS/MS). The influence of some analytical parameters on pesticide signal response was explored. Five ion trap mass spectrometry (IT-MS) operating parameters, including isolation time (IT), excitation voltage (EV), excitation time (ET), maximum excitation energy or "q" value (q), and isolation mass window (IMW) were numerically tested in order to maximize the instrument analytical signal response. For this, multiple linear regression was used in data analysis to evaluate the influence of the five parameters on the analytical response in the ion trap mass spectrometer and to predict its response. The assessment of the five parameters based on the regression equations substantially increased the sensitivity of IT-MS/MS in the MS/MS mode. The results obtained show that for most of the pesticides, these parameters have a strong influence on both signal response and detection limit. Using the optimized method, a multiclass pesticide analysis was performed for 46 pesticides in a strawberry matrix. Levels higher than the limit established for strawberries by the European Union were found in some samples.

Sol–gel immobilization of acetylcholinesterase for the determination of organophosphate pesticides in olive oil with biosensors

This paper presents the construction of amperometric biosensors for the detection of organophosphorus insecticides widely used in the treatment of olive trees. The systems are based on the immobilisation of acetylcholinesterase on screen-printed electrodes by bioencapsulation in a sol–gel composite. The enzyme activity was estimated by measuring the thiocholine produced by the enzymatic hydrolysis of the acetylthiocholine chloride using cobalt phtalocyanine as mediator. The developed devices have been used to carry out inhibition studies with three pesticides: malathion, methidathion and dimethoate (in their oxidized form), and tested using standard solutions and real samples of olive oil. These biosensors showed good operational stability as they maintained their initial analytical signal response during 10 successive measurements, and a good reproducibility with a relative standard deviation of 3%. The limits of detection of the developed devices were very compatible with the maximum residue limit tolerated by international regulations, they were as low as 10−9 M for the widely used pesticide malaoxon(oxidized malathion). The developed sensors were successfully used for the determinations of insecticides in real samples of olive oil.

Sulfadiazine determination in pharmaceuticals by electrochemical reduction on a glassy carbon electrode

Sulfadiazine was quantified in two samples of pharmaceutical preparations by square-wave voltammetry. The analytical signal response was obtained by electrochemical reduction instead of oxidation of the sulfa drug at a glassy carbon electrode. The determination was carried out in 0.04 mol L-1 Britton-Robinson pH 6.8 buffer solution. Sulfadiazine reduction was observed at -1.49 V vs. Ag/AgCl in one well-resolved irreversible peak. The analytical curve was obtained in the concentration range of 62.7 to 340 µmol L-1 (r = 0.9986) with a detection limit of 10.9 µmol L-1. For one sample analyzed, recovery values were in the range of 94.9 to 101.1%, while for the other sample they were within 96.0 to 104.6%, indicating no matrix interference effects on the analytical results for both sulfadiazine samples. The accuracy of the electroanalytical method was compared to the standard amperometric titration method.

Influence of EDTA, carboxylic acids, amino- and hydroxocarboxylic acids and monosaccharides on the generation of arsines in hydride generation atomic absorption spectrometry

Abstract The influence of EDTA, carboxylic acids, amino-and hydroxocarboxylic acids, monosaccharides and humic substances on the generation of arsines in hydride generation atomic absorption spectrometry (HGAAS) was investigated. EDTA (0.02 mol L−1), ascorbic acid (0.02 mol L−1) and glucose or fructose (0.2 mol L−1) are useful additives for levelling sensitivities for As(III), monomethylarsonate (MMA) and dimethylarsinate (DMA). The presence of glycine, malonic, tartaric acids, BICIN and soil humin extracts leads to differences in analytical signal response between these arsenic species. An analytical application to the determination of the sum of As(III), monomethylarsonate (MMA) and dimethylarsinate (DMA) as well as the sum of toxicologically relevant hydride forming arsenic fraction As(III) + As(V) + MMA + DMA in EDTA soil/sediment extracts using continuous flow HGAAS was demonstrated. The limit of detection was 0.2 mg kg−1 As. Within-day and between-day precision were in the range 3–7% and 4–10%, respectively, for arsenic contents of 0.7–25 mg kg−1, with recoveries 95–103%.

Incipient damage identification through characteristics of the analytical signal response

The analytical signal is a complex representation of a time domain signal: the real part is the time domain signal itself, while the imaginary part is its Hilbert transform. It has been observed that damage, even at a very low level, yields clearly detectable variations of analytical signal quantities such as phase and instantaneous frequency. This observation can represent a step toward a quick and effective tool to recognize the presence of incipient damage where other frequency-based techniques fail. In this paper a damage identification procedure based on an adimensional functional of the square of the difference between the characteristics of the analytical theoretical and measured signal is proposed. Numerical examples, on a single degree of freedom system and of 3 degrees of freedom building model, prove the efficacy of the proposed method, its robustness in the presence of measuring errors, and show that the use of the signal phase leads to the best damage parameter estimation. Copyright © 2008 John Wiley & Sons, Ltd.

Comparative TOF‐SIMS and MALDI TOF‐MS analysis on different chromatographic planar substrates

A comparison is made between two high resolution, surface-based, mass spectrometric methods: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and matrix-assisted laser desorption/ionisation mass spectrometry (MALDI TOF-MS) in indication of abietic and gibberellic acids molecular profiles on different chromatographic thin layers. The analytes were applied to silica gel chromatographic thin layers with SIMS on-line interfacing channel, monolithic silica gel ultra-thin layers, and thin layers specifically designed for direct Raman spectroscopic analysis. Two MALDI matrices were used in this research: ferulic acid and 2,5-dihydroxybenzoic acid. The silica gel SIMS-interfacing channel strongly supported formation of numerous different MALDI MS fragments with abietic and gibberellic acids, and ferulic acid matrix. The most intense fragments belonged to [M-OH](+) and [M](+) ions from ferulic acid. Intense conjugates were detected with gibberellic acid. The MALDI MS spectrum from the monolithic silica gel surface showed very low analyte signal intensity and it was not possible to obtain MALDI spectra from a Raman spectroscopy treated chromatographic layer. The MALDI TOF MS gibberellic acid fragmentation profile was shielded by the matrix used and was accompanied by poor analyte identification. The most useful TOF-SIMS analytical signal response was obtained from analytes separated on monolithic silica gel and a SIMS-interfacing modified silica gel surface. New horizons with nanostructured surfaces call for high resolution MS methods (which cannot readily be miniaturised like many optical and electrochemical methods) to be integrated in chip and nanoscale detection systems.

Post‐chromatographic TOF‐SIMS identification of diterpenes

AbstractMixture of two diterpenes was separated by thin layer chromatography (TLC) on different substrates and then analysed with time‐of‐flight secondary ions mass spectrometry (TOF‐SIMS). Abietic (AA) and gibberellic acids (GA) were separated on three different chromatographic thin layers: monolithic silica chromatographic ultra‐thin layer (A), aluminium backplate modified silica gel thin layer (B) and commercially available Raman spectrometric thin layer (C). GA is more polar and is stronger retained near the start of layer while AA moves with mobile phase front (ethanol–water, 40:60, v/v). Primary detection with UV lamp was possible only for AA. TOF‐SIMS macroscans of chromatographic thin layer surfaces have been collected for most intensive positive or negative charged ions. The most applicable TOF‐SIMS analytical signal response was obtained from analytes separated on monolithic silica and aluminium backplate modified thin layer surface. Thin layer produced for on‐line Raman spectroscopy is only partially suitable for TOF‐SIMS analysis and this substrate does not support construction of negative ions macroscans. The suitability of the substrates for post‐chromatographic TOF‐SIMS analysis was found in order: Raman spectroscopy thin layers &lt; monolithic silica &lt; and aluminium backplate modified surface—for negative ion macroscans. For positive‐ion macroscans formation, the order is as follows: Raman spectroscopy layer &lt; aluminium backplate modified surface &lt; and monolithic silica. The results obtained from these analyses should be applied in future coupling of TOF‐SIMS with microcolumn high‐performance liquid chromatography (µHPLC), online. TOF‐SIMS was chosen for its outstanding capabilities in molecular surface analysis and surface imaging, in particular, of mono‐, di‐, seskviterpenes. Copyright © 2006 John Wiley &amp; Sons, Ltd.

Laser-induced particulate as carrier of analytical information in LA-ICPMS direct solid microanalysis

Laser ablation in combination with plasma spectrochemistry is an ideal technique for depth profiling analysis, based on signal profiles. However, signal profiles were found to be critically influenced by the characteristics of the ablated particles, especially their composition and size distribution, and consequently transport mechanism and plasma-assisted vaporization efficiency. Even for a refractory material like ceramic, relics of melting following laser irradiation were found, so that particles were non-stoichiometric as compared to the parent material. Estimates of transport efficiency showed that this is highly variable as a function of particle size. Large particles are likely to be lost in the sample chamber. Fine particles are prone to wall reaction, especially in Ar ambient. Variability in particle delivery to the ICP-MS was suspected to be the cause for an element-dependent analyte signal response. Fluctuation in particle vaporization degree as a consequence of plasma temperature instability was also responsible for element-dependent signal profile deviation. However, for a 10-fold higher mass load into the plasma, no direct fractionation effects were observed. Differential transport of chemically-differentiated analyte-carriers is suggested to be primary cause for element-dependent signal structure.