Minimal Matrix Research Articles

Validation of an analytical method for the determination of the main ayahuasca active compounds and application to real ayahuasca samples from Brazil

Ayahuasca is a brew prepared from the water decoction of two Amazonian plants, which is legally used for religious, cultural or therapeutic activities. The potential use of ayahuasca as a natural or phytotherapeutic drug is directly linked to the action of its active compounds and their connection with the therapeutic efficacy of the beverage. In this context, the aim of the present study was to establish a selective, sensitive and reproducible analytical method for the quantification of the main active ayahuasca compounds. Thirty-eight samples from the state of São Paulo, Brazil, were analyzed and the simultaneous quantifications of N,N-dimethyltryptamine (DMT), tetrahydroharmine (THH), harmine (HME) and harmaline (HML) were performed. This study enabled the development of a fast validated analytical method with minimal matrix interference and high reproducibility for the tracing of active ayahuasca compound concentrations for the first time. This method is important as an auxiliary tool for the study of active compound effects in biological responses using different multi-omic platforms.

Simultaneous Quantification of 13 Cannabinoids and Metabolites in Human Plasma by Liquid Chromatography Tandem Mass Spectrometry in Adult Epilepsy Patients.

A sensitive, robust method was developed and validated to quantitate 13 major natural cannabinoid parent and metabolite compounds in human plasma at or below 0.5 ng/mL. A liquid chromatography tandem mass spectrometry method was developed and validated to measure 13 cannabinoid compounds: cannabidiol (CBD), cannabidiolic acid, cannabidivarin, cannabinol, cannabigerol, cannabigerolic acid, cannabichromene, Δ-tetrahydocannabinol (THC), Δ-tetrahydrocannabinolic acid A (THCA), Δ-tetrahydrocannabivarin (THCV), 11-hydroxy-Δ-tetrahydrocannbinol (11-OH-THC), 11-nor-9-carboxy-Δ-tetrahydrocannbinol (THC-COOH), and 11-nor-9-carboxy-Δ-tetrahydrocannabinol glucuronide (THC-COOH-glu). Samples (200 µL) were extracted through protein precipitation and separated with a Kinetex EVO C18 column and a 65%-95% gradient of methanol and 0.2% ammonium hydroxide/H2O at a flow rate of 0.4 mL/min. Samples were obtained from patients with epilepsy receiving cannabis for the treatment of seizures. The extracted lower limit of quantification was 0.05 ng/mL for CBD, cannabidivarin, cannabinol, and 11-OH-THC; 0.10 ng/mL for cannabidiolic acid, cannabigerol, cannabichromene, cannabigerolic acid, THC, THCA, and THCV; and 0.50 ng/mL for THC-COOH and THC-COOH-glu. Mean quality control intraday accuracy and precision for all analytes ranged 96.5%-104% and 2.7%-4.9%, respectively, whereas interday accuracy and precision ranged 98%-103.3% and 0.2%-3.6%, respectively. An absolute matrix effect was observed for some analytes, however, with minimal relative matrix effect. Lack of nonspecific drug binding to extraction glass and plasticware was verified. Patient CBD levels ranged from 0.135 to 11.13 ng/mL. The validated method met FDA guidelines for bioanalytical assays precision and accuracy criteria. The assay reliably confirmed the use of particular medical cannabis formulations in patient samples as well as reliably measured low CBD concentrations from single-dose CBD exposure.

Resonance-assisted tunneling in four-dimensional normal-form Hamiltonians.

Nonlinear resonances in the classical phase space lead to a significant enhancement of tunneling. We demonstrate that the double resonance gives rise to a complicated tunneling peak structure. Such double resonances occur in Hamiltonian systems with an at least four-dimensional phase space. To explain the tunneling peak structure, we use the universal description of single and double resonances by the four-dimensional normal-form Hamiltonians. By applying perturbative methods, we reveal the underlying mechanism of enhancement and suppression of tunneling and obtain excellent quantitative agreement. Using a minimal matrix model, we obtain an intuitive understanding.

Algorithm to compute minimal matrix representation of nilpotent lie algebras

ABSTRACTAs it is well-known there exist matrix representations of any given finite-dimensional complex Lie algebra. More concretely, such representations can be obtained by means of an isomorphic matrix Lie algebra consisting of upper-triangular square matrices. However, there is no general information about the minimal order for the matrices involved in such representations. In this way, our main goal is to revisit, debug and implement an algorithm which provides the minimal order for matrix representations of any finite-dimensional nilpotent Lie algebra from its law, as well as returning a matrix representative of such an algebra by using the minimal order previously computed. In order to show the applicability of this procedure, we have computed minimal representative for each nilpotent Lie algebra of dimensions 6 and 7 and we have also obtained the representation of some families with an arbitrary dimension.

Electrochemical Determination of Sunitinib in Biological Samples Using Polyacrylonitrile Nanofibers/Nickel-Zinc-Ferrite Nanocomposite/Carbon Paste Electrode

This article presents the novel modifier; polyacrylonitrile nanofibers/Ni0.5Zn0.5Fe2O4 nanoparticles nanoparticles as a novel modifier, which has been synthesized using an electrospinning method. This nanocomposite has been used to construct an electrochemical sensor for highly sensitive determination of sunitinib (STB) drug in biological samples. The synthesized nanocomposite was fully characterized using methods such as Fourier transform infrared spectroscopy, scanning electron microscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. For the electrochemical determination of STB, the differential pulse voltammetry signal of the drug electrooxidation on carbon paste electrode modified with the newly developed nanocomposite was investigated. Preliminary experiments showed that the nanocomposite had an electrocatalytic effect on the electrooxidation of STB and a significant improvement in the anodic current of the drug was obtained at +0.66 V. Under the optimum conditions, the analytical figures of merit were extracted and the method was fully validated. A relatively wide dynamic linear range of 0.018–18.77 μ mol L−1 with the detection limit of 0.9 n mol L−1 was obtained. Furthermore, the method was applied for the determination of STB in biological fluid samples such as human serum samples with acceptable recoveries (97–102), satisfactory precision (2–4%RSD) and minimal matrix effects.

Block minimal bases ℓ-ifications of matrix polynomials

The standard way of solving a polynomial eigenvalue problem associated with a matrix polynomial starts by embedding the matrix coefficients of the polynomial into a matrix pencil, known as a strong linearization. This process transforms the problem into an equivalent generalized eigenvalue problem. However, there are some situations in which is more convenient to replace linearizations by other low degree matrix polynomials. This has motivated the idea of a strong ℓ-ification of a matrix polynomial, which is a matrix polynomial of degree at most ℓ having the same finite and infinite elementary divisors, and the same numbers of left and right minimal indices as the original matrix polynomial. We present in this work a novel method for constructing strong ℓ-ifications of matrix polynomials of size m×n and grade d when ℓ<d, and ℓ divides nd or md. This method is based on a family called “strong block minimal bases matrix polynomials”, and relies heavily on properties of dual minimal bases. We show how strong block minimal bases ℓ-ifications can be constructed from the coefficients of a given matrix polynomial P(λ). We also show that these ℓ-ifications satisfy many desirable properties for numerical applications: they are strong ℓ-ifications regardless of whether P(λ) is regular or singular, the minimal indices of the ℓ-ifications are related to those of P(λ) via constant uniform shifts, and eigenvectors and minimal bases of P(λ) can be recovered from those of any of the strong block minimal bases ℓ-ifications. In the special case where ℓ divides d, we introduce a subfamily of strong block minimal bases matrix polynomials named “block Kronecker matrix polynomials”, which is shown to be a fruitful source of companion ℓ-ifications.

Constrained Kinematic Control in Minimally Invasive Robotic Surgery Subject to Remote Center of Motion Constraint

This paper presents kinematic control of surgical robotic systems subject to Remote Center of Motion (RCM) constraint in Minimally Invasive Robotic Surgeries (MIRS). A novel kinematic formulation for surgical systems is derived and the movement restriction in incision point, known as RCM constraint, is resolved by active control of the system through a so-called RCM-constrained Jacobian. The proposed minimal Jacobian matrix can realize fixed/moving trocar constraint effectively in comparison with the state-of-the-arts. In the following, an analysis related to the dexterity of the constrained system is introduced and an index for manipulability of the constrained system is introduced. The proposed approach is validated through several numerical simulations as well as experiments in a 7DoFs and 9DoFs MIRS scenarios. The results show the efficiency and the precision of the proposed method.

Diagenesis, burial history, and hydrocarbon potential of Cambrian sandstone in the northern continental margin of Gondwana: A case study of the Lalun Formation of central Iran

Undeformed Cambrian–Ordovician sandstones on the northern margin of Gondwana are in places important hydrocarbon reservoirs. The factors that favoured diagenetic preservation of porosity in such sandstones are reviewed and compared to the Lower Cambrian Lalun Formation of central Iran, in order to assess what aspects of geological history have controlled the cementation and porosity of the sandstones. The Lalun Formation is up to 640 m thick and comprises braided-fluvial sandstones with minor shales that are overlain by marine shales, sandstones and carbonates. In four sections along a ∼650 km traverse, the sandstones are predominantly quartzarenites, locally arkosic and lithic, and contain minimal detrital matrix. Provenance analysis and paleoflow suggest derivation from the Arabian Shield. Diagenesis was dominated by quartz overgrowths and abundant intra-grain microfractures healed by silica cement, with modest amounts of poikilotopic and mosaic calcite, authigenic clay, and iron oxide as early grain rims and late-stage fracture fills. Minor phases include dolomite, ankerite, siderite, magnetite and barite. Marine strata contain more carbonate cement, with silica cement prominent in topmost nearshore sandstones. Burial-history analysis suggests relatively rapid burial in a cratonic setting to more than 4 km by the end of the Silurian and a maximum temperature of ∼150 °C during burial diagenesis, sufficient for hydrocarbon generation by the end of the Paleozoic. Dissolution of K-feldspar, ferromagnesian grains and, locally, calcite cement generated secondary porosity, but porosity and permeability values are low, averaging 1.5% and <0.1 mD, respectively. Rapid subsidence of thick Cambrian fluvial successions at the northeastern Gondwanan margin may have limited early dissolution and promoted occlusion of primary porosity by quartz overgrowths, limiting permeability pathways for fluids that might have generated secondary porosity later in the basinal history. In contrast with Cambrian and Ordovician sandstone reservoirs across North Africa and the Middle East, the existence of Paleozoic source rocks may be problematic in central Iran.

Ultrahigh-Resolution Mass Spectrometry in Real Time: Atmospheric Pressure Chemical Ionization Orbitrap Mass Spectrometry of Atmospheric Organic Aerosol.

The accurate and precise mass spectrometric measurement of organic compounds in atmospheric aerosol particles is a challenging task that requires analytical developments and adaptations of existing techniques for the atmospheric application. Here we describe the development and characterization of an atmospheric pressure chemical ionization Orbitrap mass spectrometer (APCI-Orbitrap-MS) for the measurement of organic aerosol in real time. APCI is a well-known ionization technique, featuring minimal fragmentation and matrix dependencies, and allows rapid alternation between the positive and negative ionization mode. As a proof of principle, we report ambient organic aerosol composition in real-time, with alternating ionization, high mass resolution ( R = 140 000) and accuracy (<2 ppm). The instrument was calibrated in the negative ion mode using 3-methyl-1,2,3-butanetricarboxylic acid (MBTCA) model aerosol. We obtain a detection limit of 1.3 ng/m3. Based on the performed calibration using MBTCA particles, the ambient concentration of MBTCA in the particle phase measured in an urban area in Mainz, Germany, ranged between 10 and 80 ng/m3. For the first time, we apply a nontarget screening approach on real-time data, showing molecular variability between ambient day- and nighttime aerosol composition. The detected compounds were grouped in the night- and daytime and analyzed by ultrahigh-resolution MS (UHRMS) visualization methods. Among several prevalent biogenic secondary organic aerosol (BSOA) markers, 24 organic mononitrates and one organic dinitrate were detected. We further estimate that, on average, organic nitrates contribute to 5% and 14% of the measured particulate organic aerosol at day and night, respectively.

Lectin- and Saccharide-Functionalized Nano-Chemiresistor Arrays for Detection and Identification of Pathogenic Bacteria Infection.

Improvement upon, and expansion of, diagnostic tools for clinical infections have been increasing in recent years. The simplicity and rapidity of techniques are imperative for their adoption and widespread usage at point-of-care. The fabrication and evaluation of such a device is reported in this work. The use of a small bioreceptor array (based on lectin-carbohydrate binding) resulted in a unique response profile, which has the potential to be used for pathogen identification, as demonstrated by Principal Component Analysis (PCA). The performance of the chemiresistive device was tested with Escherichia coli K12, Enterococcus faecalis, Streptococcus mutans, and Salmonella typhi. The limits of detection, based on concanavalin A (conA) lectin as the bioreceptor, are 4.7 × 103 cfu/mL, 25 cfu/mL, 7.4 × 104 cfu/mL, and 6.3 × 102 cfu/mL. This shows that the detection of pathogenic bacteria is achieved with clinically relevant concentrations. Importantly, responses measured in spiked artificial saliva showed minimal matrix interference. Furthermore, the exploitation of the distinctive outer composition of the bacteria and selectivity of lectin-carbohydrate interactions allowed for the discrimination of bacterial infections from viral infections, which is a current and urgent need for diagnosing common clinical infections.

Development and validation of LC/APCI-MS method for the quantification of oat ceramides in skin permeation studies.

Ceramides (CERs) are the backbone of the intercellular lipid lamellae of the stratum corneum (SC), the outer layer of the skin. Skin diseases such as atopic dermatitis, psoriasis, and aged skin are characterized by dysfunctional skin barrier and dryness which are associated with reduced levels of CERs. Replenishing the depleted epidermal CERs with exogenous CERs has been shown to have beneficial effects in improving the skin barrier and hydration. The exogenous CERs such as phyto-derived CERs (PhytoCERs) can be delivered deep into the SC using novel topical formulations. This, however, requires investigating the rate and extent of skin permeation of CERs. In this study, an LC/APCI-MS method to detect and quantify PhytoCERs in different layers of the skin has been developed and validated. The method was used to investigate the skin permeation of PhytoCERs using Franz diffusion cells after applying an amphiphilic cream containing PhytoCERs to the surface of ex vivo human skin. As plant-specific CERs are not commercially available, well-characterized CERs isolated from oat (Avena abyssinica) were used as reference standards for the development and validation of the method. The method was linear over the range of 30-1050ng/mL and sensitive with limit of detection and quantification of 10 and 30ng/mL, respectively. The method was also selective, accurate, and precise with minimal matrix effect (with mean matrix factor around 100%). Even if more than 85% of oat CERs in the cream remained in the cream after the incubation periods of 30, 100, and 300min, it was possible to quantify the small quantities of oat CERs distributed across the SC, epidermis, and dermis of the skin indicating the method's sensitivity. Therefore, the method can be used to investigate the skin permeation of oat CERs from the various pharmaceutical and cosmeceutical products without any interference from the skin constituents such as the epidermal lipids. Graphical abstract ᅟ.

Minimal exponent matrix

This paper investigates the minimal exponent matrix and minimal weight functions of the admissible quiver. Found limitations for the sum of the elements of exponent matrix with a single quiver and a limitation for the sum of the elements the minimal exponent matrix with quiver which has a loop in each the top. It is shown that reducing the weight of a simple quiver cycle, can lead to an increase in the sum of elements of the exponent matrix from which you get a quiver. An example is given that refutes the hypothesis that that for a quiver with a loop in each vertex, the weight function with the weight of all simple cycles equal to 2 is minimal. It is proved that a rigid quiver is obtained from a minimal exponent matrix.

Fast and Exact Simulation of Complex-Valued Stationary Gaussian Processes Through Embedding Circulant Matrix

ABSTRACTThis article is concerned with the study of the embedding circulant matrix method to simulate stationary complex-valued Gaussian sequences. The method is, in particular, shown to be well-suited to generate circularly symmetric stationary Gaussian processes. We provide simple conditions on the complex covariance function ensuring the theoretical validity of the minimal embedding circulant matrix method. We show that these conditions are satisfied by many examples and illustrate the simulation algorithm. In particular, we present a simulation study involving the circularly symmetric fractional Gaussian noise, a model introduced in this article. Supplementary material for this article is available online.

Development of a closed-loop recycling process for discontinuous carbon fibre polypropylene composites

Abstract In this study the effects of a closed-loop recycling methodology are evaluated for degradation using a discontinuous carbon fibre polypropylene (CFPP) composite material. The process comprises two fundamental steps, reclamation and remanufacture. The material properties are analysed over two recycling loops. For neat polypropylene, the molecular weight analysis indicates evidence of minimal matrix degradation that does not affect the material behaviour, as demonstrated by the shear tests. CFPP specimens show no decrease in mechanical properties over repeated loops, the final specimens show an increase of 26% and 43% in ultimate tensile strength and ultimate strain, respectively. These are attributed to cumulative matrix residue on the fibre surface after reclamation and subsequently increased fibre-matrix adhesion. The improvement of CFPP properties and insignificant variability in the tensile properties and molecular weight distribution of neat polypropylene validate the potential of this proof-of-concept, closed-loop recyclable material. Future studies will investigate alternative, higher performance matrices.

Quantitation of 25-hydroxyvitamin D in dried blood spots by 2D LC-MS/MS without derivatization and correlation with serum in adult and pediatric studies

BackgroundDemand for measurement of 25-hydroxyvitamin D (25OHD) is growing and dried blood spot (DBS) sampling is attractive as samples are easier to collect, transport and store. MethodsA 2D LC-MS/MS assay without derivatization was developed. DBS punches (3.2 mm) were ultrasonicated with d6-25OHD3 in 70% methanol followed by hexane extraction, dry-down and reconstitution. The assay was validated and applied to two studies comparing whole blood adult DBS with serum samples (n = 40) and neonatal whole blood DBS with cord serum samples (n = 80). ResultsThe assay was validated in whole blood DBS over the range 13–106 nmol/L 25OHD3 and 11–91 nmol/L 25OHD2 with a limit of detection of 3 nmol/L. Intra- and inter-day imprecision was <13% CV and bias <12%. The assay had high recovery and minimal matrix effects. Triplicate DBS study samples had a mean CV of ≤13% for 25OHD3. No 25OHD2 was detected. DBS calculated serum 25OHD3 concentrations correlated strongly with serum concentrations in the adult DBS/serum study (r = 0.94) and moderately in the neonatal DBS/cord serum study (r = 0.69). ConclusionsDirect quantitation of 25OHD in DBS by 2D LC-MS/MS without derivatization was found to be an alternative to serum quantitation applicable to clinical research studies on adult DBS samples.

Comparison of analytical performances of inductively coupled plasma mass spectrometry and inductively coupled plasma atomic emission spectrometry for trace analysis of bismuth and bismuth oxide

The paper presents а comparison of analytical performances of inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) for trace analysis of high purity bismuth and bismuth oxide. Matrix effects in the ICP-MS and ICP-AES methods were studied as a function of Bi concentration, ICP power and nebulizer flow rate. For ICP-MS the strong dependence of the matrix effects versus the atomic mass of analytes was observed. For ICP-AES the minimal matrix effects were achieved for spectral lines of analytes with low excitation potentials. The optimum degree of sample dilution providing minimum values of the limits of detection (LODs) was chosen. Both methods let us to reach LODs from n·10−7 to n·10−4wt% for more than 50 trace elements. For most elements the LODs of ICP-MS were lower in comparison to ICP-AES. Validation of accuracy of the developed techniques was performed by “added-found” experiments and by comparison of the results of ICP-MS and ICP-AES analysis of high-purity bismuth oxide.

Method development, matrix effect, and risk assessment of 49 multiclass pesticides in kiwifruit using liquid chromatography coupled to tandem mass spectrometry

In the present study, a liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) method with a minimal matrix effect (ME) was developed and validated for simultaneous determination of a diverse range of pesticides (49) in kiwifruit. Samples extracted by the quick, easy, cheap, effective, rugged, and safe (QuEChERS) citrate-buffered method were analyzed either without purification or following purification (with primary secondary amine (PSA) or PSA + graphitized carbon black (GCB)). With the addition of a clean-up step, the suppression of the ME decreased, with a higher number of pesticides determined by the application of PSA + GCB. The method exhibited good linearity with coefficients of determination (R2) ≥ 0.9972 and satisfactory recoveries (70–120%) with a relative standard deviations (RSDs) <10%. The limits of quantification (LOQ) were lower than the maximum residue limits (MRLs) set by the Korean Ministry of Food and Drug Safety (MFDS) and the CODEX Alimentarius. The developed method was applied to the real samples and the results indicated that the quantitated levels of all pesticides, except for pyraclostrobin and carbendazim, are lower than the MRLs set by the regulatory authorities. The percentage of the acceptable daily intake was <20%, suggesting that there is no risk associated with the intake of residual pesticides through kiwifruit.

Unimodular equivalence and similarity for linear systems

ABSTRACTThe problem of finding the mapping between unimoduar transformations relating two minimal matrix fraction descriptions (MFDs) of a transfer function, and the similarity transformations relating the respective minimal state-space representations is considered. It is shown that the problem is equivalent to finding the relation of MFDs of the input-state transfer functions of the two systems. This relation turns out to be an equivalence relation involving the unimodular and the similarity matrices relating the MFDs and the state-space systems, respectively. A canonical form for MFDs under this equivalence relation is obtained and it is shown that it leads to a canonical state-space representation, via a realisation procedure.

A Simple Dilute-and-Shoot Flow-Injection Mass Spectrometric Method for Quantification of Glycocholic Acid in Human Bile

Levels of glycocholic acid are elevated in the bile of cholangiocarcinoma patients, making it a potential biomarker for the disease. The utility of liquid chromatography mass spectrometry based methods for the quantification of glycocholic acid often suffers from time-consuming extraction steps, carryover, and unavailability of blank bile matrix. To overcome the problems, we developed a dilute-and-shoot flow-injection tandem mass spectrometry (standard addition-based) method for quantification of glycocholic acid in bile. Bile was first diluted, followed by spiking the glycocholic acid standard and internal standard into the diluted bile, which was then directly flow-injected (without chromatographic separation) into the electrospray ionization source. Detection was carried out in negative multiple reaction monitoring mode with m/z transitions set at 464.1→74.0 and 401.2→249.1 for glycocholic acid and internal standard, respectively. A standard addition calibration curve was constructed to determine the amount of glycocholic acid present in human bile. The method has been validated with clinical samples according to FDA guidelines. Linearity was achieved in the spiked concentration range of 12.5 to 200 ng/mL with a correlation coefficient of 0.9857. The method has good accuracy, precision, minimal matrix effect, and is sufficiently sensitive enough to quantitate glycocholic acid even after 800,000-fold dilution. In conclusion, a dilute and shoot flow-injection MS/MS method has been developed and validated for the first time, which could be used in routine analysis of glycocholic acid in human bile in a clinical setting.

Minimal and maximal matrix convex sets

For every convex body K⊆Rd, there is a minimal matrix convex set Wmin(K), and a maximal matrix convex set Wmax(K), which have K as their ground level. We aim to find the optimal constant θ(K) such that Wmax(K)⊆θ(K)⋅Wmin(K). For example, if B‾p,d is the unit ball in Rd with the ℓp norm, then we find thatθ(B‾p,d)=d1−|1/p−1/2|. This constant is sharp, and it is new for all p≠2. Moreover, for some sets K we find a minimal set L for which Wmax(K)⊆Wmin(L). In particular, we obtain that a convex body K satisfies Wmax(K)=Wmin(K) only if K is a simplex.These problems relate to dilation theory, convex geometry, operator systems, and completely positive maps. For example, our results show that every d-tuple of self-adjoint contractions, can be dilated to a commuting family of self-adjoints, each of norm at most d. We also introduce new explicit constructions of these (and other) dilations.