Average Detection Limit Research Articles

A Validated Method for Detection and Quantitation of 2’Fucosyllactose in Infant Formula Matrices

Analytical methods to assess the content of free carbohydrates in solution range from simple tests of reductive power to combinations of chromatography and mass spectrometry. Soluble carbohydrates such as lactose, maltose, fructooligosaccharides, and galactooligosaccharides are commonly found in infant formulas either as sources of energy or soluble fibers. On the other hand, a rich repertoire of lactose-based carbohydrates occurs naturally in human milk. The advent of novel biosynthesis technologies resulted in the availability of human milk oligosaccharide structures that are being used as ingredients in infant formulas. Notably, 2’Fucosyllactose has been tested in preclinical and clinical studies to determine its safety and to explore its potential health benefits in the context of pediatric nutrition. Several chromatographic methods for the analysis of human milk oligosaccharides have been published and, the main challenge associated with 2’Fucosyllactose quantitation has been to improve its resolution from lactose, which is present at concentrations around 70 g/l in both, infant formula and human milk. We developed a high-performance anion exchange chromatography method to detect and quantify 2’ Fucosyllactose in the presence of lactose by expanding the elution time between these saccharides. We validated the analytical procedure which behaved linearly (average R=0.99951) at concentrations as low as 1.75 µg/ml (limit of quantitation) with an average limit of detection of 0.43 µg/ml.

Numerical investigation of photonic crystal ring resonators coupled bus waveguide as a highly sensitive platform

Optic and photonic sensing is a useful and novel technology for bio-sensing applications. In this paper, we have numerically designed and investigated sensitive photonic crystal ring resonators and three different structures of photonic crystal sensors are presented. The proposed sensors consist of ring resonators and bus and drop waveguides. These sensors are used to detect changes in the refractive index of the inner rod. Sensor 1 has one ring resonator between the bus and drop waveguides and has average sensitivity, quality factor, output power transmission, and detection limit of 278.5 nm/RIU, 3382, 90%, and 1.522 × 10−4 RIU, respectively. Sensor 2 has one ring resonator located above the bus waveguide and average sensitivity, quality factor, and detection limit of 231 nm/RIU, 4564, and 1.3 × 10−4 RIU, respectively. Sensor 3 has three ring resonators located between the bus and drop waveguides and has average sensitivity, quality factor, transmission, and detection limit of 228 nm/RIU, 5265, 81%, and 1.21 × 10−4 RIU respectively. The relationships of optical transmission, quality factor, and sensitivity with different wavelengths, and the resonant wavelengths with refractive index of inner rods are examined. Results from performing finite-difference time-domain simulations illustrate that the response of each detection shifts wavelengths according to the refractive index variations.

Assessing the detection limit of petroleum hydrocarbon in soils using hyperspectral remote-sensing

One of the most important characteristics of any quantitative method is its detection limit, which is the lowest detectable amount of analyte in a sample in a given method. The detection limit helps to know to which extent a method is applicable and valid. The detection of petroleum hydrocarbon contamination in bare soils is important, because of its vast distribution and its negative effects on humans and the environment. Hyperspectral remote sensing is an acceptable, cost-effective and spatially comprehensive tool, which has detection possibilities of petroleum hydrocarbon. However, previous studies that engaged with this topic did not directly consider the detection limit of the method and no detection limit has been systematically explored. In this study, an outdoor experiment was executed in which three types of soil were contaminated with 14 levels of pure crude oil and measured in outdoor conditions with a hyperspectral camera (950–2500 nm) at three distances from the camera (4, 8 and 12 m). For each soil type, and for each distance, the detection limit was systematically calculated. The results show that the detection limit is a dynamic range affected by the spatial domain and the soil type. Moreover, a significant (p < 0.001) difference between the average detection limit (1.32, 2.09 and 2.90 wt%) of the three soil types was found, suggesting that the detection limit is not only related to the PHC wt% but also depends on the soil type. The results presented in this study can help to improve our understanding of the limitations of hyperspectral remote sensing in direct detection of petroleum hydrocarbon and can be projected to other hyperspectral domains and soils.

A GBT Survey of the HALOGAS Galaxies and Their Environments. I. Revealing the Full Extent of H i around NGC 891, NGC 925, NGC 4414, and NGC 4565

Abstract We present initial results from a deep neutral hydrogen (H i) survey of the HALOGAS galaxy sample, which includes the spiral galaxies NGC 891, NGC 925, NGC 4414, and NGC 4565, performed with the Robert C. Byrd Green Bank Telescope (GBT). The resulting observations cover at least 4 deg2 around these galaxies, with an average 5σ detection limit of 1.2 × 1018 cm−2 over a velocity range of 20 km s−1 and angular scale of 9.′1. In addition to detecting the same total flux as the GBT data, the spatial distribution of the GBT and original Westerbork Synthesis Radio Telescope data match well at equal spatial resolutions. The H i mass fraction below H i column densities of 1019 cm−2 is, on average, 2%. We discuss the possible origins of low column density H i of nearby spiral galaxies. The absence of a considerable amount of newly detected H i by the GBT indicates these galaxies do not have significant extended diffuse H i structures, and suggests future surveys planned with the SKA and its precursors must go at least as deep as 1017 cm−2 in column density to significantly increase the probability of detecting H i associated with the cosmic web and/or cold mode accretion.

Diagnostic evaluation of an in-house developed single-tube, duplex, nested IS6110 real-time PCR assay for rapid pulmonary tuberculosis diagnosis

ObjectiveTo perform a prospective evaluation on the diagnostic performance of an in-house developed, duplex nested IS6110 real-time Polymerase-Chain-Reaction (PCR) assay (IS6110-qPCR assay) for rapid pulmonary TB diagnosis. MethodsA total of 503 sputum specimens were prospectively collected from July 2016 to November 2016. Diagnostic accuracy and optimal cut-off Cycle-threshold (Ct) value for IS6110-qPCR assay was determined by Receiver Operating Characteristic (ROC) curve. Using the optimal cut-off Ct, diagnostic performance of IS6110-qPCR assay was assessed with reference to both bacteriological and clinical information. Meanwhile, limit of detection (LOD) was calculated using Mycobacterium tuberculosis H37Rv as reference strain. ResultROC curve analysis of IS6110-qPCR assay showed a high Area Under the Curve (AUC) value (0.948) with optimal Ct value at 24.140. Prospective analysis of IS6110-qPCR assay with cut-off Ct = 24.140 showed a high overall sensitivity and specificity of 97.2% and 99.7%, respectively. No cross reactivity was observed among all non-tuberculous mycobacteria specimens in this study. LOD analysis on MTB-spiked sputum showed an average detection limit of 5.0 CFU/mL at Ct = 23.18 (±SD, 0.57). ConclusionIS6110-qPCR assay is a highly accurate and cost-effective assay developed for primary screening of suspected TB cases, which is particularly suitable for regions with limited resources but high TB burden.

Separation and determination of coumarins including furanocoumarins using micellar electrokinetic capillary chromatography

The conditions of micellar electrokinetic capillary chromatography for separation and simultaneous measurement of coumarins (coumarin, scoparone, isoscopoletin, esculin, esculetin, umbelliferone) including furanocoumarins (xanthotoxin, byakangelicin, isopimpinellin, bergapten, phellopterin, xanthotoxol) have been elaborated. The influence of different parameters, such as the pH of the buffer, sodium cholate (SC) or methanol concentration in the buffer, on the migration time, peak resolution, peak asymmetry, and number of theoretical plates was investigated. The optimum separation of the compounds was achieved using 50-µm i.d. capillaries with a total length of 64.5 cm (56 cm effective length) and a buffer system at pH 9.00 consisting of 50 mM sodium tetraborate, 45 mM SC, and 20% of methanol (v/v). The developed method ensured good repeatability of corrected peak areas and migration times (the relative standard deviations were in the range of 2.8–6.1% and 0.8–4.0%, respectively). The average limit of detection for all studied compounds was below 1.3 µg mL. Moreover, good linearity of the relationship between the peak corrected area and the concentration of the compounds was observed (correlation coefficient >0.99). The method was successfully applied in the quantitative analysis of two different types of samples, i.e. Heracleum sphondylium herb and Aesculus hippocastanum cortex.

Remote Detection for Glucose and Lactate Based on Flexible Sensor Array

In this paper, we develop a flexible arrayed glucose biosensor and a flexible arrayed lactate biosensor. The nickel oxide was used as the base of sensing film, and lactate dehydrogenase and glucose oxidase were used as the catalytic materials. The graphene oxide and magnetic beads were used to improve the characteristics of biosensors, according to their advantages, such as biocompatibility, high electron transfer ability, and high specific surface area. By using potentiometric measurement, the sensing characteristics of biosensors were analyzed, such as average sensitivity, linearity, response time, decay rate, drift rate, and limit of detection. The remote glucose and lactate monitoring was carried out by using wireless real-time sensing system based on XBee module, where ZigBee standard was based on IEEE 802.15.4 standard.

Hepatitis E virus in lettuce and water samples: A method-comparison study

The hepatitis E virus (HEV), which is an increasing cause of acute viral hepatitis in Europe, is a zoonotic virus that is mainly transmitted through contaminated water, consumption of raw or undercooked meat from pigs or wild boar, blood transfusion, and organ transplantation. Although the role of HEV transmission through contaminated produce has not been confirmed, the presence of HEV has been reported in irrigation waters and in vegetables. The present study used a World Health Organization (WHO) international standard and clinical samples to evaluate the performance characteristics of three RT-qPCR assays for detection and quantification of HEV. Two of the evaluated assays provided good analytical sensitivity, as 250 international units (IU) per ml could be detected. Then, experiments focused on evaluating the elution conditions suitable for HEV release from vegetables, with the method proposed by the ISO 15216:2017 selected for evaluation in three types of fresh vegetables. The concentration method proposed by the ISO 15216:2017 combined with the RT-qPCR described by Schlosser et al. (2014) resulted in average HEV recoveries of 1.29%, 0.46%, and 3.95% in lettuce, spinach, and pepper, respectively, with an average detection limit of 1.47 × 105 IU/25 g. In naturally contaminated samples, HEV was detected in sewage only (10/14), while no detection was reported in lettuce (0/36) or in irrigation water samples (0/24).

Multivariate estimation of the limit of detection by orthogonal partial least squares in temperature-modulated MOX sensors

Metal oxide semiconductor (MOX) sensors are usually temperature-modulated and calibrated with multivariate models such as partial least squares (PLS) to increase the inherent low selectivity of this technology. The multivariate sensor response patterns exhibit heteroscedastic and correlated noise, which suggests that maximum likelihood methods should outperform PLS. One contribution of this paper is the comparison between PLS and maximum likelihood principal components regression (MLPCR) in MOX sensors. PLS is often criticized by the lack of interpretability when the model complexity increases beyond the chemical rank of the problem. This happens in MOX sensors due to cross-sensitivities to interferences, such as temperature or humidity and non-linearity. Additionally, the estimation of fundamental figures of merit, such as the limit of detection (LOD), is still not standardized in multivariate models. Orthogonalization methods, such as orthogonal projection to latent structures (O-PLS), have been successfully applied in other fields to reduce the complexity of PLS models. In this work, we propose a LOD estimation method based on applying the well-accepted univariate LOD formulas to the scores of the first component of an orthogonal PLS model. The resulting LOD is compared to the multivariate LOD range derived from error-propagation. The methodology is applied to data extracted from temperature-modulated MOX sensors (FIS SB-500-12 and Figaro TGS 3870-A04), aiming at the detection of low concentrations of carbon monoxide in the presence of uncontrolled humidity (chemical noise). We found that PLS models were simpler and more accurate than MLPCR models. Average LOD values of 0.79 ppm (FIS) and 1.06 ppm (Figaro) were found using the approach described in this paper. These values were contained within the LOD ranges obtained with the error-propagation approach. The mean LOD increased to 1.13 ppm (FIS) and 1.59 ppm (Figaro) when considering validation samples collected two weeks after calibration, which represents a 43% and 46% degradation, respectively. The orthogonal score-plot was a very convenient tool to visualize MOX sensor data and to validate the LOD estimates.

Detection of Leguminous Protein in Casein by Nitrogen Stable Isotopes

Casein can legally be substituted with cheaper leguminous proteins in processed foods, such as imitation cheese, as long as the ingredients are declared. The detection of illegal admixtures of leguminous protein requires analytical procedures to identify an undisclosed adulteration of milk products. To investigate the suitability of stable isotope analyses as an alternative to more sophisticated methods, variations in d15N of soya (n = 27) and peanut (n = 10) protein, as well as casein (n = 14) were determined. Significant differences were established between d15N of casein (4.45 – 6.94‰) and soya (0.25 – 2.37‰) as well as peanut (0.70 – 2.13‰) protein. An average limit of detection for leguminous protein in casein was determined to be 2.1%, provided both components were available for additional analyses. Under practical conditions of food control, i.e., without having access to the actual ingredients, the variability of d15N resulted in an average limit of detection of 26.4%. Because protein d15N can be determined rapidly in crude food samples without elaborate sample preparation, stable isotope analysis can be used as a rapid screening method to determine the presence of higher amounts of leguminous protein in cheese and, in particular, to easily distinguish imitation cheese from cheese.

Ultraviolet differential optical absorption spectrometry: quantitative analysis of the CS2 produced by SF6 decomposition

The occurrence of partial discharge or partial overthermal fault in sulfur hexafluoride (SF6)-insulated electrical equipment frequently causes SF6 and solid insulation materials to decompose into various products. One of the most characteristic products of this process is carbon disulfide (CS2). The internal fault type and severity of the fault in the insulation equipment can be detected through the accurate quantitative detection of CS2. A device for simultaneously determining and quantifying gaseous CS2 via ultraviolet differential optical absorption spectrometry is developed in this study. A Sym14 wavelet transform and fast Fourier transform (FFT) are applied to process the spectral data of the feature regions, namely 190 nm to 210 nm. The concentration of CS2 is determined, and the detection limit of the developed device is identified. A good linear relationship is observed between the characteristic peaks of FFT and the concentration of CS2 after the operational parameters are optimized. Along the light path at 600 mm, the average detection limit for CS2 is 8.65 ppb based on three times the standard deviation of the system noises. The proposed device, which exhibits high sensitivity and effective cost, addresses the urgent demand for the monitoring and diagnosis of SF6-insulated electrical equipment via online detection of trace CS2.

Four-way calibration applied to the processing of pH-modulated fluorescence excitation-emission matrices. Analysis of fluoroquinolones in the presence of significant spectral overlapping

A new methodology involving four-way multivariate calibration with a balanced number of data points in all modes is presented. The method is based on fluorescence excitation-emission matrices modulated by a double pH gradient obtained in a flow injection system. This data array was employed for the quantitation of ciprofloxacin, ofloxacin and norfloxacin in unprocessed urine samples. Due to the presence of potential interfering compounds with overlapping profiles in the analyzed samples, it is required to achieve the second-order advantage. The four-way arrays obtained were processed by parallel factor analysis (PARAFAC), attaining satisfactory results with relative errors of prediction (REP%) between 3% and 7.5% in the analyzed samples for all analytes. The average limit of detection (mg L−1) was 0.035 for norfloxacin and ofloxacin and 0.028 for ciprofloxacin.

Analysis of bioethanol samples through Inductively Coupled Plasma Mass Spectrometry with a total sample consumption system

Bioethanol real samples have been directly analyzed through ICP-MS by means of the so called High Temperature Torch Integrated Sample Introduction System (hTISIS). Because bioethanol samples may contain water, experiments have been carried out in order to determine the effect of ethanol concentration on the ICP-MS response. The ethanol content studied went from 0 to 50%, because higher alcohol concentrations led to carbon deposits on the ICP-MS interface. The spectrometer default spray chamber (double pass) equipped with a glass concentric pneumatic micronebulizer has been taken as the reference system. Two flow regimes have been evaluated: continuous sample aspiration at 25μLmin−1 and 5μL air-segmented sample injection. hTISIS temperature has been shown to be critical, in fact ICP-MS sensitivity increased with this variable up to 100–200°C depending on the solution tested. Higher chamber temperatures led to either a drop in signal or a plateau. Compared with the reference system, the hTISIS improved the sensitivities by a factor included within the 4 to 8 range while average detection limits were 6 times lower for the latter device. Regarding the influence of the ethanol concentration on sensitivity, it has been observed that an increase in the temperature was not enough to eliminate the interferences. It was also necessary to modify the torch position with respect to the ICP-MS interface to overcome them. This fact was likely due to the different extent of ion plasma radial diffusion encountered as a function of the matrix when working at high chamber temperatures. When the torch was moved 1mm plasma down axis, ethanolic and aqueous solutions provided statistically equal sensitivities. A preconcentration procedure has been applied in order to validate the methodology. It has been found that, under optimum conditions from the point of view of matrix effects, recoveries for spiked samples were close to 100%. Furthermore, analytical concentrations for real samples following the preconcentration method and the direct determination were not significantly different. The quantification method was finally based on external calibration with standards containing 50% (v/v) ethanol content.

The determination of 22 natural brassinosteroids in a minute sample of plant tissue by UHPLC-ESI-MS/MS.

The triterpenoid plant hormones brassinosteroids (BRs) are believed to influence almost every aspect of plant growth and development. We have developed a sensitive mass spectrometry-based method for the simultaneous profiling of twenty-two naturally occurring brassinosteroids including biosynthetic precursors and the majority of biologically active metabolites. Using ultra-high performance liquid chromatographic (UHPLC) analysis, the run time was reduced up to three times (to 9min) in comparison to standard HPLC BRs analyses, the retention time stability was improved to 0.1-0.2% RSD and the injection accuracy was increased to 1.1-4.9% RSD. The procedures for extraction and for two-step purification based on solid-phase extraction (SPE) were optimised in combination with subsequent UHPLC analysis coupled to electrospray ionisation tandem mass spectrometry (ESI-MS/MS) using Brassica flowers and Arabidopsis plant tissue extracts. In multiple reaction monitoring (MRM) mode, the average detection limit for BRs analysed was close to 7pg, and the linear range covered up to 3 orders of magnitude. The low detection limits for this broad range of BR metabolites enabled as little as 50mg of plant tissue to be used for quantitative analyses. The results of determinations exploiting internal standards showed that this approach provides a high level of practicality, reproducibility and recovery. The method we have established will enable researchers to gain a better understanding of the dynamics of the biosynthesis and metabolism of brassinosteroids and their modes of action in plant growth and development.

Raman Spectroscopy as a Real-Time In Situ Analyzer for Cell Culture Bioprocesses

The development of fast and reliable methods for protein determination are of great relevance to a diversity of areas from industry to diagnostics. Molecular Imprinted Materials (MIM) has proved to be an interesting methodology for protein analysis however further studies of the effect of the experimental parameters and starting materials in the performance of the MIM are still required. Caffeic acid (CAF) is employed for the first time as a monomer to tailor a synthetic receptor for a protein target. This was done by bulk-electropolymerization, applying a constant potential of +2.0 V, for 30 s, on a carbon screen-printed electrode, immersed in a solution of protein and CAF prepared in phosphate buffer. Annexin A3 (ANXA3) was selected as protein target due to the fact that this is an emerging biomarker in prostate cancer.The assembly of the protein imprinted material (PIM) was followed by Electrochemical Impedance Spectroscopy (EIS) and Raman Spectroscopy. A non-imprinted material (NIM) was prepared in parallel as control.Square wave voltammetry (SWV) was used to monitor the electrochemical signal of the [Fe(CN)6]3−/[Fe(CN)6]4− redox for the quantification of ANXA3.The optimized PIM-based device showed average detection limits (LOD) of 0.095 ng/mL, a linear behavior against log (concentration) between 0.10, and 200 ng/mL and good selectivity. The NIM-based device showed random behavior against protein concentration. Finally, the PIM-sensor was successfully applied to the analysis of ANXA3 in spiked urine samples.

Protein Imprinted Material electrochemical sensor for determination of Annexin A3 in biological samples

The development of fast and reliable methods for protein determination are of great relevance to a diversity of areas from industry to diagnostics. Molecular Imprinted Materials (MIM) has proved to be an interesting methodology for protein analysis however further studies of the effect of the experimental parameters and starting materials in the performance of the MIM are still required. Caffeic acid (CAF) is employed for the first time as a monomer to tailor a synthetic receptor for a protein target. This was done by bulk-electropolymerization, applying a constant potential of +2.0V, for 30s, on a carbon screen-printed electrode, immersed in a solution of protein and CAF prepared in phosphate buffer. Annexin A3 (ANXA3) was selected as protein target due to the fact that this is an emerging biomarker in prostate cancer.The assembly of the protein imprinted material (PIM) was followed by Electrochemical Impedance Spectroscopy (EIS) and Raman Spectroscopy. A non-imprinted material (NIM) was prepared in parallel as control.Square wave voltammetry (SWV) was used to monitor the electrochemical signal of the [Fe(CN)6]3−/[Fe(CN)6]4− redox for the quantification of ANXA3.The optimized PIM-based device showed average detection limits (LOD) of 0.095ng/mL, a linear behavior against log (concentration) between 0.10, and 200ng/mL and good selectivity. The NIM-based device showed random behavior against protein concentration. Finally, the PIM-sensor was successfully applied to the analysis of ANXA3 in spiked urine samples.

Emergence of Sub-Clonal Drug Resistance Mutations during CML Therapy

▪Tyrosine kinase inhibitors (TKIÕs) vastly improve survival in chronic myeloid leukemia (CML). However resistance is a common occurrence, and is most frequently mediated by point mutations in the Abl kinase. There have been conflicting reports regarding the frequency of resistance mutations in the Abl kinase at the time of CML diagnosis, with some studies indicating that a large number of resistance mutations are pre-existing in many patients. However, a high burden of pre-existing resistance mutations is seemingly at odds with the ability of TKIÕs to initially control CML for months to years in the large majority of patients.Nearly all prior studies have used dozens of cycles of PCR amplification to enrich the Abl gene prior to mutation detection. PCR amplification introduces thousands of errors throughout the gene, which makes accurate identification of mutations challenging. Methods of mutation detection such as next-generation sequencing (NGS) are also error prone, with a background error rate near 1%. These high rates of background mutation render accurate detection of minority variants difficult or impossible.We have developed an alternate DNA mutation detection method, termed Duplex Sequencing (Schmitt MW et al, Nature Methods 2015;12:423-425), which improves on the accuracy of DNA sequencing by >100,000 fold. In Duplex Sequencing, the two strands of single DNA molecules are individually tagged and sequenced. True mutations are present at the same position in both strands and are complementary, whereas artifacts arising from amplification or sequencing errors are seen in only one strand and are not scored. We have additionally developed methods for >1,000,000 fold enrichment of the Abl gene from human cells. This enrichment protocol allows for unbiased detection of all possible mutations throughout the Abl gene, with an accuracy exceeding 99.9999%.We applied Duplex Sequencing to 18 patients with newly diagnosed chronic phase CML (CP-CML). We sequenced the active site exons of Abl from tens of thousands of individual CML genomes; no sub-clonal resistance mutations were seen in any patient. We demonstrate that prior reports indicating frequent resistance mutations at the time of CML diagnosis may be attributable to artifactual mutations introduced by reverse transcription and PCR amplification.We are now studying patients from the PACE trial (Cortes JE et al. N Engl J Med. 2013;369:1783-1796); these patients were heavily pre-treated, with the majority having received 3 or more prior TKIÕs. We identified 29 patients from the trial with a treatment-emergent mutation not detectable at baseline by conventional methods (NGS or Sanger), and have performed Duplex Sequencing on 9 of these patients to date. In contrast to treatment-naïve patients, we find that these heavily pre-treated patients commonly harbor multiple co-existing resistant sub-clones, most of which fall below the detection limit of conventional methods but are readily detected by Duplex Sequencing. In addition, in 44% of patients, mutations that emerged during ponatinib treatment were found as rare sub-clones at baseline (average detection limit of 1 in 11,412 cells), indicating that the mutant sub-clones pre-existed prior to ponatinib therapy. We are now sequencing the remainder of the cohort, and are increasing our detection limit through interrogation of a larger number of cells per patient.Our results indicate the feasibility of detecting sub-clonal resistance mutations at the time of initiation of next-line TKI therapy in order to guide treatment, and argue that high-sensitivity methods for mutation detection are required to optimally stratify patients to the most appropriate TKI. Moreover, our approach can detect sub-clonal mutations in any gene, and could be broadly applicable for identification of sub-clonal drug resistance mutations relevant to other targeted therapies. [Display omitted] DisclosuresPritchard:ARIAD: Employment, Equity Ownership. Hodgson:ARIAD Pharmaceuticals: Employment, Equity Ownership. Rivera:ARIAD: Employment, Equity Ownership.

Surface Termination Effect of Boron‐Doped Diamond on the Electrochemical Oxidation of Adenosine Phosphate

AbstractElectrochemical oxidation of adenosine phosphates, including adenosine 5′‐monophosphate (AMP), adenosine 5′‐diphosphate (ADP), and adenosine 5′‐triphosphate (ATP), have been studied using boron‐doped diamond (BDD) electrodes. Cyclic voltammograms in phosphate buffer solution pH 7.4 showed a typical oxidation peak at the potential of around +1.3 V (vs. Ag/AgCl) attributable to the oxidation of adenine base moiety. This peak appears at both cathodically and anodically treated BDD. However, investigation at low pH showed, whereas the oxidation peak could be well observed for the oxidation of each AMP, ADP, and ATP at cathodically treated BDD, it was only found for the oxidation of AMP at anodically‐treted BDD electrodes. Linear calibration curve can be achieved in the concentration range of 20 to 200 μM with an average detection limit of 2 μM (S/N=3). Furthermore, cathodic treatment has demonstrated its ability to maintain the electrode surface from biofouling, resulting in the excellent stability of current responses.

A sensitive non-derivatization method for apramycin and impurities analysis using hydrophilic interaction liquid chromatography and charged aerosol detection

A sensitive non-derivatization method was developed for the analysis of apramycin and impurites using hydrophilic interaction liquid chromatography (HILIC) and charged aerosol detection (CAD). Sample was pretreated with an effective SPE method (recovery >90%) to remove interference with apramycin impurities from sulfate, then analyzed with direct injection. Different chromatography modes of separation and choices of HILIC column were investigated in search of a direct analysis method. The HILIC-CAD method was optimized using a cysteine-bonded zwitterionic HILIC column and compared to the strong cation exchange-ultraviolet (SCX-UV) method with post-column derivatization recommended by the Chinese Pharmacopoeia (veterinary) 2010. The improved chromatographic resolution and peak shape with the HILIC-charged aerosol detection method allows for increase of sample load to 48.9µg from only 2.8µg with the SCX-UV approach. More than 16 impurities were detected with this method with improved resolution, and four were identified with MS, while only 7 impurities were detected with the SCX-UV method. Moreover, the current method has a good precision and reproducibility. The intra-day and inter-day of peak area variability was less than or equal to 4.760% RSD and 9.950%, respectively. The average limit of detection and quantization was 80ng and 200ng injected on the column, respectively. The overall results demonstrated that the presented method can be used as an alternative to SCX-UV method in the analysis of apramycin and impurities.

A switchable reagent ion high resolution time-of-flight chemical ionization mass spectrometer for real-time measurement of gas phase oxidized species: characterization from the 2013 southern oxidant and aerosol study

Abstract. A novel configuration of the Aerodyne high resolution time-of-flight chemical ionization mass spectrometer (HR-TOF-CIMS) as a switchable reagent ion (SRI) HR-TOF-CIMS is presented and described along with data collected at the Southern Oxidant and Aerosol Study (SOAS) during the summer of 2013. The calibration system and reduced pressure gas phase inlet are characterized. The average limit of detection and limit of quantification for formic acid during SOAS are 82 and 863 ppt, respectively, corresponding to an average sensitivity of 13 ± 5 Hz ppt−1. Hourly background determinations and calibrations are shown to be essential for tracking instrument performance and accurately quantifying formic acid. Maximum daytime formic acid concentrations of 10 ppb are reported during SOAS, and a strong diel cycle is observed leading to nighttime concentrations below the limit of quantification. Other species presented exhibit diel behavior similar to formic acid. The concept of the mass defect enhancement plot and the use of signal-to-noise are described in detail as a method for investigating HR-TOF-CIMS spectra in an effort to reduce data complexity.