Comparison Of Detection Limits Research Articles

Quantitative analysis of polycyclic aromatic hydrocarbons using high-performance liquid chromatography-photodiode array-high-resolution mass spectrometric detection platform coupled to electrospray and atmospheric pressure photoionization sources.

Polycyclic aromatic hydrocarbons (PAHs) are common pollutants present in atmospheric aerosols and other environmental mixtures. They are of particular air quality and human health concerns as many of them are carcinogenic toxins. They also affect absorption of solar radiation by aerosols, therefore contributing to the radiative forcing of climate. For environmental chemistry studies, it is advantageous to quantify PAH components using the same analytical technics that are commonly applied to characterize a broad range of polar analytes present in the same environmental mixtures. Liquid chromatography coupled with photodiode array and high-resolution mass spectrometric detection (LC-PDA-HRMS) is a method of choice for comprehensive characterization of chemical composition and quantification of light absorption properties of individual organic compounds present in the environmental samples. However, quantification of non-polar PAHs by this method is poorly established because of their imperfect ionization in electrospray ionization (ESI) technique. This tutorial article provides a comprehensive evaluation of the quantitative analysis of 16 priority pollutant PAHs in a standard reference material using the LC-MS platform coupled with the ESI source. Results are further corroborated by the quantitation experiments using an atmospheric pressure photoionization (APPI) method, which is more sensitive for the PAH detection. The basic concepts and step-by-step practical guidance for the PAHs quantitative characterization are offered based on the systematic experiments, which include (1) Evaluation effects of different acidification levels by formic acid on the (+)ESI-MS detection of PAHs. (2) Comparison of detection limits in ESI+ versus APPI+ experiments. (3) Investigation of the PAH fragmentation patterns in MS2 experiments at different collision energies. (4) Calculation of wavelength dependent mass absorption coefficient (MACλ) of the standard mixture and its individual PAHs using LC-PDA data. (5) Assessment of the minimal injected mass required for accurate quantification of MACλ of the standard mixture and of a multi-component environmental sample.

Sensitivity analysis towards trace-uranium detection with γ-γ coincidence NAA

We present an improved approach for detection of trace amounts of 238U by means of neutron activation analysis (NAA). The analysis enhancement is obtained by utilizing γ-γ coincidence counting. An empirical method for evaluating the sensitivity gain in the presence of a large source-related background is presented. A comparison of detection limits is made between two counting schemes; namely, counting single gammas using one HPGe detector versus counting coincident gammas using two HPGe detectors placed face-to-face. A data-validated radiation transport model, created in GEANT4 for a single HPGe detector, is extended to handle the two-detector setup. In this counting scheme, a 238U-detection sensitivity enhancement of about a factor of 8 is predicted for a sample of Saint-Gobain G3 Sapphire when compared to the simpler singles counting approach.

Development of a quantitative real time RT-PCR assay for sensitive and rapid detection of emerging Atypical Porcine Pestivirus associated with congenital tremor in pigs

Atypical Porcine Pestivirus (APPV) is reported as the etiologic agent for type AII congenital tremors in newborn piglets. Initial PCR-based diagnostic tests to detect APPV were designed based on the limited sequence information and are not capable of detecting the majority of APPV strains. A sensitive and reliable PCR-based diagnostic test is critical for accurate detection of APPV. In this study, a quantitative reverse transcription PCR (RT-qPCR) assay was developed for reliable detection of all currently known APPV strains. The assay design also included swine 18S rRNA gene as an internal control to monitor RNA extraction efficiency. Two APPV gene fragments, one each from NS5b and NS3, were cloned and used to determine the dynamic range of detection, linearity and analytical sensitivity/limit of detection (LOD). Both individual and multiplex assays (duplex and triplex) had correlation coefficients of >0.99 and PCR amplification efficiencies of >90 %. Comparison of detection limit and analytical sensitivity between individual, and multiplex assays indicated no inhibition of PCR sensitivity upon multiplexing. The detection limit for APPV target, based on analytical sensitivity, is 7.75 copies (NS5b) and 5.2 copies (NS3) per reaction. Assay specificity was verified by testing nucleic acids of other closely related pestiviruses and clinical samples that are positive for other common swine pathogens. Assay sensitivity was also assessed on synthesized gene fragments of the most divergent China strains. Testing 339 known APPV-positive and 202 negative clinical samples demonstrated a good diagnostic sensitivity and specificity. Data from six independent runs, including 5 replicates of three clinical samples with three Ct ranges, were utilized to assess inter-assay repeatability and intra-assay reproducibility. This analysis demonstrated intra-assay/inter-assay coefficients of variation of 0.71 % and 0.01 %, respectively, with a PCR efficiency of 92.71 % for the triplex assay. Testing of 1785 clinical samples revealed ∼19 % prevalence of APPV in the US swine herds and oral fluids demonstrates to be a reliable specimen for viral detection. This multiplex RT-qPCR assay offers a rapid and reliable detection of APPV in swine herds and serves as useful tool in APPV surveillance and epidemiological investigations.

Comparison of detection limit in fiber-based conventional, amplified, and gain-clamped cavity ring-down techniques

Relative performance and detection limit of conventional, amplified, and gain-clamped cavity ring-down techniques (CRDT) in all-fiber configurations are compared experimentally for the first time. Refractive index measurement using evanescent field in tapered fibers is used as a benchmark for the comparison. The systematic optimization of a nested-loop configuration in gain-clamped CRDT is also discussed, which is crucial for achieving a constant gain in a CRDT experiment. It is found that even though conventional CRDT has the lowest standard error in ring-down time (Δτ), the value of ring-down time (τ) is very small, thus leading to poor detection limit. Amplified CRDT provides an improvement in τ, albeit with two orders of magnitude higher Δτ due to amplifier noise. The nested-loop configuration in gain-clamped CRDT helps in reducing Δτ by an order of magnitude as compared to amplified CRDT whilst retaining the improvement in τ. A detection limit of 1.03×10−4 RIU at refractive index of 1.322 with a 3 mm long and 4.5 μm diameter tapered fiber is demonstrated with the gain-clamped CRDT.

Chemical Vapor Generation with Slurry Sampling: A Review of Applications to Atomic and Mass Spectrometry

A critical review of published analytical methods and techniques for chemical vapor generation (CVG) with slurry sample introduction for detection by atomic and mass spectrometry is presented. The nstrumentation used for the reaction as well as separation and transport of the species, influence of chemical and physical factors, and efficiency of the process are considered. A brief comparison of detection limits obtained with atomic absorption, emission, and fluorescence as well as mass spectrometry along with practical applications to analytical samples are summarized. The current state-of-the-art, including advantages and limitations of this approach, is discussed.

Comparison of detection limits, for two metallic matrices, of laser-induced breakdown spectroscopy in the single and double-pulse configurations

Limits of detection have been studied for several elements in aluminium and steel alloys, at atmospheric pressure in air, by use of the single and collinear double-pulse configurations of laser-induced breakdown spectroscopy. For this purpose, calibration plots were constructed for Mg, Al, Si, Ti, Cr, Mn, Fe, Ni, and Cu using a set of certified aluminium alloy samples and a set of certified steel samples. The investigation included optimization of the experimental conditions to furnish the best signal-to-noise ratio. Inter-pulse delay, gate width, and acquisition delay were studied. The detection limits for the elements of interest were calculated under the optimum conditions for the double-pulse configuration and compared with those obtained under the optimum conditions for single-pulse configuration. Significantly improved detection limits were achieved, for all the elements investigated, and in both aluminium and steel, by use of the double-pulse configuration. The experimental findings are discussed in terms of the measured plasma conditions (particle and electron density, and temperature).

Comparison of detection limits in environmental analysis--is it possible? An approach on quality assurance in the lower working range by verification.

Detection limit, reporting limit and limit of quantitation are analytical parameters which describe the power of analytical methods. These parameters are used for internal quality assurance and externally for competing, especially in the case of trace analysis in environmental compartments. The wide variety of possibilities for computing or obtaining these measures in literature and in legislative rules makes any comparison difficult. Additionally, a host of terms have been used within the analytical community to describe detection and quantitation capabilities. Without trying to create an order for the variety of terms, this paper is aimed at providing a practical proposal for answering the main questions for the analysts concerning quality measures above. These main questions and related parameters were explained and graphically demonstrated. Estimation and verification of these parameters are the two steps to get real measures. A rule for a practical verification is given in a table, where the analyst can read out what to measure, what to estimate and which criteria have to be fulfilled. In this manner verified parameters detection limit, reporting limit and limit of quantitation now are comparable and the analyst himself is responsible to the unambiguity and reliability of these measures.

Synchrotron radiation X-Ray fluorescence at the LNLS: beamline instrumentation and experiments

The x-ray fluorescence heamline of the Laboratorio Nacional de Luz Sincrotron (LNLS) is described. The main optical component of the beamline is a silicon (111) channel-cut monochromator, which can tune energies between 3 and 14 keV. A general description of two experimental stations is given. Beam characterization was done by measuring experimental parameters such as vertical profile and monochromatic flux. These results show that the photon flux at 8 keV in an area of 20 mm 2 is 4.2 × 10 9 photons s -1 . The possibility of achieving fine tuning of energies (high resolution) was confirmed. This paper presents some original results derived from the commissioning of the beamline, such as a comparison of detection limits in different experimental conditions, and a novel mechanical system to align capillaries together with a semi-automatic adjustment procedure. So far, there have been several proposals to perform a variety of experiments at this beamline, covering different fields, such as physics, chemistry, geology and biology.

Effects of preparation methods of biomedical samples on PIXE measurement sensitivity

Instrumental sample preparation techniques for PIXE measurements of human blood serum and bovine muscle were investigated. The techniques studied were direct measurement of a drop, drying on a foil and on an Al cup, lyophilization on a foil, pellet pressing of dried material, microtome sectioning and biopsy preparation. The same serum and muscle were used in each procedure allowing the comparison of detection limits between different methods. The most beneficial technique for both samples was lyophilization and pellet pressing.

Thin-layer chromatography and enzyme inhibition techniques : Introduction

Thin-layer chromatography continues to be an integral part of analytical chemistry because it is versatile, sensitive, simple and rapid. The application of enzymatic methods to thin-layer chromatography is becoming more important. This chromatographic-enzymatic technique has been developed for studies of metabolic pathways of pesticides, residue analyses and forensic chemistry. The discussions deal with the development of chromatographic techniques using encymatic reactions to detect pesticides ad other biologically active compounds, principles of the technique, comparison of detection limits by various methods and enzymes, and practical applications of the technique and methods of quantitation.

Comparison of Detection Limits in Atomic Fluorescence and Absorption Spectroscopy

Abstract Dagnall, Taylor, and West have recently compared detection limits for a number of metals in atomic fluorescence and absorption spectroscopy and have concluded that “atomic fluorescence measurements using an electrodeless discharge tube are inherently more sensitive than those obtainable by atomic absorption measurements”. Likewise West and Williams have compared the two techniques for magnesium2and silver3, using high-intensity hollow-cathode lamps as sources, and have found much lower detection limits in fluorescence than in absorption.