Photolysis-assisted, long-path FT-IR detection of air pollutants in the presence of water and carbon dioxide

Seven important air pollutants have been investigated by photolysis-assisted FT-IR spectroscopy. This technique renders invisible the spectra of water and carbon dioxide, which are two of the main concerns in long-path infrared spectroscopy. A cell, equipped with a UV lamp, was used to oxidise the analyte in the air sample and the spectrum recorded was used as a new background for the original sample spectrum. The optimum UV irradiation time and correctness of the concentrations were determined for this technique and compared with those from traditional methods. The signal-to-noise (S/N) ratios of the so-called “shadow spectra” were better than, or at least comparable to, the S/N ratios in the absorbance spectra obtained by using as background an air or an evacuated cell reference and subtraction of the spectra of water and carbon dioxide from a spectral library. The detection limits for the volatile organic compounds investigated have been improved by using this new method in which an appropriate background spectrum can be obtained quickly. The limitations of the method are that it cannot be applied to non-UV reactive compounds, such as methane, and the detection limits can be appreciably degraded when bands due to ozone in the shadow spectra overlap with those of the compounds under investigation.     

Figures of merit of pneumatic and ultrasonic sample introduction systems in inductively coupled plasma–multichannel-based emission spectrometry in an ultra-clean environment

Conventional figures of merit such as limits of detection, signal to background ratio or repeatability, are used to determine the performance of pneumatic and ultrasonic sample introduction systems in an ultra-clean environment with an axially viewed inductively coupled plasma-atomic emission spectrometry and multichannel detection. We observed that the ultrasonic nebuliser offered a large improvement of signal intensity (10-133 greater) compared to a cyclone chamber coupled with a pneumatic Meinhard nebuliser. This improvement is associated with an average increase of signal to background ratio by a factor 86 and an average decrease of detection limits by a factor 6. The improvement factors generally depend on the element and for the same element on spectral lines. Typically, the observed values of detection limits in this work are lower than those published and obtained in non-ultra-clean conditions. The results emphasize that the environmental conditions of cleaning and analysis are essential to avoid and control cross contamination of the samples and hence to obtain low detection limits.     

毛细管电泳-量子点间接激光诱导荧光检测5种食品防腐剂

以碲化镉量子点为荧光背景物质,建立了毛细管电泳-间接激光诱导荧光检测食品中对羟基苯甲酸丙酯、脱氢乙酸钠、山梨酸、苯甲酸和丙酸钠含量的方法,紫外吸收很弱的丙酸钠在本方法中显示为正峰,可被有效检出.研究了碲化镉量子点浓度、背景电解质浓度、pH值、分离电压对分析物峰高和迁移时间的影响.在最佳条件下,对羟基苯甲酸丙酯、脱氢乙酸钠、山梨酸、苯甲酸和丙酸钠在8.5 min内得到分离,检出限分别为0.21,0.32,0.50,0.30和0.36 mg/L,相对标准偏差分别为3.9％,2.1％,2.5％,1.9％和2.3％,平均加标回收率分别为96.8％,93.4％,96.3％,98.1％和99.1％.本方法的检出限及线性范围均优于文献报道结果,对食品中这5种防腐剂检测的结果与高效液相色谱法结果一致.     

Comparison of synchrotron radiation total reflection X-ray fluorescence excitation–detection geometries for samples with differing matrices

The linear polarization of synchrotron radiation (SR) in the orbital plane leads to a background reduction in total reflection X-ray fluorescence (TXRF) analysis if a side-looking detector is used. The optimum orientation of the sample carrier in a SR-TXRF experiment, however, is determined by a trade-off between the exploitation of the linear polarization, the efficiency of excitation and the solid angle of detection and depends on the nature and size of the sample. SR-TXRF measurements on different sample types and using different reflector orientations have been carried out at the Hamburger Synchrotronstrahlungslabor bending magnet beamline L. A NIST standard water sample, a steel sample and an oil standard were analyzed with both a horizontal and a vertical sample carrier orientation. Strongly scattering samples led to lower detection limits with a horizontal reflector whereas weakly scattering samples showed lower detection limits with a vertical reflector configuration. On an intentionally contaminated wafer absolute detection limits of 6.6 fg for Ni could be extrapolated.     

The function of radon in curing respiratory diseases in the therapeutic cave of Tapolca

For the evaluation of the detection and measurement limits for gamma-spectrometry measurements formulas were elaborated assuming the presence of the background component, which correlates with the analytical peak in the sense of: (1) linear relation between the expectation value of the peak and background counts, and (2) statistical correlation between peak and background counts. It is shown that neglecting the correlated background component can lead to a significant overestimation of the detection and measurement limits. The problem of evaluating of the correlated background component by applying experimental and computational approaches is also considered.     

Improved detectability and signal strength for rotating phase fluorescence immunoassays through image processing

Fluorescence immunoassays based on rotating solid phase have shown promise of lowered detection limits, among other advantages. However, intrinsic background distortion effects have limited their utility. Here, novel image processing strategies are used to minimize these effects and improve the estimate of concentration and lower the detection limit. This initial demonstration of a new processing capability is performed on data for a protein, myoglobin, which is a biomarker for acute myocardial infarction. For these data, compared with published results, the detection limit is improved by a factor of approximately one hundred (to 700 fM), which is competitive with or better than other immunoassay strategies (ELISA, for example) that are fully developed. This work suggests that image and video processing technologies can provide a valuable alternative approach to biochemical detection and concentration estimation.     

Optimization of operating conditions for the determination of perchlorate in biological samples using preconcentration/preelution ion chromatography

Perchlorate originates as a contaminant in the environment from the use of salts in the manufacture of solid rocket fuels and munitions. Monitoring potential perchlorate contamination in the environment is of interest, however, very few analytical methods have been developed for perchlorate determination in biological samples. Analysis of complex samples by ion chromatography is complicated by matrix components that can interfere with perchlorate determination. However, a recently developed preconcentration/preelution (PC/PE) ion chromatography method has demonstrated the capability to analyze certain complex samples such as high salinity water, milk, and hydroponic fertilizers. The ability of this method to reduce sample background and lower detection limits in ion chromatography for various biological samples was evaluated in this study. The PC/PE method was applicable to the analysis of kidneys, livers, zebrafish, quail eggs, lettuce, and urine. Optimal operating conditions were determined for each matrix. Ranges of optimal wash volumes were shorter when 15 mM NaOH prewash solutions were used compared with 10mM and good recovery was achieved for most matrices with an injection period > or =60s. Prewash solution concentration did not appear to significantly affect matrix background. The PC/PE method was capable of reducing sample background when compared to EPA Method 314.0, which resulted in detection limits, with the exception of zebrafish and urine, that were two-fold lower than those achieved with EPA Method 314.0.     

Urinary selenium speciation by high-performance liquid chromatography-inductively coupled plasma mass spectrometry: advantages of detection with a double-focusing mass analyser with a hydride generation interface

A detailed comparison of the performance of inductively coupled plasma mass spectrometry (ICP-MS), with quadrupole and double-focusing instruments for the speciation of selenium in urine has been carried out. Selenium sensitivity about 23-59 times higher with double-focusing ICP-MS detection was observed, but limits of detection were only 1-8.7 times better because of background noise. Selenium species separation has been carried out by both reversed-phase and vesicle-mediated high-performance liquid chromatography (HPLC), coupled on-line with the detector via conventional nebulization and via on-line focused microwave digestion-hydride generation. A remarkable improvement in sensitivity (28-110 times better for (77)Se depending on the chromatographic system) and elimination of interference problems from the urinary matrix or the components of the mobile phases were achieved when an on-line microwave digestion-hydride generation interface was used, but the background noise was much higher than with conventional nebulization. Therefore, the limits of detection were not as low as expected from such improvement in the sensitivity. More selenocompounds can be separated, and a slight improvement in the sensitivity and limits of detection was obtained when the vesicle-mediated HPLC system was used as compared with reverse-phase chromatography. However, the use of several complementary chromatographic systems, such as reverse-phase HPLC, is recommended to bring some light on the selenocompounds present in basal human urine. Comparative data of rat urine speciation are also given.     

Studies on the long-term stabilities of the background of radionuclides in inductively coupled plasma mass spectrometry (ICP-MS)

The long-term stabilities of the ICP-MS background of nine radionuclides are studied, of which the signals are partially superimposed by polyatomic interferences or affected from carry-over and memory effects. The background generated by the ICP flame, by two pure waters, and by nitric acid (2% v/v) was investigated in detail. A minimum of 50 measurement points was used for each long-term investigation. The detection limits of the radionuclides of the masses 90 amu ((90)Sr: 30 Bq/mL), 99 amu ((99)Tc: 4 mBq/mL), 238 amu ((238)U: 10 nBq/mL), and 244 amu ((244)Pu: 0.6 microBq/mL) are calculated from the mean standard deviation of the background signals. For all nine radioisotopes, the calculated detection limits are between 0.8 and 6 pg/mL. While the detection limit of the mass 90 amu is blank limited, those of the mass 99 amu and the actinides are totally uneffected by the blank solutions. The detection limits are compared with those given in literature.     

Potentials of Electron Probe Microanalysis in Studying Zircons

Potentials of electron probe microanalysis in determining hafnium, uranium, thorium, lead, niobium, titanium, manganese, iron, chromium, calcium, aluminum, tin, tungsten, yttrium, and lanthanide impurities in zircons have been studied. It was found that the background signal depends on the composition of the zircon crystal, including the concentration of hafnium. Methods have been proposed to improve the measurements of the background intensity and to optimize analytical conditions for attaining the lowest detection limits.     

Determination of diphenylmethane antihistaminic drugs and their analogues in body fluids by gas chromatography with surface ionization detection.

Eleven diphenylmethane antihistaminic drugs and their analogues were tested for their detection by capillary gas chromatography (GC) with surface ionization detection (SID). The GC-SID response was highest for doxylamine, diphenhydramine and orphenadrine and lowest for terodiline, clemastine and pipethanate. The detection limits for drugs with the highest response were 2-5 pg (ca. 6-20 fmol) on-column (100-250 pg/ml of body fluid). The detection limits with GC-SID were 10-100 times higher than those with GC with nitrogen-phosphorus detection. A detailed procedure for the isolation of the antihistaminics from human whole blood and urine by the use of Sep-Pak C18 cartridges, prior to GC-SID, is also presented. The recoveries of the drugs (50 or 500 pmol), which had been added to 1 ml of body fluids, were > 60%. The baselines remained steady as the column temperature was increased and the background was clean, especially for whole blood extracts.     

Development of a procedure for measuring nitrogen by cold neutron prompt gamma-ray activation analysis

An instrument for cold neutron prompt gamma-ray activation analysis (CNPGAA) has been used for the nondestructive determination of nitrogen. The samples were analyzed in an evacuated box to minimize background from neutron capture by atmospheric nitrogen. The system features lower background and lower detection limits than obtainable with the University of Maryland-National Institute of Standards and Technology (NIST) thermal neutron PGAA instrument. CNPGAA has been used to measure nitrogen in standard reference materials which included biological materials and soils; the results are in agreement with certified values. The detection limit for nitrogen in most biological and geological samples is near 1000 mg kg-1.     

Performance and selectivity of polymeric pseudostationary phases for the electrokinetic separation of amino acid derivatives and peptides

Two polymeric pseudostationary phases, one an acrylamide polymer and the second a siloxane polymer, have been investigated for the separation of naphthalene-2,3-dicarboxaldehyde (NDA)-derivatized amino acids and small peptides. The dervatized amino acids were detected by UV absorbance and laser-induced fluorescence (LIF) detection. The polymers provided very high efficiency and good selectivity for the separation of the amino acids. The separation selectivity using the polymers was significantly different from that of SDS micelles, and there were subtle differences in selectivities between the polymers. Although very good detection limits were obtained with LIF detection, a significant background signal was observed when the polymers were not washed to remove fluorescent impurities. The polymers did not separate the peptides very well. It is postulated that the fixed covalent structure of the polymers prevents them from interacting strongly or efficiently with the peptides, which are large in relation to the analytes typically separated by electrokinetic chromatography using polymers.     

Immunoanalytical techniques for pesticide monitoring based on fluorescence detection

In the field of environmental analysis there is still great potential for development and application of immunoanalytical techniques (IT). Heterogeneous and homogeneous immunoassays (IA), flow-injection immunoanalysis (FIIA) and immunosensors (IS) with different detection principles have been developed. In this review we focus on fluorescence methods for pesticide monitoring published since 1992. These techniques offer a high degree of selectivity and, in principle, sensitivity. Restrictions on the limits of detection (LOD) due to background signals are minimized by development of solid-phase separation systems, new fluorescent probes, and new instrumentation.     

Liposomes in analyses

The use of liposomes as analytical and bioanalytical reagents has been shown to be successful of in a variety of different applications that will be reviewed here. Due to their high surface area, large internal volume, and ability to conjugate bilayer lipids with a variety of biorecognition elements liposomes have been used in homogenous and heterogeneous assays, providing signal amplification both as intact or lysed vesicles. This review covers the discussion of their application in recent liposome-based immunoassay publications and includes the growing number of other non-immunoassay applications as an evidence of their immense versatility. In this article, a general background about liposomes is given first that extends past the use of liposomes as analytical tools. The main discussion is then divided by the manner in which liposomes are utilized as signaling reagents for the assays. Where available, the detection limits for common analytes that have been assayed using multiple liposome-based detection systems are presented. The advantages of using liposomes in terms of sensitivity versus other techniques are also discussed.     

Immunoanalytical techniques for pesticide monitoring based on fluorescence detection

In the field of environmental analysis there is still great potential for development and application of immunoanalytical techniques (IT). Heterogeneous and homogeneous immunoassays (IA), flow-injection immunoanalysis (FIIA) and immunosensors (IS) with different detection principles have been developed. In this review we focus on fluorescence methods for pesticide monitoring published since 1992. These techniques offer a high degree of selectivity and, in principle, sensitivity. Restrictions on the limits of detection (LOD) due to background signals are minimized by development of solid-phase separation systems, new fluorescent probes, and new instrumentation.     

Laser-excited atomic-fluorescence spectrometry in an electrothermal atomizer with Zeeman background correction

A pulsed excimer-pumped dye laser was used to excite atomic flourescence in graphite tube electrothermal atomizer. A 60-Hz ac magnitude field was applied around the atomizer and parallel to the excitation beam, for Zeeman background correction. The correction system was found to degrade the detection limits for silver, cobalt, indium, manganese, lead, and thallium by a factor of between 1 and 10. An increase in magnetic field strength, or a decrease in laser linewidth, should improve the detection limits, but was not possible here. For copper, the application of Zeeman background correction was unsuccessfull because the instrumentation was unable to resolve the sigma components from the laser emission profile sufficiently during the background correction measurement. For elements that exhibit sufficient Zeeman splitting, the linear dynamic range was the same with or without background correction Zeeman background correction was used to correct for scatter, in the resonance flourescence determination of manganese in a zinc chloride matrix and in mouse brain tissue.     

Laboratory and synchrotron radiation total-reflection X-ray fluorescence: new perspectives in detection limits and data analysis

Having established detection limits for transition elements exceeding current requirements of the semiconductor industry, our recent efforts at the Stanford Synchrotron Radiation Laboratory (SSRL) have focused on the improvement of the detection sensitivity for light elements such as Al. Data analysis is particularly challenging for Al, due to the presence of the neighboring Si signal from the substrate. Detection limits can be significantly improved by tuning the excitation energy below the Si–K absorption edge. For conventional TXRF systems this can be done by using a W–Mα fluorescence line (1.78 keV) for excitation. At a synchrotron radiation facility energy tunability is available. However, in both cases this results in a substantial increase in background due to resonant X-ray Raman scattering. This scattering dominates the background under the Al Kα fluorescence line, and consequently limits the achievable sensitivity for the detection of Al surface contaminants. In particular, we find that for a precise determination of the achievable sensitivity, the specific shape of the continuous Raman background must be taken into account in the data analysis. The data deconvolution presented here opens a new perspective for conventional TXRF systems to mitigate this background limitation. This results in a minimum detection limit of 2.4×10⁹ atoms/cm² for Al. Based on these results it will also be demonstrated that by improving the detector resolution, the minimum detection limit can be improved significantly. For a detector resolution of 15 eV as predicted for novel superconducting tunnel junction detectors, an improvement in minimum detection limit of approximately a factor of 3 can be estimated.     

Activatable Molecular Probes for Second Near‐Infrared Fluorescence,Chemiluminescence, and Photoacoustic Imaging

Optical imaging plays a crucial role in biomedicine. However, due to strong light scattering and autofluorescence in biological tissue between 650–900 nm, conventional optical imaging often has a poor signal‐to‐background ratio and shallow penetration depth, which limits its ability in deep‐tissue in vivo imaging. Second near‐infrared fluorescence, chemiluminescence, and photoacoustic imaging modalities mitigate these issues by their respective advantages of minimized light scattering, eliminated external excitation, and ultrasound detection. To enable disease detection, activatable molecular probes (AMPs) with the ability to change their second near‐infrared fluorescence, chemiluminescence, or photoacoustic signals in response to a biomarker have been developed. This Minireview summarizes the molecular design strategies, sensing mechanisms, and imaging applications of AMPs. The potential challenges and perspectives of AMPs in deep‐tissue imaging are also discussed.