Significant Improvement In Detection Limits Research Articles

A Blood Drying Process for DNA Amplification.

The presence of numerous inhibitors in blood makes their use in nucleic acid amplification techniques difficult. Current methods for extracting and purifying pathogenic DNA from blood involve removal of inhibitors, resulting in low and inconsistent DNA recovery rates. To address this issue, a biphasic method is developed that simultaneously achieves inhibitor inactivation and DNA amplification without the need for a purification step. Inhibitors are physically trapped in the solid-phase dried blood matrix by blood drying, while amplification reagents can move into the solid nano-porous dried blood and initiate the amplification. It is demonstrated that the biphasic method has significant improvement in detection limits for bacteria such as Escherichia coli, Methicillin-resistant Staphylococcus aureus, Methicillin-Sensitive Staphylococcus aureus using loop-mediated isothermal amplification (LAMP) and recombinase polymerase amplification (RPA). Several factors, such as drying time, sample volume, and material properties are characterized to increase sensitivity and expand the application of the biphasic assay to blood diagnostics. With further automation, this biphasic technique has the potential to be used as a diagnostic platform for the detection of pathogens eliminating lengthy culture steps.

A simple filter-based approach to surface enhanced Raman spectroscopy for trace chemical detection

We demonstrate an extremely simple and practical surface enhanced Raman spectroscopy (SERS) technique for trace chemical detection. Filter membranes first trap silver nanoparticles to form a SERS-active substrate and then concentrate analytes from a mL-scale sample into a μL-scale detection volume. We demonstrate a significant improvement in detection limit as compared to colloidal SERS for the pesticide malathion and the food contaminant melamine. The measured SERS intensity exhibits low variation relative to traditional SERS techniques, and the data can be closely fit with a Langmuir isotherm. Thus, due to the simple procedure, the low-cost of the substrates, the quantitative results, and the performance improvement due to analyte concentration, our technique enables SERS to be practical for a broad range of analytical applications, including field-based detection of toxins in large-volume samples.

Metal matrices to optimize ion beam currents for accelerator mass spectrometry

We report experiments designed to help optimize accelerator mass spectrometry (AMS) of 10Be (in the form of BeO) for geochronologic and geomorphologic applications. In many applications, the precision of AMS is restricted by counting statistics for 10Be, which are in turn limited by the intensity of BeO− beam currents. We show that ion beam currents depend strongly on the metal matrix in which BeO is dispersed, on the matrix:BeO ratio, and for some metals, such as Ag, on the depth to which the sample is packed in the AMS cathode. Typical instantaneous Be3+ currents (μA) produced by the LLNL CAMS Cs sputter ion source and measured in a Faraday cup after the accelerator are 7.6 for samples in Ag, 19.9 in Ta, 20.9 in Mo, 21.1 in W, 25.5 in Nb and 27.5 in V. The AMS counting efficiency (ions detected per Be atom loaded) for a routine analysis time (300s) for equimolar mixtures of BeO and matrix is in the range 2×10−4–6×10−4 in the order V>Ta>Mo>W>Nb>Ag. Additionally, an inverse linear correlation between electron affinity of the matrix and beam current is observed, suggesting that the propensity of the metal matrix to attach electrons impacts the ion signal. These data and the process inferences they allow will provide for significant improvements in detection limits for a widely applied geological dating and tracing technique.

Performance of ICP-MS with Hexapole Collision Cell and Application for Determination of Trace Elements in Bio-Assays

The application of a hexapole collision cell in quadrupole based inductively coupled plasma mass spectrometry (HEX-ICP-QMS) was studied systematically in order to characterize the performance of this approach for multielement analysis. Additionally, the performance of different solution introduction systems was studied for use with HEX-ICP-QMS (Platform, Micromass Ltd., Manchester, UK) and the developed methods were applied in the multielement analysis of biological tissue. A significant improvement in detection limits was achieved for ions affected by interferences with argon ions and argon-based molecular ions due to the removal of Ar+ and ArX+ ions (X = H, C, N, O, Ar) as well as for heavy elements (m > 100 u) due to better ion transmission through the hexapole ion guide. Metal oxide ion formation was reduced by up to ten times by the application of hexapole bias potential. Accuracy of the HEX-ICP-QMS measurements was assessed by analyzing standard reference material SRM 1566a Oyster Tissue and comparison with neutron activation analysis. Good agreement of measured trace element concentrations with certified values was found for most elements.

Air quality work at Guelph: GAViM and a traffic tunnel study

The Guelph Aerosol and Visibility Monitoring (GAViM) program presently runs three monitoring sites: two rural sites compatible with the IMPROVE protocol and one urban site mostly for special comparison studies. Fine aerosol is analyzed by the Laser Integrated Plate Method (LIPM), Proton Elastic Scattering Analysis (PESA), Proton Induced X-ray Emission (PIXE) and gravimetric analysis. Air quality data from the presently running sites and from two rural sites operated in the past are available through the WWW. The Guelph Scanning Proton Laboratory also participates in other aerosol programs: PIXE was employed to determine the composition of the ambient aerosol in a Vancouver traffic tunnel, to identify the main emission sources and to make estimates of vehicle emission factors. The PIXE facility was also modified for analysis of size-fractionated samples from the PIXE International Cascade Impactor (PCI) sampler. Significant improvement in detection limits for light elements due to the two-detector PIXE system used in Guelph, was justified particularly because of low air particulate loadings in case of PCI.

Performance of the Packard Tri-Carb® 2770TR/SL Liquid Scintillation Analyzer for 14C Dating

We present results that demonstrate the potential of the Packard Tri-Carb® Model 2770TR/SL for radiocarbon dating. For 2 g of sample benzene, a stable background count rate of 0.307 cpm and a stable counting efficiency of 64.78% were determined using a 13–75 keV counting window. Changes to the mathematical routines for t-SIE (quench indicating parameter) calculation and a reduction in the activity of the external standard have enabled stability of the t-SIE to be achieved, and combined with the use of a suitable balance point counting window; all of these factors give the stability of performance required for 14C dating. Calculations based on the above parameters indicate that the limit of detection for 2 g samples, counted for 5000 min, is >48,900 yr bp. The great advantage of this system is that these data were acquired using inexpensive standard 7-mL low potassium borosilicate glass vials. Vial holders manufactured from BGO reduced the background to 0.15 cpm with a minimum effect on efficiency (64.46% for 13–75 keV). A similar calculation of the limit of detection gave >51,700 bp. The use of the BGO vial holders in other instruments employing time-resolved liquid scintillation counting (TR-LSC) (Models 2250CA and 2260XL) also brought about significant improvements in detection limits.

Methods for Improving the Sensitivity in Atom Trapping Flame Atomic Absorption Spectrometry: Analytical Scheme for the Direct Determination of Trace Elements in Beer

A method is described for the atomic absorption (AA) determination of Ag, Cd, Cu, Fe, In, Mn, Pb, Tl and Zn in beer using an ‘integrated atom trap’ system mounted on a standard AA air–acetylene flame burner. A new design of atom trapping technique that would exceed the operational capabilities of existing arrangements (a water-cooled single or dual silica tube or a double-slotted quartz tube) and permit construction of an ‘integrated trap’ was investigated. A significant improvement in detection limit was achieved compared with that obtained using either of the above atom trapping techniques separately. Rapid, accurate analyses can be achieved using continuous aspiration. The concentration detection limits were 3.0, 5.0, 1.2, 4.0 and 0.1 ng ml–1 for Cu, Fe, Mn, Pb and Zn, respectively, using a 2 min in situ preconcentration time. The relative standard deviations are of the order of 3.0–6.0% for this technique. Basic analytical performance characteristics are also given for Ag, Cd, In and Tl using various designs of atom trap. The designs studied include both slotted tube and single silica tube water-cooled atom traps.

Cold neutron prompt gamma-ray activation analysis at NIST — Recent developments

The cold neutron capture prompt γ-ray activation analysis (CNPGAA) spectrometer located in the Cold Neutron Research Facility (CNRF) at NIST has proven useful for the analysis of hydrogen and other elements in a wide variety of materials. Modifications of the instrument and the CNRF have resulted in improved measurement capabilities for PGAA. The addition of an atmosphere-controlled sample chamber and Compton suppression have reduced γ-ray background and increased signal-to-noise ratio. More recent revisions are expected to yield still further improvement in analytical capabilities. Replacement of the D2O ice cold source with a liquid H2 moderator is expected to yield a 5–10 fold increase in neutron capture rate, and improved neutron and γ-ray shielding will result in further reduction of the background. Other modifications to the instrument allow easier sample mounting and more precise positioning of samples in the neutron beam. Significant improvements in detection limits and analytical accuracy are expected.

Characterization of a spectrally segmented photodiode-array spectrometer for inductively coupled plasma atomic emission spectrometry

The utility of a spectrally segmented photodiode array (PDA) spectrometer (Plasmarray, The Leco Corporation) was examined in its application to inductively coupled plasma atomic emission spectrometry (ICP-AES). The spectrometer employed in this study utilizes a unique optical design, which incorporates a series of dispersion gratings and an optical mask to block undesired portions of the emission spectrum. The final multiplexed spectrum observed at the PDA is highly dispersed (reciprocal linear dispersion of approximately 0.09 nm mm at 300 nm) yet covers a wide spectral range (190–415 nm). Detection limits for several elements (Ag, Al, As, B, Cd, Co, Cr, Cu, Fe, Mg, Mn, Ni, P, Pb, Se, Sn, Ti, V, W and Zn) were determined and found to be better, on average, than those from typical photomultiplier-based instruments. However, as has previously been noted with PDA-based systems, sensitivity was reduced at shorter wavelengths (< 250 nm). No significant improvements in detection limits were observed for signal integration periods greater than 10 s. Detection limits were found to be governed by noise in the measured background signal observed at the PDA, not by random noise associated with diode readout. The susceptibility of the spectrometer to spectral interferences and its capability for simultaneous multielement determinations were also assessed. In addition, the influence of spectral interferences from major elements (Al, Ca, Fe, K, Mg, Na, P, Ti and V) upon the analytical lines of several trace elements was examined. Scattered light from the echelle portion of the spectrometer could become a serious problem for multielement determinations in which both major (Mg) and minor (Cd, Cu and Cr) species were observed simultaneously. The potential vulnerability of the spectrometer to spectral interferences requires that optical masks be designed for specific applications in which potential spectral interferences are carefully considered.

Improvement of detection limits in flow injection analysis

When using a conventional UV/VIS-Spectrophotometer with a large sample compartment as a detector for FIA, flow cells with longer pathlengths can be applied. Despite of a unavoidable band broadening a significant improvement of detection limit can be achieved compared to standard cells. Band broadening is compensated by slight modifications of the manifold, so that the dispersion is in the same range for long path cells and standard flow cells. With a 5 cm flow cell phosphate can be detected down to 0.005 mg/l P.

Dünnschichtchromatographischer screening-test über die hemmeigenschaften von phenylharnstoff-herbiziden gegenüber einigen enzymen

A thin-layer chromatographic screening test for the detection of inhibiting properties of phenylurea herbicides on certain enzymes The possibility of employing a thin-layer chromatographic enzymatic inhibition technique using bovine liver esterase, alkaline and acid phosphatase, trypsin and chymotrypsin, α- and β-amylase, and urease for the detection of phenylurea herbicides is studied. While the untreated substances, with the exception of benzomarc and metoxymarc have some influence on bovine liver esterase, only at high concentrations, identification is possible for most of the herbicides after UV irradiation at concentrations below 1 μg. Both phosphatases in most cases are very strongly inhibited and in some cases UV irradiation brings about significant improvement in detection limits. The proteases trypsin and chymotrypsin are inhibited by only a few phenylureas at high concentrations, chymotrypsin being more sensitive than trypsin. α-Amylase is inhibited by only a few herbicides at high concentrations, while β-amylase is moderately inhibited by all substances. Finally, urease is moderately inhibited too by most of the phenylurea herbicides studied.

Spectroscopy in separated flames—VI: The argon or nitrogen-sheathed nitrous oxide-acetylene flame in atomic-absorption spectroscopy

The separation of the premixed nitrous oxide—acetylene flame at a 50-mm slot burner by sheathing with argon or nitrogen is described. In comparison with the conventional flame, the interconal zone of the hot, slightly fuel-rich separated flames provides better conditions for the maintenance of free atoms of elements which form refractory oxides. Optimum conditions for the determination by atomic-absorption spectroscopy of the elements Al, Be, Ge, Mo, Si, Ti, V and Zr in both separated and conventional flames at the same burner have been established. Significant improvement in detection limits and sensitivities is obtained in the separated flames.