Showing papers on "Detection limit published in 1999"
TL;DR: Concentrations of butyltin compounds measured in blood were less than that affected human natural killer lymphocytes (a primary immune defense against...
Abstract: Residues of butyltin compounds, including mono- (MBT), di- (DBT) and tributyltins (TBT), were measured in human blood collected from central Michigan, U.S.A. MBT, DBT, and TBT were detected in 53, 81, and 70% of the 32 blood samples examined. Concentrations of butyltins were in the order of MBT > DBT ≥ TBT, with total butyltin concentrations ranging from less than the limit of detection to 101 ng/mL. Exposure of humans to butyltin compounds used as stabilizers or as biocides in household articles has been regarded as a source in addition to the ingestion of contaminated foodstuffs. There was no significant difference in concentrations of butyltin compounds between sexes. Concentrations of butyltin compounds did not exhibit pronounced age-dependency, which is different from those observed for persistent pollutants such as polychlorinated biphenyls (PCBs). In general, concentrations of butyltins measured in blood were less than that affected human natural killer lymphocytes (a primary immune defense against...
243 citations
TL;DR: In this paper, the authors investigated the influence of the composition of the internal electrolyte solution on the response of Pb2+ and Ca2+-selective membrane electrodes and showed that the lower detection limit is improved by generating, in the membrane, ionic gradients that lead to a flux of primary ions toward the inner reference electrolyte.
Abstract: The influence of the composition of the internal electrolyte solution on the response of Pb2+- and Ca2+-selective membrane electrodes is investigated. It is shown that the lower detection limit is improved by generating, in the membrane, ionic gradients that lead to a flux of primary ions toward the inner reference electrolyte solution. If the ion flux is too strong, it may cause analyte depletion at the membrane surface and, as a consequence, apparent super-Nernstian response. Such electrodes are not adequate to measure low analyte activities but can be used to determine unbiased selectivity factors. The results are interpreted in terms of a steady-state model, introduced in the companion paper, that describes the influence of concentration gradients generated by ion-exchange and coextraction processes on both sides of the membrane.
225 citations
TL;DR: In this article, the processes determining the lower detection limit of carrier-based ion-selective electrodes (ISEs) are described by a steady-state ion flux model under zero-current conditions.
Abstract: The processes determining the lower detection limit of carrier-based ion-selective electrodes (ISEs) are described by a steady-state ion flux model under zero-current conditions. Ion-exchange and coextraction equilibria on both sides of the membrane induce concentration gradients within the organic phase and, through the resulting ion fluxes, influence the lower detection limit. The latter is shown to improve considerably when very small gradients of decreasing primary ion concentration toward the inner electrolyte solution are created. By merely altering the concentration of the inner electrolyte, detection limits may vary by more than 5 orders of magnitude. Very large gradients, however, are predicted to lead to significant depletion of analyte ions in the outer membrane surface layer and thus to apparent super-Nernstian response. The currently recommended IUPAC definition of the lower detection limit leads to nonrealistic values in such cases. Small changes in the concentration profiles within the memb...
202 citations
TL;DR: This assay allowed the first real-time monitoring of the germination of bacterial spores by continuously quantifying exuded DPA, representing a substantial improvement over previous rapid tests.
Abstract: Delayed gate fluorescence detection of dipicolinic acid (DPA), a universal and specific component of bacterial spores, has been appraised for use in a rapid analytical method for the detection of low concentrations of bacterial spores. DPA was assayed by fluorimetric detection of its chelates with lanthanide metals. The influence of the choice and concentration of lanthanide and buffer ions on the fluorescence assay was studied as well as the effects of pH and temperature. The optimal system quantified the fluorescence of terbium monodipicolinate in a solution of 10 µM terbium chloride buffered with 1 M sodium acetate, pH 5.6 and had a detection limit of 2 nM DPA. This assay allowed the first real-time monitoring of the germination of bacterial spores by continuously quantifying exuded DPA. A detection limit of 104Bacillus subtilis spores ml–1 was reached, representing a substantial improvement over previous rapid tests.
195 citations
TL;DR: Simply by mixing in water, a liphophilic dipeptide, a surfactant, and a fluorophore self-assemble to give a sensor able to detect Cu(II) ions (see scheme).
Abstract: Simply by mixing in water, a liphophilic dipeptide (L), a surfactant (S), and a fluorophore (F) self-assemble to give a sensor able to detect CuII ions (see scheme). Despite the ease of construction, the sensor displays high selectivity and a low detection limit for the target ion. This new modular approach to sensing devices allows easy variations of the components, making optimization of the system very simple and fast.
190 citations
TL;DR: In this paper, the basic electrochemical properties of high quality diamond thin-films (3-6μm thick) are highlighted, and the use of diamond for the voltammetric detection of trace metal ions is also illustrated.
189 citations
TL;DR: In this paper, two digestion procedures have been tested on plant samples for application in the determination of a wide range of major, minor, and trace elements by a combination of inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupling plasma mass spectrometer (ICP-MS).
167 citations
TL;DR: In this paper, a reagent-injection chemiluminescent method for the determination of hydrogen peroxide (H2O2) has been developed, which is based on the catalytic (cobalt (II)) oxidation of luminol by H2O 2 in an alkaline solution.
Abstract: A reagent-injection chemiluminescent method for the determination of hydrogen peroxide (H2O2) has been developed. The method is based on the catalytic (cobalt (II)) oxidation of luminol by hydrogen peroxide in an alkaline solution. One mixed reagent is used for the analysis using the reagent injection method. The mixed reagent is optimized for pH and concentration of luminol and Co2+. Apart from Fe2+, none of the 14 species tested showed interference at their seawater levels. Because Fe2+ oxidation is rapid compared to the rate of decay of hydrogen peroxide, the Fe2+ interference can be eliminated by storing seawater samples for 1 h. The combination of reagents and the adaptation of reagent injection lead to a subnanomolar detection limit. The accuracy of the method is at least 0.42 nM. The precision of the method is 17 pM (for a 0.57 nM sample). The method has been used aboard ship to determine the concentrations of hydrogen peroxide in seawater samples in the open ocean as well as on the continental shelf.
167 citations
TL;DR: A new detection method that uses a six-potential waveform to detect all amino acids without derivatization is described, and results of waveform optimization experiments designed to minimize gradient artifacts and to achieve optimum conditions for the quantitative analysis of common amino acids are presented.
Abstract: This paper describes a new detection method that uses a six-potential waveform to detect all amino acids without derivatization. The detection limits are less than 1 pmol for most of the analytes. The anion-exchange separation uses a ternary gradient with water, 0.25 M sodium hydroxide, and 1.0 M sodium acetate. We present results of waveform optimization experiments designed to minimize gradient artifacts and to achieve optimum conditions for the quantitative analysis of common amino acids. Analytical results for protein hydrolysates are discussed and compared with those obtained by cation exchange followed by ninhydrin derivatization and spectrophotometric detection.
139 citations
136 citations
TL;DR: An ion chromatography system for the determination of glyphosate was described and it was found that the method was simple, rapid, reliable and inexpensive.
TL;DR: A method involving the semirobotic liquid-liquid extraction in deep-well 96-well plates was developed and demonstrated to be robust with high precision and accuracy for the quantitation of the anti-cancer/antiinflammatory drug methotrexate and its major metabolite, 7-hydroxymethotrexate (7OH-MTX) in human plasma.
Abstract: A method involving the semirobotic liquid−liquid extraction (LLE) in deep-well 96-well plates was developed for the quantitation of the anti-cancer/antiinflammatory drug methotrexate (MTX) and its major metabolite, 7-hydroxymethotrexate (7OH-MTX) in human plasma. The extraction time for the sample preparation was relatively short with four 96-well plates (384 samples) prepared in approximately 90 min by one person. The sample extracts were each analyzed within 1.2 min using a positive ion turbo-ionspray selected reaction monitoring liquid chromatography/mass spectrometric (SRM LC/MS) method in which 768 samples were easily analyzed within 22 h (maximum of 820 samples in 24 h). Deuterated internal standards, MTX-d3 and 7OH-MTX-d3, were used. The calibration curves for MTX and 7OH-MTX were linear (R2 > 0.997) and ranged from 0.5 to 250 and 0.75 to 100 ng/mL, respectively. The limit of quantitation (LOQ) for MTX and 7OH-MTX was 0.5 and 0.75 ng/mL, respectively; persistent carryover from the autosampler limit...
TL;DR: In this paper, the authors presented an alternative approach to trace metal determination in liquids in which 1.0 mL of liquid is deposited onto a carbon planchet and then evaporated, thus transforming the liquid analysis to a solid surface analysis.
Abstract: Laser-induced breakdown spectroscopy (LIBS) has been widely pursued for trace elemental determination in gases, solids, and liquids. Application to liquids has proved problematic due to high spatial confinement of the LIBS plasma and rapid quenching of the excited-state emission. This work presents an alternative approach to trace metal determination in liquids in which 1.0 mL of liquid is deposited onto a carbon planchet and then evaporated, thus transforming the liquid analysis to a solid surface analysis. Using optimized excitation and detection conditions, we have identified spectral regions for sensitive detection of 15 metals (Mg, Al, Si, Ca, Ti, Cr, Fe, Co, Ni, Cu, Zn, As, Cd, Hg, Pb). The limit of detection (LOD) for the technique ranged from 10 ppb to 10 ppm for these elements. A 100 ppb LOD represents detection of 130 picograms of metal (approximately 2 picomoles) in a single measurement calculated from the laser spot size on the sample. Scanning electron microscopy (SEM) images and energy-dispersive X-ray (EDX) spectra of the samples provide insight into the observed reproducibility and linearity of the technique for several of the metals studied.
TL;DR: In this article, a micro-total analytical system (μTAS) is described for the determination of nitrite based on its reaction with sulphanilamide to form the diazonium salt which when coupled with N -(1-naphthyl) ethylene diamine yields an azo dye whose absorbance was measured at 526nm.
TL;DR: The materials demonstrated high stability against enzyme-denaturing, leaching, and photobleaching when stored under ambient conditions and direct determination of enzyme-catalyzed neurotoxin hydrolysis is provided by the self-referencing, pH-sensitive dye SNAFL-1.
Abstract: A simple approach is described for preparing poly(ethylene glycol) hydrogel materials with encapsulated seminapthofluorescein (SNAFL)−organophosphorus hydrolase enzyme conjugates. Direct determination of enzyme-catalyzed neurotoxin hydrolysis is provided by the self-referencing, pH-sensitive dye SNAFL-1, whose emission spectrum changes at λ = 550 in response to pH. Using spectrofluorimetry and paraoxon as a model organophosphate, paraoxon concentrations as low as 8 × 10-7 M could be readily detected. On the basis of the signal-to-noise ratio, a detection limit of 16 nM was determined. The materials demonstrated high stability against enzyme-denaturing, leaching, and photobleaching when stored under ambient conditions.
TL;DR: In this article, a novel chemiluminescence flow system for sulfite based on auto-oxidation sensitized by rhodamine 6G in the presence of Tween 80 surfactant micelles is described.
TL;DR: A modified reversed phase-HPLC method with o-phthalaldehyde pre-column-derivatization for determination of N ϵ -carboxymethyllysine in food samples is presented in this paper.
TL;DR: The application of on-line HPLC-UV-APCI (atmospheric pressure chemical ionization) mass spectrometry (MS) coupling for the separation and determination of different carotenoids as well as cis/trans isomers of beta-carotene is reported.
TL;DR: An analytical method using double focusing sector field inductively coupled plasma mass spectrometry (ICP-SMS) for rapid simultaneous determination of 50 elements in digested human blood is described in this paper.
Abstract: An analytical method using double focusing sector field inductively coupled plasma mass spectrometry (ICP-SMS) for rapid simultaneous determination of 50 elements in digested human blood is described. Sample preparation consisted of microwave digestion with nitric acid followed by dilution with ultrapure water. The importance of controlling possible contamination sources at different sample preparation and analysis stages in order to achieve adequate method detection limits (MDL) is emphasised. Correction for matrix effects was made using scandium, indium and lutecium as internal standards. Accuracy of the data for elements suffering from spectral interferences was improved by applying either a high resolution capability of the ICP-SMS or mathematical corrections. Different approaches for accuracy assessment in blood analysis are evaluated. Additional information on trace elements concentration in selected blood reference materials is given. The between-batch precision was assessed from replicate analysis (including sample preparation) of reference materials and was better than 10% RSD for 21 elements and better than 30% RSD for 36 elements under consideration. A statistical summary for results obtained for 31 blood samples from non-exposed subjects is presented. The majority of elements tested was found in the samples at concentrations higher than MDL.
TL;DR: A rapid and sensitive capillary electrophoretic method for analysis of resveratrol in wine was established and it was found that the concentration of trans-res Veratrol ranged from 0.987 to 25.4 micromol/L, whereas the concentration in cis-res veratrol was much lower.
Abstract: A rapid and sensitive capillary electrophoretic method for analysis of resveratrol in wine was established. The protocol consists of sample preparation using a C-18 solid-phase extraction cartridge. Baseline separation of trans- and cis-resveratrol from other compounds in wine was achieved in ∼8 min using a micellar mode. The limits of detection for trans- and cis-resveratrol were 0.1 and 0.15 μmol/L, respectively. Recovery rates for trans-resveratrol using the protocol described ranged from 94.6 ± 8.5 to 101.9 ± 7.2%. These procedures were used to analyze the trans- and cis-resveratrol levels in 26 wines. It was found that the concentration of trans-resveratrol ranged from 0.987 to 25.4 μmol/L, whereas the concentration of cis-resveratrol was much lower. Keywords: Resveratrol; wine; capillary electrophoresis
TL;DR: Comparative analysis of 28 naturally or artificially contaminated wheat samples using DONtest-HPLC and the GC-ECD method of Tacke and Casper showed that DON test-HP LC is a statistically significant predictor of the GC -ECD method.
TL;DR: The reversed-phase HPLC assay coupled with electrochemical detection for simultaneously measuring plasma levels of norepinephrine, epinephrine, dopamine, and 3,4-dihydroxyphenylacetic acid (DOPAC) has been applied successfully to measure plasma concentrations of these catecholamines in humans, rabbits and rats.
TL;DR: This paper investigates the suitability of ICG as a fluorescent label for the separation and detection of human serum albumin (HSA) by CE with diode-LIF detection.
TL;DR: In this article, a method allowing the determination of iodine species in milk and infant formulas was developed based on the coupling of size-exclusion chromatography (SEC) with on-line selective detection of iodide by ICP MS.
Abstract: A method allowing the determination of iodine species in milk and
infant formulas was developed. It was based on the coupling of
size-exclusion chromatography (SEC) with on-line selective detection of
iodine by ICP MS. Iodine species were quantitatively eluted with 30 mM
Tris buffer within 40 min and detected by ICP MS with a detection limit
of 1 µg l–1 (as I). A systematic study of
iodine speciation in milk samples of different animals (cow, goat) and humans,
of different geographic origin (several European countries) and in infant
formulas from different manufacturers was carried out. Whey obtained after
centrifugation of fresh milk or reconstituted milk powders contained more than
95% of the iodine initially present in milk in all the samples
investigated with the exception of the infant formulas in which only
15–50% of the total iodine was found in the milk whey. An addition
of sodium dodecyl sulfonate (SDS) improved considerably the recovery of iodine
from these samples into the milk whey. Iodine was found to be principally
present as iodide in all the samples except infant formulas. In the latter, more
than half of the iodine was bound to a high molecular (>1000 kDa)
species. The sum of all the species recovered from a size-exclusion column
accounted for more than 95% of the iodine present in a milk sample. For
the determination of total iodine in milk a rapid method based on
microwave-assisted digestion of milk with ammonia followed by ICP MS was
optimized and validated using CRM 151 Skim Milk Powder.
TL;DR: Methodology with inductively coupled plasma-mass spectrometry (ICP-MS) for the determination of total arsenic in nails suggested that washing once with 1% Triton Χ-100 for 20 min for cleaning nail samples prior to ICP-MS analysis is satisfactory and there was no significant difference among the various sample preparation techniques.
Abstract: The analysis of trace elements in biological samples will extend our understanding of the impact that environmental exposure to these elements has on human health. Measuring arsenic content in nails has proven useful in studies evaluating the chronic body burden of arsenic. In this study, we developed methodology with inductively coupled plasma-mass spectrometry (ICP-MS) for the determination of total arsenic in nails. We assessed the utility of the washing procedures for removing surface contamination. Four types of preanalysis treatments (water bath, sonication, water bath plus sonication, and control) after sample decomposition by nitric acid were compared to evaluate the digestion efficiencies. In addition, we studied the stability of the solution over 1 wk and the effect of acidity on the arsenic signal. Arsenic content in the digested solution was analyzed by using Ar-N2 plasma with Te as the internal standard. The results suggest that washing once with 1% Triton Χ-100 for 20 min for cleaning nail samples prior to ICP-MS analysis is satisfactory. Repeated measurement analysis of variance revealed that there was no significant difference among the various sample preparation techniques. Moreover, the measurements were reproducible within 1 wk, and acidity seemed to have no substantial influence on the arsenic signal. A limit of detection (on the basis of three times the standard deviation of the blank measurement) of 7 ng As/g toenail was achieved with this system, and arsenic recoveries from reference materials (human hair and nails) were in good agreement (95–106% recovery) with the certified/reference values of the standard reference materials. ICP-MS offers high accuracy and precision, as well as highthroughput capacity in the analysis of total arsenic in nail samples.
TL;DR: The detection of dopamine in an individual Aplysia californica cerebral ganglion neuron is demonstrated and more than an order of magnitude improvement in the limits of detection is achieved by maintaining the basic separation conditions and an acidified sheath buffer.
Abstract: Separation conditions in capillary electrophoresis with native fluorescence detection often represent a compromise in terms of the separation and detection figures of merit. As both the separation and fluorescence properties greatly depend on pH, the ability to independently optimize pH in the separation capillary and the detection region can improve many complex separations. When using a sheath flow cell, the pH at the detection zone can be adjusted independently of the electrophoresis buffer pH. Using capillary electrophoresis with 257-nm excitation and native fluorescence detection, more than an order of magnitude improvement in the limits of detection for dopamine (from 1400 to 120 nM) and epinephrine (from 850 to 60 nM) is achieved by maintaining the basic separation conditions and an acidified sheath buffer. The detection of dopamine in an individual Aplysia californica cerebral ganglion neuron is demonstrated.
TL;DR: A simple and rapid HPLC method with diode array-UV detection has been developed and excellent separation of trans-resveratrol is achieved, thus allowing a rapid analysis of the sample for absorption, distribution, and metabolism studies.
Abstract: trans-Resveratrol (trans-3,5,4'-trihydroxystilbene), a phenolic compound present in grapes, wines, and peanuts, has been reported to have health benefits including anticarcinogenic effects and protection against cardiovascular diseases. Despite its importance, little is known about its bioavailability in both humans and animals. A fundamental step for this evaluation consisted in measuring this stilbene in blood. In the present work, a simple and rapid HPLC method with diode array-UV detection has been developed. Resveratrol contained in plasma was purified by solid-phase extraction using a C18 cartridge. The sample was rinsed with water and methanol-water (25:75 v/v), and trans-resveratrol was finally eluted with methanol. The collected fraction was evaporated under nitrogen and analyzed by HPLC. The method was validated by obtaining a linear correlation, a detection limit of 20 micrograms/L, and a good precision with a coefficient of variation of 2.85%. trans-Resveratrol administered orally to rats was detected in plasma. With this procedure, excellent separation of trans-resveratrol is achieved, thus allowing a rapid analysis of the sample for absorption, distribution, and metabolism studies.
TL;DR: A selective and versatile fluorescence spectroscopic method for the determination of nitrite in waters has been developed and a photometric standard procedure was successfully employed to validate the new methods with an independent technique.
Abstract: A selective and versatile fluorescence spectroscopic method for the determination of nitrite in waters has been developed. Nitrite reacts in the presence of mineral acids with the nonfluorescent N-methyl-4-hydrazino-7-nitrobenzofurazan forming N-methyl-4-amino-7-nitrobenzofurazan, which can be detected by fluorescence spectroscopy with an excitation maximum at λ = 468 nm and an emission maximum at λ = 537 nm in acetonitrile. Three new methods based on this reaction have been developed: Direct fluorescence spectroscopy, HPLC/fluorescence, or HPLC with UV/vis detector may be selected as detection techniques. On microplates, high-throughput fluorescence spectroscopy is achieved, while HPLC/fluorescence provides lower limits of detection, and HPLC with UV/vis detection enables evaluation of the reaction with standard instrumentation. Different water samples were investigated using all detection modes, and a photometric standard procedure was successfully employed to validate the new methods with an independe...
TL;DR: In this paper, an ion-guiding gas-filled hexapole collision/reaction cell was used in ICP-MS to characterize the analytical figures of merit that can be achieved with this approach.
Abstract: The application of an ion-guiding gas-filled hexapole collision/reaction cell in ICP-MS has been studied to characterize the analytical figures of merit that can be achieved with this approach. For the elements investigated, application of a buffer and a reaction gas resulted in improved sensitivities which are lowest for Be with about 7 · 107 cps per μg mL–1 and highest for Ba with about ¶6 · 108 cps per μg mL–1. Relative standard deviations (RSD) < 0.1% were obtained. Application of the reaction gas H2 was used to suppress polyatomic ions caused by argon. The reduction amounted up to four orders of magnitude so that elements such as Ca, K, Cr, Fe, As and Se could be analyzed in nitric and hydrochloric acid or in methanol. Detection limits of 6 pg mL–1 for Cr in 2% methanol, 23 pg mL–1 for As and 9 pg mL–1 for Se in 0.28 M HCl were achieved. For other elements detection limits ¶< 1 pg mL–1 were realized in the medium and high mass range. Accuracy was proved using the NIST 1643d standard reference material.
TL;DR: The differential-pulse sono-cathodic stripping voltammetric technique was used to determine successfully the manganese content of two instant tea samples, giving excellent agreement with independent AAS analyses.
Abstract: Ultrasonically assisted cathodic stripping voltammetry at a boron-doped diamond electrode was developed for the detection of manganese. Differential-pulse voltammetry was used to give the analytical signal from a cathodic strip of electrodeposited MnO2; linearity was observed from 10–11 M to at least 3 × 10–7 M, with 10–1l M being the detection limit for a 2 min deposition. The procedure involves both ultrasonic–anodic deposition of MnO2 and ultrasonic–cathodic stripping. This novel analytical tool is robust, reproducible, mercury free, oxygen insensitive and highly specific towards manganese. The differential-pulse sono-cathodic stripping voltammetric technique was used to determine successfully the manganese content of two instant tea samples, giving excellent agreement with independent AAS analyses.