Showing papers on "Detection limit published in 2002"

Inorganic Carbon Analysis by Modified Pressure-Calcimeter Method

Abstract: Soil organic C (SOC) analyses using high temperature induction furnace combustion methods have become increasing popular because of advances in instrumentation. Combustion methods, however, also include C from CaCO 3 and CaMg(CO 3 ) 2 found in calcareous soils. Separate analysis of the inorganic C (IC) must be done to correct C data from combustion methods. Our objective was to develop a efficient and precise IC method by modification of the pressure-calcimeter method. We modified the method by using Wheaton serum bottles (20-mL and 100-mL) sealed with butyl rubber stoppers and aluminum tear-off seals as the reaction vessel and a pressure transducer monitored by a digital voltmeter. Our gravimetric IC determination of six soils showed a strong correlation when regressed against IC from the modified pressure-calcimeter method (slope of 0.99, r 2 = 0.998). The method detection limit (MDL) was 0.17 g IC kg -1 for the 20-mL serum bottles and the limit of quantification (LOQ) was 0.30 g IC kg -1 . The 100-mL serum bottle had a MDL of 0.42 with a LOQ of 2.4 g IC kg -1 . When using a 100-mL Wheaton serum bottle as the reaction vessel with a 0.50-g sample size, soils containing up to 120 g IC kg -1 , which represent a 100 % CaCO 3 equivalent, can be analyzed within the V output range of the pressure transducer. Soil organic C determined by subtraction of IC from total C from combustion analysis correlated well with SOC determined by the Walkley-Black.

Hollow fiber-protected liquid-phase microextraction of triazine herbicides.

Abstract: A new microextraction technique termed hollow fiber-protected liquid-phase microextraction (LPME) was developed. Triazines were employed as model compounds to assess the extraction procedure and were determined by gas chromatography/mass spectrometry. Toluene functioned as both the extraction solvent and the impregnation solvent. Some important extraction parameters, such as effect of salt, agitation, pH, and exposure time were optimized. The new method provided good average enrichment factors of >150 for eight analytes, good repeatability (RSDs <3.50%, n = 7), and good linearity (r2 ≥ 0.9995) for spiked deionized water samples. The limits of detection (LODs) were in the range of 0.007−0.063 μg/L (S/N = 3) under selected ion monitoring mode. In addition to enrichment, hollow fiber-protected LPME also served as a technique for sample cleanup because of the selectivity of the membrane, which prevented large molecules and extraneous materials, such as humic acids in solution, from being extracted. The utiliz...

Development and characterization of an annular denuder methodology for the measurement of divalent inorganic reactive gaseous mercury in ambient air.

Abstract: Atmospheric mercury is predominantly present in the gaseous elemental form (Hg0). However, anthropogenic emissions (e.g., incineration, fossil fuel combustion) emit and natural processes create particulate-phase mercury (Hg(p)) and divalent reactive gas-phase mercury (RGM). RGM species (e.g., HgCl2, HgBr2) are water-soluble and have much shorter residence times in the atmosphere than Hg0 due to their higher removal rates through wet and dry deposition mechanisms. Manual and automated annular denuder methodologies, to provide high-resolution (1−2 h) ambient RGM measurements, were developed and evaluated. Following collection of RGM onto KCl-coated quartz annular denuders, RGM was thermally decomposed and quantified as Hg0. Laboratory and field evaluations of the denuders found the RGM collection efficiency to be >94% and mean collocated precision to be <15%. Method detection limits for sampling durations ranging from 1 to 12 h were 6.2−0.5 pg m-3, respectively. As part of this research, the authors observe...

Rational Design of Potentiometric Trace Level Ion Sensors. A Ag + -Selective Electrode with a 100 ppt Detection Limit

Abstract: Submicromolar to picomolar lower detection limits have recently been obtained with various polymer membrane ion-selective electrodes by minimizing biases due to ion fluxes through the membrane. For the best performance, the compositions of the membrane and inner solution should be optimized for each application. Given the number of parameters to be adjusted, it has been difficult to find the best parameters for a target sample. In this paper, a much simplified and more practical steady-state model of zero-current ion fluxes is derived, which is based on measurable parameters. The model allows one to predict achievable lower detection limits for a membrane with given selectivities. It can also be used to predict the optimal composition of the inner filling solution for the measurement of samples with a known, typical ionic background. Selectivity coefficients of monovalent and divalent analyte ions required for desired detection limits in drinking water are calculated. As an application of the proposed gen...

Development and testing of a detection method for liquid chromatography based on aerosol charging.

Abstract: Aerosol-based detection methods for HPLC in which HPLC effluent is converted to an aerosol and detected optically have been employed in the past. This paper describes a new aerosol-based detection method for HPLC, which we name aerosol charge detection. This detection method also involves generation of an aerosol but with aerosol detection by charging aerosol particles and measuring the current from the charged particle flux. A commercial electrical aerosol size analyzer was used for the aerosol detection. The constructed detector was tested using flow injection analysis with water as the mobile phase, and the signal response was found to be linear for sodium sulfate over the concentration ranges of 0.2−100 μg mL-1 using one of the nebulizers. Minimum mass and concentration detection limits using the more efficient nebulizer were estimated to be 0.2 ng and 10 ng mL-1, respectively. Behavior for most of the other compounds tested was similar with some differences in sensitivity. Testing the detector using ...

Detection of ultratrace phosphorus and sulfur by quadrupole ICPMS with dynamic reaction cell

Abstract: A method of detection of ultratrace phosphorus and sulfur that uses reaction with O2 in a dynamic reaction cell (DRC) to oxidize S+ and P+ to allow their detection as SO+ and PO+ is described. The method reduces the effect of polyatomic isobaric interferences at m/z = 31 and 32 by detecting P+ and S+ as the product oxide ions that are less interfered. Use of an axial field in the DRC improves transmission of the product oxide ions 4−6 times. With no axial field, detection limits (3σ, 5-s integration) of 0.20 and 0.52 ng/mL, with background equivalent concentrations of 0.53 and 4.8 ng/mL, respectively, are achieved. At an optimum axial field potential (200 V), the detection limits are 0.06 ng/mL for P and 0.2 ng/mL for S, respectively. The method is used for determining the degree of phosphorylation of β-casein, and regular and dephosphorylated α-caseins at 10−1000 fmol/μL concentration, with 5−10% v/v organic sample matrix (acetonitrile, formic acid, ammonium bicarbonate). The measured degree of phosphory...

Limits of detection for time of flight secondary ion mass spectrometry (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS): detection of low amounts of adsorbed protein.

Abstract: Characterization of biomaterial surfaces requires analytical techniques that are capable of detecting a wide concentration range of adsorbed protein. This range includes detection of low amounts of adsorbed protein (<10 ng/cm2) that may be present on non-fouling biomaterials. X-ray Photoelectron Spectroscopy (XPS) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) are surface sensitive techniques capable of detecting adsorbed proteins. We have investigated the lower limits of detection of both XPS and ToF-SIMS on four model substrates each presenting unique challenges for analysis by XPS and ToF-SIMS: mica, poly(tetrafluoroethylene), allyl amine plasma polymer and heptyl amine plasma polymer. The detection limit for XPS ranged from 10 ng/cm2 of fibrinogen (on mica) to 200 ng/cm2 (on allyl amine plasma polymers). The detection limit for ToF-SIMS ranged from 0.1 ng/cm2 of fibrinogen to 100 ng/cm2, depending on the substrate and data analysis. Optimal conditions provided detection limits between 0.1 ng/cm2 and 15 ng/cm2 on all of the substrates used in this study. While both techniques were shown to be effective in detecting protein, the sensitivity of both XPS and ToF-SIMS was shown to be dependent on substrate surface chemistry and the organization of the adsorbed protein film. This study specifically highlights the applicability of ToF-SIMS in the characterization of low level protein adsorption.

Enzyme sensor array for the determination of biogenic amines in food samples.

Abstract: An enzyme sensor array for the simultaneous determination of the three biogenic amines (histamine, tyramine and putrescine) by pattern recognition using an artificial neural network and its application to different food samples is described. A combination of a monoamine oxidase, a tyramine oxidase and a diamine oxidase (with specific activities sufficient for rapid detection) are immobilised each on a separate screen-printed thick-film electrode via transglutaminase and glutaraldehyde to compare these cross-linking reagents with regard to their suitability. To calculate the amount of a specific biogenic amine, the raw data from multichannel software were transferred to a neural network. The sensor array takes 20 min to complete (excluding statistical data analysis) with only one extraction and subsequent neutralisation step required prior to sensor measurement. The lower detection limits with the enzyme sensor were 10 mg/kg for histamine and tyramine, and 5 mg/kg for putrescine with a linear range up to 200 mg/kg for histamine and tyramine and 100 mg/kg for putrescine. The application area of the enzyme sensor array was tested from fish to meat products, sauerkraut, beer, dairy products, wine and further fermented foods and compared with the data of conventional LC analyses (mean correlation coefficient: 0.854).

High-voltage capacitively coupled contactless conductivity detection for microchip capillary electrophoresis.

Abstract: Contactless conductivity detection was carried out on a planar electrophoresis device by capacitive coupling using an ac excitation voltage of 500 V(p-p) and a frequency of 100 kHz. It was possible to carry out detection in this way through a cover plate of 1 mm thickness. Better sensitivity is obtained, however, by placing the electrodes into troughs that allow tighter coupling to the separation channel. The 3 x S/N detection limits are 0.49, 0.41, and 0.35 microM for the small inorganic ions K+, Na+, and Mg2+. The detection of heavy metals is demonstrated with the example of Mn2+, Zn2+, and Cr3+ with detection limits of 2.1, 2.8, and 6.8 microM, respectively. The universal nature of the method is further illustrated by the detection of citric and lactic acids, which are of interest in food and beverage analysis, and detection of three antiinflammatory nonsteroid drugs, 4-acetamidophenol, ibuprofen, and salicylic acid, as examples of species of pharmaceutical interest.

Potentiometric Stripping Analysis at Bismuth-Film Electrode

Abstract: A bismuth-film electrode (BiFE) operated in the constant-current potentiometric stripping mode exhibits an attractive performance for trace heavy metal detection. The BiFEs are prepared in situ on a glassy-carbon supporting electrode from the 0.1 M acetate buffer solution (pH 4.5) containing 500 μg/L of bismuth(III) together with target heavy metal ions. The constant-current potentiometric stripping mode of such electrodes yields well-defined, undistorted, reproducible and sharp stripping signals (RSD 1.5% for cadmium, 2.5% for lead) with good resolution for multiple heavy metal measurements (Zn, Cd, Pb). Along with an extremely low baseline, low limit of detection (0.2 and 0.8 μg/L for cadmium and lead, respectively), and short deposition times, these electrodes compare favorably with “toxic” mercury film electrodes. Several key parameters of the constant-current potentiometric stripping mode were examined and optimized, including the stripping current, deposition potential, and deposition time. The constant-current potentiometric stripping mode of BiFE compares favorably to their voltammetric stripping analogues. Additional insights are given into application of BiFEs for constant-current potentiometric stripping analysis.