Showing papers on "Detection limit published in 2006"

Simultaneous Quantitative Analysis of Metabolites Using Ion-Pair Liquid Chromatography−Electrospray Ionization Mass Spectrometry

Abstract: We have developed an analytical method, consisting of ion-pair liquid chromatography coupled to electrospray ionization mass spectrometry (IP-LC-ESI-MS), for the simultaneous quantitative analysis of several key classes of polar metabolites, like nucleotides, coenzyme A esters, sugar nucleotides, and sugar bisphosphates The use of the ion-pair agent hexylamine and optimization of the pH of the mobile phases were critical parameters in obtaining good retention and peak shapes of many of the above-mentioned polar and acidic metabolites that are impossible to analyze using standard reversed-phase LC/MS Optimum conditions were found when using a gradient from 5 mM hexylamine in water (pH 63) to 90% methanol/10% 10 mM ammonium acetate (pH 85) The IP-LC-ESI-MS method was extensively validated by determining the linearity (R2 > 0995), sensitivity (limit of detection 01-1 ng), repeatability, and reproducibility (relative standard deviation <10%) The IP-LC-ESI-MS method was shown to be a useful tool for microbial metabolomics, ie, the comprehensive quantitative analysis of metabolites in extracts of microorganisms, and for the determination of the energy charge, ie, the cellular energy status, as an overall quality measure for the sample workup and analytical protocols © 2006 American Chemical Society

Preparation of functionalized copper nanoparticles and fabrication of a glucose sensor

Abstract: Dimethylglycoxime (DMG) functionalized copper nanoparticles (DMG-CuNPs) were prepared by a microwave heating method and characterized by TEM, FTIR, and XRD. The as-prepared nanoparticles were used to construct a new glucose sensor. Experimental results showed that DMG could be used to encapsulate the copper nanoparticles to control their growth during the preparation process and could chelate copper ions which were produced during the positive scan in the electrochemical experiments. The sensor showed good selectivity and sensitivity. A wide linearity range and a low detection limit have been assessed for it. A linear response to glucose in the concentration range between 1.0 × 10−6 and 5.0 × 10−3 M and a detection limit of 5.0 × 10−7 M were observed. Most important of all, the common drawback of copper electrode fouling was overcome in this sensor.

Detection of bacteria by surface-enhanced Raman spectroscopy

Abstract: The detection and identification of dilute bacterial samples by surface-enhanced Raman spectroscopy has been explored by mixing aqueous suspensions of bacteria with a suspension of nanocolloidal silver particles. An estimate of the detection limit of E. coli was obtained by varying the concentration of bacteria. By correcting the Raman spectra for the broad librational OH band of water, reproducible spectra were obtained for E. coli concentrations as low as approximately 103 cfu/mL. To aid in the assignment of Raman bands, spectra for E. coli in D2O are also reported.

Gold-based screen-printed sensor for detection of trace lead

Abstract: The application of a novel gold-based screen-printed sensor to lead detection is described. The sensor consists of a screen-printed three electrode cell: a gold working electrode, a silver pseudo-reference electrode and a graphite counter electrode. It is used in combination with square wave anodic stripping voltammetry (SWASV). Sensor characterisation experiments as well as the optimisation of the analytical procedure are reported. The optimised parameters allow the detection of micrograms per litre of lead concentrations following short analysis time (detection limit 0.5 μg l−1 at 120 s deposition). Measurements of other metals such as copper, cadmium and mercury are reported.

Rapid determination of fumonisin B1 in food samples by enzyme-linked immunosorbent assay and colloidal gold immunoassay

Abstract: A rapid enzyme-linked immunosorbent assay (ELISA) test (microwell plate) and a membrane-based colloidal gold immunoassay in flow-through and lateral-flow formats for the rapid detection of fumonisin B1 (FB1) were developed. The rapid microwell assay can be completed within 20 min with the detection limit of 0.5 +/- 0.2 microg/L. Membrane-based colloidal gold immunoassays had a visual detection limit of 1.0 microg/L for FB1 with the detection time of <10 min. Matrix interference was eliminated by 15-fold dilutions of methanol extracts with buffer. These immunoassays can be used as quantitative or qualitative tools for the rapid detection of FB1 residues in 10-20 min on-site.

Fluorescence sensor using a molecularly imprinted polymer as a recognition receptor for the detection of aluminium ions in aqueous media

Abstract: This paper describes the investigation of a molecularly imprinted polymer (MIP) as a sensing receptor for Al3+ ion detection by using an optical approach. Al3+ ion was adopted as the template molecule and 8-hydroxyquinoline sulfonic acid ligand as the fluorescence tag. The polymer was synthesised using acrylamide as monomer, 2-hydroxyethyl methacrylate as co-monomer and ethylene glycol dimethracylate as cross-linker. The free radical polymerisation was performed in methanol and initiated by 2,2′-azobisisobutyronitrile at 70 °C. The imprinted polymer was fluorometrically characterised using a fibre optic attachment in a self-designed flow-cell. NaF was used to leach the Al3+ ion from the MIP. The optimum pH for the rebinding of Al3+ ion with the leached polymer was found to be pH 5 and the fluorescence response was found to be stable within the buffer strength range of 0.05–0.10 M. The fluorescence intensity during Al3+ ion rebinding was inversely dependent on temperature, and a low interference response (<3%) toward metal ions except for Cu2+ and Zn2+ ions was observed. The polymer rebinding repeatability study conducted over 9 cycles with Al3+ ion (0.8×10−4 M) was found to give an RSD value of 2.82% with a standard deviation of 0.53. The dynamic range of the system was found to be linear up to 1.0×10−4 M Al3+ ion with a limit of detection of 3.62 μM.

Simultaneous determination of 405 pesticide residues in grain by accelerated solvent extraction then gas chromatography-mass spectrometry or liquid chromatography-tandem mass spectrometry

Abstract: A new method has been established for simultaneous determination of 405 pesticide residues in grain, using accelerated solvent extraction (ASE), solid-phase extraction (SPE), and GC-MS and LC-MS-MS. The method was based on appraisal of the GC-MS and LC-MS-MS characteristics of 660 pesticides, their efficiency of extraction from grain, and their purification. Samples of grain (10 g) were mixed with Celite 545 (10 g) and the mixture was placed in a 34-mL cell of an accelerated solvent extractor and extracted with acetonitrile in the static state for 3 min with two cycles at 1,500 psig and at 80°C. For the 362 pesticides determined by GC-MS, half of the extracts were cleaned with an Envi-18 cartridge and then further cleaned with Envi-Carb and Sep-Pak NH2 cartridges in series. The pesticides were eluted with acetonitrile-toluene, 3:1, and the eluates were concentrated and used for analysis after being exchanged with hexane twice. For the 43 pesticides determined by LC-MS-MS the other half of the extracts were cleaned with Sep-Pak Alumina N cartridge and further cleaned with Envi-Carb and Sep-Pak NH2 cartridges. Pesticides were eluted with acetonitrile-toluene, 3:1. After evaporation to dryness the eluates were diluted with acetonitrile-water, 3:2, and used for analysis. In the linear range of each pesticide the linear correlation coefficient r was equal to or greater than 0.956 and 94% of linear correlation coefficients were greater than 0.990. At low, medium, and high fortification levels, at the limit of detection (LOD), twice the LOD and ten times LOD, respectively, recoveries ranged from 42 to 132%; for 382 pesticides, or 94.32%, recovery was from 60 to 120%. The relative standard deviation (RSD) was always below 38% and was below 30% for 391 pesticides, or 96.54%. The LOD was 0.0005–0.3000 mg kg−1. The proposed method is suitable for determination of 405 pesticide residues in grain such as maize, wheat, oat, rice, and barley, etc.

Electrochemical microfluidic biosensor for the detection of nucleic acid sequences

Abstract: A microfluidic biosensor with electrochemical detection for the quantification of nucleic acid sequences was developed. In contrast to most microbiosensors that are based on fluorescence for signal generation, it takes advantage of the simplicity and high sensitivity provided by an amperometric and coulorimetric detection system. An interdigitated ultramicroelectrode array (IDUA) was fabricated in a glass chip and integrated directly with microchannels made of poly(dimethylsiloxane) (PDMS). The assembly was packaged into a Plexiglas® housing providing fluid and electrical connections. IDUAs were characterized amperometrically and using cyclic voltammetry with respect to static and dynamic responses for the presence of a reversible redox couple—potassium hexacyanoferrate (II)/hexacyanoferrate (III) (ferri/ferrocyanide). A combined concentration of 0.5 µM of ferro/ferricyanide was determined as lower limit of detection with a dynamic range of 5 orders of magnitude. Background signals were negligible and the IDUA responded in a highly reversible manner to the injection of various volumes and various concentrations of the electrochemical marker. For the detection of nucleic acid sequences, liposomes entrapping the electrochemical marker were tagged with a DNA probe, and superparamagnetic beads were coated with a second DNA probe. A single stranded DNA target sequence hybridized with both probes. The sandwich was captured in the microfluidic channel just upstream of the IDUA via a magnet located in the outside housing. Liposomes were lysed using a detergent and the amount of released ferro/ferricyanide was quantified while passing by the IDUA. Optimal location of the magnet with respect to the IDUA was investigated, the effect of dextran sulfate on the hybridization reaction was studied and the amount of magnetic beads used in the assay was optimized. A dose response curve using varying concentrations of target DNA molecules was carried out demonstrating a limit of detection at 1 fmol assay−1 and a dynamic range between 1 and 50 fmol. The overall assay took 6 min to complete, plus 15–20 min of pre-incubation and required only a simple potentiostat for signal recording and interpretation.

Validation of a Reversed-Phase HPLC Method for Quantitative Amino Acid Analysis

Abstract: A semi-automated method for amino acid derivatization and analysis has been validated for use in analysis of protein biopharmaceuticals The method includes protein hydrolysis, o-phthalaldehyde derivatization, and reversed-phase high-performance liquid chromatography analysis in a general-purpose UV-visible high-performance liquid chromatography system Amino-acid derivatization is performed automatically by the high-performance liquid chromatography autosampler right before injection The required validation parameters, ie, specificity, linearity, accuracy, precision, limit of detection, and limit of quantification, were studied for bovine serum albumin and for a recombinant human Fab fragment The method can be employed as an absolute quantification method for determination of extinction coefficients of recombinant proteins

Electrochemical detection of arsenic(III) using iridium-implanted boron-doped diamond electrodes

Abstract: Iridium-modified, boron-doped diamond electrodes fabricated by an ion implantation method have been developed for electrochemical detection of arsenite (As(III)). Ir+ ions were implanted with an energy of 800 keV and a dose of 1015 ion cm-2. An annealing treatment at 850 °C for 45 min in H2 plasma (80 Torr) was required to rearrange metastable diamond produced by an implantation process. Characterization was investigated by SEM, AFM, Raman, and X-ray photoelectron spectroscopy. Cyclic voltammetry and flow injection analysis with amperometric detection were used to study the electrochemical reaction. The electrodes exhibited high catalytic activity toward As(III) oxidation with the detection limit (S/N = 3), sensitivity, and linearity of 20 nM (1.5 ppb), 93 nA μM-1 cm-2, and 0.999, respectively. The precision for 10 replicate determinations of 50 μM As(III) was 4.56% relative standard deviation. The advantageous properties of the electrodes were its inherent stability with a very low background current. Th...