Average Detection Limit Research Articles

Impurities in multicrystalline silicon wafers for solar cells detected by synchrotron micro-beam X-ray fluorescence analysis

We report on the trace analysis of copper and iron impurities in multicrystalline silicon wafers with the microbeam X-ray fluorescence (μ-XRF) technique. The efficiency of solar cells, which are based on multicrystalline silicon wafers, is strongly influenced by minor contamination with metals such as copper and iron. Application of compound refractive lenses (CRLs) in μ-XRF allows versatile two-dimensional mapping of relevant contaminations and localization of their sites of deposition. In this context, the measured bulk average limit of detection (LOD) was one picogram of iron and copper per gram of silicon. We suggest that μ-XRF is a valuable tool for non-destructive spatial (3D) quantification of metal impurities in a wide range of materials and devices whose functioning could be critically affected by impurities.

Speciation of Dissolved Inorganic Arsenic by Diffusive Gradients in Thin Films: Selective Binding of AsIII by 3-Mercaptopropyl-Functionalized Silica Gel

A diffusive gradients in thin films (DGT) technique for selectively measuring As(III) utilizes commercially available 3-mercaptopropyl-functionalized silica gel. Deployment of the new technique alongside the Metsorb-DGT for total inorganic arsenic allows the calculation of As(III) directly and As(V) by difference. Uptake of As(III) by mercapto-silica was quantitative and elution with a mixture of 1 mol L(-1) HNO(3) and 0.01 mol L(-1) KIO(3) gave a recovery of 85.6 ± 1.7%. DGT validation experiments showed linear accumulation of As(III) over time (R(2) > 0.998). Accumulation was unaffected by varying ionic strength (0.0001-0.75 mol L(-1) NaNO(3)) and pH (3.5-8.5). Deployment of mercapto-silica DGT and Metsorb DGT in seawater spiked with As(III) and As(V) demonstrated the ability of the combined approach to accurately quantify both species in the presence of potential competing ions. Ferrihydrite DGT, which has been previously reported for the measurement of total inorganic arsenic, was evaluated in seawater and shown to underestimate both As(III) and As(V) at longer deployment times (72 h). Reproducibility of the new mercapto-silica DGT technique was good (relative standard deviations < 9%), and the average method detection limit was sufficiently low to allow quantification of ultratrace concentrations of As(III) (0.03 μg L(-1); 72 h deployment).

Differential diagnosis of pandemic (H1N1) 2009 infection by detection of haemagglutinin with an enzyme-linked immunoassay

A sensitive and convenient immunoassay that can directly differentiate pandemic (H1N1) 2009 (pH1N1) virus from seasonal influenza virus can play an important role in the clinic. In the presented study, a double-sandwich ELISA (pH1N1 ELISA), based on two monoclonal antibodies against haemagglutinin (HA) of the pH1N1 virus, was developed. After laboratory determination of the sensitivity and specificity characteristics, the performance of this assay was evaluated in a cohort of 904 patients with influenza-like illness. All seven strains of pH1N1 virus tested were positive by pH1N1 ELISA, with an average lower detection limit of 103.0 ± 0.4 tissue culture infective dose (TCID)50/mL (or 0.009 ± 0.005 HA titre). Cross-reaction of the assay with seasonal influenza virus and other common respiratory pathogens was rare. In pH1N1-infected patients, the sensitivity of the pH1N1 ELISA was 92.3% (84/91, 95% CI 84.8–96.9%), which is significantly higher than that of the BD Directigen EZ Flu A + B test (70.3%, p <0.01). The specificity of pH1N1 ELISA in seasonal influenza A patients was 100.0% (171/171, 95% CI 97.9–100.0%), similar to that in non-influenza A patients (640/642, 99.7%, 95% CI 98.9–100.0%). The positive predictive value for pH1N1 ELISA was 97.7% and the negative predictive value was 99.1% in this study population with a pH1N1 prevalence of 10.1%. In conclusion, detection of HA of pH1N1 virus by immunoassay appears to be a convenient and reliable method for the differential diagnosis of pH1N1 from other respiratory pathogens, including seasonal influenza virus.

Size separation of proteins by capillary zone electrophoresis with cationic hitchhiking.

The paper describes a method of size separation of proteins by capillary sieving electrophoresis with cationic surfactant. Proteins are separated within 12 min with repeatability of migration times better than 0.2%. Some proteins achieve the separation efficiency of 200,000 theoretical plates. The method can be used for determination of protein relative molecular masses. The accuracy of the determined relative molecular masses and the limitation of the method were investigated by the analysis of more than 60 proteins. The method also allows separation of protein oligomers. Proteins can be quantitated after the electrokinetic injection in the concentration range 0.07-0.43 g/L. The average detection limit is about 2 mg/L.

SodC-Based Real-Time PCR for Detection of Neisseria meningitidis

Real-time PCR (rt-PCR) is a widely used molecular method for detection of Neisseria meningitidis (Nm). Several rt-PCR assays for Nm target the capsule transport gene, ctrA. However, over 16% of meningococcal carriage isolates lack ctrA, rendering this target gene ineffective at identification of this sub-population of meningococcal isolates. The Cu-Zn superoxide dismutase gene, sodC, is found in Nm but not in other Neisseria species. To better identify Nm, regardless of capsule genotype or expression status, a sodC-based TaqMan rt-PCR assay was developed and validated. Standard curves revealed an average lower limit of detection of 73 genomes per reaction at cycle threshold (Ct) value of 35, with 100% average reaction efficiency and an average R2 of 0.9925. 99.7% (624/626) of Nm isolates tested were sodC-positive, with a range of average Ct values from 13.0 to 29.5. The mean sodC Ct value of these Nm isolates was 17.6±2.2 (±SD). Of the 626 Nm tested, 178 were nongroupable (NG) ctrA-negative Nm isolates, and 98.9% (176/178) of these were detected by sodC rt-PCR. The assay was 100% specific, with all 244 non-Nm isolates testing negative. Of 157 clinical specimens tested, sodC detected 25/157 Nm or 4 additional specimens compared to ctrA and 24 more than culture. Among 582 carriage specimens, sodC detected Nm in 1 more than ctrA and in 4 more than culture. This sodC rt-PCR assay is a highly sensitive and specific method for detection of Nm, especially in carriage studies where many meningococcal isolates lack capsule genes.

Multiplex PCR assay for detection of four major bacterial pathogens causing rainbow trout disease

A multiplex PCR (mPCR) method was designed for the simultaneous detection of 4 major fish pathogens, Flavobacterium psychrophilum, Lactococcus garvieae, Pseudomonas aeruginosa, and P. putida. Each of the 4 pairs of oligonucleotide primers exclusively amplified the 16S rDNA gene of their targeted microorganism. The average detection limits for each organism amplified by mPCR were 2 colony-forming units (CFU) of F. psychrophilum, 3 CFU of L. garvieae, 3 CFU of P. aeruginosa, and 5 CFU of P. putida in mixed cultures. Multiplex PCR did not produce any nonspecific amplification products when tested against 28 related species of bacteria. High amounts of DNA from 1 bacterial species had a significant effect on the amplification sensitivity of the other bacterial species when these were present in lower concentrations in the multiplex reaction. The mPCR assay proved useful for the detection of the bacteria in naturally infected fish. The assay is a sensitive, specific, and reproducible diagnostic tool for the simultaneous detection of 4 pathogenic bacteria that cause disease in fish and offers a potentially useful alternative to the conventional culture-based method.

A simplified poly(dimethylsiloxane) capillary electrophoresis microchip integrated with a low‐noise contactless conductivity detector

A contactless conductivity detector integrated into a poly(dimethylsiloxane) microchip for electrophoresis is presented. It adopted the simplest configuration of electrodes commonly used in this detection mode for capillary electrophoresis microchips. Although the chip is based on a simple and effective design, it is able to obtain low detection levels due to the low noise of the detection circuit. A circuit based on a lock-in amplifier was designed on printed circuit boards to read out the signal. The property of the detection cell was studied by applying excitation signals of different frequencies and different amplitudes. It was found that the best detection limit could be achieved with a frequency of 50 kHz and amplitude of 20 V. The performance of the detector was demonstrated by successfully separating and detecting several inorganic ions and also a mixture of heavy metal ions. An average detection limit of 0.4 μM was obtained for inorganic cations. This value is significantly improved compared to similar microchip-based detectors. The presented detector could be promising for mass production due to its properties, such as simple construction, high degree of integration, high performance and low cost.

A rapid method for the in-field analysis of amphetamines employing the Agilent Bioanalyzer

This paper reports the first analysis of small molecules on the Agilent bio-analyser. The Bioanalyzer is a commercial lab-on-a-chip instrument designed for the analysis of DNA and proteins. We demonstrate that the instrument is suitable for analyses beyond its design specifications. Amphetamine, methamphetamine and pseudoephedrine were separated with a 50 mM borate and 50 mM sodium dodecyl sulfate (SDS) buffer at pH 9.66. The analytes were derivatised with fluorescein isothiocyanate (FITC) in 3 minutes with a heating block set at 90 °C, reducing the typical time of 12 hours required for amine-labelling. Analytes were detected by LED-induced fluorescence (λex = 525 nm and λem = 470 nm). Furthermore, five amphetamine analogues were baseline separated within 1 minute. An average limit of detection of 0.6 μg mL−1 and limit of quantification of 2.2 μg mL−1 were obtained for all analytes. These rapid analyses in conjunction with a fast and reliable derivatisation method with FITC demonstrate its potential use for the in-field analysis of samples of forensic significance.

H I CLOUDS IN THE M81 FILAMENT AS DARK MATTER MINIHALOS—A PHASE-SPACE MISMATCH

Cosmological galaxy formation models predict the existence of dark matter minihalos surrounding galaxies and in filaments connecting groups of galaxies. The more massive of these minihalos are predicted to host H i gas that should be detectable by current radio telescopes such as the Robert C. Byrd Green Bank Telescope (GBT). We observed the region including the M81/M82 and NGC 2403 galaxy groups, searching for observational evidence of an H i component associated with dark matter halos within the "M81 Filament," using the GBT. The map covers an 87 × 213 (480 kpc × 1.2 Mpc) region centered between the M81/M82 and NGC 2403 galaxy groups. Our observations cover a wide velocity range, from −890 to 1320 km s−1, which spans much of the range predicted by cosmological N-body simulations for dark matter minihalo velocities. Our search is not complete in the velocity range −210 to 85 km s−1, containing Galactic emission and the HVC Complex A. For an H i cloud at the distance of M81, with a size ⩽10 kpc, our average 5σ mass detection limit is 3.2 × 106 M☉, for a linewidth of 20 km s−1. We compare our observations to two large cosmological N-body simulations and find that the simulation predicts a significantly greater number of detectable minihalos than are found in our observations, and that the simulated minihalos do not match the phase space of observed H i clouds. These results place strong constraints on the H i gas that can be associated with dark matter halos. Our observations indicate that the majority of extragalactic H i clouds with a mass greater than 106 M☉ are likely to be generated through tidal stripping caused by galaxy interactions.

Generation of anti-trenbolone monoclonal antibody and establishment of an indirect competitive enzyme-linked immunosorbent assay for detection of trenbolone in animal tissues, feed and urine

Trenbolone (TRE) is a steroid used by veterinarians on livestock to increase appetite and body weight. The use of TRE has been restricted because of its harmful side effect for consumers. To effectively control TRE residue in food and food product, a rapid and convenient immunoassay was developed by preparing an anti-TRE monoclonal antibody. The immunogen and coating antigen were prepared by coupling TRE hapten with carrier proteins via 1-ethyl-3-(dimethylaminopropyl)carbodiimide hydrochloride (EDC) method. The optimized method gave an average IC 50 value of 0.323 ng mL −1 towards TRE and an average detection limit (LOD) of 0.06 ng mL −1, which is much lower than the maximum residue levels (2.0 ng g −1) accepted by the Joint FAO/WHO Expert Committee on Food Additives (JECFA). The specificity of the antibody was evaluated by measuring cross-reactivity of six structurally related compounds, including 19-nortestosterone (9.7%), testosterone (0.13%), methyltestosterone (<0.01%), methandrostenolone (<0.01%), (+)-dehydroisoandrosterone (<0.001%) and β-estradiol (<0.001%). The recovery rates of the test in detection of TRE-fortified animal tissue, urine and animal feed samples were in the range of 81.3–89.4%, while the intra- and inter-assay coefficients of variation were less than 12.0%.

Development of a three-dimensional detection method of cam deformities in femoroacetabular impingement

The description of femoral head sphericity and related risk for femoroacetabularimpingement is currently limited to an angular estimate-the alpha angle-whose relevance and accuracy have been challenged. We developed a three-dimensional approach for both automated digital measurement of the alpha angle and the detection of camdeformities. Accuracy and diagnostic relevance of the alpha angle estimated by means of the oblique axial and multiple radial plane protocol were compared with the computed results. Using subject-specific statistical information of the femur head and mid-neck region, a method was developed to accurately compute the maximum alpha angle and to define aspherical eccentric areas at the femoral head-neck junction. The method was evaluated on 102 dry cadaver femur specimens. Average detection limit for bony prominences at the head-neck transition was 0.98mm. Pixel size of the investigated CT data was 0.79 mm. Mean maximum computed alpha angle of the femurs with cam-type morphology as identified by the morphological method was 67.72° (range 53.04-88.02°). Mean maximum computed alpha angle of the femurs without cam deformity was 47.65° (range 38.67-59.81°). Alpha angle estimates obtained by means of the multiple radial plane protocol correlated better (R = 0.88) and showed higher diagnostic agreement (phi = 0.77) with the 3D computational analysis compared to the oblique axial protocol (R = 0.60; phi = 0.67). The alpha angle seems to be a relevant screening tool when obtained by 3D computed analysis or when estimated according to the multiple radial plane protocol. Estimates obtained by means of the oblique axial protocol have insufficient diagnostic and measurement accuracy.

Analysis of amphetamine‐type substances by capillary zone electrophoresis using capacitively coupled contactless conductivity detection

CE with capacitively coupled contactless conductivity detection (C(4)D) was employed for the separation and detection of seven amphetamine analogues as well as amphetamine, dextroamphetamine, methamphetamine and 3,4-methylenedioxymethamphetamine. The separation electrolyte was 30 mM hydroxypropyl-beta-cyclodextrin (HPbetaCD) in a 75 mM acetic acid+25 mM sodium acetate buffer adjusted to pH 4.55. Conductivity detection was compared with UV detection using this same electrolyte. Average detection limits for C(4)D and UV were 1.3 and 1.0 ppm, respectively. The effects of HPbetaCD concentration and BGE composition on the selectivity of the separation were also investigated. An illicit, street-grade sample of 3,4-methylenedioxymethamphetamine (Ecstasy) and a prescription dextroamphetamine tablet were also analysed.

Pressurised hot water extraction followed by simultaneous derivatization and headspace solid-phase microextraction and gas chromatography-tandem mass spectrometry for the determination of aliphatic primary amines in sewage sludge

In this paper we describe an environmentally friendly and sensitive method for the determination of ten primary amines in sewage sludge. The method is based on pressurised hot water extraction (PHWE) followed by simultaneous derivatization with pentafluorobenzaldehyde (PFBAY) and headspace solid-phase microextraction (HS-SPME) and subsequent gas-chromatography ion-trap tandem mass spectrometry (GC-IT-MS–MS) analysis. The influence of the main factors on the PHWE of sludge was optimized by a central composite design. For all species the optimal conditions were water at pH 4 as the extracting solvent, an extraction temperature of 100 °C and an extraction time of 15 min. The separation and detection of the ten amines by GC-IT-MS–MS took just 10 min and the entire process took approximately 1 h. Repeatability and reproducibility between days, expressed as RSD (%) ( n = 5), were less than 19 and 24%, respectively. The average limit of detection (LOD) was of 65 μg kg −1 s (range found 9–135) and the average limit of quantification (LOQ) was of 230 μg kg −1 (range found 50–450) of dry weight (d.w.). Under optimized conditions we used this method to determine the compounds in industrial and municipal sewage sludge samples and in sludge from a potable water treatment plant. Methylamine and isobutylamine showed the highest levels in one of the industrial sewage sludge samples (404 and 543 mg kg −1 (d.w.), respectively). To our knowledge, this paper presents for the first time the determination of ten primary amines in sewage sludge samples using PHWE.

Flow injection spectrophotometric determination of fenoxaprop-p-ethyl herbicide in different grain samples after derivatization

A spectrophotometric method for determination of fenoxaprop-p-ethyl herbicide using flow injection system has been proposed. The fenoxaprop-p-ethyl was converted into hydroxamic acid in the presence of hydroxylamine hydrochloride in alkaline media. The hydroxamic acid produced was further reacted with iron(III) to form red color tris iron hydroxamate complex. The absorbance of the complex was measured at 500 nm using flow injection system. The method shows a linear range between 1.0-20.0 µg mL-1 with molar absorptivity of 1.81 × 10(4) L mol-1 cm-1. The limit of detection and limit of quantification were calculated and found to be 0.29 ± 0.1 µg mL-1 and 0.96 ± 0.1 µg mL-1 respectively. Similarly the average limit of detection and limit of quantification were calculated for residue determination and were found 0.35 and 0.45 µg g-1 respectively for wheat grains and 1.2 and 1.5 µg g-1 respectively for barley grains. The sample through put was 90 samples h-1. The method was successfully applied to different grain samples.

Horseradish peroxidase covalent grafting onto screen-printed carbon electrodes for levetiracetam chronoamperometric determination

A new enzymatic electrochemical biosensor based on disposable transducers, namely screen-printed carbon electrodes, has been developed for the determination of the antiepileptic drug levetiracetam. Horseradish peroxidase was immobilized onto the carbon working electrode previously modified by an aryl diazonium salt. The formation of amide bonds between the amino and carboxylic groups of the enzyme surface, catalyzed by hydroxysuccinimide and carbodiimide, leads to the electrode functionalization. This orientated enzymatic modification results in high reproducibility, with an associated relative standard deviation of 6.21% for the slopes of several calibration curves in the calibration range from 0.10 to 0.83 mM. Experimental variables that can affect levetiracetam chronoamperometric response, such as hydrogen peroxide concentration, pH, and applied potential, were optimized to perform a selective determination. An average limit of detection of 1.75 × 10 −5 M ( α = β = 0.05) was obtained. The biosensors were finally applied to the determination of levetiracetam in complex matrices such as pharmaceutical drugs, yielding successful results.

Broad range evaluation of the matrix solubilization (matrix lysis) strategy for direct enumeration of foodborne pathogens by nucleic acids technologies.

A previously published rapid (<5 h) proof-of-concept protocol for the concentration of the foodborne pathogen Listeria monocytogenes from milk, based on the solubilization of the food matrix, was further evaluated. The original protocol was modified to detect gram-negative and other gram-positive bacteria and to broaden the range of food matrices by using Lutensol instead of sodium dodecyl sulfate as the main detergent in the buffer. A new protocol using a protease and sucrose buffer was established for the analysis of meat and fish. Matrix lysis was used for dairy products, ice cream, milk, fish, meat, eggs, and blood. Solubilization of the foodstuffs resulted in bacterial pellets of reasonable size for further quantification. Using L. monocytogenes, Staphylococccus aureus, Bacillus cereus, Escherichia coli, and Salmonella Typhimurium as model organisms, microscopic analysis of the remaining bacterial pellets revealed that the recovered bacteria remained physically intact, albeit their viability was compromised. In model experiments using free DNA, the free target DNA was reduced by 5 log units. The compatibility of matrix lysis with subsequent real-time PCR analysis has been demonstrated with salmon, chicken, egg, ice cream, cheese, and blood samples that were artificially contaminated with L. monocytogenes, S. aureus, and Salmonella Typhimurium. These experiments resulted in an average recovery of 48.7% (relative standard error, 83.4%) of the inoculated bacterial cells with the real-time PCR assay. The average detection limit of the method was 7.3 CFU/ml for all examined foodstuffs and bacterial target organisms.

Bisphenol A in Baby Food Products in Glass Jars with Metal Lids from Canadian Markets

A method based on solid phase extraction and derivatization with acetic anhydride followed by gas chromatography-mass spectrometry was validated for the determination of bisphenol A (BPA) in baby foods. The average method detection limit (MDL) was 0.18 ng/g for a 5 g sample. Method repeatability was demonstrated with the replicate analyses of various different types of baby foods; relative standard deviations (RSD) ranged from 1.2 to 16.1% with an average of 8.7%. Extraction recoveries ranged from 93.5 to 102.5% for different types of baby foods spiked at levels of 1-8 ng/g. This method was used to analyze 122 baby food products of 7 brands in glass jars with metal lids for BPA. The presence of BPA could not be confirmed and quantified for 23 of the 122 products due to interference from sample matrices. For the other 99 products, 15% had BPA levels of less than the average MDL, about 70% had BPA levels of less than 1 ng/g, and the average BPA levels in all 99 products was 1.1 ng/g. The average BPA level in the baby food products from brand E (3.9 ng/g) is higher than the average BPA levels in the products from the other brands (0.54-1.1 ng/g). The highest level of BPA, 7.2 ng/g, was found in two products from brand E as well. The average BPA level in the fruit products from all brands (0.60 ng/g) is lower than those in the mixed-dish products (1.1 ng/g) and the vegetable products (1.2 ng/g).

An automated microfluidic-based immunoassay cartridge for allergen screening and other multiplexed assays

A microfluidic cartridge and system for multiplexed immunoassays is described. The passive microfluidic cartridge was composed of three layers of injection molded plastic sealed together using a thermal staking technique. Using this platform technology, a specific immunoglobulin E (IgE) panel assay was constructed. Allergen extract targets, positive and negative controls, and IgE calibration standards were immobilized within the cartridge as a microarray. A computer-controlled solenoid array provided the necessary actuation force for pumping reagents within the cartridge to perform an automated, chemiluminescent indirect immunoassay. A 20-target allergen extract panel was demonstrated on the device with a total analysis time of 27 min. Allergen screening results showed 84% agreement for 3 house dust mites ( N = 300) compared with a commercial test and 80% agreement overall ( N = 978). Average coefficients of variation ( N = 80) were measured as 20.5% for low/medium levels and 20.4% for medium/high levels. The average limit of detection ( N = 160) was measured at 0.535 AU, and cutoff levels of 1.0 AU were estimated at less than 1 IU/ml (2.4 ng/ml). Such a system has potential applications in decentralized allergen screening as well as in other near-patient diagnostic immunoassays where multiplexed analysis, ease of use, and short analysis time are critical.

An isotope dilution headspace method with gas chromatography–mass spectrometry for determination of propylene oxide in food

A method based on isotope dilution headspace and gas chromatography–mass spectrometry was developed for the determination of propylene oxide in foods. Optimum method sensitivity was achieved by the addition of NaCl in water at saturation and with the sample solution incubated at 90°C. The method had good repeatability with relative standard deviations of 6.0, 7.6 and 2.2% at 5, 20 and 40 µg l−1, respectively. The method was used to determine propylene oxide in 36 selected food composite samples from the 2007 Canadian total diet study. Propylene oxide was not detected in any samples analyzed with an average method detection limit of 0.5 ng g−1. Hydrolysis of propylene oxide in water was observed as a first-order reaction with a half-life of 15 h at room temperature and less than 10 min at 90°C. This confirms that it is very unlikely to find propylene oxide in foods as consumed due to its volatility and reaction with water.

Levels of Bisphenol A in Canned Soft Drink Products in Canadian Markets

The method developed previously for the determination of bisphenol A (BPA) in liquid infant formula was adapted and validated for determination of BPA in soft drink products. This method was based on solid phase extraction and derivatization with acetic anhydride followed by gas chromatography-mass spectrometry in selected-ion monitoring mode. The average method detection limit was 0.045 microg/L for a 10 mL sample. The average extraction recoveries were 101 and 99.9% obtained with seven different soft drink products spiked with BPA at 0.5 and 2.5 microg/L, respectively. Good repeatability of the method was observed with replicate analyses of seven different soft drinks; relative standard deviations ranged from 1.3 to 6.6%. This method was used to analyze samples of 72 canned soft drink products for BPA. Except for three products from which BPA-d16 could not be recovered at all due to interference of product compositions (e.g., quinine hydrochloride in tonic water), BPA was detected in samples of all the other products at levels ranging from 0.032 to 4.5 microg/L. About 75% of the products had BPA levels of <0.5 microg/L, and 85% of the products had BPA levels of <1 microg/L. Exposure to BPA through consumption of canned soft drink products is low; dietary intake of BPA was estimated at 0.027 microg/kg of body weight/day on the basis of the consumption of one canned soft drink with the highest BPA level (4.5 microg/L) for an adult with a 60 kg body weight, well below the provisional tolerable daily intake of 25 microg/kg of body weight/day established by Health Canada.