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Results for “Repeatability and Reproducibility”

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PubMed2006

Layer-by-layer hydroxymethyl ferrocene modified sensor for one-step flow/stop-flow injection amperometric immunoassay of alpha-fetoprotein.

A rapid one-step flow/stop-flow injection amperometric immunoassay for alpha-fetoprotein (AFP) using a novel home-produced electrochemical sensor was proposed. The sensor was prepared using layer-by-layer adsorption of positively charged poly(allylamine) (PAA) and negatively charged hydroxymethyl ferrocene on a screen-printed electrode (SPE). The electrochemistry of the immobilized ferrocene moieties showed a surface-controlled electrode process. Based on an electrochemical enzyme-linked immunoassay with the immobilized ferrocene moieties as an electron transfer mediator between the electrode and the horseradish peroxidase (HRP)-labeled anti-AFP antibody, a calibration curve with two linear ranges from 5 to 20 and 20 to 150 ng ml-1 and a detection limit of 2 ng ml-1 for AFP determination was obtained under the optimized conditions of 0.891 ml min-1 flow rate, 20 microl injection volume and +25 mV applied potential. The sensor showed good repeatability and reproducibility and retained more than 95% of its original signal after 15 days of storage. The proposed method eliminated the need for washing and addition of any substrate or mediator. The complete assay could be handled in less than 25 min with a one-step injection of a 40 microl sample solution. The proposed method would be valuable for the diagnosis and monitoring of carcinoma and its metastasis.

Biosensing Techniques↗

PubMed2003

Rapid determination by reversed-phase high-performance liquid chromatography of Vitamins A and E in infant formulas.

A rapid, sensitive method has been developed for the simultaneous determination of retinol acetate, delta-, gamma-, alpha-tocopherol and alpha-tocopherol acetate. We compare two experimental procedures for simultaneous direct solvent extraction of these vitamins without previous saponification. Method I: the fat milk sample was extracted with ethanol-hexane and injected directly into the chromatographic column. Method II: the power milk sample was extracted with ethanol-hexane and also injected directly into the column. Under optimum conditions the limits of detection for retinol acetate, delta-, gamma-, alpha-tocopherol and alpha-tocopherol acetate were 0.33, 21.2, 32.9, 32.5 and 3.2 ng and the limits of quantification were 0.42, 25.3, 37.9, 36.8 and 6.3 ng, respectively. The precision results showed that the relative standard deviations of repeatability and reproducibility were between 0.74 and 5.7%.

Chromatography, High Pressure Liquid↗

PubMed2004

Stir bar sorptive extraction for the analysis of wine cork taint.

A magnetic stir bar with a polydimethylsiloxane coating was used to absorb 2,4,6-trichloroanisole, 2,3,4,5-tetrachloroanisole, pentachloroanisole and their respective phenols from synthetic and real wine samples. The stir bar sorptive extraction method was optimised to obtain the best extraction conditions in terms of temperature, time, pH and NaCl addition. The stir bar was desorbed in a thermal desorption system coupled to a gas chromatograph-mass spectrometer. The method proposed showed good linearity over the concentration range tested and correlation coefficients ranged from 0.96 to 0.99 for all the analytes. The reproducibility and repeatability of the method was estimated between 1.29 and 4.02%. With no a pre-concentration step and with a much reduced analysis time, all the analyzed compounds showed detection and quantification limits that were lower than those observed with other methods found in the bibliography. Except for pentachlorophenol due to its poor absorptivity in polydimethysiloxane, in red wines, LOD ranged between 7.56 and 61.56 pg/l, and LOQ ranged between 17.21 and 205.11 pg/l; while in white wines, the LOD ranged between 5.82 and 30.50 pg/l and LOQ ranged between 19.41 and 101.61 pg/l. These concentrations were always lower than their respective olfactory thresholds values.

Gas Chromatography-Mass Spectrometry↗

PubMed2004

Headspace gas chromatographic method for determining volatile compounds in infant formulas.

Powder infant milk formula quality deterioration and consequently the termination of shelf life results in the appearance of off-flavors mainly determined by a composite effect of spoilage volatiles. A headspace gas chromatographic method to determine propanal, pentanal and hexanal as the main volatiles present in the headspace of powder infant formula oxidation is described as a rapid indication of oxidative status. Under optimum conditions the limits of detection for propanal, pentanal and hexanal were 17.19, 16.87 and 19.60 ng and the limits of quantification were 37.37, 31.96 and 35.97, respectively. The calibration graphs of the method were linear from 25 to 1500, 20 to 3500 and 30 to 8500 ng for propanal, pentanal and hexanal, respectively, with determination coefficients exceeding 0.99. The precision results showed that the relative standard deviations of the repeatability and reproducibility were between 2.2 and 5.5%. The analytical method was simple, rapid, and reliable and permitted the analysis of a large number of formulas using small sample volumes.

Calibration↗

PubMed2004

Comparative study of analytical methods involving gas chromatography-mass spectrometry after derivatization and gas chromatography-tandem mass spectrometry for the determination of selected endocrine disrupting compounds in wastewaters.

Two GC-MS methods, based on the application of N,O-bis(trimethylsilyl)trifluoroacetamide-derivatization-GC-MS (selected-ion monitoring) and GC-MS-MS without derivatization, respectively, were optimised and applied to the determination of a group of five selected endocrine disrupting compounds (EDCs) in wastewaters. Both methods included solid-phase extraction with Oasis HLB cartridges allowing an enrichment factor for wastewater samples of 100-fold. The investigated EDCs were estrone, 17beta-estradiol, 17alpha-ethynylestradiol, 4-tert-octylphenol and bisphenol A. Results obtained from the validation studies yielded comparable results in both cases. Recoveries in spiked wastewaters at 50 ng/l were higher than 90% for all the compounds, except for 4-tert-octylphenol (75%). Repeatability and reproducibility were adequate, varying from 1.6 to 14%, except for estrone which reproducibility was 28% when the derivatization-GC-MS method was applied. Limits of detection calculated ranged from 2.5 to 27.5 ng/l with differences between both methods from 1.1 (estrone) to 10.4 (bisphenol A) times. Both methods were successfully applied to the analysis of the target compounds in sewage treatment plant influents and effluents. Traces of bisphenol A, 4-tert-octylphenol, estrone and 17beta-estradiol were detected at concentration levels ranging from 13.3 to 1105.2 ng/l.

Endocrine Glands↗

PubMed2004

New considerations about the separation and quantification of antimony species by ion chromatography-hydride generation atomic fluorescence spectrometry.

A new method for the speciation of inorganic [Sb(III) and Sb(V)] and organic (Me3SbCl2) antimony species by using a polystyrene-divinylbenzene-based anion-exchange HPLC column (Hamilton PRP-X100) coupled to hydride generation atomic fluorescence spectrometry (HG-AFS) is presented. Several mobile phases were tested for the baseline separation of these three antimony species, investigating in detail experimental parameters such as concentration and pH. The best efficiency and resolution was achieved by using a gradient elution between diammonium tartrate 250 mmol l(-1) pH 5.5 (A) and KOH 20 mmol l(-1) pH 12 (B). The gradient programme used was 100% B for 1.5 min, decreasing to 0% B in 0.1 min and maintained the elution with 100% A for 5.5 min. Analysis time was less than 7 min. Equilibration of the column with the complexing mobile phase was found to be critical in order to avoid Sb(III) double peak formation. Dilution in diammonium tartrate medium was necessary in order to avoid Sb(III) oxidation at microg l(-1) concentration level. Detection limits of 0.06 microg l(-1) for Sb(V), 0.09 microg l(-1) for Me3SbCl2 and 0.04 microg l(-1) for Sb(III) as well as repeatability and reproducibility better than 5% R.S.D. (n = 10) and 9% R.S.D. (n = 30) (for 1 and 5 microg l(-1) of Sb(V) and Sb(III) and 5 and 10 microg l(-1) of Me3SbCl2) were obtained. Accuracy and recovery studies were carried out by analysing one river freshwater sample and two water certified reference materials. The proposed methodology can be considered reliable and straightforward for antimony speciation in fresh water samples.

Antimony↗

PubMed2005

Dynamic ultrasound-assisted extraction of colistin from feeds with on-line pre-column derivatization and liquid chromatography-fluorimetric detection.

A dynamic ultrasound-assisted extraction (UAE) method with on-line pre-column derivatization/high performance liquid chromatography (HPLC) and fluorimetric detection is proposed for the analysis of colistin in feed. A flow injection manifold is used for the development of the extraction and derivatization steps and for interfacing them with the separation/detection step, thus providing an on-line approach with the advantage of minimum sample handling. The derivatization was performed with ortho-phthaldialdehyde and 2-mercaptoethanol. The optimum conditions for colistin extraction and formation of the fluorescent derivative have been obtained by experimental design methodology. The use of a high-intensity probe sonication makes UAE an expeditious (7 min versus > 1 h) and efficient (93.1-98.2% versus 87.5-94% of recovery) alternative as compared with extraction using an ultrasonic bath. The within-laboratory reproducibility and repeatability, expressed as percentage of relative standard deviation, were 5.2 and 5.8, respectively.

Animal Feed↗

PubMed2005

Determination of (fluoro)quinolone antibiotic residues in pig kidney using liquid chromatography-tandem mass spectrometry. I. Laboratory-validated method.

A new LC-MS/MS method has been developed for the multiresidue determination of 11 (fluoro)quinolone antibiotics (FQs), including acidic and amphoteric species, around their maximum residue level (MRL) in pig kidney. The procedure involves a common sample preparation by solid-phase extraction on disposable extraction cartridges followed by a fast reversed-phase liquid chromatography-tandem mass spectrometry analysis. The method was validated according to the Commission Decision 2002/657/CE. The accuracy of the method was satisfactory with recoveries included in the interval 80-100%. The precision results showed mean repeatability and reproducibility coefficients of 7.4% and 11.8%, respectively. Limits of quantification much lower than the MRLs could be obtained.

Animals↗

PubMed2005

On-matrix derivatisation-extraction of precursors of nitrogen- and sulfur-mustards for verification of chemical weapons convention.

Development and refinement of sample preparation protocols for retrospective detection and identification of chemical warfare agents (CWAs) and their markers is of paramount importance from verification point of view of chemical weapons convention (CWC). Precursors of nitrogen- and sulfur-mustards (NMPs and SMPs) are polar adsorptive markers of vesicant class of CWAs. Their detection in a given environmental sample may imply past contamination with mustards. For the efficient extraction of NMPs and SMPs from soil, on-matrix derivatisation-extraction (OMDEX) method was developed and optimized. The method involved trifluoroacetylation of analytes on soil itself, followed by extraction with suitable solvent. The extracted samples were analyzed by gas chromatography-mass spectrometry (GC-MS). This virtually single-step sample preparation offered better recoveries of NMPs and SMPs in comparison to conventionally used extraction, evaporation and derivatisation. The best recoveries of analytes were obtained with acetonitrile by OMDEX method. Dynamic linearity range of trifluoroacetylated (TFA) derivatives of NMPs and SMPs was 1-12 microg/L in GC-MS analysis in SIM mode. Repeatability and reproducibility of this technique containing 5 and 10 microg analytes/gm soil was <3.3% and <4.6%, respectively. OMDEX technique was finally applied for the detection of TFA derivatives of NMPs in the soil sample supplied in 16th official proficiency test conducted by OPCW in October 2004.

Calibration↗

PubMed2005

Capillary zone electrophoresis method for the simultaneous determination of cations in honey.

A capillary electrophoresis system for the simultaneous determination of cations in honey samples has been developed. The complete separation and quantification of K+, Ca2+, Na+, Mg2+, Mn2+, Ni2+ and Li+, which represent more than 99% of the total content of cations in honey, can be achieved in 4 min with only a dilution and filtration of the honey sample. Electrolyte solution was composed by 10 mM imidazole as the carrier buffer and background absorbance provider and acetic acid as the complexing agent (pH 3.60). The running voltage was + 25 kV at 25 degree C. Indirect UV detection was achieved at 185 nm. Under the optimum conditions the detection limits ranged from 0.02 to 48.2 mg/kg and the quantification limits have ranged from 0.41 to 48.7 mg/kg. Precision data in honey samples analysed have shown repeatability and reproducibility RSD (%) lower than 2.84 and 6.62%, respectively. Recoveries of cations in honey samples analysed have ranged from 88.5 to 101.8%. These cations were identified by their relative migration times with regard to Ba2+ migration time used as reference standard and they were quantified by using an external standard calibration. Twenty-five honey samples were analysed to test the proposed method. Mean contents of 1.22 x 10(3), 93, 85, 54, 11, 1.9 and 2.3 mg/kg were found, respectively, for K+, Ca2+, Na+, Mg2+, Mn2+, Ni2+ and Li+ cations in analysed honeys. These results were similar than the obtained by other authors.

Calcium↗

PubMed2005

Analysis of polymeric phenolics in red wines using different techniques combined with gel permeation chromatography fractionation.

A multiple-step analytical method was developed to improve the analysis of polymeric phenolics in red wines. With a common initial step based on the fractionation of wine phenolics by gel permeation chromatography (GPC), different analytical techniques were used: high-performance liquid chromatography-diode array detection (HPLC-DAD), HPLC-mass spectrometry (MS), capillary zone electrophoresis (CZE) and spectrophotometry. This method proved to be valid for analyzing different families of phenolic compounds, such as monomeric phenolics and their derivatives, polymeric pigments and proanthocyanidins. The analytical characteristics of fractionation by GPC were studied and the method was fully validated, yielding satisfactory statistical results. GPC fractionation substantially improved the analysis of polymeric pigments by CZE, in terms of response, repeatability and reproducibility. It also represented an improvement in the traditional vanillin assay used for proanthocyanidin (PA) quantification. Astringent proanthocyanidins were also analyzed using a simple combined method that allowed these compounds, for which only general indexes were available, to be quantified.

Chemical Fractionation↗

PubMed2006

Non-destructive method to determine halophenols and haloanisoles in cork stoppers by headspace sorptive extraction.

The new solvent-free technique called headspace sorptive extraction (HSSE) was used to determine 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, 2,4,6-trichloroanisole, 2,3,4,6-tetrachloroanisole, 2,4,6-tribromoanisole, pentachloroanisole in cork stoppers, without grinding them, as these may be responsible for the cork taint off-flavour in wine. The best HSSE sorption kinetics for the target analytes were obtained after submitting the spiked corks to 100 degrees C for 1h, followed by a 30 min stabilization time at room temperature. The stir bar was desorbed in a thermal desorption system coupled to a gas chromatograph-mass spectrometer. The method proposed showed good linearity over the concentration range tested, 1-70 ngg(-1), and correlation coefficients ranged from 0.90 to 0.99 for all the analytes. The reproducibility and repeatability of the method were estimated between 4.91 and 12.67%. The effect of the different cork matrixes on the extraction recovery of the target compounds was studied, with the natural corks showing the higher recovery percentage in relation to agglomerate ones.

Anisoles↗

PubMed2006

Determination of polybrominated diphenyl ethers at trace levels in environmental waters using hollow-fiber microporous membrane liquid-liquid extraction and gas chromatography-mass spectrometry.

In this study, we present a simple and easy-to-use extraction method that is based on a hollow-fiber microporous membrane liquid-liquid extraction (HF-MMLLE), as an extraction technique, followed by gas chromatography-mass spectrometry (GC-MS) to determine a group of brominated flame retardants (BFRs), polybrominated diphenyl ethers (PBDEs), at trace levels in aqueous samples. The hollow-fiber membrane (HF) filled with organic solvent was immersed into the aqueous sample, spiked with the analytes at ng l(-1) level, and stirred for 60 min. The proposed method could attain enrichment factors (E(e)) up to 5200 times, after optimising parameters, such as organic solvent, stirring speed and extraction time, that affect the extraction. The HF-MMLLE-GC-MS method was successfully applied to the extraction of PBDEs from tap, river and leachate water samples with spike recoveries ranging from 85% to 110%. The method validation with reagent and leachate water samples provided good linearity, detection limits of 1.1 ng l(-1) or lower, both in reagent and leachate water, as well as satisfactory precision in terms of repeatability and reproducibility with values of % relative standard deviation (%RSD) lower than 8.6 and 16.9, respectively.

Bromine↗

PubMed2006

Simultaneous determination of the endocrine disrupting compounds nonylphenol, nonylphenol ethoxylates, triclosan and bisphenol A in wastewater and sewage sludge by gas chromatography-mass spectrometry.

An integrated analytical method for the simultaneous determination of 4-n-nonylphenol (4-n-NP), nonylphenol monoethoxylate (NP1EO), nonylphenol diethoxylate (NP2EO), bisphenol A (BPA) and triclosan (TCS) in wastewater (dissolved and particulate phase) and sewage sludge was developed based on gas chromatography-mass spectrometry. Chromatographic analysis was achieved after derivatization with bis(trimethylsilyl)trifluoroacetamide (BSTFA). Extraction from water samples was performed by solid-phase extraction (SPE). The optimization of SPE procedure included the type of sorbent and the type of the organic solvent used for the elution. Referred to solid samples, the target compounds were extracted by sonication. In this case the optimization of the extraction procedure included the variation of the amount of the extracted biomass, the duration and the temperature of sonication and the type of the extraction organic solvent. The developed extraction procedures resulted in good repeatability and reproducibility with relative standard deviations (RSDs) less than 13% for all the tested compounds for both types of samples. Satisfactory recoveries were obtained (>60%) for all the compounds in both liquid and solid samples, except for 4-n-NP, which gave recoveries up to 35% in wastewater samples and up to 63% in sludge samples. The limits of detection (LODs) of the target compounds varied from 0.03 (4-n-NP) to 0.41 microg l(-1) (NP2EO) and from 0.04 (4-n-NP) to 0.96 microg kg(-1) (NP2EO) for liquid and solid samples, respectively. The developed methods were successfully applied to the analysis of the target compounds in real samples.

Endocrine Disruptors↗

PubMed2006

Development of a simple hollow fibre supported liquid membrane extraction method to extract and preconcentrate dinitrophenols in environmental samples at ng L(-1) level by liquid chromatography.

An easy and rapid hollow-fibre supported liquid membrane method (HFSLM) has been developed to extract and determinate the total concentration of four dinitrophenols in environmental water at ng L(-1) level. This extraction method provides a high selectivity, short extraction time and very low cost for real samples. It is a three-phase system, aqueous-organic-aqueous, where the organic solvent is held into the fibre pores, being in contact with the two other phases. The organic phase is formed by two different organic solvents, with two different polarities, n-undecane and toluene (1:1). The optimization step was performed using a three-variable Doehler design, involving three factors, stirring speed, fibre length and sample volume. The organic phase composition, as well as the pH of the acceptor and donor phases was also optimized. The extraction equilibrium was reached after 30 min, after which essentially the total amount (90-80%) of the four dinitrophenolic compounds were extracted from the sample. Better repeatability and reproducibility at the expense of lower enrichment factors was obtained compared with other methods, employing incomplete extraction during a fixed time. The matrix effect was tested by performing extractions from leachate water and river water. This method is linear in the range 0.1-100 microgL(-1) in different matrices, with detection limit around 100 ng L(-1), after extraction of 6 mL of sample and using high performance liquid chromatography for final analysis.

Analytic Sample Preparation Methods↗

PubMed2006

Static coefficient of friction between stainless steel and PMMA used in cemented hip and knee implants.

BACKGROUND: Design of cemented hip and knee implants, oriented to improve the longevity of artificial joints, is largely based on numerical models. The static coefficient of friction between the implant and the bone cement is necessary to characterize the interface conditions in these models and must be accurately provided. The measurement of this coefficient using a repeatable and reproducible methodology for materials used in total hip arthroplasty is missing from the literature. METHODS: A micro-topographic surface analysis characterized the surfaces of the specimens used in the experiments. The coefficient of friction between stainless steel and bone cement in dry and wet conditions using bovine serum was determined using a prototype computerized sliding friction tester. The effects of surface roughness (polished versus matt) and of contact pressure on the coefficient of friction have also been investigated. FINDINGS: The serum influences little the coefficient of friction for the matt steel surface, where the mechanical interactions due to higher roughness are still the most relevant factor. However, for polished steel surfaces, the restraining effect of proteins plays a very relevant role in increasing the coefficient of friction. INTERPRETATION: When the coefficient of friction is used in finite element analysis, it is used for the debonded stem-cement situation. It can thus be assumed that serum will propagate between the stem and the cement mantle. The authors believe that the use of a static coefficient of friction of 0.3-0.4, measured in the present study, is appropriate in finite element models.

Biocompatible Materials↗

PubMed2004

Rapid and quantitative detection of mumps virus RNA by one-step real-time RT-PCR.

We developed a new TaqMan-based one-step real-time reverse transcription-polymerase chain reaction (RT-PCR) assay for detection and quantification of mumps virus RNA. Oligos targeting the matrix protein gene of mumps virus were designed by using our oligo designing and analyzing software, Oligoware 1.0. Oligos's specificity was tested with 5 strains (4 laboratory isolated and 1 Jeryl Lynn strain) of mumps virus. The suggested TaqMan-based one-step real-time RT-PCR assay correctly detected the 4 laboratory-isolated strains and 1 Jeryl Lynn strain. To confirm the specificity of the TaqMan PCR assay, parainfluenza type 1, 2, 3 strains, sendai virus, and measles virus (vaccine strain) were tested, and no cross-reactivity was observed between mumps and tested strains. In addition, a BLAST (NCBI) search showed no genomic cross-reactivity with other viruses or cells. Testing of the assay's reproducibility was repeated several times, and the same results were achieved. The new assay was able to quantify the concentrations of mumps virus gene ranging from 10(1) to 10(8) copies per reaction sensitively with generated plasmid standards. In addition, it was shown that a significant correlation (R2 = 0.9564) between genome number as determined by one-step real-time RT-PCR and the corresponding number of plaque in paired samples was found with regression analysis. The results of one-step real-time RT-PCR assay also corresponded well to those of nested PCR. We conclude that our one-step real-time RT-PCR assay is a reliable, specific, and sensitive tool for the diagnosis of mumps virus. We consider that these results come from highly conserved primers and probe set that were designed with Oligoware 1.0.

Base Sequence↗

PubMed2006

Aortic valve-sparing repair with autologous pericardial leaflet extension has a greater early re-operation rate in congenital versus acquired valve disease.

OBJECTIVE: We sought to establish whether there was a difference in outcome after aortic valve repair with autologous pericardial leaflet extension in acquired versus congenital valvular disease. METHODS: One hundred and twenty-eight patients underwent reparative aortic valve surgery at our institution from 1997 through 2005 for acquired or congenital aortic valve disease. The acquired group (43/128) (34%) had a mean age of 56.4+/-20.3 years (range, 7.8-84.6 years) and the congenital group (85/128) (66%) had a mean age of 16.9+/-19.2 years (range, 0.3-82 years). The endpoints of the study were mortality and reoperation rates. RESULTS: Thirty-day mortality was 0/43 (0%) in the congenital group and 1/85 (1.1%) in the acquired group. Late mortality in the acquired group was 3/43 (7%) and 3/84 (3.5%) in the congenital group (neither early nor late proportion of mortality is significantly different between the two groups, according to the nonparametric Binomial test for proportions). There were 13 total reoperations among 11 patients: 1/43 (2.3%) in the acquired group and 10/85 (11.7%) in the congenital group (p=0.07). Two patients from the congenital group were reoperated on twice. The mean interval between original repair and reoperation was 3.6+/-5 years (range, 0-7 years) for acquired and 3.5+/-2.5 years (range, 0-7 years) for the congenital group (Wilcoxon 2-sample test, p=0.7). Total early reoperation rate (<30 days after first surgery) was 11/128 (8.5%); for the congenital group 9/85 (10.5%) and for the acquired group 2/43 (4.6%). Early reoperation rate was significantly higher among the congenital group (p=0.013). The remaining patients are well at mean follow-up of 2.8+/-2.4 years (range 0-7.9). In the acquired group, the mean postoperative aortic regurgitation and stenosis grade by echocardiography was 0.5+/-0.3 (scale, 0-4) and 0.3+/-0.1, respectively. In the congenital group, the follow-up, mean aortic regurgitation and stenosis were 0.9+/-0.8 and 0.5+/-0.3, respectively. CONCLUSIONS: There was no significant difference in early or late mortality and late reoperation rate between the two groups. Early reoperation rate was higher in the congenital versus the acquired aortic valvular disease group. This study supports the fact that the valve-sparing technique is safe and reproducible and repeatable in patients with acquired valve disease.

Adolescent↗