Search results for " limit"

Costruzioni in zone sismiche - progetto e verifica a presso-flessione agli stati limite ultimi.

2004

Investigating the level of significance of the coherence function in cardiovascular variability analysis

2002

Although the presence of significant coupling between cardiovascular variability series is usually verified according to the threshold value of 0.5 in the coherence function (CF), spectral estimator parameters should also be considered. In this study, the surrogate data technique was introduced to define the level of significance of the CF. The proposed method determined a frequency-dependent threshold over which the hypothesis of zero coherence was rejected. The weighted covariance method and the autoregressive method were used to estimate the CF on simulated series with different degrees of linear coupling and on real cardiovascular data. The threshold was dependent on the type and parame…

Development of immunoaffinity columns for pyraclostrobin extraction from fruit juices and analysis by liquid chromatography with UV detection

2010

Abstract Pyraclostrobin belongs to a new generation of fungicides widely used to preserve high valuable crops. In the present study, three monoclonal antibodies with different affinities to this modern strobilurin have been evaluated for their usefulness in the production of immunoaffinity columns suitable for the solid-phase extraction, concentration, and clean-up of residues from food commodities. Different immunosorbents were produced and characterized in terms of antibody immobilization efficiency, immunosorbent binding capacity, optimum elution conditions, and reusability. Covalent coupling of the antibodies to Sepharose–CNBr gel took place with high yield (over 90%), whereas the immun…

Selective determination of trimethylamine in air by liquid chromatography using solid phase extraction cartridges for sampling.

2004

Abstract The selective determination of trimethylamine (TMA) in air by liquid chromatography is reported. Sampling is effected by flushing air through C18-packed solid-phase extraction (SPE) cartridges at a flow rate of 15 mL/min for 15 min. Next, TMA is desorbed from the cartridges and injected into the chromatographic system. The analyte is then selectively retained on a precolumn ( 20 mm ×2.1 mm i.d., packed with 30 μm, Hypersil C18 phase), and derivatized on-line by injecting 9-fluorenylmethyl chloroformate (FMOC). Finally, the TMA-FMOC derivative is transferred to the analytical column ( 125 mm ×4 mm i.d., LiChrospher 100 RP18, 5 μm), and monitored at 262 nm. The method was applied to …

Tuning the selectivity of molecularly imprinted polymer extraction of arylcyclohexylamines: From class-selective to specific

2020

Abstract A molecularly imprinted polymer (MIP) has been prepared in presence of 3-hydroxy phencyclidine (3-OH PCP) as template by bulk polymerization using N,N-dimethylformamide, as porogenic solvent, for the selective solid-phase extraction (SPE) of arylcyclohexylamines from oral fluids. Experimental variables of the extraction procedure have been studied in order to increase both, extraction recovery of 3-OH PCP, used as model analyte, and imprinting factor. By modifying the composition of the washing solvent, the selectivity of the MIP extraction procedure can be tuned, moving from an arylcyclohexylamine selective method to a 3-OH PCP specific method. The applicability of the synthesized…

Synergistic combination of polyamide-coated paper-based sorptive phase for the extraction of antibiotics in saliva.

2021

Abstract The development of analytical methods that allow the simultaneous determination of a wide range of analytes with different properties is one of the focuses of attention in Analytical Chemistry. This work describes a proof-of-concept of the synergistic extraction of a planar paper-based sorptive phase modified with a polyamide such as nylon. This as-prepared sorptive phase enables the extraction of six penicillin-derived antibiotics of different polarity from human saliva samples in the same analysis, since the analytes either interact with the paper or with the nylon. The synthesis of the sorptive phase is simple as it only requires dipping the paper into an organic solution of the…

Amphetamine-type stimulants analysis in oral fluid based on molecularly imprinting extraction

2018

Abstract A methamphetamine-based molecularly imprinted polymer (MIP) has been prepared by bulk polymerization to recognize new psychoactive substances (NPS) of the amphetamine, cathinones and 2C families in oral fluid samples, being the first precedent of a synthetized MIP for the extraction and preconcentration 32 NPS including amphetamine type substances and synthetic cathinones from oral fluids. Pre-polymerization complex and resulting materials were appropriately characterized by infrared spectroscopy, scanning electron microscopy, and nitrogen adsorption-desorption isotherms. Appropriateness of the material for the specific recognition of the target analytes was also evaluated through …

Control of propranolol intake by direct chromatographic detection of alpha-naphthoxylactic acid in urine.

2002

A rapid chromatographic procedure with a C18 column, a mobile phase of 0.15 M sodium dodecyl sulfate (SDS)-10% (v/v) 1-propanol at pH 3 (0.01 M phosphate buffer), and fluorimetric detection, is reported for the control of propranolol (PPL) intake in urine samples, which are injected directly without any other treatment than filtration. The peak of PPL was only observed in samples taken a few hours after ingestion of the drug due to its extensive conjugation and metabolisation. The detection of several unconjugated PPL metabolites was therefore considered: desisopropylpropranolol (DIP), propranolol glycol (PPG), alpha-naphthoxylactic acid (NLT) and alpha-naphthoxyacetic acid (NAC). NLT showe…

Determination of the herbicide benfuresate by its photo-induced chemiluminescence using flow multicommutation methodology.

2007

The present paper deals with an analytical strategy based on coupling photo-induced chemiluminescence in a multicommutation continuous-flow methodology for the determination of the herbicide benfuresate. The solenoid valve inserted as small segments of the analyte solution was sequentially alternated with segments of the NaOH solution for adjusting the medium for the photodegradation. Both flow rates (sample and medium) were adjusted to required time for photodegradation, 90 s; and then, the resulting solution was also sequentially inserted as segments alternated with segments of the oxidizing solution system, hexacyanoferrate (III) in alkaline medium. The calibration range from 1 microg L(…

Evaluation of analytical performance of gas chromatography coupled with atmospheric pressure chemical ionization Fourier transform ion cyclotron reso…

2019

Abstract A new analytical method was established and validated for the analysis of eighteen halogenated flame retardants (HFRs)in food products. Gas chromatography (GC) coupled to Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) employing atmospheric pressure chemical ionization (APCI) was used for the identification and quantitation of contaminants. Intra-laboratory validation of the method was performed with respect to recovery, repeatability, linear calibration ranges, instrumental and method limits of quantitation (i-LOQ and m-LOQ), and trueness was verified where possible by analysis of reference materials (RMs). The validation results indicated recoveries of ana…