Search results for "Standard solution"
showing 10 items of 29 documents
Improved detection limit for ammonium/ammonia achieved by Berthelot's reaction by use of solid-phase extraction coupled to diffuse reflectance spectr…
2005
Abstract The proposed procedure is based on the extraction of the indothylmol blue into C 18 solid-phase extraction (SPE) membranes and direct quantification on the membrane surface by diffuse reflectance spectroscopy. The analytical performance of the proposed method has been evaluated for standard solutions of ammonium using reflectance values, R , as well as the Kubelka–Munk function, F ( R ). The results have been compared with those obtained by the conventional method, which uses UV–vis absorption spectroscopy with a sensor-based method. The described methodology provided satisfactory linearity and reproducibility within the ammonium concentration intervals 25–250 μg L −1 and 25–500 μg…
Uptake and translocation monitoring of imidacloprid to chili and tomato plants by molecularly imprinting extraction - ion mobility spectrometry
2019
Abstract The degradation of imidacloprid in soil and its uptake and translocation to chili and tomato plants was evaluated, as a proof of concept, of the possibilities of the combination of molecularly imprinted polymers (MIPs) and ion mobility spectrometry (IMS) for a fast and sensitive bioprocesses monitoring tool. To do it, a method based on the selective extraction of imidacloprid from soil and plant materials was developed. In the selected conditions, the MIP-IMS procedure provided a recovery of imidacloprid in soil and plant samples from 102 to 114%, for spiked concentration levels from 0.2 to 2.0 μg g−1. Precision of the methodology, expressed as the relative standard deviation (RSD)…
A rapid HPLC assay for zearalenone in laboratory cultures ofFusarium graminearum
1993
A high pressure liquid chromatographic (HPLC) method to determine zearalenone in corn contaminated withFusarium graminearum is described. After extraction with methanol-water and solvent partition, samples were cleaned up by applying the extract to a disposable silica cartridge and by eluting the toxin with a mixture of hexane/dry ethyl ether (5/5). Separation was achieved by a reverse phase μBondapak C18 column followed by fluorescence detection using an excitation wavelength at 274 nm and an emission wavelength at 440 nm. Detection limit was about 5 ng. Recoveries ranging from 85.37 to 100.97%, in standard solutions range 30–0.5 µg/ml, were found.
Flow injection Fourier transform infrared determination of caffeine in coffee
1999
Abstract A fully automatized procedure has been developed for the Fourier transform infrared (FT-IR) spectroscopic determination of caffeine in coffee samples. The method involves the on-line extraction of caffeine with CHCl3. Samples, weighed inside empty PTFE cartridges of 0.5 cm internal diameter (i.d.) and 1.5 ml volume, were humidified with four drops of 0.25 M NH3. The cartridge was installed in a flow manifold, in which samples were extracted in a closed-flow system with 1 ml CHCl3 during 6 min. Four hundred microliters of the extract were introduced in a microflow cell and absorbance measured as a function of time at 1659 cm−1, with a baseline established between 1900 and 830 cm−1, …
Method development of levoglucosenone analysis by UHPLC-UV-MS in fast pyrolysis samples and aspects of its degradation in aqueous samples
2020
Levoglucosenone ((1S,5R)-6,8-dioxabicyclo[3.2.1]oct-2-en-4-one or LGO; CAS number: 37112-31-5) is an extensively studied biomass based chemical and its potential applications in organic synthesis, as well as in the extraction of various natural substances, have been established; therefore developing dependable, yet fast and simple analytical methods for determining LGO in the products of thermochemical biomass processing is of great importance. In this work different UHPLC methods have been developed and compared for the determination of LGO in wood pyrolysis products. In addition to UV detection, LGO determination conditions by single quadrupole mass spectrometry have been adjusted with an…
Assessment of air passive sampling uptakes for volatile organic compounds using VERAM devices
2017
Abstract A calibration chamber has been designed and employed for the simple and easy determination of uptake sampling rate (RS) of volatile organic compounds (VOCs) from air using passive samplers. A flow of clean air was continuously spiked, at a constant VOC concentration, by the microinjection of a standard solution by means of a T-type tube. The developed system allowed the complete evaporation at room temperature of the standard solution in acetone and the air concentration of VOCs was easily controlled by the regulation of the clean air flow, the standard solution concentration and its flow. Active sampling was employed for monitoring the true concentration of the evaluated compounds…
Extension of the dynamic range of flame atomic absorption spectrometry using flow injection analysis with variable-volume dilution chambers
1996
Abstract A simple and inexpensive procedure is proposed for the extension of the dynamic range of flame atomic absorption spectrometry measurements using on-line dilution. The proposed methodology is based on the use of a manifold with two coupled dilution chambers and a zone injection system. The samples are prediluted in a closed system which includes a variable-volume mixing chamber (10–120 ml) and two injection valves. The samples are injected through one of these valves, and the other is employed to take 100 μl of prediluted samples which are then passed through a new dilution chamber (volume 1–10 ml) and aspirated by the nebulizer of the instrument. A third injection valve mounted in …
Flow injection-FTIR determination of dithiocarbamate pesticides
2000
A flow injection Fourier transform infrared spectrometric procedure has been developed for the determination the dithiocarbamate pesticides Ziram and Thiram in solid samples. All the operations involved, such as extraction, filtration and measurement, were integrated in the experimental set-up in order to avoid excessive manipulation of samples and standards. Ultrasonic assisted and mechanical extraction were evaluated for the solubilization of the analytes and, additionally, the effect of carrier flow rate, sample loop volume and the ratio between sample mass and volume of solvent employed were studied. Quantitative extractions with chloroform were obtained for both Ziram and Thiram, after…
On-line coupling of gel electrophoresis and inductively coupled plasma-sector field-mass spectrometry for the determination of dsDNA fragments.
2005
The on-line coupling of gel electrophoresis (GE) and inductively coupled plasma-mass spectrometry (ICPMS) is described for the first time. The new method combines the separation power of GE for large biomolecules and the high sensitivity and elemental selectivity of ICPMS. This coupling has been achieved by means of gels housed in glass tubes (length 2.5-20 cm; i.d. 0.5-5 mm). The gel is fixed by glass frits permeable for the analytes. After the electrophoretic separation at voltages up to 500 V, the analytes are transferred to the nebulizer of the ICPMS by an eluent stream, which is separated from the electrode chamber by a membrane. This filter blocks molecules with molecular masses large…
Quantitative colorimetric-imaging analysis of nickel in iron meteorites.
2011
A quantitative analytical imaging approach for determining the nickel content of metallic meteorites is proposed. The approach uses a digital image of a series of standard solutions of the nickel-dimethylglyoxime coloured chelate and a meteorite sample solution subjected to the same treatment as the nickel standards for quantitation. The image is processed with suitable software to assign a colour-dependent numerical value (analytical signal) to each standard. Such a value is directly proportional to the analyte concentration, which facilitates construction of a calibration graph where the value for the unknown sample can be interpolated to calculate the nickel content of the meteorite. The…