Search results for "Detection limit"
showing 10 items of 810 documents
In-tube solid-phase microextraction and liquid chromatography using a monolithic column for the selective determination of residual ethylenediamine i…
2009
The selective determination of the diamine ethylenediamine (EDA) in the presence of a higher amount of residual dimethylamine in cationic polymers has been developed. The strategy uses both a solution derivatization with a selective agent of primary amines such as o-phthaldialdehyde-N-acetyl-L-cysteine (OPA-NAC) and an in-tube solid-phase microextraction (IT-SPME) coupled to liquid chromatography (LC). A 70 cm long, 0.32 mm internal diameter, and 3 microm thick commercially available capillary column coated with 95% polydimethylsiloxane and 5% polydiphenylsiloxane was employed to replace the injection loop of a Rheodyne injection valve. A volume of 1 mL of derivatized sample was passed thro…
A cost-effective method for estimating di(2-ethylhexyl)phthalate in coastal sediments.
2013
This study describes the development of a new method for the analysis of di(2-ethylhexyl)phthalate (DEHP) using 0.1-0.3 g of sediment sample, based on matrix solid phase dispersion (MSPD) using C18 as dispersant phase (0.4 g) and acetonitrile-water as eluting solvent (3.4 mL 1:3.25, v/v). No evaporation step is required. 3 mL of extracts were processed on-line by in-tube solid phase microextraction (IT-SPME) coupled to capillary liquid chromatography (CapLC) and diode array detector (DAD). A short analytical column Zorbax SB C18 (35×0.5 mm, 5 μm) provided suitable results. FTIR-ATR was employed for characterizing sediment samples and MSPD procedure. The total analysis time was less than 20 …
Combining high performance thin layer chromatography with minispectrometer-fiber optic probe-coupled to smartphone for in place analysis: Lactose qua…
2021
ABSTRACT An in place colorimetric method has been proposed for estimation of the quantity of lactose in several matrix (milk, water effluents and surfaces). Analyzing the amount of this carbohydrate it can be control the product, the cleanliness of the parts of the dairy companies and it can avoid contamination of milk products produced there. This method combines the use of HPTLC for sugars separation with novel analytical devices as minispectrophotometer with fiber optic coupled to a smartphone. In order to measure the lactose a colorimetric reaction has been used. Variable volumes of samples or stock solutions were deposited in nano-silica gel layer, a mobile phase of acetonitrile:water:…
Enantiomeric separation of amphetamine and related compounds by liquid chromatography using precolumn derivatization witho-phthaldialdehyde
2002
The utility of the derivatization reagento-phthaldialdehyde (OPA) in combination with the chiral thiol N-acetyl-L-cysteine (NAC) for the enantioselective analysis of primary amphetamines and structurally related substances has been investigated. The diastereomers obtained have been chromatographed on an achiral, reversed phase C18 column (125 mm×4 mm i.d., 5 μm), and detected fluorimetrically. The influence of parameters affecting the chromatographic separation as well as the derivatization reaction has been optimized, using amphetamine, norephedrine, norepinephrine and 3,4-methylenedioxyamphetamine (MDA) as model compounds. On the basis of the results obtained, possible conditions for the …
Rapid screening of organophosphorus pesticides in honey and bees by liquid chromatography—Mass spectrometry
2002
Twenty-two organophosphorus pesticide residues were simultaneously determined in honey and honeybee samples by extraction procedures based on solid-phase and liquid chromatography-atmospheric pressure chemical ionization-mass in positive and negative ionization modes. Pesticides in honeybee samples were extracted by matrix solid phase dispersion with C18 silica and subsequently eluted with a mixture of dichloromethane-methanol (85∶15, v/v). The average recoveries from spiked honeybees (0.5–10 μg g−1) ranged from 76% for coumaphos to 100% for omethoate, with relative standard deviations between 3 and 17%. Limits of detection were ≤0.13 μg g−1 and limits of quantification were ≤0.43 μg g−1. H…
Identification of lipid binders in old oil paintings by separation of 4-bromomethyl-7-methoxycoumarin derivatives of fatty acids by liquid chromatogr…
2005
A HPLC-fluorescence method for identification of drying oils from binding media or protective film used in pictorial works of art prior to conservation or restoration is proposed. Fluorescence derivatization of fatty acids released by hydrolysis of structural drying oils is studied. The derivatization reagent was 4-(bromomethyl)-7-methoxycoumarin with 18-crown-6 as catalyst. Mobile phase was programmed from methanol-water (90:10 v/v) to methanol-water (100:0 v/v) in 25 min. The excitation and emission wavelengths were 325 and 395 nm, respectively. Under these chromatographic conditions, coumarin derivatives of myristic, palmitic, oleic and stearic acids were satisfactorily resolved. The met…
Flow-injection spectrophometric determination of propoxur with p-aminophenol
1992
Abstract The spectrophotomeric determination of propoxur [2-(1-methyxlthoxy)phenyl methyl carbamate] was carried out with p -aminophenol (PAP) in a flow system. The method involves the on-line hydrolysis with NaOH of propoxur to 2-isopropoxyphenol and the oxidation of PAP to its relative quinone imine with KIO 4 and the reaction between the phenolate and the quinone imine. A four-channel flow manifold was employed to carry out all the different steps of the reaction considered, monitoring the indo dye formed at 600 nm. The developed procedure provides a typical calibration line of A = 0.000 7 + 1.8 × 10 3 C ( A = absorbance; C = concentration in M) with a regression coefficient of 0.9998 an…
Environmental and food applications of LC-tandem mass spectrometry in pesticide-residue analysis: An overview
2003
An overview is given on pesticide-residue determination in environmental and food samples by liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS). Pesticides comprise a large number of substances that belong to many completely different chemical groups, the only common characteristic is that they are effective against pests. They still constitute a challenge in MS because there is no collective pathway for fragmentation. A brief introduction to the theory of tandem MS permits a discussion of which parameters influence the ionization efficiency when the ions are subjected to different actions. Emphasis is placed on the different tandem MS instruments: triple and ion-trap quad…
Rapid and sensitive ultra-high-pressure liquid chromatography-quadrupole time-of-flight mass spectrometry for the quantification of amitraz and ident…
2008
Liquid chromatography under high pressure in combination with quadrupole time-of-flight mass spectrometry (QqTOF-MS and MS/MS) has been used to detect amitraz degradation products in pears, to characterize their structures, and to evaluate their occurrences in samples of different origins. Using the proposed approach, the parent pesticide and four degradation products were identified. To this end, pear samples were extracted with ethyl acetate and anhydrous sodium sulphate. Amitraz was found to be rapidly decomposed into four related compounds, of which N-(2,4-dimethylphenyl)formamidine (DMPF) was the most abundant and persistent. N,N'-bisdimethylphenylformamidine (BDMPF), 2,4-dimethylforma…
Development of monoclonal antibody-based competitive immunoassays for the detection of picoxystrobin in cereal and oilseed flours
2012
Picoxystrobin is a new generation fungicide primarily developed to be used in cereal crops. In the present study a novel collection of specific monoclonal antibodies has been produced using different immunizing haptens based on a carboxy-functionalized identical spacer arm attached to alternative positions of the target pesticide molecule. Two competitive enzyme-linked immunosorbent assays have been developed employing hapten heterology, one using the antibody-coated direct format and the other in the conjugate-coated indirect format. Both immunoassays have been characterized in terms of selectivity, solvent tolerance, and buffer conditions, affording similar limits of detection at or below…