Search results for "Detection limit"
showing 10 items of 810 documents
Fast Separation and Determination of Sterols in Vegetable Oils by Ultraperformance Liquid Chromatography with Atmospheric Pressure Chemical Ionizatio…
2010
A method for the determination of sterols in vegetable oils by ultraperformance liquid chromatography (UPLC) with atmospheric pressure chemical ionization mass spectrometry detection has been developed. The separation of sterols was optimized in terms of mobile phase composition, column temperature and flow rate. The optimal conditions were achieved using an Acquity UPLC BEH C18 column (50 x 2.1 mm, 1.7 microm) with a mobile phase consistent of acetonitrile/water (0.01% acetic acid) using a linear gradient, at a flow rate of 0.8 mL min(-1) and column temperature of 10 degrees C, giving a total analysis time below 5 min. The determination was performed in selective ion recording mode. The li…
Optimization of a microwave-assisted extraction large-volume injection and gas chromatography–ion trap mass spectrometry procedure for the determinat…
2006
Abstract A sensitive and rapid method for the determination of polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs) and polychlorinated naphthalenes (PCNs) in sediment samples is proposed. The method involving microwave-assisted extraction (MAE) and large-volume injection (LVI) gas chromatography (GC)–ion trap mass spectrometry (ITMS), and the experimental conditions were optimized using the statistical design of experiments (DOE). A Plackett–Burman (P–B) design was chosen to estimate the influence of five factors, such as resonance excitation voltage (EV), isolation time (IT), excitation time (ET), ion source temperature (IST) and electron energy (EE) on the analytical r…
Comparison of gas and liquid chromatography coupled to mass spectrometry for the residue analysis of pesticides in organges
2001
Liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI), and gas chromatography-mass spectrometry (GC-MS) with electron impact ionization (EI), are compared for the determination of eight pesticides in oranges. Seven of the selected pesticides, chlorpyriphos, chlorpyriphos-methyl, imazalil, α and β-endosulfan, endosulfan sulphate and dicofol, are commonly determined by GC whereas one, thiabendazole, can only be directly determined by LC. Primary ions [M-H]− or [M-Cl+O]− are obtained using LC-APCI-MS in negative ionization (NI) mode. In contrast, a high degree of fragmentation is reported with GC-MS. Both techniques were applied to oranges, which …
Determination of fungicide residues in fruits and vegetables by liquid chromatography–atmospheric pressure chemical ionization mass spectrometry
2002
Abstract A liquid chromatography (LC) method for the quantitative determination of five fungicide residues (dichloran, flutriafol, o -phenylphenol, prochloraz and tolclofos methyl) in oranges, lemons, bananas, peppers, chards and onions is described. The residues were extracted by matrix solid-phase dispersion (MSPD) using C 8 . Quantitative analysis was performed by isocratic LC coupled to quadrupole mass spectrometer using atmospheric pressure chemical ionization in the negative ionization mode. The limit of quantification was 0.01 mg kg −1 for flutriafol, o -phenylphenol and dichloran, and 0.1 mg kg −1 for prochloraz and tolclofos methyl. The MSPD method is also suitable for LC–UV analys…
Multiple-stage mass spectrometric analysis of six pesticides in oranges by liquid chromatography–atmospheric pressure chemical ionization–ion trap ma…
2004
Abstract Six pesticides were determined by liquid chromatography (LC) with positive ion (PI) atmospheric pressure chemical ionization quadrupole ion-trap tandem mass spectrometry (APCI–MS–MS). Ion fragmentation was studied by MS, MS 2 and MS 3 . Fragmentation of the pesticides produced ions formed by various losses from the side-chains and through heterocyclic ring opening, but without any common fragmentation pathway. Multiple reaction monitoring (MRM) of MS, MS 2 and MS 3 was used to identify and quantify the pesticides. The samples were extracted with ethyl acetate and dried over anhydrous sodium sulfate. Comparison of the three MS modes showed that MS 3 is slightly less sensitive but mu…
Determination of carbamate residues in fruits and vegetables by matrix solid-phase dispersion and liquid chromatography-mass spectrometry.
2000
Abstract Thirteen carbamates were analysed in orange, grape, onion and tomatoes by matrix solid-phase dispersion (MSPD) followed by liquid chromatography–mass spectrometry (LC–MS). Electrospray (ES) and atmospheric pressure chemical ionisation (APCI) were compared and both gave similar results in terms of sensitivity and structural information because at 20 V fragmentor voltages the fragmentation is minimal. The efficiency of different solid-phases (C18, C8, cyano, amine and phenyl) for the MSPD was compared. Mean recoveries using C8 varied from 64 to 106% with relative standard deviations of 5–15% in the concentration range of 0.01–10 mg kg−1. Matrix constituents did not interfere signific…
Analysis of organophosphorus pesticides in honeybee by liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry.
2001
Pesticides applied in extended agricultural fields may be controlled by means of bioindicators, such as honeybees, in which are the pesticides bioaccumulate. Liquid chromatography-atmospheric pressure chemical ionization-mass spectrometry (LC-APCI-MS) experiments with positive (PI) and negative (NI) ion modes were optimized for the analysis of 22 organophosphorus pesticides in honeybee samples. The extraction required 3 g of sample, which was extracted with acetone. The extract was purified with coagulating solution and reextracted with Cl(2)CH(2). Pesticides studied could be detected by both ionization modes except for parathion, parathion-methyl, and bromophos, which did not give signals …
Metal speciation in solid matrices
1994
The literature on metal ion speciation in solid matrices is reviewed, taking into account its applications in the analysis of soil, sediment, biological materials, foodstuff and other solid samples. The pretreatment methods of various solid materials required for carrying out speciation studies have been highlighted. The basis of the methods of separation of different species from matrices, such as sequential extraction, selective extraction, etc. is discussed. The instrumental techniques used for the characterization of different chemical species in solid matrices have been mentioned. The literature survey reveals the analytical details of the developed methodologies, and these have been e…
New flow-multicommutation method for the photo-chemiluminometric determination of the carbamate pesticide asulam
2004
This paper deals with a straightforward automated method for the determination of asulam in water based on the use of a flow manifold including three computer-controlled solenoid valves. The method involves irradiating on an aqueous solution of asulam in glycine buffer at pH 8.3 with UV light during 90 s, then follows the oxidation with potassium permanganate in a sulphuric medium and chemiluminescence-based detection of the resulting photoproducts. The limit of detection thus achieved is 40 mug l(-1). The detector response is linear up to a 5 mg l(-1) asulam concentration and the throughput is 30 samples h(-1). In parallel tests, oxidation with alkaline ferricyanide was also assessed and t…
A tandem-flow assembly for the chemiluminometric determination of hydroquinone
2003
A direct chemiluminescent procedure for determination of hydroquinone based on the emergent flow methodology known as multicommutation or tandem-flow is presented for first time. The manifold was based on a set of three channels and three solenoid valves; and, the determination was performed at 60degreesC and at flow-rate of 7.5 ml min(-1). The complete cycle lasted 35 s, which resulted in a sample flow trough of 103 h(-1). The chemical process was the hydroquinone oxidation with the system sulphuric acid-potassium permanganate; and the light emission was clearly enhanced by the presence of quinine sulphate and benzalkonium chloride reaching a detection limit of 30 Rg l(-1). The dynamic int…