Ultraviolet detection HPLC

These authors noted the potential for the assay to underestimate the concentration of TSR due to decreased binding of metabolites relative to parent spinosad. However, the major residue found was parent spinosad, so underestimation of residues is not likely to be problematic. Overall, this method was validated in 34 matrices and showed excellent agreement with results obtained with a high-performance liquid chromatography/ultraviolet detection (HPLC/UV) method. ... 

Residue analytical methods for neonicotinoids in crops, soil and water samples have been developed. The basic principle of these methods consists of the following steps extraction of the crop and/or soil samples with acetone or the other organic solvent, cleanup by liquid-liquid partition or column chromatography, and quantitative analysis by high-performance liquid chromatography with ultraviolet detection (HPLC/UV). Simple column cleanup procedures are used to improve the accuracy and sensitivity of these methods. 

The analytical situation for DA is much better than for other phycotoxins groups and a HPLC method with ultraviolet detection (HPLC-UVD) [25-27] is used in most countries for official control. A liquid chromatography-mass spectrometry (LC-MS) method is being used in Australia and New Zealand for regulatory purposes [28, 29],... 

For the determination of the herbicide adsorption to the passive membranes, those were put in 100 ml of methanol (in experiments A-F) or acetone (in experiments G and H-K) and submitted to sonication with a Bandelin Sonarex Super RK102 H for lOmin. The obtained extracts were concentrated to 10ml and filtered by Acrodisc Gelman (Gelman Sciences, Inc., Arbor, MI) filters (0.45 tm in diameter) before being submitted to analysis by ELISA, in the case of atrazine (experiments A-D), or to gas chromatography with flame ionization detector (GC-FID) in the case of molinate (experiments E and F), or to HPLC with ultraviolet detection (HPLC-UV) in the case of molinate and bentazone (experiments G and H-K). 

The method for chloroacetanilide soil metabolites in water determines concentrations of ethanesulfonic acid (ESA) and oxanilic acid (OXA) metabolites of alachlor, acetochlor, and metolachlor in surface water and groundwater samples by direct aqueous injection LC/MS/MS. After injection, compounds are separated by reversed-phase HPLC and introduced into the mass spectrometer with a TurboIonSpray atmospheric pressure ionization (API) interface. Using direct aqueous injection without prior SPE and/or concentration minimizes losses and greatly simplifies the analytical procedure. Standard addition experiments can be used to check for matrix effects. With multiple-reaction monitoring in the negative electrospray ionization mode, LC/MS/MS provides superior specificity and sensitivity compared with conventional liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/ultraviolet detection (LC/UV), and the need for a confirmatory method is eliminated. In summary,... 

Heat and reflux a 5-g portion of soil sample with 50 mL of methanol-phosphate buffer (pH 7)-water (15 7 28, v/v/v) solvent mixture in a round-bottom flask for 1 h. After cooling, transfer a 10-mL portion of the supernatant to a test-tube and mix with 11 mL of 0.02M H3PO4 solution. Load this solution on to a silica-based SPE cartridge (Analytichem International Clin-Elut 1020) at a flow rate of 1-2 drops per second. Discard this fraction. Elute the analytes with 30 mL of dichloromethane. Concentrate the eluate to dryness with air in a water-bath at a temperature of 40 °C (do not use vacuum). Dissolve the residues in 5mL of HPLC injection solution [900 mL of water - - 50 mL of phosphate buffer (pH 7) 4-50 mL of ACN 4-4 g of TBABr]. Pinal analysis is performed using liquid chromatography/ultraviolet detection (LC/UV) with a three-column switching system. 

Extracts of all matrices were analyzed by reversed-phase HPLC using ultraviolet detection at a wavelength of 266 nm (Soekhoe and Kerstens, 1995). The limit of detection (LOD) was 10 mg/L for all matrices. Recovery was > 90% and "between days" CV of the analytical chemical method was < 10%. 

Detection in 2DLC is the same as encountered in one-dimensional HPLC. A variety of detectors are presented in Table 5.2. The choice of detector is dependent on the molecule being detected, the problem being solved, and the separation mode used for the second dimension. If MS detection is utilized, then volatile buffers are typically used in the second-dimension separation. Ultraviolet detection is used for peptides, proteins, and any molecules that contain an appropriate chromophore. Evaporative light scattering detection has become popular for the analysis of polymers and surfactants that do not contain UV chromophores. Refractive index (RI) detection is generally used with size exclusion chromatography for the analysis of polymers. 

Buchberger et al. [104] carried out a selective determination of iodide in brine. The performance of a potentiometric method using an ion-selective electrode and of liquid chromatography coupled with ultraviolet detection at 230 nm were compared as methods for the determination of iodide in the presence of other iodide species. Satisfactory results were obtained from the potentiometric method provided the solution was first diluted tenfold with 5 M sodium nitrate, and external standards were used. Better reproducibility was, however, achieved with HPLC, provided precautions were taken to prevent reduction of iodine to iodide in the mobile phase, for which extraction of iodine with carbon tetrachloride prior to analysis was recommended. This was the pre-... 

Elsohly HN, Croom EM, Elsohly MA. (1987) Analysis of the antimalarial sesquiterpene artemisinin in Artemisia annua by high-perfomance liquid chromatography (HPLC) with postcolumm derivation and ultraviolet detection. Pharm Res 4 258-260. 

V-Nitrosodiethanolamine can be determined in air and bulk process samples. Air samples are collected on glass fibre filters, extracted with 2-propanol and analysed by gas chromatography with thermal energy analyser detection. The limit of detection is 200 ng per sample (0.42 pg/m ). Bulk samples can be screened for 7V-nitrosodiethanol-amine by high-performance liquid chromatography (HPLC) with ultraviolet detection (Occupational Safety and Health Administration, 1990). 

Free fatty acids are separable by GC by the inclusion of phosphoric acid in the packing so, for HPLC analysis, the phosphoric acid or other equivalent strong acid is included in the mobile phase. On a SUPELCOSIL LC 18 column, a model mixture of free fatty acids was separated with a mobile phase containing tetrahydrofuran, acetonitrile, water, and phosphoric acid (6 64 30 0.1) at pH 2 (Fig. 1) (15). Oleic and elaidic acids, palmitoleic and palmitelaidic acids, and linoleic and linoelaidic acids were well separated, but margarine fatty acids presented a difficult problem. Ultraviolet detection of 220 nm was used to prepare this chromatogram. 

Acetonitrile was used in the mobile phase when ultraviolet detection of the carbonyl group at 205 nm was used for the various dimers. Separation of the thermal dimer of methyl linoleate and the dehydrodimer of methyl oleate was again incomplete. The sample at concentrations as low as those required for UV detection (1-5 mg/ml) was sparingly soluble in the mobile phase, resulting in increased retention times. Finally, incomplete separation was obtained when various systems of acetonitrile/methyl chloride were used as the mobile phase in HPLC with infrared detection of the carbonyl group at 5.72 /xm. 

Andrikopoulos et al. (124) separated triglycerides, together with nine synthetic phenolic antioxidants most commonly used to prevent oxidation of edible oils and fats, as well as the natural antioxidants tocopherol and alpha-tocopherol acetate by HPLC using a reversed-phase Cl8 column and gradient elution with water/acetonitrile/methanol/isopropanol. Except for dilution of the oil with isopropanol/hexane, no further sample preparation was required. Ultraviolet detection was applied. The synthetic antioxidants PG, OG, DG, BHA, TBHQ, BHT, Ionox 100, THBP, and NDGA, as well as alpha- and delta-tocopherol and alpha-tocopherol acetate were separated. 

Direct determination of urea pesticides by high-performance liquid chromatography has been widely reported in the literature (10,32-36,127-130). Ultraviolet detection has often been used (32,33,35,36,60,127) with usually acceptable sensitivity, although this detector is nonspecific and the sensibility is, in general, low. To overcome this problem, several techniques have been assayed, such as precolumn enrichment (60), postcolumn derivatization (34,10), and the use of other detection techniques such as the electrochemical (129), photoconductivity (128,130), and fluorescence detectors (9,10,34). Table 9 summarizes representative papers using these techniques in HPLC analysis. 

Isocratic conditions have been established for HPLC with ultraviolet detection to determine trace levels of five pesticides frequently used in fruits, e.g., paraoxon, guthion, methyl-parathion, ethyl-parathion, and fenitrothion, in fruits and surface water (95). And HPLC was adapted for the determination of trace concentrations of seven OPP pesticides in drinking water. The analytes concentrated on the precolumn were eluted and separated on a C18 analytical column with an elution gradient program and determined by measuring their UV absorption (48). 

While HPLC does not always produce superior results to those with TLC it allows greater versatility and is more suitable for the analysis of complex organic matrices such as cereals. HPLC coupled to sensitive detection and sophisticated data retrieval has improved the identification of selected mycotoxins at levels much less than achieved by TLC. Additional chromatographic modes such as normal-phase, reverse phase and ion-exchange chromatography have been employed. There are no truly universal detectors available for HPLC. Detectors presently in use include Fourier transform infrared detections (FT-IRD), diode array ultraviolet detection (DAD) and mass selection detectors (MSD) (Coker, 1997). 

Orsulak, P. J., Kenney, J. T., Debus, J. R., Crowley, G., Wittman, P. D. Determination of the Antidepressant Fluoxetine and Its Metabolite Norfluoxetine in Serum by Reversed-Phase HPLC, with Ultraviolet Detection. Clin. Chem. 1988, 34, 1875-1878. 

Specialized Stationary Phases for Liquid Chromatography Chiral Stationary Phases for Liquid Chromatography Detectors for Liquid Chromatography Ultraviolet Detection of Chromophoric Groups Derivatizing Reagents for HPLC... 

Reversed phase isocratic HPLC with ultraviolet detection at 280 nm was used to separate and identify eugenol in the ethanolic extract of whole tobacco and clove cigarettes [25]. The samples were analyzed at 30°C on a RP 18 column using methanol-water (80 20) as the mobile phase. This method was also applied to determine the eugenol content within the total particulate matter of mainstream tobacco condensate [26]. 

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