Ultraviolet detection

Analytical Techniques. Sorbic acid and potassium sorbate are assayed titrimetricaHy (51). The quantitative analysis of sorbic acid in food or beverages, which may require solvent extraction or steam distillation (52,53), employs various techniques. The two classical methods are both spectrophotometric (54—56). In the ultraviolet method, the prepared sample is acidified and the sorbic acid is measured at 250 260 nm. In the colorimetric method, the sorbic acid in the prepared sample is oxidized and then reacts with thiobarbituric acid the complex is measured at - 530 nm. Chromatographic techniques are also used for the analysis of sorbic acid. High pressure Hquid chromatography with ultraviolet detection is used to separate and quantify sorbic acid from other ultraviolet-absorbing species (57—59). Sorbic acid in food extracts is deterrnined by gas chromatography with flame ionization detection (60—62). 

K. Yamashita, M. Motohashi and T. Yashiki, Column-switching techniques for high-performance liquid cliromatography of ibuprofen and mefenamic acid in human serum with shoit-wavelength ultraviolet detection , J. Chromatogr. 570 329-338 (1991). 

K. Yamashita, M. Motohaslii and T. Yashiki, Sensitive high-performance liquid cliro-matographic determination of propranolol in human plasma with ultraviolet detection using column switcliing combined with ion-pair cliromatography , J. Chromatogr. 527 196-200(1990). 

T. Miyabayashi, K. Yamashita, E Aoki, M. Motohashi, T. Yashiki and K. Yatani, Determination of manidipine and pyridine metabolite in human serum by liigh-perfor -mance liquid cliromatography with ultraviolet detection and column switching , J. Chromatogr. 494 209 - 217 (1989). 

The derivatization process (5) is accomplished in aqueous media at basic pH (pH 7-10) in a matter of approximately 15 min to yield a 2-cyanobenz[f]isoindole (CBI), which is stable for 10 to 12 hr in solution. As shown in Figure 1, the absorption characteristics of the CBI adducts are also readily accessible for assay by standard fluorescence or ultraviolet detection. In addition to the absorption between 200 and 300 nm, there are two maxima in the visible spectrum at approximately 420 and 440 nm accessible for fluorescence or ultraviolet detection. A probable mechanism (5,11) for the CBI formation is illustrated in Scheme 1. 

ECD = electron capture detector FID = flame ionization detection GC = gas chromatography HECD = Hall electrolytic conductivity detector HRGC = high-resolution gas chromatography HSD = halogen-specific detector H2SO4 = sulfuric acid MS = mass spectrometry NR = not reported PID = photoionization detection UV = ultraviolet detection... 

E. Sanchez, L.S. Ramos and B.R. Kowalski, Generalized rank annihilation method. I. Application to liquid chromatography-diode array ultraviolet detection data. J. Chromatog., 385... 

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. 

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. ... 

A variety of formats and options for different types of applications are possible in CE, such as micellar electrokinetic chromatography (MEKC), isotachophoresis (ITP), and capillary gel electrophoresis (CGE). The main applications for CE concern biochemical applications, but CE can also be useful in pesticide methods. The main problem with CE for residue analysis of small molecules has been the low sensitivity of detection in the narrow capillary used in the separation. With the development of extended detection pathlengths and special optics, absorbance detection can give reasonably low detection limits in clean samples. However, complex samples can be very difficult to analyze using capillary electrophoresis/ultraviolet detection (CE/UV). CE with laser-induced fluorescence detection can provide an extraordinarily low LOQ, but the analytes must be fluorescent with excitation peaks at common laser wavelengths for this approach to work. Derivatization of the analytes with appropriate fluorescent labels may be possible, as is done in biochemical applications, but pesticide analysis has not been such an important application to utilize such an approach. 

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. 

Grosjean, D. J., Van Neste, A., and Parmar, S. S., Analysis of atmospheric carboxylic acids using single column ion exclusion chromatography with ultraviolet detection, J. Liq. Chromatogr., 12, 3007, 1989. 

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%. 

Lores EM, Bristal DW, Moseman RF (1978) Determination of electro- chemical and ultraviolet detection. J Chromatogr Sci 16 358-362... 

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. 

Sternson et al. [58] used a high performance liquid chromatographic method for the analysis of miconazole in plasma. Miconazole was extracted from alkalinized plasma with n-heptane-isamyl alcohol (98.5 1.5) and separated by high performance performance liquid chromatography on p-Bondapak Ci8 with ultraviolet detection at 254 nm. The mobile phase was methanol-tetrahydrofuran-acetate buffer (pH 5) (62.5 5 32.5) containing 5 mmol octanesulfonate per liter. The flow rate was 2 mL/min. Recovery was 100%. The relative standard deviation for injection-to-injection reproducibility was 0.4% and that for sample-to-sample variation was 5% at high miconazole concentrations (30 pg/mL) and 1% at low (1 pg/mL) concentrations. The limit of detection was 250 ng/mL. 

Fan used a high performance liquid chromatographic method for the qualitative and quantitative analysis of miconazole [59], Miconazole sample was dissolved in methanol and determined by high performance liquid chromatography using methanol-water (75 25) as the mobile phase and ultraviolet detection at 214 nm, the recovery was more than 99.4% and the accuracy was satisfactory for the qualitative and quantitative analysis. 

S. Hakkinen and S. Auriola, High performance liquid chromatography with electrospray ioniza tion mass spectrometry and diode array ultraviolet detection in the identification of flavonol aglycones and glycosides in berries, J. Chromatogr. A, 829, 91 100 (1998). 

Herrera MC and Luque de Castro MD. 2005. Ultrasound-assisted extraction of phenolic compounds from strawberries prior to liquid chromatographic separation and photodiode array ultraviolet detection. J Chromatogr A 1100(1) 1 —7. 

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-... 

Riu et al. [542] has reported the determination of linear ethyl benzane-sulfates in coastal waters using automated solid-phase extraction followed by capillary electrophoresis with ultraviolet detection, and confirmed by capillary electrophoresis-mass spectrometry. The detection limits were 1 pg/1 when 250 ml of coastal water was preconcentrated. 

Brown and Rhead [307] improved the sensitivity of high-performance liquid chromatography to 0.2 xg/l. This procedure consists ofbromination, extraction of the a, /i-dibromopropionamide with ethyl acetate, and quantification using high-performance liquid chromatography with ultraviolet detection. Samples... 

Increasing the load on the TLC plate will help increase the LOD. Also, if only ultraviolet detections had been used so far, de-rivatizing agents should be explored to find one that would increase sensitivity, thus increasing the LOD. 

Gori G, Bartolucci GB, Sturaro A, et al. 1995. High performance liquid chromatographic determination of urinary 2,5- hexanedione as mono 2,4-dinitrophenylhydrazone using ultraviolet detection. J ChromatogrB 673 165-172. 

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