摘要:

Some phenolic acids from the flowers ofDelphinium formosumhave been determined quantitatively by reversed-phase high-performance liquid chromatography with diode-array detection. A comparative study was performed by extracting the following phenolic acids: p-hydroxy benzoic, p-coumaric, caffeic, protocatechuic and vanillic acids with four different methods. The results were supported with recovery studies.

ISSN:0003-2719    

DOI:10.1080/00032719908543010

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An analytical method for the determination of 15 Volatile Organic Compounds (VOC): benzene, n-heptane, toluene, n-octane, chlorobenzene, ethylbenzene, m-xylene, o-xylene, p-xylene, isopropylbenzene, n-propylbenzene, n-decane, 1,4-dichlorobenzene, 1,3-dichlorobenzene and 1,2-dichlorobenzene, by thermal desorption coupled with gas chromatography (GC) was proposed. The flame ionisation detector (FID) and mass spectrometry (MS) detector were used. The variables that have an influence on the desorption process (time, inert gas flow and temperature) were studied, obtaining detection limit ranges from 15 to 120 pg (GC-FID), 3.8 to 32 pg (GC-MS, SIM mode) and 15 to 300 pg (GC-MS, SCAN mode). In order to detect possible VOC urban sources, samples were taken from 6 points in A Coruña (N.W. Spain) to analyse. Sampling time and flow rate were 30 minutes and 50 mL/min respectively. VOC profile and their total concentrations can be considered as typical of an urban area. Other samples were also obtained from a nearly rural zone to determine the influence of these VOC sources.

ISSN:0003-2719    

DOI:10.1080/00032719908543011

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The catalytic effect of Se(IV) on the reduction reaction of thionine(TN) by sulfide ion is used for determination of trace amounts of selenium(IV) ion by a kinetic-spectrophotometric method. This new method is simple and highly sensitive. The reaction was monitored spectrophotometrically by measuring the decrease in absorbance of the reaction mixture at 598 nm. The fixed time method was used for the first 45s from initiation of the reaction. Under the optimum conditions, in the concentration range of 2-90 ng ml−of selenium(IV), a quite linear regression equation (r = 0.9984, n = 14) was obtained. The experimental detection limit of the method (S/N = 3) was 1.3 ng ml−. The relative standard deviation of ten replicate measurements is 2.51% for a 40 ng ml−solution of selenium. The proposed method is used to the study of selenium (IV,VI) speciation in water at ng ml−levels. This method was extended for the determination of selenium in real samples.

ISSN:0003-2719    

DOI:10.1080/00032719908543012

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

A flow-injection catalytic spectrophotometric method is proposed for the determination of nitrite based on its catalytic effect on potassium bromate oxidation of acridine orange in phosphoric acid medium. The reaction is monitored spectrophotometrically by measuring the decrease in absorbance of acridine orange at 491.5 nm coupling with the stopped-flow technique. The calibration curve was linear between 3.4 and 65 ng/mL, and the detection limit was 2.2 ng/mL. Up to 30 samples can be analyzed per hour with a relative precision of ca. 1.9%. The proposed method was successfully applied to the determination of nitrite in waters and food samples with satisfactory results.

ISSN:0003-2719    

DOI:10.1080/00032719908543013

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The generalized rank annihilation method (GRAM) is a method for curveresolution and quantitation that uses two data matrices simultaneously, i.e., onefor the unknown and one for the calibration sample. Requirements have beenderived that ensure the unique resolution of the analyte of interest in thepresence of unknown interferences if the data matrices are free fromexperimental error. In this paper, it is shown that the same requirements allowfor correct determination of bias and variance in the quantitative results obtainedby GRAM if the data matrices are not free from experimental error.

ISSN:0003-2719    

DOI:10.1080/00032719908543014

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

ISSN:0003-2719    

DOI:10.1080/00032719908543015

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor