University of North Florida
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Stuart Chalk, Ph.D.
Department of Chemistry
University of North Florida
Phone: 1-904-620-1938
Fax: 1-904-620-3535
Email: schalk@unf.edu
Website: @unf

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Leaves

Classification: Plant -> tea -> leaves

Citations 8

"Coupled Flow Injection Analysis - Flame-atomic Absorption Spectrometry For The Quantitative Determination Of Aluminum In Beverages And Waters Incorporating Online Cation-exchange"
Anal. Chim. Acta 1992 Volume 269, Issue 1 Pages 1-7
Henryk J. Salacinski, Philip G. Riby, Stephen J. Haswell*

Abstract: Tea leaf samples (0.5 g) were digested at 85°C for 45 min in a mixture of HNO3 (4 ml) and HClO4 (1 ml) and diluted to 10 mL with 5% HNO3. Samples of tea and coffee infusions and water were acidified with 5% HNO3. These samples (250 µL) were injected via a loop into a SCX preparative column (500 mg) with water as the carrier, followed by elution with 4 M HCl (250 µL) directly into the nebulizer of a flame AAS for the determination of Al. The AAS and nebulizer were optimized for max. absorbance prior to the determination and the peristaltic pump of the flow system set to give an equivalent delivery. Rectilinear calibrations were obtained from 0.07 to 6.45 µg mL-1 of Al from various timed depositions with a coefficient of variation of 1.1% and a detection limit of 75 ng mL-1. A method for determining the aluminum levels in local water, tea leaf digest, tea and coffee infusions by means of online cation exchange flow injection - flame atomic absorption spectrometry (FIA-FAAS) is described. Quant. results can be carried out down to 75 ng mL-1 of Al using sample volumes in the range 6.0-24.0 mL. The method using a conventional FAAS system was found to be rapid, simple and relatively inexpensive offering good selectivity and typical relative standard deviation of 1-2% (n=10) with a relative error of about 2%.
Aluminum Ion exchange Sample preparation Sample preparation Spectrophotometry Nebulizer Column

"Speciation Analysis Of Chromium(III) And Chromium(VI) Using Flow Injection Analysis With Fluorometric Detection"
Analyst 1998 Volume 123, Issue 5 Pages 1005-1009
Evangelos K. Paleologos, Spyros I. Lafis, Stella M. Tzouwara-Karayanni and Miltiades I. Karayannis

Abstract: A relatively simple, sensitive, selective, automatic fluorometric method for the simultaneous determination of Cr(III) and Cr(VI) by flow injection analysis (FIA) was developed. The method is based on the selective oxidation of the nonfluorescing reagent 2-(α-pyridyl)thioquinaldinamide (PTQA), which with Cr(VI) yields an intensely fluorescent product (λex = 360 nm; λem = 500 nm). Cr(III) is oxidized online to Cr(VI) with sodium metaperiodate and the Cr(VI) is subsequently treated with PTQA. Fluorescence due to the sum of Cr(III) and Cr(VI) is measured and Cr(III) is determined from the difference in fluorescence values. The effects of various anal. parameters, such as acidity, flow rate, sample volume, temperature, reagent concentration and interfering species, were studied. Kinetic studies using both the stopped-flow technique and the FIA procedure were used to study and optimize the oxidation conditions for Cr(III) from its oxidation efficiency. The calibration graphs were rectilinear in the ranges 0.1-10 µg mL-1 for Cr(VI) and 0.1-1.0 µg mL-1 for Cr(III). The method was successfully verified by performing recovery experiments of Cr in several standard reference materials (peach leaves, sediments and tea), and it was applied to the speciation analysis of Cr(III)-Cr(VI) in environmental waters (mineral, tap and distilled water), a food sample (tomato juice) and synthetic mixtures. Up to 30 samples per h can be analyzed with a relative standard deviation of ~0.1-2%.
Chromium(III) Chromium(VI) Fluorescence Speciation Stopped-flow Kinetic Reference material Indirect Interferences Optimization

"Determination Of Anti-carcinogenic Polyphenols Present In Green Tea Using Capillary Electrophoresis Coupled To A Flow Injection System"
J. Chromatogr. A 1998 Volume 827, Issue 1 Pages 113-120
Lourdes Arce, Angel Ríos and Miguel Valcárcel*

Abstract: A capillary electrophoresis (CE) method was developed for the simultaneous determination of a number of major ingredients of green tea. The components analyzed were caffeine, adenine, theophylline, epigallocatechin 3-gallate, epigallocatechin, epicatechin 3-gallate, (-)-epicatechin, (+)-catechin, gallic acid, quercetin and caffeic acid. Separation was achieved using a fused capillary column with 0.15 M H3BO3 as buffer at a pH of 8.5, UV detection at 210 nm and 20 kV of voltage. Analysis was carried out after treatment (extraction, filtration and dilution) of the samples in a flow injection system which was coupled to a CE equipment via a programmable arm. The procedure allows the determination of these compounds in <20 min. Quantitative analysis was performed by the standard addition method. Limits of detection ranged between 0.04 µg/mL for flavonols and 1.2 µg/mL for caffeine.
Polyphenols Caffeine Adenine Theophylline Epigallocatechin 3-gallate Epigallocatechin Epicatechin 3-gallate Epicatechin Catechin Gallic acid Quercetin Caffeic acid Electrophoresis Spectrophotometry Standard additions calibration

"Development Of Transient Data-acquisition System For Hyphenated Techniques Coupled With Inductively Coupled Plasma Atomic-emission Spectrometry"
Spectrochim. Acta B 1996 Volume 51, Issue 14 Pages 1753-1759
Xiaoru Wang*, Zhixia Zhuang, Chenglong Yang, Pengyuan Yang, Xiaomei Yan and Jianming Lin

Abstract: The apparatus described is suitable for use with FIA, HPLC, ET vaporization and laser ablation coupled with multielement ICP-AES. The internal computer of the spectrophotometer scans ten preselected photomultiplier channels at a maximum rate of 100 data points per s with a minimum integration time of 0.01 s per channel, and the data are transferred at 4800 baud through an RS-232C port to a Compaq 486 computer, which both collects and manipulates the data according to QuickBASIC routines. Good results are demonstrated for the determination of metals in serum by flow injection ICP-AES and in hair by ET-vaporization ICP-AES and for the speciation of metals in tea by HPLC-ICP-AES.
Metals Spectrophotometry HPLC Speciation Computer

"Enzymatic Determination Of Gallotannin In Green-tea Infusions By A Photometric Flow Injection Analytical Method"
Anal. Sci. 1995 Volume 11, Issue 5 Pages 777-780
R. L. C. CHEN and K. MATSUMOTO

Abstract: Tea leaves (2.5 g) were extracted with 50 mL water at 90°C for 30 min. Portions (5 ml) of 0.1 M phosphate buffer of pH 6.8 were added to the extract and the solution was diluted to 100 mL with water (solution A). Portions (30 ml) of solution A were incubated with 0.5-1 mg tannase at 37°C for 1 h and the hydrolysates produced were incubated at 90°C for 30 min on a water bath. Portions (150 µL) of solution A and of the hydrolysates were injected into a mixed stream of 0.67% rhodanine solution and 0.2 M KOH in aqueous 67% methanol (2.8 ml/min) and mixed in the flow cell of an automatic glucose analyzer.. The absorbance of the mixture was measured at 520 nm. The calibration graph was linear from 0.001 to 0.1% of free gallic acid (I). The difference in the concentration of I between the tea infusion and its enzyme lysate was used to calculate the amount of gallotannin present in the tea infusion. Results agreed well with those obtained by HPLC.
Gallic acid Spectrophotometry Method comparison

"Banana Tissue Electrode Sensitized For Oxalate"
Fenxi Huaxue 1992 Volume 20, Issue 2 Pages 186-189
Song, Y.;Shen, G.

Abstract: The cited electrode was prepared by coupling banana pulp tissue with an O electrode. The electrode response was rectilinear at steady-state and flow conditions from 88 µM to 0.63 mM and from 50 µM to 1.8 mM oxalate, respectively. The effects of buffer composition, pH, temp., flow speed, sample volume and immobilization are discussed. The selectivity and life-span of the electrode were also determined. Of the 19 foreign ions studied only catechol interfered. Average recoveries for 7 types of sample (such as tea leaves, vegetables and fruits) using the statical response and flow injection methods were 98.4 and 98.9%, respectively. Results agreed well with literature values.
Oxalate Electrode Electrode Optimization Interferences

"Flow Injection Spectrophotometric Determination Of Molybdenum In Plants"
Fenxi Huaxue 1992 Volume 20, Issue 3 Pages 319-321
Xu, Q.;Yuan, X.

Abstract: The method is based on the formation of Mo - SCN- - Rhodamine B (I) complex. Onion, spinach or tea is dried at 60°C for 24 h under reduced pressure, weighed, heated at 520°C for 2 h and the ash is dissolved with 5 mL of 5 M HCl. The solution is diluted with 5 mL of de-ionized water and boiled for 5 min. After filtration, the solution is diluted to 25 mL with water and analyzed by the cited method (flow diagram given). Beer's law is obeyed for up to 1.6 µg mL-1 of Mo. The detection limit is 0.02 µg mL-1 of Mo. The coefficient of variation (n = 5) for 1 µg mL-1 of Mo is 0.7%. Alkaline metals and alkaline-earth metals do not interfere.
Molybdenum Spectrophotometry Interferences Complexation

"Flow Injection Analysis Of Polyphenols In Tea"
Huaxue Shijie 1989 Volume 30, Issue 8 Pages 24-27
Sun, Xiaoping; Xu, Yiyun; Wu, Xiaozhen; Tian, Liqing

Abstract: Polyphenols were extracted from dried tea leaves with boiling water. Polyphenols in solution reacted with Fe(II) in a flow injection system to form a colored complex which was quantitated by absorbance at 540 nm. The recovery rate was 98.5-105.5%. Seven dried tea leaf extracts contained 20.6-23.3% polyphenol.
Polyphenol index Spectrophotometry Extraction