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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Ana R.A. Nogueira

Abbrev:
Nogueira, A.R.A.
Other Names:
Ana Rita de Araujo Nogueira, Ana Rita A. Nogueira
Address:
Centro de Pesquisa de Pecuaria do Sudeste, Empresa Brasileira de Pesquisa Agropecuaria, P.O. Box 339, 13560-970 Sao Carlos SP, Brazil
Phone:
+55-16-261-5611
Fax:
+55-16-261-5754

Citations 12

"Potentiometric Determination Of Urea By Sequential Injection Using Jack Bean Meal Crude Extract As A Source Of Urease"
Talanta 2000 Volume 53, Issue 2 Pages 331-336
Fernando V. Silva, Ana Rita A. Nogueira, Gilberto B. Souza, Boaventura F. Reis, Alberto N. Araújo, Maria C. M. B. S. Montenegro and José L. F. C. Lima

Abstract: A sequential injection system was proposed to accomplish the potentiometric determination of urea. This procedure used an ammonium tubular selective electrode to assess ammonium concentration produced by enzymatic hydrolysis of urea from Jack bean meal (Canavalia ensiformis DC) crude extract. A gaseous diffusion device was coupled to the flow set-up allowing on-line sampling and suitable selectivity for determinations. A detection limit of 6.0 x 10^-4 mol urea L-1, a relative standard deviation of 1.9% (n = 10) and a sampling rate of 20 samples h-1 were observed when 172 Sumner units (SU) of urease and 900 µL of sample were used. Results agreeing with a comparative method were obtained by the proposed procedure and the use of the crude extract solution combined with the sequential injection approach improved the performance, producing reproducible results and low costs in comparison with procedures using commercial enzymes.

"Vanillin-condensed Tannin Study Using Flow Injection Spectrophotometry"
Talanta 2000 Volume 51, Issue 1 Pages 1-6
Edilene C. Ferreira and Ana Rita A. Nogueira

Abstract: Studies involving the kinetic reaction between vanillin and condensed tannins were developed using a flow injection system with spectrophotometric determination. A solution of the monomeric compound (-)-epicatechin was used as the analytical standard. This compound was chosen due to its structure, which is similar to a polymeric unit of the condensed tannin present in plants. The results indicated that the vanillin-condensed tannin reaction is time dependent and affected by the degree of polymerization of the condensed tannin. The flow system allowed (-)-epicatechin to be used without overestimating the content of the tannin present in the forage legume, guandu (Cajanus cajan (L.) Millsp.), studied. A relative standard deviation (RSD) of <1% was found for a 4 h period work and allowed the determination of about 60 samples h-1 with a detection limit of 1.05 mg L-1 for condensed tannin. When compared to the manual vanillin procedure, the proposed approach can be used with various advantages.
Vanillin Guandu Seed Spectrophotometry Method comparison Optimization Kinetic

"FIA-FAAS Method For Tannin Determination Based On A Precipitation Reaction With Hemoglobin"
J. Braz. Chem. Soc. 2003 Volume 14, Issue 2 Pages 329-333
Edilene C. Ferreira; Gilberto B. SouzaI; Ana Rita A. Nogueira

Abstract: A flow system, coupled with flame atomic absorption spectrometry (FIA-FAAS), was developed for tannin determination in pigeon pea samples, exploring the precipitation reaction between tannins and proteins. Sample extracts obtained by sonication with a 50% (v/v) methanol solution were introduced into the system and induced to react with a hemoglobin solution. The precipitate produced was retained on a filter located in the analytical flow. A reversed flow of 1% (w/v) sodium dodecyl sulfate solution was used for solubilization of the precipitate from the filter and to conduct the tannin-hemoglobin complex to the FAAS, to quantify the iron ions present in the hemoglobin structure. A tannic acid solution was used to prepare the analytical curve. The proposed method allowed determination of 30 samples per hour, a standard deviation of 9.7% (n=10), and a quantification limit of 0.27 mg L-1 for tannic acid.

"Orthophosphate, Phytate, And Total Phosphorus Determination In Cereals By Flow Injection Analysis"
J. Agric. Food Chem. 2004 Volume 52, Issue 7 Pages 1800-1803
Edivan Carvalho Vieira and Ana Rita A. Nogueira

Abstract: A flow injection spectrophotometric procedure with enzymatic hydrolysis was developed for determination of orthophosphate, phytate and total phosphorus in cereal samples. Phosphorus species were extracted from cereals with 0.05 mol L-1 potassium hydrogen phthalate buffer solution at pH 5.7. Orthophosphate was directly determined in the extracts by molybdenum blue spectrophotometric method. The phytate was hydrolyzed by the enzyme phytase coupled to a solid phase packed into an enzymatic reactor, and the resulting hydrolyzed orthophosphate was also determined by spectrophotometry at 650 nm. After optimization for phosphorus species extraction and enzymatic hydrolysis, a linear calibration graph was obtained up to 196 x 10^-6 mol L-1 orthophosphate ([P] = -2.67 + 0.52x, r = 0.9998). Measurements are characterized by relative standard deviation of 1.6% for a standard of 72 x 10^-6 mol L-1 orthophosphate and no baseline drift was observed during 4 h operation periods. It provides 72 measurements per hour, with 2.4 x 10^-6 mol L-1 and 7.9 x 10^-6 mol L-1 as detection and quantification limits, respectively. Keywords: Enzymatic hydrolysis; immobilization; phytase; phytic acid; and spectophotometry

"Effect Of Drying Method And Length Of Storage On Tannin And Total Phenol Concentrations In Pigeon Pea Seeds"
Food Chem. 2004 Volume 86, Issue 1 Pages 17-23
Edilene C. Ferreira, Ana Rita A. Nogueira, Gilberto B. Souza and Luiz A. R. Batista

Abstract: Total phenols and condensed tannins in Pigeon pea seeds were determined by flow injection spectrophotometry. Folin-Denis and vanillin assays were used for total phenol and condensed tannin, respectively. Three Pigeon pea accessions were cultivated in a greenhouse. After harvesting, one access was separated into two aliquots. One aliquot was freeze-dried (-196°C), and the other was dried in a forced air oven at 50°C, like the other access samples, to evaluate drying temperature interference. The seeds were initially analyzed and then stored at around -10°C, 16°C or at ambient temperature (25±10°C). The stored samples were analyzed every 30 days, for a 90 day period. A significant difference (PP<0.05) for total phenols, indicating that tannin quantification has to be done immediately after harvesting to avoid formation of protein complexes or polymerisation, which lead to erroneous results. In accordance with results, freeze-drying proved to be best for preserving the characteristics of the sample. In order to compare the tannin and phenol contents within accessions, fresh seeds should be used.

"Determination Of Chloride In Milk Using Sequential Injection Automated Conductimetry"
Food Chem. 1999 Volume 67, Issue 3 Pages 317-322
Fernando V. Silva, Gilberto B. Souza, Luiz F. M. Ferraz and Ana Rita A. Nogueira

Abstract: A new conductimetric sequential injection procedure is proposed for the automatic chloride determination in milk. The preparations of milk samples are time consuming procedures. The use of a sequential injection system coupled to a dialysis camera permitted easy automation and improved process control over the parameters, giving high throughput analyzes. In this work, a fast and reliable automated sample addition method is described. An untreated sample of milli (142 µl) was injected with a standard reference solution (750 µl) in a carrier stream and dialysed for the conductimetric chloride determination. Potential interferences and ideal work conditions were appraised. Data acquisition and device control were achieved by computer. Results were precise(RSD < 1.0%) in agreement with both the official titration procedure and with the milk standard reference materials. The system was designed for conductimetric samples addition analysis, and no major problems were observed.
Dialysis

"Determination Of Total, Volatile And Acid Detergent Insoluble Nitrogen In Silage By Sequential Injection"
Anal. Sci. 2000 Volume 16, Issue 4 Pages 361-364
Fernando V. Silva, Ana Rita A. Nogueira, Gilberto B. Souza And Geraldo M. Cruz

Abstract: This work proposes a sequential injection procedure to determine the total, volatile and acid detergent insoluble nitrogen content in silage. An ammonium tubular selective electrode coupled to a sequential injection manifold was used as detector to accomplish the potentiometric determinations made after on-line ammonia diffusion in alkaline medium through a Teflon membrane and NH3/NH4+ conversion. Different sample treatments, taking into account the species to be analyzed, were adopted to apply the proposed procedure to silage samples. An analytical frequency of 30 samples h-1 and a detection limit of 3.0 mg N L-1 were observed when 300 µl of 3.0 mol L-1 NaOH solution and a sample volume of 150 µl were employed. The use of the proposed procedure allowed the automation of the determinations, low sample and reagent consumption and small waste production, emphasizing the versatility and potentiality of the flow methods when applied to animal nutrition laboratories.

"Determination Of Cobalt In Animal Feces By Tungsten Coil Atomic Absorption Spectrophotometry"
Anal. Sci. 1999 Volume 15, Issue 2 Pages 165-171
Gisele S. Lopes, Ana Rita A. Nogueira, Pedro V. Oliveira And Joaquim A. N&oacute;brega

Abstract: An alternative analytical procedure for cobalt determination by tungsten coil electrothermal atomic absorption spectrophotometry (TCAAS) was developed to determine the liquid ruminal passage rate (turnover) of Co-EDTA in sheep feces. A matrix-matching procedure and a selective extraction of Co in 1.0 mol L-1 HCl were evaluated in order to correct and minimize the interference effects caused by sample matrices. As application, six sheep received at the same time one dose of the marker (Co-EDTA); thier fecal samples were collected in intervals of 6 h during 90 h. The Co amounts determined in the dry sheep feces by TCAAS were compared with those obtained by a flow injection catalytic spectrophotometric method. The characteristic mass and the detection limit, both based on peak height absorbance, were 23.1 and 19.1 pg, respectively, for 10 mi of sample volume in the samples of sheep feces. The rsd was 0.5% for 10 consecutive injections of 20.0 mg Co L-1. The accuracy was assessed by employing the paired t-test at 95% confidence level; there was no significant difference for Co content determined by TCAAS and by flow injection spectrophotometry.

"Flow System To Gas Capture From A Nebulized Solution"
Anal. Chim. Acta 2003 Volume 479, Issue 2 Pages 167-172
Marcos Y. Kamogawa and Ana Rita A. Nogueira

Abstract: The use of aerosol produced in a nebulization chamber is proposed as an alternative to gas sample capture in flow systems. This paper describes the coupling of a sampling interface with a flow system, for in situ gas monitoring. Aspects related with the behavior of aerosol formation and gas solubilization in liquid drops are discussed. The method is applied to the determination of residual lime in acidic soils. Aliquots of 5.0 mL of 1.0 mol L-1 HCl were mixed with soil samples (1 g). The CO2 released from these samples was captured by a nebulized aerosol and determined conductivity. The analytical curve from 1.0 x 10^-2 to 5.0 x 10^-2 mol kg-1 CaCO3 was ploted applying the matrix matching approach. This proposition, allowed an increase in the sensibility with detection limit of 6.0 x 10^-3 mol kg-1. The precision was good (RSD <3%) for an analytical frequency of 22 determinations per hour. A fair agreement, at 95% confidence level, was found between the results from the proposed method and certified values of the investigated samples.

"Determination Of Soil Calcareous Efficiency Using Flow System With Pervaporative Separation"
Anal. Chim. Acta 2001 Volume 438, Issue 1-2 Pages 273-279
M. Y. Kamogawa, A. R. A. Nogueira, M. Miyazawa, J. Artigas and J. Alonso

Abstract: A method is described for the conductimetric determination of CO2. The proposed system was constructed with a pervaporator chamber coupled to a flow system comprised of a six-way solenoid valve, a conductivity cell, a conductivimeter and a PC microcomputer for data acquisition and external controls. An amount of 2 g of dry soil samples were directly weighted in the donor compartment of the pervaporation chamber. The CO2 was determined from an analytical curve within 5.0 x 10^-3-5.0 x 10^-2 mol kg-1 CaCO3. This curve was constructed with the matrix matching approach and presented a linear regression of y=13.58+584.77r (r=0.9962). Soils with different lime amounts were analyzed by the proposed methodology and with the official method, that uses the calcium difference between the total, extracted with HCl 1 mol L-1 and exchangeable, extracted with the KCl 1 mol l-1. After paired t-test application, no significant difference between the methods was found at the 95% probability level. The proposed method presented sampling rate of 17 h-1, detection limit of 8.0 x 10^-4 mol kg-1 CaCO3, and RSD<3%. The use of the pervaporator allowed the in situ soil pretreatment for the residual lime determination.

"A Polyvalent Flow Injection System For Multielemental Spectrophotometric Analysis Of Plant Materials"
Anal. Chim. Acta 1998 Volume 370, Issue 1 Pages 39-46
F. V. Silva, A. R. A. Nogueiraa,*, G. B. Souzaa and E. A. G. Zagattob

Abstract: A polyvalent flow injection system consisting of a single manifold suitable to perform different determinations after only minor adaptations was conceived. Its use is particularly attractive for labs. processing a large number of samples including several analytes. The system was applied to spectrophotometric determination of iron, copper, manganese and zinc (micronutrients) as well as calcium, magnesium and phosphorus (macronutrients) in plants. With the proposed system, slight variations in the coefficients of the calibration equations (usually <3%) were found after 4 h working periods. Results were precise (0.8% Iron Copper Manganese Zinc Calcium Magnesium Phosphorus Plant Spectrophotometry Reference material Optimization

"Catalytic Determination Of Cobalt By Flow Injection Spectrophotometry Application In Animal Feces Analysis Using Hydrochloric Acid As Extracting Medium"
Anim. Feed Sci. Technol. 1998 Volume 74, Issue 1 Pages 79-84
A. R. A. Nogueira, G. B. Souza, L. A. R. Batista, M. A. Z. Arruda and M. Miyazawac

Abstract: A flow injection system for cobalt determination in feces of bovines and equines receiving Co-EDTA as a tracer in animal nutrition studies is proposed, using 1.0 mol HCl L-1 as extracting medium, and detection by flow injection spectrophotometric procedure based on the catalytic effect of Co(II) on the oxidation of Tiron by hydrogen peroxide. Linearity was observed up to 8.0 Co µg l-1, and the detection limit was 0.2 µg Co L-1 (3s blank). The system requires 0.12 mg Tiron per determination and handles 65 samples hr-1. No baseline drift was observed during extended operation periods (8 h) and precise results (RSD <1%) were detected. Accuracy was confirmed by running several feces samples already analyzed by flame atomic absorption spectrometry. Results related to the HCl extraction procedure were in close agreement with those obtained using the nitric-perchloric digestion (y=0.978x+0.101, R2=0.9848), suggesting that HCl extraction and flow injection determination can be used routinely for rapid anal. of cobalt in feces.
Cobalt Pig Faeces Cow Faeces Spectrophotometry EDTA Catalysis Indirect Method comparison Extraction