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      Determinación de cafeína en café mediante espectrometría infrarroja de transformada de Fourier Translated title: Determination of caffeine in coffee by means Fourier transform infrared spectrometry

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          Abstract

          En el presente trabajo se desarrolló un método para determinar cafeína en café, basado en un sistema de análisis en flujo con detección por espectrometría infrarroja de transformada de Fourier (AF-IRTF). El método involucra la extracción de la cafeína, fuera de línea, a partir de la muestra de café sólido con agua a 80°C, la retro-extracción de la cafeína -en línea- en cloroformo y el análisis directo de la fase orgánica por IRTF. El criterio de medida seleccionado fue el valor absoluto de la medida pico-valle (1668-1649 cm-1) de la derivada de primer orden del espectro de absorción en la banda de 1659 cm-1. El límite de detección fue de 0,001% (p/v), la desviación estándar relativa del procedimiento completo, desde la preparación de la muestra, de 1,2% ([Cafeína] » 0,05% (p/v), n = 5) y la frecuencia de análisis real (triplicado), de aproximadamente 12 muestras h-1. El método se validó mediante estudios de adición de estándar, recuperación y precisión entre días; así como por análisis comparativos con el método oficial para el análisis de cafeína en café. Se analizaron 20 muestras comerciales de café tostado, encontrando concentraciones de cafeína en el intervalo de 0,60 a 1,16% (p/p).

          Translated abstract

          In this work a flow analysis-Fourier transform infrared spectrometric (FA-FTIR) method for the determination of caffeine in coffee was developed. The method involves the extraction, in batch, of caffeine from solid samples of roasted coffee with hot water (80°C), on-line retro-extraction of caffeine in chloroform and direct analysis of the organic phase by FTIR spectrometry. The measurement criterion selected for the quantification of caffeine was the absolute peak-valley value (1668-1649 cm-1) of the first order derivate of the absorption spectrum, corresponding to the 1659 cm-1 band. The method provides a limit of detection (3s) of 0.001% (w/v) caffeine, a relative standard deviation corresponding to the whole procedure, until the sample preparation, of 1.2% ([Caffeine] » 0.05% (w/v), n = 5) and a sample throughput (triplicate) of approximately 12 samples h-1. The method was validated by means of standard addition, recovery and inter-day precision studies and by comparative analysis of real samples with the official chromatographic-spectrophotometric procedure. The method was applied to the analysis of commercial samples, obtaining a caffeine content ranging from 0.60 to 1.16% (w/w).

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          Most cited references27

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          Statistics for Analytical Chemistry

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            Near- and Mid-Infrared Spectroscopies in Food Authentication:  Coffee Varietal Identification

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              Determination of caffeine and its metabolites by micellar electrokinetic capillary electrophoresis.

              The determination of caffeine and its analogues is important for a wide variety of analyses and is performed in an assortment of matrices ranging from food to clinical samples. While reversed-phase HPLC has become the standard analysis protocol in most laboratories, capillary electrophoresis has the advantages of higher separation efficiency and shorter separation time. The micellar capillary electrophoresis (MECC) separation of caffeine and its metabolites, theobromine, paraxanthine, theophylline and 1,3,7-trimethyluric acid was investigated using sodium dodecyl sulphate (SDS) as the micellar phase. The effects of pH, micelle concentration, buffer concentration, ionic strength, buffer salts, applied voltage and injection time were studied to select the optimum conditions for the determination of caffeine and its four analogues in drugs, foods and body fluids. Caffeine and its three analogues were resolved within 120 s with detection limits less than 1 microgram/ml. Samples could be analyzed utilizing direct injection with satisfactory resolution and reproducibility.
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                Author and article information

                Contributors
                Role: ND
                Role: ND
                Role: ND
                Role: ND
                Journal
                rtfiuz
                Revista Técnica de la Facultad de Ingeniería Universidad del Zulia
                Rev. Téc. Ing. Univ. Zulia
                Facultad de Ingeniería, Universidad del Zulia (Maracaibo )
                0254-0770
                August 2008
                : 31
                : 2
                : 159-168
                Affiliations
                [1 ] Universidad de los Andes ULA Venezuela
                Article
                S0254-07702008000200007
                522830e1-e948-4eaf-8a60-320c78bcd8de

                http://creativecommons.org/licenses/by/4.0/

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                SciELO Venezuela

                Self URI (journal page): http://www.scielo.org.ve/scielo.php?script=sci_serial&pid=0254-0770&lng=en
                Categories
                ENGINEERING, MULTIDISCIPLINARY

                General engineering
                Cafeína,café,infrarrojo,IRTF,análisis en flujo,Caffeine,coffee,infrared,FTIR,flow analysis
                General engineering
                Cafeína, café, infrarrojo, IRTF, análisis en flujo, Caffeine, coffee, infrared, FTIR, flow analysis

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