Juan Zuriarrain

Quantitative determination of caffeine, formic acid, trigonelline and 5-(hydroxymethyl)furfural in soluble coffees by 1H NMR spectrometry.

A quantitative method for the determination of caffeine, formic acid, trigonelline and 5-(hydroxymethyl)furfural (5-HMF) in soluble coffees by applying the proton nuclear magnetic resonance technique ((1)H NMR) is proposed. Each of these compounds records a singlet signal at the 7.6-9.5 ppm interval of the spectrum, and its area is used to determine the concentration. 3-(Trimethylsilyl)-2,2,3,3-tetradeuteropropionic acid is added in an exact known concentration as a reference for delta=0.00 ppm and as an internal standard. The method is applied to commercial soluble coffees and satisfactorily compared with results obtained by standard methods. The limits of detection and the coefficients of variation (N=10) are, respectively, 1.32 mg/g of solid product and 4.2% for caffeine, 0.45 mg/g and 2.6% for formic acid, 0.58 mg/g and 2.4% for trigonelline, and 0.30 mg/g and 7.3% for 5-HMF. The described method is direct and no previous derivatization is needed.

Quantitative determination of carboxylic acids, amino acids, carbohydrates, ethanol and hydroxymethylfurfural in honey by (1)H NMR.

A method using (1)H NMR spectroscopy has been developed to quantify simultaneously thirteen analytes in honeys without previous separation or pre-concentration steps. The method has been successfully applied to determine carboxylic acids (acetic, formic, lactic, malic and succinic acids), amino acids (alanine, phenylalanine, proline and tyrosine), carbohydrates (α- and β-glucose and fructose), ethanol and hydroxymethylfurfural in eucalyptus, heather, lavender, orange blossom, thyme and rosemary honeys. Quantification was performed by using the area of the signal of each analyte in the honey spectra, together with external standards. The regression analysis of the signal area against concentration plots, used for the calibration of each analyte, indicates a good linearity over the concentration ranges found in honeys, with correlation coefficients higher than 0.985 for the thirteen quantified analytes. The recovery studies give values over the 93.7-105.4% range with relative standard deviations lower than 7.4%. Good precision, with relative standard deviations over the range of 0.78-5.21% is obtained.

Flatbed scanners as a source of imaging. Brightness assessment and additives determination in a nickel electroplating bath

Desktop flatbed scanners are very well-known devices that can provide digitized information of flat surfaces. They are practically present in most laboratories as a part of the computer support. Several quality levels can be found in the market, but all of them can be considered as tools with a high performance and low cost. The present paper shows how the information obtained with a scanner, from a flat surface, can be used with fine results for exploratory and quantitative purposes through image analysis. It provides cheap analytical measurements for assessment of quality parameters of coated metallic surfaces and monitoring of electrochemical coating bath lives. The samples used were steel sheets nickel-plated in an electrodeposition bath. The quality of the final deposit depends on the bath conditions and, especially, on the concentration of the additives in the bath. Some additives become degraded with the bath life and so is the quality of the plate finish. Analysis of the scanner images can be used to follow the evolution of the metal deposit and the concentration of additives in the bath. Principal component analysis (PCA) is applied to find significant differences in the coating of sheets, to find directions of maximum variability and to identify odd samples. The results found are favorably compared with those obtained by means of specular reflectance (SR), which is here used as a reference technique. Also the concentration of additives SPB and SA-1 along a nickel bath life can be followed using image data handled with algorithms such as partial least squares (PLS) regression and support vector regression (SVR). The quantitative results obtained with these and other algorithms are compared. All this opens new qualitative and quantitative possibilities to flatbed scanners.

Polyphenolic profile in cider and antioxidant power

BACKGROUND The aim of this work was to find the effect of polyphenolic compounds in Basque ciders on the following parameters: antioxidant activity, browning, protein-precipitating capacity, turbidity and reduction potential. These five parameters are highly important, as they affect the taste, the visual aspect and the preservation of cider, and are mainly related to polyphenolic compounds. RESULTS Procyanidin B1 and procyanidin B2 showed a significant positive effect on antioxidant activity. p-Coumaric acid, (-)-epicatechin and hyperin had a significant positive effect on protein-precipitating capacity. Tyrosol had a significant negative effect on reduction potential. CONCLUSION Procyanidin B1 and procyanidin B2 are the most powerful antioxidants in Basque cider, while p-coumaric acid, (-)-epicatechin and hyperin are those with greatest capacity to precipitate proteins. Ciders with higher tyrosol concentration will have less reduction potential and higher antioxidant reservoir.

Uncertainty in CCD detectors with and without cooling devices when used for molecular fluorescence measurements

The performance of CCD detectors for fluorescence measurements is evaluated through uncertainty studies, mainly as a function of both the signal intensity and the detector temperature. Two CCD detectors, one furnished with a cooling device and the other without a cooling device, were used, and the results were compared. The dependence of uncertainty on the instrumental signal was evaluated simultaneously for both detectors at temperatures ranging between −23 and 23 °C. The tested detectors required temperature increments between 30 and 50 °C to double dark noise (the random part of dark current). The detector temperature affects uncertainty, but this is basically related to dark noise in fluorescence measurements. The consequence of this is that the temperature does not significantly affect the signal-to-noise ratio (S/N); thus, the presence of a cooling device does not significantly improvement the performance, and the limit of detection (LOD) does not depend strongly on the detector temperature. The quality of the two-dimensional array does affect uncertainty, the value of S/N, and the LOD. A good CCD detector can perform at a level similar to a spectrofluorometer furnished with a photomultiplier tube. Laboratory data are given to show how the three components of uncertainty (dark noise, shot noise and flicker noise) behave at different signal intensities and temperatures. Dark noise is the most important factor, shot noise has relevance only at high signal values, and flicker noise is practically irrelevant. The classical model of the dependence of S/N on the fluorescence signal is applied, and the uncertainty constants that govern the performance of the apparatus used are given.

A multi-syringe flow system for monitoring moderately fast chemical reactions

O modo zona de interrupcao da tecnica de analise por injeccao em fluxo baseada em multiseringas (MSFIA) foi explorado para monitoramento de reacoes moderadamente rapidas. O desempenho da MSFIA se baseia na utilizacao de duas câmaras de mistura eficientes (unioes cruzadas) e um motor que impulsiona uma barra que empurra um numero de seringas que fornecem tempos mortos de cerca de 20 ms. A bem-conhecida geracao de bromo a partir de uma mistura de bromato-brometo em meio acido e utilizada como sistema quimico. A taxa encontrada (3,9 ± 0,7 mol -3 L 3 s -1 ) concorda com valores apresentados na literatura. Reagentes em statu nascendi tambem foram produzidos e usados uma vez. Como exemplo, bromo foi gerado e usado imediatamente na bromacao de acido salicilico, evitando a manipulacao de produtos quimicos perigosos; a taxa encontrada (5,5 ± 0,8 mmol-1 L s-1) concorda com valores fornecidos na literatura. A metodologia e uma alternativa facil para o sistema tradicional de fluxo interrompido utilizado em reacoes moderadamente rapidas. The zone stopping mode of the multi-syringe flow injection analysis (MSFIA) technique was exploited for monitoring of moderately fast reactions. The performance of MSFIA relies on the use of both efficient mixing chambers (cross unions) and a motor that propels a bar pushing up a number of syringes to provide dead times of about 20 ms. The well-known bromine generation from a bromate-bromide mixture in acidic medium is used as chemical system. The rate constant found (3.9 ± 0.7 mol -3 L 3

Process analytical chemistry in a nickel electroplating bath. Automated sequential injection for additive determination

Most of the useful parameters of a nickel electroplating bath can be monitored along the bath life. Process analytical chemistry (PAC) has been applied to follow parameters such as temperature, pH, chloride or nickel concentration. The monitoring of additives has special relevance because the final quality of finish depends on them. Two out of the four additives used in the commercial nickel bath used in this paper show UV absorption (A-5(2X) and SPB) and a sequential injection (SI) method has been developed to conduct and automatically dilute aliquots from the bath to a diode-array detector where UV spectra are acquired. Because the UV bands of the absorbing additives overlap, partial least squares (PLS) regression is used as a calibration method to resolve the mixture. A commercial software program has been used for the automated data acquisition. The program configuration and the SI manifold are given. The results obtained for additives are compared with those obtained from a manual method that is used as a reference. Mean random errors under 8% were always obtained. The limits of detection (LOD) found for A-5(2X) and SPB were 0.2 mL L−1 and 0.09 mL L−1 respectively. The SI methodology was applied with excellent results along a whole bath life and can be used to maintain the proper coating conditions.