Carolina C. Acebal

Application of DV-SIA manifold for determination of thiocyanate ions in human saliva samples

An automated, simple and inexpensive double-valve sequential injection analysis (DV-SIA) spectrophotometic method with online liquid-liquid extraction, for the determination of thiocyanate has been developed. The method has been based on the formation of an ion associate between thiocyanate and Astra Phloxine in acidic medium, and the subsequent extraction with amylacetate. The absorbance of the extracted ion associate was measured at 550nm. The calibration function was linear in the range 0.05-0.50mmolL(-1) and the regression equation was A=(1.887±0.053) [SCN(-)mmolL(-1)]+(0.037±0.014) with a correlation coefficient of 0.995. The precision of the proposed method was evaluated by the relative standard deviation (RSD) values at two concentration levels: 0.20 and 0.50mmolL(-1). The obtained results were 1.0 and 2.8%, respectively, for the intra-day precision, and 4.2 and 3.8%, respectively for the inter-day precision. The calculated detection limit was 0.02mmolL(-1). The developed method has been successfully applied for determining thiocyanate ions in human saliva samples.

Application of a fully integrated photodegradation-detection flow-batch analysis system with an on-line preconcentration step for the determination of metsulfuron methyl in water samples

This work presents the development of a fully automated flow-batch analysis (FBA) system as a new approach for on-line preconcentration, photodegradation and fluorescence detection in a lab-constructed mixing chamber that was designed to perform these processes without sample dispersion. The system positions the mixing chamber into the detection system and varies the instrumental parameters according to the required photodegradation conditions. The developed FBA system is simple and easily coupled with any sample pretreatment without altering the configuration. This FBA system was implemented to photodegrade and determine the fluorescence of the degradation products of metsulfuron methyl (MSM), a naturally non-fluorescent herbicide of the sulfonylurea׳s family. An on-line solid phase extraction (SPE) and clean up procedure using a C18 minicolumn was coupled to the photodegradation-detection mixing chamber (PDMC) that was located in the spectrofluorometer. An enrichment factor of 27 was achieved. Photodegradation conditions have been optimized by considering the influence of the elution solvent on both the formation of the photoproduct and on the fluorescence signal. Under optimal conditions, the calibration for the MSM determination was linear over the range of 1.00-7.20 µg L(-1). The limit of detection (LOD) was 0.28 µg L(-1); the relative standard deviation was 2.0% and the sample throughput for the entire process was 3h(-1). The proposed method was applied to real water samples from the Bahía Blanca׳s agricultural region (Bahía Blanca, Buenos Aires, Argentina). This method obtained satisfactory recoveries with a range of 94.7-109.8%.

Successive projections algorithm applied to spectral data for the simultaneous determination of flavour enhancers.

A novel variable selection strategy for multiple lineal regression (MLR), the successive projections algorithm (SPA), was applied to spectrophotometric data (190-320 nm) for the simultaneous determination of monosodium glutamate (MSG), guanosine-5-monophosphate (GMP) and inosine-5-monophosphate (IMP) in dehydrated broths samples. This selection method uses simple operations in a vector space to minimize variable collinearity and has become an interesting variable selection strategy for multivariate calibration. In this work, nine, six and four wavelengths for MSG, GMP and IMP, respectively, were selected to construct calibrations models in order to solve successfully the serious spectral overlapping in samples containing these analytes. The relative errors of prediction (REP) for the validation set were 2.3%, 0.9% and 1.8% for MSG, GMP and IMP, respectively. Commercial samples were analysed and a recovery study was carried out to verify the accuracy of the proposed method with satisfactory results. A continuous flow system was used to develop a simple, cheap and rapid method (sample throughput: 200 h(-1)), without any previous extraction step.

Multilayered particle-packed column: Evaluation and comparison with monolithic and core-shell particle columns for the determination of red azo dyes in Sequential Injection Chromatography

A recently presented new type of multilayered organic-inorganic hybrid silica particle packed column YMC-Triart C18 (50xa0mm × 4.6xa0mm, 5xa0μm) was used for the development of a sequential injection chromatography method for determination of five azo dyes (Sudan I, Sudan II, Sudan III, Sudan orange G, and para red) in selected food seasonings. The use of a novel sorbent brings attractive features, reduced backpressure, and broader chemical stability together with high separation performance, which are discussed and compared with that of three types of columns typically used in medium-pressure flow chromatography techniques (classic monolithic, narrow monolithic, and core-shell particle columns). The separation was performed in gradient elution mode created by the zone mixing of two mobile phases (acetonitrile/water 90:10, 1.5xa0mL + acetonitrile/water 100:0, 2.3xa0mL) at a flow rate of 0.60xa0mL/min and time of analysis <9.5xa0min. The spectrophotometric detection wavelengths were set to 400, 480, and 500xa0nm. The high performance of the developed method with multilayered particle column was well documented and the results indicate a broad capability of sequential injection chromatography.

Automated Method for the Total Creatinine Determination in Dehydrated Broths

Abstract In order to improve the quality control of dehydrated broth, a new automated method was developed to determine total creatinine in dehydrated broths. The sample pretreatment was coupled on‐line with the Flow Injection Analysis (FIA) system for analyte determination by the classical Jaffé reaction, stopped flow methodology, and spectrophotometric detection. The time consumed was reduced from 7 h, which is necessary with the official method, to 25 min. The calibration graph is linear between 0.342–1.368 mg creatinine/100 mL. The relative standard deviation (RSD%) was 1.7%, the sample throughput was 7 h−1, and the detection limit was 0.185 mg creatinine/100 mL. The validation of the proposed method was carried out with real samples. The obtained results were compared with those obtained from the Association of Official Analytical Chemists (AOAC) reference method.

Flow-batch analysis of clenbuterol based on analyte extraction on molecularly imprinted polymers coupled to an in-system chromogenic reaction. Application to human urine and milk substitute samples

A fully automated spectrophotometric method based on flow-batch analysis has been developed for the determination of clenbuterol including an on-line solid phase extraction using a molecularly imprinted polymer (MIP) as the sorbent. The molecularly imprinted solid phase extraction (MISPE) procedure allowed analyte extraction from complex matrices at low concentration levels and with high selectivity towards the analyte. The MISPE procedure was performed using a commercial MIP cartridge that was introduced into a guard column holder and integrated in the analyzer system. Optimized parameters included the volume of the sample, the type and volume of the conditioning and washing solutions, and the type and volume of the eluent. Quantification of clenbuterol was carried out by spectrophotometry after in-system post-elution analyte derivatization based on azo-coupling using N- (1-Naphthyl) ethylenediamine as the coupling agent to yield a red-colored compound with maximum absorbance at 500nm. Both the chromogenic reaction and spectrophotometric detection were performed in a lab-made flow-batch mixing chamber that replaced the cuvette holder of the spectrophotometer. The calibration curve was linear in the 0.075-0.500mgL-1 range with a correlation coefficient of 0.998. The precision of the proposed method was evaluated in terms of the relative standard deviation obtaining 1.1% and 3.0% for intra-day precision and inter-day precision, respectively. The detection limit was 0.021mgL-1 and the sample throughput for the entire process was 3.4h-1. The proposed method was applied for the determination of CLB in human urine and milk substitute samples obtaining recoveries values within a range of 94.0-100.0%.

A study of the effect of organic solvents on the fluorescence signal in a sequential injection analysis system

A study of the effect of different organic solvents and their mixtures with water on the fluorescence intensity of two model compounds (quinine sulphate as a naturally fluorescent substance and metsulfuron methyl with fluorescent properties upon UV irradiation) was carried out in a sequential injection analysis system.