Rafael Forteza

The use of anion-exchange disks in an optrode coupled to a multi-syringe flow-injection system for the determination and speciation analysis of iron in natural water samples

A combination of multi-syringe flow-injection analysis (MSFIA) technique with an optical fibre reflectance sensor for the determination of iron in water samples has been developed in this work. Anion-exchange solid phase extraction (SPE) disks have been used as solid phase. Ammonium thiocyanate has been chosen as chromogenic reagent for Fe(III). The complex Fe[SCN](6)(3-) is retained onto the SPE disk and spectrophotometrically detected at 480nm. The complex is eluted with 0.25moll(-1) hydrochloric acid in 75% ethanol. Total iron can be determined by oxidising Fe(II) to Fe(III) with hydrogen peroxide. A mass calibration was run within the range of 0.4-37.5ng. The detection limit (3s(b)/S) was 0.4ng. The repeatability (RSD), calculated from 9 replicates using 0.5ml injections of a 25microgl(-1) concentration, was 3.6%. The repeatability between five anion-exchange disks was 5.4%. An injection throughput of 7 injections per hour for a sampling volume of 1ml has been achieved. The applicability of the proposed methodology in natural water samples has been proved. The properties of anion-exchange and chelating SPE disks have been studied and compared.

Analysis of cocaine and benzoylecgonine in urine by using multisyringe flow injection analysis-gas chromatography-mass spectrometry system.

In this paper, a method was described to determine cocaine (COC) and benzoylecgonine (BZE) in human urine samples by GC-MS detection. The extraction of analytes from urine samples was achieved in an Oasis hydrophilic-lipophilic balance column (20 mmx3.9 mm id, dp=25 microm; Waters, USA), incorporated in a multisyringe flow injection system, used for the sample treatment. Finally, to improve the volatility of the BZE, an in-line derivatization reaction with N,O-bis (trimethylsilyl) trifluoroacetamide with 1% trimethylchlorosilane was made microwave-assisted in order to reduce the reaction time. The results showed that the proposed method is a good alternative for the analysis of COC and BZE in urine samples because it offers advantages compared with those described in the literature, which include simplicity in the sample treatment, the sensitivity and selectivity necessary to determine the analytes of interest at low levels in the urine and high sample throughput.

Volatile organic compounds in landfill odorant emissions on the island of Mallorca

This study provides data on the occurrence of volatile organic compounds (VOCs) in the biogas emission from a landfill located on the island of Mallorca (Balearic Islands, Spain), where 200,000 tonnes of urban solid wastes are dumped every year. Three different sampling cells, of differing waste ageing were investigated in August 2008, during the main tourist season and the warmest possible weather conditions. Samples were collected in Nalophan™ bags according to the standard European method EN 13725 followed by VOCs adsorption onto Carboxen 1000™ and Tenax TA™ materials prior to thermal desorption and analysis by GC-MS. In total 42 VOCs were analysed, using external standards, out of which 36 were positively identified. Detected VOCs in µg m−3 were alkanes (19–62), aldehydes (65–98), ketones (78–129), alcohols (67–78), esters (25–33), BTEX (83–106), halogenated compounds (16–39), terpens (1.4–2.4) and reduced sulphur compounds (2.6–4.2), showing different concentrations on each one of the three cells. Emitted VOCs showed some similarities with other previous studies from China and Turkey, while large differences to an Italian study. The benzene-to-toluene ratio (B:T) showed values in the range of 0.13 to 0.20 characteristic of biogas. H2S and NH3 gases emitted by the landfill were measured in-situ utilising Dräger™ Tubes for Short-Term-Measurements, showing concentration levels of ≤800 µg m−3 and <300 µg m−3, respectively, which is higher than the determined VOCs in accordance with previous studies. Samples were examined with dynamic olfactometry following standard European method EN 13725, to determine a potential statistical linear correlation between odour and VOC concentrations. Such correlations were not observed probably owing to the large number of compounds emitted from garbage which are not quantified, yet causing positive results in olfactometry.

A multisyringe flow injection system coupled with a gas diffusion cell for ammonium determination

A multisyringe flow injection system for ammonium determination based on the coupling of a gas-diffusion separation cell has been developed. By using a multisyringe burette equipped with additional three-way solenoid valves, the system allows the use of different reagents or samples with further propelling into a gas-diffusion unit. Two possibilities were tested to increase the sensitivity and repetitivity: flow delay during the diffusion of the ammonia formed and use of successive flow reversals. The proposed MSFIA system is compared with the FIA and SIA techniques based on the same principle and has been validated applying the method to the determination of ammonium in environmental samples.

Online coupling lab on valve-dispersive liquid–liquid microextraction-multisyringe flow injection with gas chromatography-mass spectrometry for the determination of sixteen priority PAHs in water

A novel approach exploiting lab on valve-dispersive liquid–liquid microextraction-multisyringe flow injection analysis (LOV-DLLME-MSFIA) coupled to gas chromatography-mass spectrometry (CG-MS) is presented. The method is based on the aspiration and mixing of the sample and all required reagents in the holding coil of a LOV-MSFIA system and delivering it into a miniaturized LOV platform equipped with a conical tube used as an extraction chamber (EC), where the mixture of extraction solvent and disperser solvent is added at a high flow rate, resulting in the formation of a cloudy state and extraction of analytes of interest. Because the extraction and dispersive solvent mixture used has a density significantly higher than water, the resulting fine droplets in the mixture, which contain the extracted analyte, are self-sedimented in thirty seconds, not requiring centrifugation for separation of the extraction phase. Afterwards, the extracted fraction is aspirated and transferred to a rotary micro-volume injection valve (MIV), where finally it is introduced via an air stream into the injector of the GC, through a silica capillary transfer line with no stationary phase, used as interface. The potential of the devised LOV-DLLME-MSFIA/CG-MS assembly was demonstrated in the determination of polycyclic aromatic hydrocarbons (PAHs) in tap water, rain water, river surface water and raw landfill leachates. Under optimized conditions, good enrichment factors (EFs) (27–38) and acceptable total DLLME yields (80–102%) were obtained. Calibration curves were linear with correlation coefficients higher than 0.996 in the working range level of 0.25–250 μg L−1, and relative standard deviations (RSD%) were lower than 5% (n = 5). Detection limits were within the range of 0.01–0.07 μg L−1.

Kinetic enthalpimetric determination of vanadium(V) by its catalytic effect on the oxidation rate of Pyrogallol Red by potassium bromate

The VV-catalysed oxidation of Pyrogallol Red by BrO3– was monitored enthalpimetrically. The rate of the reaction was determined graphically from the initial linear slope of the temperature–time curve recorded and was found to be proportional to the VV concentration over the range 10–150 ng ml–1. The relative standard deviation obtained for the determination of a 100 ng ml–1 concentration of the analyte was 6%. Foreign species did not interfere at concentrations as high as 20 µg ml–1. The method was applied to the determination of VV in steel with good results.

Multisyringe Chromatography (MSC): An Effective and Low Cost Tool for Water-Soluble Vitamin Separation

The advent of monolithic columns has facilitated the combination of chromatographic techniques with nonseparation flow techniques by virtue of the low overpressure introduced by them. Thus far, these combinations have provided excellent results derived from the high selectivity of liquid chromatography and ease of sample handling in nonseparation flow techniques. The joint use of multisyringe flow injection analysis and monolithic columns has provided multisyringe chromatography (MSC). Simultaneous spectrophotometric determination of ascorbic acid, nicotinic acid, nicotinamide, pyridoxine hydrochloride, thiamine hydrochloride, and riboflavin in commercial drinks using a MSC method, is described in this contribution as an inexpensive alternative to classical HPLC. The MSC method provides baseline separation of all these compounds with resolutions values greater than 2, except for B1 and B6 with resolution of 1,2. A ChromolithTM Flash RP-18e (50 mm × 4.6 mm) column, a multisyringe burette provided with two 10 mL high-precision bidirectional syringes and an 8-port multiposition valve were used for a dual isocratic chromatographic separation in our study.

Implementation and optimisation of a high-temperature loading strategy of liquid standards in the quantification of volatile organic compounds using solid sorbents.

High-temperature liquid standard loading strategy onto solid sorbent traps for calibration of thermal desorption-GC-MS techniques for the analysis of volatile organic compounds is evaluated and optimised. With this proposed set-up, volatilised liquid-loaded standards interact in gas phase with solid sorbent particles. Response factor for 15 volatile compounds with different vapour pressures have been evaluated and compared with common strategies based on liquid matrix interactions. Using gas matrix strategy improves signal output in the range 10-700%. Average increase for benzene, toluene, ethylbenzene and xylenes is 480%. Reported systematic bias between liquid standards and gas samples are reduced, enhancing thermal desorption methodologies on one of its more important issues. In addition, the proposed system improves the average repeatability to a 3.2%, over 13 times some reported data. The use of an ultra-thin GC capillary column of 150 μm id performs better peak resolution in about 60% the time with usual 250 μm id capillary columns. The usefulness of this proposed optimised procedure has been proved in real air matrix samples, through a large study with the reliable characterisation of 93 different volatile compounds in the ambient air of a municipal solid waste treatment area.