José Manuel Estela

Flow analysis techniques for phosphorus: an overview.

A bibliographical review on the implementation and the results obtained in the use of different flow analytical techniques for the determination of phosphorus is carried out. The sources, occurrence and importance of phosphorus together with several aspects regarding the analysis and terminology used in the determination of this element are briefly described. A classification as well as a brief description of the basis, advantages and disadvantages of the different existing flow techniques, namely; segmented flow analysis (SFA), flow injection analysis (FIA), sequential injection analysis (SIA), all injection analysis (AIA), batch injection analysis (BIA), multicommutated FIA (MCFIA), multisyringe FIA (MSFIA) and multipumped FIA (MPFIA) is also carried out. The most relevant manuscripts regarding the analysis of phosphorus by means of flow techniques are herein classified according to the detection instrumental technique used with the aim to facilitate their study and obtain an overall scope. Finally, the analytical characteristics of numerous flow-methods reported in the literature are provided in the form of a table and their applicability to samples with different matrixes, namely water samples (marine, river, estuarine, waste, industrial, drinking, etc.), soils leachates, plant leaves, toothpaste, detergents, foodstuffs (wine, orange juice, milk), biological samples, sugars, fertilizer, hydroponic solutions, soils extracts and cyanobacterial biofilms are tabulated.

Multisyringe flow injection analysis: characterization and applications

In this paper, the new multisyringe flow injection analysis (MSFIA) technique is reviewed and contrasted with previous flow techniques. Also covered are its fundamental background and instrument evolution, together with its proposed injection modalities and various analytical applications.

Determination of losartan, telmisartan, and valsartan by direct injection of human urine into a column-switching liquid chromatographic system with fluorescence detection.

Column-switching high-performance liquid chromatographic (HPLC) method has been developed and validated for quantification of losartan, telmisartan, and valsartan in human urine. Urine samples were diluted on the extraction mobile phase (1:4, v/v) and a volume of 20 microL of this mixture were directly injected onto the HPLC system. The analytes were extracted from the matrix using an on-line solid-phase extraction procedure involving a precolumn packed with 25 microm C(18) alkyl-diol support (ADS), and a solution 2% methanol in 5mM phosphate buffer (pH 3.8) at a flow-rate of 0.8 mL/min for isolation and preconcentration of losartan, telmisartan, and valsartan. The enriched analytes were back-flushed after, onto the analytical column with a mixture of 5mM phosphate buffer (pH 3.8)-acetonitrile-methanol (65:20:15, v/v/v) at a flow-rate of 3.0 mL/min and detected by fluorescence at 259 and 399 nm as excitation and emission wavelength respectively. The separation of losartan, telmisartan, and valsartan was achieved on a Chromolith RP-18e monolithic column. The method provides extraction recoveries from spiked urine samples greater than 93%. Intra-day and inter-day precision were generally acceptable; the intra-day-assay C.V. was <3.5 for all compounds and the inter-day-assay C.V. was < 3.7%. The estimated calibration range was 0.001-2.5 microg/mL(-1) with excellent coefficient of determination (>0.9981). The detection limits for losartan, telmisartan, and valsartan at a signal-to-noise ratio of 5:1 were 0.002, 0.0002 and 0.001 microg/mL(-1) when a sample volume of 20 microL was injected. The proposed method permitted the simultaneous determination of losartan, telmisartan, and valsartan in 8 min, with an adequate precision and sensitivity. However, the overlap of the sample cleanup step with the analysis increases the sampling frequency to 12 samples/h. The developed column-switching method was successfully applied for the determination of these analytes in human urine samples of patients submitted at ARA-IIs therapy.

Application of flowing stream techniques to water analysis. Part I. Ionic species: dissolved inorganic carbon, nutrients and related compounds

This paper summarizes the most relevant manuscripts issued from 1990 to date referred to water analysis using flowing stream techniques. Concretely, reported flow methods applied to the determination or monitoring of inorganic analytes (viz. carbon, nitrogen, phosphorous and silicon species) together with some related compounds to assess water quality in drinking, rain, underground, marine, river, estuarine, waste and industrial samples are reviewed. For the first time, the most widespread flow techniques of analysis described in the literature (viz. segmented flow analysis (SFA), continuous flow analysis (CFA), flow injection analysis (FIA), sequential injection analysis (SIA), multicommuted FIA (MCFIA), multisyringe FIA (MSFIA), along with the different exploited injection modalities are included in the same review.

Interfacing on-line solid phase extraction with monolithic column multisyringe chromatography and chemiluminescence detection: An effective tool for fast, sensitive and selective determination of thiazide diuretics.

A new, multisyringe flow injection set-up has been developed for the completely automated determination of trace thiazide compounds with diuretic action in different types of samples. The proposed instrumental set-up exploits for the first time, a low pressure on-line solid phase extraction-liquid chromatography-chemiluminescence detection method. This novel combination of sample treatments in flow systems expands the current applicability of low pressure liquid chromatography due to the isolation/preconcentration of the target compounds, besides high selectivity and sensitivity. For the determination of three thiazide compounds named hydroflumethiazide, furosemide and bendroflumethiazide, the proposed set-up provided with the preconcentration of only 1mL of sample, limits of detection of 3, 60 and 40microgL(-1), respectively. Furthermore wide linear dynamic ranges of 6-4000, 140-20,000 and 90-40,000microgL(-1), respectively, were obtained. Besides of this, a high injection throughput of 12h(-1) was also achieved. As in sports, thiazide diuretics are prohibited substances, the proposed method has been applied to their determination in urine samples. Furthermore the potential of the proposed method as a fast-screening approach for emerging contaminants in waters has been also tested by applying it to well water and leachates from a solid waste landfill.

Sequential injection spectrophotometric analysis of nitrite in natural waters using an on-line solid-phase extraction and preconcentration method

An automatic sequential injection analysis (SIA) set-up for the isolation, preconcentration and spectrophotometric determination of nitrite in waters based on the Shinn reaction was designed and evaluated. The system performs the on-line azo dye formation and its subsequent extraction on a solid phase (monofunctional C18), which is held inside a glass column incorporated into the system. A large sample volume (maximum, 10 ml) is sequentially segmented with sulfanilamide and N-(1-naphthyl)ethylenediamine dihydrochloride by using an iterative method. The azo dye collected is eluted with a small volume of 80% methanol and conducted to a diode-array spectrophotometer for quantitative analysis. It has been proved that the retention efficiency is maintained for up to 45 sample injections of 10 ml in spite of the high chromogenic reagent acidity. Nitrite has been determined within the 13.4–160 ng ml−1 and 0.83–20 ng ml −1 ranges for 1 and 10 ml of sample, respectively. For these volumes, the detection limits are 5.9 and 0.32 ng ml −1, the enhancement factors 17 and 170 and the sample throughput 15 and 3 h−1, respectively. A maximum RSD of 4.0% was achieved in all determinations. It is an advantage of this approach that it is possible to use the same mass calibration graph for any sample volume.

Automatic In-Syringe Dispersive Microsolid Phase Extraction Using Magnetic Metal–Organic Frameworks

A novel automatic strategy for the use of micro- and nanomaterials as sorbents for dispersive microsolid phase extraction (D-μ-SPE) based on the lab-in-syringe concept is reported. Using the developed technique, the implementation of magnetic metal-organic framework (MOF) materials for automatic solid-phase extraction has been achieved for the first time. A hybrid material based on submicrometric MOF crystals containing Fe3O4 nanoparticles was prepared and retained in the surface of a miniature magnetic bar. The magnetic bar was placed inside the syringe of an automatic bidirectional syringe pump, enabling dispersion and subsequent magnetic retrieval of the MOF hybrid material by automatic activation/deactivation of magnetic stirring. Using malachite green (MG) as a model adsorption analyte, a limit of detection of 0.012 mg/L and a linear working range of 0.04-2 mg/L were obtained for a sample volume equal to the syringe volume (5 mL). MG preconcentration was linear up to a volume of 40 mL, obtaining an enrichment factor of 120. The analysis throughput is 18 h(-1), and up to 3000 extractions/g of material can be performed. Recoveries ranging between 95 and 107% were obtained for the analysis of MG in different types of water and trout fish samples. The developed automatic D-μ-SPE technique is a safe alternative for the use of small-sized materials for sample preparation and is readily implementable to other magnetic materials independent of their size and shape and can be easily hyphenated to the majority of detectors and separation techniques.

Flow-through optical fiber sensor for automatic sulfide determination in waters by multisyringe flow injection analysis using solid-phase reflectometry

A software-controlled flow-through optical fiber diffuse reflectance sensor capitalized on the implementation of disk-based solid-phase pre-concentration schemes in a multisyringe flow injection analysis (MSFIA) set-up is proposed for the trace determination of sulfide in environmental waters and wastewaters. The fully automated flowing methodology is based on Fischers coupling reaction of sulfide with N,N-dimethyl-p-phenylenediamine (DMPD) in the presence of Fe(iii) as oxidizing reagent in a 0.5 M HCl medium. The on-line generated methylene blue dye is subsequently delivered downstream to a dedicated optode cell furnished with an octadecyl-chemically modified (C(18)) disk, while continuously recording the diffuse reflectance spectrum of the pre-concentrated compound. A double regeneration protocol is finally executed to warrant minimum background noise and negligible baseline. Under the optimized chemical and hydrodynamic conditions, the optosensing MSFIA method features coefficients of variation better than 0.7%(n= 10) at 50 microg l(-1) concentration, a linear working range of 20-200 microg l(-1) sulfide, a 3sigma(blank) detection limit of 2.9 microg l(-1) sulfide and an injection throughput of 8 h(-1) for a pre-concentration sample volume of 2.9 ml. The interfacing of the robust and versatile multisyringe flow injection-based optode with a plug-in spectrophotometer furnished with a light emitting diode assures the miniaturization of the overall flow analyzer, which is, thus, readily adaptable to real-time monitoring schemes. The potential of the multisyringe flow method was assessed via the determination of sulfide traces in water samples of different complexity (namely, freshwater, seawater and wastewater).

Multi-syringe chromatography (MSC) system for the on-line solid-phase extraction and determination of hydrochlorothiazide and losartan potassium in superficial water, groundwater and wastewater outlet samples

In this paper, a combination of multi-syringe chromatography analysis technique with extraction disks sorbents for the pre-concentration and determination of hydrochlorothiazide and losartan potassium in superficial water, groundwater and wastewater outlet samples has been developed. The system developed was proved for the determination of hydrochlorothiazide and losartan potassium in spiked water samples with recoveries ranging from 95 to 118%. The method involves the on-line enrichment of the targeted analytes from spiked water samples onto a Cation-SR sorbent material. The analytes are subsequently eluted and transported to the monolithic column, Chromolith Flash RP-18e column (25 mmx4.6 mm i.d.). The mobile phase used was 10 mM potassium dihydrogen phosphate (pH 3.0):acetonitrile:methanol (60:30:10 v/v/v), flow-rate 0.8 mL min(-1). UV detection is carried out at 226 nm. Under the optimized chemical and physical variables, the detection limit for hydrochlorothiazide and losartan potassium calculated as 3Syx/b was 0.07 and 0.09 mgL(-1), respectively, for a sample loading volume of 1.0 mL.

Application of flowing-stream techniques to water analysis: Part II. General quality parameters and anionic compounds: halogenated, sulphur and metalloid species

In the first part of this review [Talanta 60 (2000) 867], flowing-stream methods (namely, segmented flow analysis (SFA), continuous-flow analysis (CFA), flow-injection analysis (FIA), sequential-injection analysis (SIA), multicommuted flow-injection analysis (MCFIA) and multisyringe flow-injection analysis (MSFIA)) were presented as powerful analytical tools for nutrient determination in water samples when coupled to photometric/fluorimetric detection, flow-through ion-selective electrodes or amperometric sensors. In the present paper, relevant flow methods applied to the monitoring of anionic species as well as to the determination of general parameters for water quality evaluation (such as pH, alkalinity, chemical and biochemical oxygen demand, conductivity and total ionic content) are reviewed, and their background, detection technique and noteworthy analytical features are detailed. Furthermore, other techniques, such as flow systems connected to hydride-generation atomic absorption spectrometry, should be highlighted as practical approaches for metalloid determination since a series of speciation schemes are demonstrated to be readily adaptable.