Recent trends in the use of organized molecular systems combined with chromatographic techniques in environmental analysis

The establishment of new analytical methods which improve quality and sensitivity in the determination of environmental pollutants in liquid and solid samples is demanded. The use of micellar systems have become an advantageous tool for the extraction of pollutant compounds, due to their easy handling, biodegradability, and the one-step procedure, and they are compatible with the hydroalcoholic mobile phases used in HPLC. The focus of this review is to present recently developed methods and the main trends in the use of micellar media combined with solid-phase microextraction and solid-phase extraction in the chromatographic analysis of organic compounds in different types of environmental matrix, including water, sediments, and biological samples. Selected samples illustrate the benefits of these systems in the whole of analytical process. The advantages of micellar media over conventional extractants are reduction of solvent usage, low cost, easy handling, and non-toxic procedure.     

Development of a sequential injection chromatography (SIC) method for determination of simazine,atrazine, and propazine

This paper describes the development of a sequential injection chromatography (SIC) procedure for separation and quantification of the herbicides simazine, atrazine, and propazine exploring the low backpressure of a 2.5 cm long monolithic C₁₈ column. The separation of the three compounds was achieved in less than 90 s with resolution >1.5 using a mobile phase composed by ACN/1.25 mmol/L acetate buffer (pH 4.5) at the volumetric ratio of 35:65 and flow rate of 40 μL/s. Detection was made at 223 nm using a flow cell with 40 mm of optical path length. The LOD was 10 μg/L for the three triazines and the quantification limits were of 30 μg/L for simazine and propazine and 40 μg/L for atrazine. The sampling frequency is 27 samples per hour, consuming 1.1 mL of ACN per analysis. The proposed methodology was applied to spiked water samples and no statistically significant differences were observed in comparison to a conventional HPLC–UV method. The major metabolites of atrazine and other herbicides did not interfere in the analysis, being eluted from the column either together with the unretained peak, or at retention times well‐resolved from the studied compounds.     

Flow-injection fluorimetric determination of menadione using on-line photo-reduction in micellar media

A very sensitive fluorimetric method for the determination of menadione using a flow injection system is proposed. The method is based on the on-line reduction of menadione in dodecylsulphate micelles upon irradiation with UV light. The strong fluorescence of the reduced menadione in micellar medium is measured at 410 nm with excitation at 340 nm. The method shows a linear range between 2.42 and 245 ng ml⁻¹ and a limit of detection of 0.18 ng ml⁻¹. The sample throughput was 90 injections per hour. The applicability of the assay was demonstrated by analysing this vitamin in commercial pharmaceutical preparations.     

Dual-response colorimetric sensor array for the identification of amines in water based on supramolecular host-guest complexation

Amines have been found as a challenging compound class in previous works on chemical tongues. Herein, we describe the successful application of libraries based on host-guest inclusion complexes in cyclodextrins (CDs) and cucurbiturils (CBs) for the discrimination of primary, secondary, tertiary, aliphatic and aromatic as well as linear and branched amines in water. Besides the clear need for new detection, identification and quantification techniques of organic compounds in water, the main advantage of our approach is that an array made by combining six simple basic dyes with seven commercial organic capsules allows a perfect discrimination among 14 amines (see list in Table S1 in Supplementary data) with only very subtle structural differences.     

Pesticide analysis by micellar electrokinetic capillary chromatography

On-capillary sample concentration using sample stacking for the improvement of detection limits for various pesticides separated by micellar electrokinetic capillary chromatography was examined. The dependence of the stacking on different parameters was investigated. An approximately 30-fold preconcentration was achieved by applying sample stacking. Employing a two-step enrichment process (solid-phase extraction combined with sample stacking), detection limits were improved and the sample volume for SPE was reduced. In addition, the total time for the analysis was considerably reduced. Detection limits were between 0.01 and 0.1 ng/ml under these enrichment conditions.     

Applications of microfluidic systems in environmental analysis

During the past few decades, rapid growth in the applications of microfluidic systems to environmental analysis or environmentally related species has been observed. This review presents and critically discusses the published literature on the applications of microfluidic systems to real environmental samples or samples simulating environmental conditions. The subjects covered include integrated pretreatments, separation modes, detection methods and monitoring sensors used in these platforms. The main challenges in this field and the author’s perspectives on future directions for environmental analysis based on microfluidic systems are also proposed.     

Sequential injection fluorimetric determination of Sn in juices of canned fruits

The present work describes the development of a fast and robust sequential injection fluorimetric procedure for the determination of Sn in juices of canned fruits. The developed automatic methodology is based on the complexation of Sn with 8-hydroxyquinoline-5-sulfonic acid (HQSA) to form a fluorimetric product (λ_exc = 354 nm; λ_em = 510 nm). The influence of dimethylsulfoxide (DMSO) and cetylpyridinium bromide (CPB) on the sensitivity of the fluorimetric determination was evaluated.Linear calibration plots were obtained for Sn concentrations between 1 and 10 mg L⁻¹, with a detection limit of 0.38 mg L⁻¹. In each analytical cycle 0.006 mg of HQSA and 0.47 mg of CPB were consumed and 1.5 mL of effluent was generated.The developed methodology was applied to the determination of Sn in juices of canned fruits and the results complied with those furnished by an electrothermal atomic absorption spectrometry comparison procedure, with relative deviations lower than 5.2%.The automatic procedure exhibited good precision (R.S.D. < 1.4%) and the sampling rate was about 70 determinations per hour.     

Environmental and pharmaceutical analysis of dithiocarbamates

The current review aims at a comprehensive survey of analytical methods for the determination of dithiocarbamates (DTCs) in environmental and pharmaceutical samples. Besides parent compounds, analytical approaches for various metabolites and degradation products of DTCs are considered. Special emphasis is given to analyte stability as DTCs are considerably reactive interacting with various organic and inorganic compounds; in addition, depending on the chemical nature of the substance, DTCs are prone to oxidation and hydrolysis under alkaline and acidic conditions, respectively. The review mainly focuses on chromatography but also covers applications in electrophoresis, spectrophotometry, and biosensing.     

Multiwavelength fluorescence based optosensor for simultaneous determination of fuberidazole, carbaryl and benomyl

In the present work, a novel approach is proposed for the simultaneous determination of three widely used pesticides (namely, fuberidazole (FBZ), carbaryl (CBL) and benomyl (BNM)). The proposed method is based on a single continuous-flow solid surface fluorimetric multi-optosensor implemented with the use of a minicolumn placed just before the flow-through cell and filled with C₁₈ silica gel. The three pesticides are determined from an only injection (simultaneous determination): the minicolumn strongly retains two of them while the third develops a transitory signal when passing through the sensing solid microzone. Then, two alternate eluting solutions appropriately selected perform the sequential elution of the two pesticides from the minicolumn, achieving the detection zone and developing their transitory signals. The proposed optosensor works under optimal sensitivity conditions for all the three analytes because of the use of multi-wavelength fluorescence detection mode, so recording three different signals corresponding at three pairs of optima excitation/emission wavelengths. Using a sample volume of 2100 μl, the system was calibrated in the range 0.5-15, 40-800 and 50-1000 μg l⁻¹ with detection limits of 0.09, 6 and 9 μg l⁻¹ for FBZ, CBL and BNM, respectively. The R.S.D values (n=10) were lower than 2% in all cases. The proposed methodology was applied satisfactorily to water samples. Recovery percentages ranging from 97.8 to 101.1%, 97.9 to 103% and from 97 to 105% for FBZ, CBL and BNM, respectively, were obtained.     

Cyclodextrin-enhanced fluorescence and photochemically-induced fluorescence determination of five aromatic pesticides in water

The effect of β-cyclodextrin (β-CD) and hydroxypropyl-β-cyclodextrin (HP-β-CD) aqueous solutions upon the fluorescence and photochemically-induced fluorescence (PIF) properties of five pesticides, including coumatetralyl, pirimiphos-methyl, chlorpyriphos, deltamethrin and fenvalerate was investigated. A 1:1 stoichiometry was found for the β-CD and HP-β-CD complexes formed with all compounds. Binding constant values, ranging between about 90 and 830 M⁻¹ were calculated using the iterative nonlinear least-squares regression approach. Cyclodextrin-enhanced fluorescence and PIF methods were developed for the determination of these pesticides with linear dynamic ranges over two orders of magnitude, and limits of detection (LOD) between 0.2 and 54 ng ml⁻¹ according to the compound. Application to the analysis of tap water and river water samples yielded satisfactory recoveries (88–116%). The method seems to be suitable for environmental water analysis.     

Comparison and evaluation of cloud point extraction and low-temperature directed crystallization as preconcentration tools for the determination of trace elements in environmental samples

A comparative study between cloud point extraction (CPE) and low-temperature directed crystallization (LTDC) is presented. Trace elements (Cd, Pb, Cr, Cu, Zn, Ni and Fe) were preconcentrated by both methods from model and natural water samples and the results were evaluated with respect to extraction efficiency, accuracy, precision, sample throughput and interferences. Flame atomic absorption spectrometry (FAAS) and inductively coupled plasma atomic emission spectrometry (ICP-AES) were used for the final measurements. The results indicate that these extraction and preconcentration procedures ensure the required accuracy and precision for the reliable identification and quantification of trace elements in natural waters. Drawbacks of each method identified can further assist the analyst towards a better application of each method depending on the target species, the detector employed and the application intended (routine analysis, trace analysis, speciation analysis, etc.).     

Partial least squares multicomponent fluorimetric determination of fluoroquinolones in human urine samples

Ternary mixtures of fluoroquinolones, with a 7-piperazinyl substituted group have been simultaneously determined in human urine samples by application of a multivariate calibration partial least squares (PLS) model. The calibration set was designed with 15 urine samples containing different concentrations of the three fluoroquinolones and 16 blank urine samples. The concentration range for the fluoroquinolones were up to 25 ng ml⁻¹ for norfloxacin (NOR), 80 ng ml⁻¹ for ofloxacin (OFLO) and 300 ng ml⁻¹ for enoxacin (ENO). The method is based on the native fluorescence emission of these compounds in sodium dodecyl sulfate (SDS) medium, at pH 4.0, when exciting at 277 nm. A selection of the emission wavelength range used for the analysis was made for each component. Intraday and interday precision values were determined. Figures of merit as selectivity, sensitivity, limit of detection (LOD) and analytical sensitivity were also calculated. Using the standard addition methodology, five urine samples from five different persons, fortified with three concentration levels of the fluoroquinolones, were analyzed. The limits of detection in urine were 10.0, 0.5 and 0.8 ng ml⁻¹ for ENO, NOR and OFLO, respectively.     

Multiresidue Analysis of Pesticides in Environmental Waters by Capillary Electrophoresis Using Simultaneous UV and Electrochemical Detection

A rapid multiresidue method has been developed for the analysis of eight pesticides (triazines, triazinones and ureas) in environmental waters. A simple end‐column electrochemical detector was used in combination with an available commercial capillary electrophoresis instrument with UV detection. The determination of these pesticides using micellar electrokinetic capillary chromatography (MEKC) with dual electrochemical and UV detection is the first time reported. In both detection systems, a linear range was obtained for the eight pesticides, concentrations lower than 5.0×10^?5 mol L^?1, in 0.020 mol L^?1 boric acid at pH 8.3 and containing 0.025 mol L^?1 of sodium dodecylsulfate, to obtain selectivity in the additional separation by micellar distribution process. Under these conditions a lower detection limit than 2.0×10^?6 mol L^?1 (0.15 pmol of pesticide) was achieved for the most of them. The eight pesticides are resolved in less than 14 min.     

Environmental analysis of organic compounds in water using solid phase micro extraction

Solid Phase Micro Extraction (SPME) involves exposing a fused silica fiber coated with stationary phase to a contaminated water sample. The organic analytes become partitioned between the stationary phase and the water and when equilibrium is reached the fiber is removed from the solution and the analytes are thermally desorbed in the injector of a gas chromatograph. The fiber is contained in a syringe to facilitate handling. Factors which affect linear range, limit of detection, and total analysis time are discussed with regard to the development of a method for analysis of volatile compounds in environmental water samples. The sensitivity of the method was determined by the thickness of the film of stationary phase; the equilibration time, however, increased with the film thickness, although it can be minimized by use of a cross-shaped stirrer bar. Increasing the thickness of stationary phase in the analytical column enables the cryofocusing temperature to be increased from ?40 to ?15°C. With an ion trap mass spectrometer, detection limits required by the US Environmental Protection Agency are met for all compounds except chloromethane and chloroethane. The method has been applied to environmental water samples.     

荧光光度法直接测定环境水中的苯酚和苯胺

了用荧光分光光度法通过控制酸度直接测定环境水中苯酚和苯胺两种水中污染物的新方法。在ｐＨ＝１时，直接测定苯酚的含量，波长为λｅｘ／λｅｍ＝２７０／２９７ｎｍ，检出限为４．０ｎｇ／ｍＬ，线性范围为０～３．２μｇ／ｍＬ。在ｐＨ＝１２时，直接测定苯胺的含量，波长为λｅｘ／λｅｍ＝２８０／３４０ｎｍ检出限为４．３ｎｇ／ｍＬ，线性范围为０～２．０ｕｇ／ｍＬ，回收率达９９～１０１％。     

A novel fluorescent and colorimetric anion sensor based on thiourea derivative in competitive media

A novel and simple fluorescent receptor bearing thiourea moiety as recognition site was described. The recognition behavior of the receptor toward different anions was investigated in DMSO/H(2)O (95:5 v/v) and dry DMSO through two various channels: the colorless-yellow color change and a remarkable enhancement of the fluorescence. And the enhancement of the fluorescence was attributed to an anion-induced increase of the rigidity of the host molecule.     

Simultaneous kinetic determination of Fe(II) and Fe(III) based on their reactions with NQT4S in micellar media by using PLS and PCR methods

Simultaneous determination of Fe(II) and Fe(III) was studied using partial least squares regression (PLS) and principal component regression (PCR) methods. The models were based on the difference observed in the rates of the complex formation of iron in its two oxidation states with 1,2-naphthaquinone-2-thiosemicarbazone-4-sulphonic acid (NQT4S) at pH 4.0 in cetyltrimethylammoniumbromide (CTAB) as micellar media. The results showed that simultaneous determination of Fe(II) and Fe(III) could be performed in their concentration ranges of 0.10-2.10 and 0.25-2.25 μg/ml, respectively. The models used can proceed the data with low percent relative error of prediction (i.e. <5.5%). The procedure was successfully applied for the simultaneous determination of Fe(II) and Fe(III) in some environmental samples. The method would allow the transformation of the two oxidation states of iron to be monitored overtime in a water sample.     

Multiresidue analysis of phenylurea herbicides in environmental waters by capillary electrophoresis using electrochemical detection

A rapid multiresidue method has been developed for the analysis of seven phenylurea herbicides in the presence of two s-triazines in environmental waters. A simple end-column electrochemical detector was used in combination with a commercially-available capillary electrophoresis instrument with UV detection. The determination of phenylurea pesticides using micellar electrokinetic capillary chromatography with electrochemical detection represents the first such determination that has been reported. In both detection systems, linear ranges were obtained for the seven phenylurea herbicides at concentrations lower than 2.0×10^–5 mol l^–1, in 0.020 mol l^–1 phosphoric acid at pH 7.0 and containing 0.020 mol l^–1 of sodium dodecylsulfate, in order to obtain selectivity in the additional separation by a micellar distribution process. Under these conditions a detection limit lower than 5.0×10^–6 mol l^–1 (0.25 pmol of pesticide) was achieved for most of them. The pesticides were resolved in less than 30 min.     

Determination of various alcohols based on a new immobilized enzyme fluorescence capillary analysis

A novel method for the determination of ethanol in tequila based on the immobilized enzyme fluorescence capillary analysis (IE-EFCA) has been proposed. Alcohol dehydrogenase (ADH) was immobilized in inner surface of a capillary and an immobilized enzyme capillary bioreactor (IE-ECBR) was formed. After nicotinamide adenine dinucleotide (NAD⁺) as an oxidizer is mixed with alcohol sample solution, it was sucked into the IE-ECBR. The fluorescence intensity of the mixed solution in the IE-ECBR was detected at λ_ex = 350 nm and λ_em = 459 nm. The experimental conditions are as follows: The reaction time is 20 min; temperature is 40 °C; the concentrations of phosphate buffer solution (pH 7.5) and NAD⁺ are 0.1 mol L⁻¹ and 5 mmol L⁻¹, respectively; immobilization concentration of ADH is 10 U L⁻¹. The determination range of ethanol is 2.0-15.0 g L⁻¹ (F = 10.44C + 6.6002, r > 0.9958); its detection limit is 1.11 g L⁻¹; and relative standard deviation is 1.9%. IE-EFCA method is applicable for the determination of the samples containing alcohol in medicine, industry and environment.