Simultaneous distillation-extraction of high-value volatile compounds from Cistus ladanifer L

The present paper describes a procedure to isolate volatiles from rock-rose (Cistus ladanifer L.) using simultaneous distillation-extraction (SDE). High-value volatile compounds (HVVC) were selected and the influence of the extraction conditions investigated. The effect of the solvent nature and extraction time on SDE efficiency was studied. The best performance was achieved with pentane in 1 h operation. The extraction efficiencies ranged from 65% to 85% and the repeatability varied between 4% and 6% (as a CV%).The C. ladanifer SDE extracts were analysed by headspace solid phase microextraction (HS-SPME) followed by gas chromatography with flame ionization detection (GC-FID). The HS-SPME sampling conditions such as fiber coating, temperature, ionic strength and exposure time were optimized. The best results were achieved with an 85 μm polyacrylate fiber for a 60 min headspace extraction at 40 °C with 20% (w/v) of NaCl. For optimized conditions the recovery was in average higher than 90% for all compounds and the intermediate precision ranged from 4 to 9% (as CV %). The volatiles α-pinene (22.2 mg g⁻¹ of extract), 2,2,6-trimethylcyclohexanone (6.1 mg g⁻¹ of extract), borneol (3.0 mg g⁻¹ of extract) and bornyl acetate (3.9 mg g⁻¹ of extract) were identified in the SDE extracts obtained from the fresh plant material.     

Enzymatic reverse FIA method for total phenols determination in urine samples

A reverse flow injection spectrophotometric enzymatic method is proposed to quantify total phenols in urine samples. The polyphenol oxidase (PPO; EC 1.14.18.1) obtained as a crude extract from sweet potato root (Ipomoea batatas) was used as enzymatic catalyze. The detection limit, the sample throughput and relative standard deviation were 7.7 mg l⁻¹ of total phenols, 49 h⁻¹ and 0.9%, respectively. The method was applied to real samples and a recovery study was carried out in order to its validation.     

Preliminary evaluation of new polymer matrix for solid-phase extraction of nonylphenol from water samples

Molecularly imprinted (MIP) and blank polymers with affinity for nonylphenol were designed using computational modelling. Chromatographic tests demonstrated higher affinity of imprinted polymers towards the template nonylphenol as compared with blank polymers. The performance of both polymers in solid-phase extraction was however very similar. Both blank and imprinted polymers appeared to be suitable for the removal and pre-concentration of nonylphenol from contaminated water samples with 99% efficiency of the recovery. The commercial resins PH(EC) (Biotage) and C18 (Varian) tested in the same conditions used for comparative purposes had recovery rate <84%. The polymer capacity for nonylphenol was 231 mg g⁻¹ for blank and 228 mg g⁻¹ for MIP. The synthesised materials can have significance for sample pre-concentration and environmental analysis of this class of compounds.     

Feasibility of high-resolution continuum source molecular absorption spectrometry in flame and furnace for sulphur determination in petroleum products

For the first time, high-resolution molecular absorption spectrometry with a high-intensity xenon lamp as radiation source has been applied for the determination of sulphur in crude oil and petroleum products. The samples were analysed as xylene solutions using vaporisation in acetylene-air flame or in an electrothermally heated graphite furnace. The sensitive rotational lines of the CS molecule, belonging to the ?ν = 0 vibrational sequence within the electronic transition X¹∑⁺ → A¹П, were applied. For graphite furnace molecular absorption spectrometry, the Pd + Mg organic modifier was selected. Strong interactions with Pd atoms enable easier decomposition of sulphur-containing compounds, likely through the temporal formation of Pd_xS_y molecules. At the 258.056 nm line, with the wavelength range covering central pixel ± 5 pixels and with application of interactive background correction, the detection limit was 14 ng in graphite furnace molecular absorption spectrometry and 18 mg kg⁻¹ in flame molecular absorption spectrometry. Meanwhile, application of 2-points background correction found a characteristic mass of 12 ng in graphite furnace molecular absorption spectrometry and a characteristic concentration of 104 mg kg⁻¹ in flame molecular absorption spectrometry.The range of application of the proposed methods turned out to be significantly limited by the properties of the sulphur compounds of interest. In the case of volatile sulphur compounds, which can be present in light petroleum products, severe difficulties were encountered. On the contrary, heavy oils and residues from distillation as well as crude oil could be analysed using both flame and graphite furnace vaporisation. The good accuracy of the proposed methods for these samples was confirmed by their mutual consistency and the results from analysis of reference samples (certified reference materials and home reference materials with sulphur content determined by X-ray fluorescence spectrometry).     

Molecular imprinting solid phase extraction for selective detection of methidathion in olive oil

A specific adsorbent for extraction of methidathion from olive oil was developed. The design of the molecularly imprinted polymer (MIP) was based on the results of the computational screening of the library of polymerisable functional monomers. MIP was prepared by thermal polymerisation using N,N’-methylene bisacrylamide (MBAA) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker. The polymers based on the itaconic acid (IA), methacrylic acid (MAA) and 2-(trifluoromethyl)acryl acid (TFMAA) functional monomers and one control polymer which was made without functional monomers with cross-linker EGDMA were also synthesised and tested. The performance of each polymer was compared using corresponding imprinting factor. As it was predicted by molecular modelling the best results were obtained for the MIP prepared with MBAA. The obtained MIP was optimised in solid-phase extraction coupled with high performance liquid chromatography (MISPE-HPLC-UV) and tested for the rapid screening of methidathion in olive oil. The proposed method allowed the efficient extraction of methidathion for concentrations ranging from 0.1 to 9 mg L⁻¹ (r² = 0.996). The limits of detection (LOD) and quantification (LOQ) in olive oil were 0.02 mg L⁻¹ and 0.1 mg L⁻¹, respectively. MIPs extraction was much more effective than traditional C18 reverse-phase solid phase extraction.     

Development and validation of ultra-high performance supercritical fluid chromatography method for determination of illegal dyes and comparison to ultra-high performance liquid chromatography method

A novel simple, fast and efficient ultra-high performance supercritical fluid chromatography (UHPSFC) method was developed and validated for the separation and quantitative determination of eleven illegal dyes in chili-containing spices. The method involved a simple ultrasound-assisted liquid extraction of illegal compounds with tetrahydrofuran. The separation was performed using a supercritical fluid chromatography system and CSH Fluoro-Phenyl stationary phase at 70 °C. The mobile phase was carbon dioxide and the mixture of methanol:acetonitrile (1:1, v/v) with 2.5% formic acid as an additive at the flow rate 2.0 mL min⁻¹. The UV–vis detection was accomplished at 500 nm for seven compounds and at 420 nm for Sudan Orange G, Butter Yellow, Fast Garnet GBC and Methyl Red due to their maximum of absorbance. All eleven compounds were separated in less than 5 min. The method was successfully validated and applied using three commercial samples of chili-containing spices – Chili sauce (Indonesia), Feferony sauce (Slovakia) and Mojo sauce (Spain). The linearity range of proposed method was 0.50–9.09 mg kg⁻¹ (r ≥ 0.995). The detection limits were determined as signal to noise ratio of 3 and were ranged from 0.15 mg kg⁻¹ to 0.60 mg kg⁻¹ (1.80 mg kg⁻¹ for Fast Garnet) for standard solution and from 0.25 mg kg⁻¹ to 1.00 mg kg⁻¹ (2.50 mg kg⁻¹ for Fast Garnet, 1.50 mg kg⁻¹ for Sudan Red 7B) for chili-containing samples. The recovery values were in the range of 73.5–107.2% and relative standard deviation ranging from 0.1% to 8.2% for within-day precision and from 0.5% to 8.8% for between-day precision. The method showed potential for being used to monitor forbidden dyes in food constituents. The developed UHPSFC method was compared to the UHPLC-UV method. The orthogonality of Sudan dyes separation by these two methods was demonstrated. Benefits and drawbacks were discussed showing the reliability of both methods for monitoring of studied illegal dyes in real food constituents.     

Fast determination of chlorogenic acid in tobacco residues using microwave-assisted extraction and capillary zone electrophoresis technique

In this work, for the first time, capillary zone electrophoresis (CZE) technique combined with microwave-assisted extraction (MAE) was developed for the fast quantification of chlorogenic acid (CA) in tobacco residues. CA in tobacco residue samples were extracted by MAE technique, and then analyzed by CZE. As a new sample preparation method for tobacco residues, the MAE procedure is optimized, validated and compared with conventional methods including ultrasonic extraction (USE) and reflux extraction (RE). It is found that MAE gives the best result due to the highest extraction efficiency within shortest extraction time (only 4.0 min). Here, CA is determined by CZE based on the calibration curve of its authentic standard. The method linearity, detection limit, precision and recovery are studied. The results show that the combined MAE and CZE method has a linearity (R² 0.991, 0.003-0.5 mg ml⁻¹), a limit of detection (0.003 mg ml⁻¹), a limit of quantification (0.01 mg ml⁻¹), good precision (R.S.D. = 4.28%) and a finer recovery (89.0%). The proposed method was successfully applied to the analysis of CA in tobacco residue samples. The experiment results have demonstrated that the CZE combined with MAE is a convenient, fast, economical and reliable method for the determination of CA in tobacco residues.     

Ultrasonication-assisted extraction and preconcentration of medicinal products from herb by ionic liquids

Ionic liquid-based extraction of medicinal or useful compounds from plants was investigated as an alternative to supercritical fluid, cloud point and conventional organic solvent extractions. The method integrated extraction and preconcentration. Medicinal products were first extracted by an ionic liquid solution, part of which was then converted to a hydrophobic form by anion metathesis for preconcentration. The remaining soluble ionic liquid acted as a dispersive agent to enhance the efficiency of preconcentration. Protein in the extract was precipitated spontaneously without addition of further solvents. Ultrasonication assisted this method for extraction and preconcentration of cryptotanshinone, tanshinone I and tanshinone II A from Salvia Miltiorrhiza Bunge. 0.233 mg g⁻¹, 0.695 mg g⁻¹ and 0.682 mg g⁻¹ of each, respectively, were extracted using [OMIM][Cl], and preconcentrated in a [OMIM][PF₆] phase at respective concentrations of 148.1, 507.1 and 486.1 μg mL⁻¹. The method exhibited potential applicability with other medicinal products.     

Sensitized synchronous fluorimetric determination of trans-resveratrol and trans-piceid in red wine based on their immobilization on nylon membranes

It has been carried out the determination of trans-resveratrol and trans-piceid in red wine samples by using room temperature synchronous fluorescence, sensitized through their retention on nylon membranes, in front-face mode. These compounds are weakly fluorescent in solution but their retention allows using the native fluorescence of these compounds as analytical signal, due to the increase in the medium rigidity. To determine these compounds in red wine, a previous liquid-liquid extraction is necessary and in the case of trans-resveratrol it is also necessary a previous cleanup stage using C18 cartridges. Diethylether and ethyl acetate are the selected extractant solvents for trans-resvertarol and trans-piceid, respectively. The retention on nylon membranes was carried out by immersion of the membranes in solutions of these compounds. Variables involved in the retention and measurement processes were optimized, and the analytical figures of merit were obtained under optimal conditions. Ethanol:water 10:90 v:v and ethyl acetate were the solvents used for the retention of trans-resveratrol and trans-piceid, respectively and, for each case a immersion time of 300 and 600 s was selected. Satisfactory linear relation between fluorescence intensity and concentration was found in the intervals 0.040 and 0.242 mg L⁻¹ of trans-resvertarol and 0.009 and 0.288 mg L⁻¹ of trans-piceid. Concentration of 1.08 ± 0.21 mg L⁻¹ for trans-resveratrol and 1.49 ± 0.36 mg L⁻¹ for trans-piceid were found in a wine sample obtained from a pool of commercial red wines.     

Analysis of potassium formate in airport storm water runoff by headspace solid-phase microextraction and gas chromatography–mass spectrometry

Potassium formate was extracted from airport storm water runoff by headspace solid-phase microextraction (HS-SPME) and analyzed by GC–MS. Formate was transformed to formic acid by adding phosphoric acid. Subsequently, formic acid was derivatized to methyl formate by adding methanol. Using sodium [²H]formate (formate-d) as an internal standard, the relative standard deviation of the peak area ratio of formate (m/z 60) and formate-d (m/z 61) was 0.6% at a concentration of 208.5 mg L⁻¹. Calibration was linear in the range of 0.5–208.5 mg L⁻¹. The detection limit calculated considering the blank value was 0.176 mg L⁻¹. The mean concentration of potassium formate in airport storm water runoff collected after surface de-icing operations was 86.9 mg L⁻¹ (n = 11) with concentrations ranging from 15.1 mg L⁻¹ to 228.6 mg L⁻¹.     

Optimization of experimental parameters in single-drop microextraction-gas chromatography-mass spectrometry for the determination of periodate by the Malaprade reaction, and its application to ethylene glycol

The aim of present work was to optimize the experimental parameters in single drop microextraction under solution immersion (SDME) and headspace (HS-SDME) extraction modes for the determination of periodate using guaifenesine [3-(2′-methoxyphenoxy)-1,2-propane diol] and norephedrine (phenylpropanolamine) as new and alternative reagents for the Malaprade reaction. The reactions were complete within 5 min resulting in the formation of 2-(2′-methoxyphenoxy)-acetaldehyde and benzaldehyde, respectively. SDME/HS-SDME of oxidation products with 2 μl of anisole or 1 μl of toluene, respectively, has permitted the determination of periodate at μg l⁻¹ concentration levels. The results indicated that HS-SDME (range 0.01-10 mg l⁻¹, r² = 0.9990; limit of detection 1.55 μg l⁻¹) was more sensitive than SDME (range 0.05-50 mg l⁻¹, r² = 0.9984; limit of detection 3.42 μg l⁻¹), and was inexpensive, rapid and convenient. Tolerance of excess of iodate has permitted the application of this method in the determination of ethylene glycol in motor oil; the average recovery on spiked sample was 98.6% with R.S.D. of 4.2%.     

Direct chiral resolution and its application to the determination of fungicide benalaxyl in soil and water by high-performance liquid chromatography

A simple chiral high-performance liquid chromatography (HPLC) method with ultraviolet (UV) and circular dichroism (CD) detection was developed and validated for measuring benalaxyl enantiomers using (R,R) Whelk-O 1 column. The effects of mobile phase composition and column temperature on the entioseparation were investigated. A CD detector was used to determine the elution order of the enantiomers. Excellent resolution was easily obtained using n-hexane-polar organic alcohols mobile phase. The chiral recognition mechanism was also discussed. Based on the developed chiral HPLC method, enantioselective analysis methods for this fungicide in environment matrix (soil and water) were developed and validated. Good linearities were obtained over the concentration range of 0.25-25 mg L⁻¹ for both enantiomers. Liquid-liquid extraction and solid phase extraction (SPE) were used for the enrichment and cleanup of soil and water samples. Recoveries for the two enantiomers were 79-91% at 0.02, 0.04 and 0.2 mg kg⁻¹ levels from soil, and 89-101% at 0.0025, 0.01 and 0.05 mg L⁻¹ levels from water. Run-to-run and day-to-day assay precisions were below 10% for both enantiomers at concentrations of 0.5, 1 and 5 mg L⁻¹. Individual detection limits of the two enantiomers were both 2 ng. Limits of detection (LOD) were 0.004 mg kg⁻¹ in soil and 0.001 mg L⁻¹ in water.     

Accelerated solvent-based extraction and enrichment of selected plasticisers and 4-nonylphenol, and extraction of tin from organotin sources in sediments, sludges and leachate soils

Enrichment techniques have become an important feature in the trace analysis of oestrogen mimicking chemicals in the environment. Recent developments such as accelerated solvent extraction (ASE) have improved extraction recoveries in a wide variety of solid matrices including sediments, sludges and leachate soils. Such samples taken from the Irish Midlands Shannon Catchment region during the winter of 2004/5 and suspected to contain certain xenooestrogens or hormonally active agents were extracted using this technique, which was then coupled with high performance liquid chromatography (HPLC) for quantification purposes. ASE was thus employed to both isolate and pre-concentrate targeted analytes using the minimum amount of solvent hence making extractions more conservational. Two simple, yet extremely sensitive liquid chromatographic methods were developed based on UV detection; one for phthalates and one for alkylphenols, with recoveries reaching up to 92.0%. Acid digestion was used for the extraction of the tin and organotin compounds with analysis by polarography. In river sediment, levels of up to 24.4 mg kg⁻¹ phthalate, 1.14 mg kg⁻¹ 4-nonylphenol and 118 mg kg⁻¹ tin were found. In leachate sediments, values up to 49.8 mg kg⁻¹ phthalate, 1.57 mg kg⁻¹ 4-nonylphenol, and 36.0 mg kg⁻¹ tin were determined. In sludge, values up to 174 mg kg⁻¹ phthalate and 22.8 mg kg⁻¹ 4-nonylphenol were quantified. The highest value of tin (118 mg kg⁻¹) was found present in an area of high leisure craft activity. Typical sediment levels of tin at other river locations ranged between 1.20 and 37.5 mg kg⁻¹.     

Simultaneous determination of neutral nitrogen compounds in gasoline and diesel by differential pulse voltammetry

The presence of trace neutral organonitrogen compounds as carbazole and indole in derivative petroleum fuels plays an important role in the car's engine maintenance. In addition, these substances contribute to the environmental contamination and their control is necessary because most of them are potentially carcinogenic and mutagenic. For those reasons, a reliable and sensitive method was proposed for the determination of neutral nitrogen compounds in fuel samples, such as gasoline and diesel using preconcentration with modified silica gel (Merck 70-230 mesh ASTM) followed by differential pulse voltammetry (DPV) technique on a glassy carbon electrode. The electrochemical behavior of carbazole and indole studied by cyclic voltammetry (CV) suggests that their reduction occurs via a reversible electron transfer followed by an irreversible chemical reaction. Very well resolved diffusion controlled voltammetric peaks were obtained in dimethylformamide (DMF) with tetrabutylammonium tetrafluoroborate (TBAF₄ 0.1 mol L⁻¹) for indole (−2.27 V) and carbazole (−2.67 V) versus Ag|AgCl|KCl_sat reference electrode. The proposed DPV method showed a good linear response range from 0.10 to 300 mg L⁻¹ and a limit of detection (L.O.D) of 7.48 and 2.66 μg L⁻¹ for indole and carbazole, respectively. The results showed that simultaneous determination of indole and carbazole presents in spiked gasoline samples were 15.8 ± 0.3 and 64.6 ± 0.9 mg L⁻¹ and in spiked diesel samples were 9.29 ± 1 and 142 ± 1 mg L⁻¹, respectively. The recovery was evaluated and the results shown the values of 88.9 ± 0.4 and 90.2 ± 0.8% for carbazole and indole in fuel determinations. The proposed method was also compared with UV-vis spectrophotometric measures and the results obtained for the two methods were in good agreement according to the F and t Student's tests.     

Comparison of supercritical fluid and Soxhlet extractions for the quantification of hydrocarbons from Euphorbia macroclada

This study compares conventional Soxhlet extraction and analytical scale supercritical fluid extraction (SFE) for their yields in extracting of hydrocarbons from arid-land plant Euphorbia macroclada. The plant material was firstly sequentially extracted with supercritical carbon dioxide, modified with 10% methanol (v/v) in the optimum conditions that is a pressure of 400 atm and a temperature of 50 °C and then it was sonicated in methylene chloride for an additional 4 h. E. macroclada was secondly extracted by using a Soxhlet apparatus at 30 °C for 8 h in methylene chloride. The validated SFE was then compared to the extraction yield of E. macroclada with a Soxhlet extraction by using the Student’s t-test at the 95% confidence level. All of extracts were fractionated with silica-gel in a glass column to get better hydrocarbon yields. Thus, the highest hydrocarbons yield from E. macroclada was achieved with SFE (5.8%) when it compared with Soxhlet extractions (1.1%). Gas chromatography (GC) analysis was performed to determine the quantitative hydrocarbons from plant material. The greatest quantitative hydrocarbon recovery from GC was obtained by supercritical carbon dioxide extract (0.6 mg g⁻¹).     

Determination of bromide ions in seawater using flow system with chemiluminescence detection

A simple flow-based procedure with chemiluminescence (CL) detection is proposed for bromide ion determination in seawater. The procedure was based on the oxidation of bromide to bromine by chloramine-T followed by the reaction of bromine with luminol resulting in CL emission. Since no significant reaction within chloramine-T and luminol was observed, the detection was carried out without bromine extraction from the oxidant medium. The proposed flow system had a sampling rate of 40 determinations per hour, reagents consumption of 100 μg luminol and 60 μg chloramine-T per determination, a limit of detection of 0.5 mg l⁻¹ bromide ions, a linear concentration range (r = 0.999 and n = 7) between 0 and 100 mg l⁻¹, and a coefficient of variance better than 2.5% (for 10 measurements of a 10 mg l⁻¹ Br⁻ solution) were achieved. The analytical system was applied for the determination of bromide in seawater and estuarine-water samples, obtaining an analyte recovery ranging from 94 to 102% and comparing the results with a reference spectrophotometric method no significant difference was observed in 95% confidence level.     

Flow injection system with in-line Winkler's procedure using 16-way valve and spectrofluorimetric determination of dissolved oxygen in environmental waters

Flow injection spectrofluorimetry with in-line Winklers procedure was developed for the dissolved oxygen (DO) determination. 2-Thionaphthol reacted with iodine produced by Winkler’s method to form fluorescence inactive disulfide compound. To automate the process completely, a 5-channel flow system with a newly designed 16-way valve was assembled. The system consisted of a dispersion coil (DC), a precipitate formation coil (PFC), a precipitate dissolving coil (PDC), and extraction coil (EC). A calibration can be constructed by using a standard iodine solution for dissolved oxygen. The calibration graph was linear over the range 1.2×10⁻⁴∼6.0×10⁻⁴ mol l⁻¹ iodine (1.96∼9.80 mg O l⁻¹)). The relative standard deviation (n=6) was below 0.3% for the 4×10⁻⁴ mol l⁻¹ iodine (6.27 mg O l⁻¹) determination. The sample throughput was 12/h.     

Synthesis and application of a carbamazepine-imprinted polymer for solid-phase extraction from urine and wastewater

A molecularly imprinted polymer (MIP) designed to enable the selective extraction of carbamazepine (CBZ) from effluent wastewater and urine samples has been synthesised using a non-covalent molecular imprinting approach. The MIP was evaluated chromatographically in the first instance and its affinity for CBZ also confirmed by solid-phase extraction (SPE). The optimal conditions for SPE consisted of conditioning of the cartridge using acidified water purified from a Milli-Q system, loading of the sample under basic aqueous conditions, clean-up using acetonitrile and elution with methanol. The attractive molecular recognition properties of the MIP gave rise to good CBZ recoveries (80%) when 100 mL of effluent water spiked with 1 μg L⁻¹ was percolated through the polymer. For urine samples, 2 mL samples spiked with 2.5 μg L⁻¹ CBZ were extracted with a recovery of 65%. For urine, the linear range was 0.05-24 mg L⁻¹, the limit of detection was 25 μg L⁻¹ and precision, expressed as relative standard deviation at 0.5 mg L⁻¹ (n = 3), was 3.1% and 12.6% for repeatability and reproducibility between days, respectively.     

Optimisation of derivatisation for the analysis of estrogenic compounds in water by solid-phase extraction gas chromatography-mass spectrometry

An optimisation of derivatisation methods for the simultaneous determination of endocrine disrupting chemicals (EDCs) in water by solid-phase extraction (SPE) gas chromatography-mass spectrometry (GC-MS) was developed in this study. Seven highly potent EDCs including 17β-estradiol (E2), estrone (E1), 16α-hydroxyestrone, 17α-ethynylestradiol (EE2), bisphenol A, 4-nonylphenol and 4-tert-octylphenol were selected as the target compounds. The SPE technique, followed by the derivatisation with N,O-bis(trimethylsilyl)trifluoroacetamide (BSTFA) was used for the extraction recoveries of compounds from water and effluent samples. The stability of the silylation derivatives under different reaction conditions was investigated. The combined use of BSTFA and pyridine as derivatisation reagents, together with the use of hexane as the final solvent, was preferred in order to generate more stable derivatives of EDCs. The relative response factor (RRF) of all derivatives except that of EE2 was stable 120 h after derivatisation. The addition of pyridine as derivatisation reagent with BSTFA can prevent the conversion of EE2 to other products during the reaction. Several parameters that may affect the recovery of EDCs, such as the SPE flow rate, and water properties including aquatic colloid content and surfactant concentration were tested. The results showed that the flow rate (1-25 mL min⁻¹), colloid concentration (0-50 mg L⁻¹) and surfactants concentration (0-10 μg L⁻¹) did not cause significant decrease in the EDCs recovery.     

A green analytical procedure for flow-injection determination of nitrate in natural waters

Nitrate determination in waters is generally carried out with cadmium filings and carcinogenic reagents or by reaction with phenolic compounds in highly concentrated sulfuric acid medium. In this work, it was developed a green analytical procedure for nitrate determination in natural waters based on direct spectrophotometric measurements in ultraviolet, using a flow-injection system with an anion-exchange column for separation of nitrate from interfering species. The proposed method employs only one reagent (HClO₄) in a minimum amount (equivalent to 18 μL concentrated acid per determination), and allowed nitrate determination within 0.50-25.0 mg L⁻¹, without interference of up to 200.0 mg L⁻¹ humic acid; 1.0 mg L⁻¹ NO₂⁻; 200.0 mg L⁻¹ PO₄³⁻; 75.0 mg L⁻¹ Cl⁻; 50.0 mg L⁻¹ SO₄²⁻ and 15.0 mg L⁻¹ Fe³⁺. The detection limit (99.7% confidence level) and the coefficient of variation (n = 20) were estimated as 0.1 mg L⁻¹ and 0.7%, respectively. The results obtained for natural water samples were in agreement with those achieved by the reference method based on nitrate reduction with copperized cadmium at the 95% confidence level.