On-line sample treatment and FT-IR determination of doxylamine succinate in pharmaceuticals

A low solvent consumption method for Fourier transform infrared spectroscopy (FT-IR) determination of doxylamine succinate in pharmaceuticals has been developed. The analyte was continuous and selectively extracted with a 13% (v/v) ethanol:chloroform solvent mixture, recirculating the solvent through the sample and monitoring the process by FT-IR. Doxylamine succinate was determined by on-line standard addition measuring the peak area in the regions 1730–1710 and 1485–1462 cm⁻¹ corrected with a two-point baseline established between 2000 and 1800 cm⁻¹. This new method implies low volumes of chloroformic solvent mixture, only 2.6 mL per sample, in front of classical batch FT-IR methods, improving analytical efficiency and reducing waste generation. The on-line extraction and standard addition determination of doxylamine succinate allowed a throughput of 10 h⁻¹.     

Flow injection determination of nitrite by fluorescence quenching

A simple, sensitive and selective fluorimetric method for the determination of nitrite ion in waters using a merging zones flow injection system is described. The fluorimetric determination is based on the measurement of the quenching effect produced by nitrite on proflavine (3,6-diaminoacridine) fluorescence (λ_ex/λ_em=290/519 nm).

The optimum experimental conditions were investigated by merging 0.5 ml of the sample and 0.5 ml of a solution of 5 mg l⁻¹ of proflavine (in 0.1 M HCl) in a flow injection system, on-line connected to a flow-cell placed in the conventional sample compartment of a spectrofluorimeter. The selected carrier solution and final flow rate were 0.1 M HCl and 0.5 ml min⁻¹, respectively. A reaction coil of 2 ml was used. As a result of the simplicity of this system, a sample throughput of about 50 samples h⁻¹ can be achieved with the proposed methodology.

The detection limit was 1.1 ng ml⁻¹ (3σ criterion) of nitrite. The repeatability for five sample injections containing 100 ng ml⁻¹ of nitrite was ±0.3% and the observed linear range extended up to 400 ng ml⁻¹. Also, the effect of interferences from various metals and anions commonly present in waters was also studied.

The method was successfully applied to the determination of low levels of nitrite in different water samples (river, fountain, tap and commercial drinking waters).     

Spectrophotometric simultaneous determination of nitrite, nitrate and ammonium in soils by flow injection analysis

A new rapid flow injection procedure for the simultaneous determination of nitrate, nitrite and ammonium in single flow injection analysis system is proposed. The procedure combines on-line reduction of nitrate to nitrite and oxidation of ammonium to nitrite with spectrophotometric detection of nitrite by using the Griess-llosvay reaction. The formed azo dye was measured at 543 nm. The influence of reagent concentration and manifold parameters were studied. Nitrite, nitrate and ammonium can be determined within the range of 0.02–1.60 μg mL⁻¹, 0.02–1.60 μg mL⁻¹ and 0.05–1.40 μg mL⁻¹, respectively. R.S.D. values (n = 10) were 2.66; 1.41 and 3.58 for nitrate, nitrite and ammonium, respectively. This procedure allows the determination and speciation of inorganic nitrogen species in soils with a single injection in a simple way, and high sampling rate (18 h⁻¹). Detection limits of 0.013, 0.046 and 0.047 μg mL⁻¹were achieved for nitrate, nitrite and ammonium, respectively. In comparison with others methods, the proposed one is more simple, it uses as single chromogenic reagent less injection volume (250 mL in stead of 350 mL) and it has a higher sampling rate.     

Seafood freshness determination through vapour phase Fourier transform infrared spectroscopy

A new vapour-phase manifold has been developed to determine trimethylamine (TMA) in fish and cephalopod samples by Fourier transform infrared (FT-IR) spectroscopy. Samples were treated off-line for 1 h with trichloroacetic acid (TCA), filtered and washed. The obtained extracts were aspirated and alkalinized with NaOH 2.0 M, in an on-line system. TMA was separated from the solution in a gas phase separator and then transported by means of a nitrogen carrier into a home made 10 cm pathlength IR gas cell, where the corresponding FT-IR spectra were acquired by accumulating 30 scans per spectrum with 2 cm⁻¹ nominal resolution. The method was applied to the determination of TMA in natural samples providing concentration values statistically comparables with those obtained by a head space gas chromatography (HS-GC) reference procedure. The sample throughput by FT-IR is increased by a factor of 6 as compared with HS-GC.     

Far infrared spectra, conformational equilibria, vibrational assignments, ab initio calculations and structural parameters for 2-bromoethanol

The far infrared spectrum from 370 to 50 cm⁻¹ of gaseous 2-bromoethanol, BrCH₂CH₂OH, was recorded at a resolution of 0.10 cm⁻¹. The fundamental O–H torsion of the more stable gauche (Gg′) conformer, where the capital G refers to internal rotation around the C–C bond and the lower case g to the internal rotation around the C–O bond, was observed as a series of Q-branch transitions beginning at 340 cm⁻¹. The corresponding O–H torsional modes were observed for two of the other high energy conformers, Tg (285 cm⁻¹) and Tt (234 cm⁻¹). The heavy atom asymmetric torsion (rotation around C–C bond) for the Gg′ conformer has been observed at 140 cm⁻¹. Variable temperature (−63 to −100°C) studies of the infrared spectra (4000–400 cm⁻¹) of the sample dissolved in liquid xenon have been recorded. From these data the enthalpy differences have been determined to be 411±40 cm⁻¹ (4.92±0.48 kJ/mol) for the Gg′/Tt and 315±40 cm⁻¹ (3.76±0.48 kJ/mol) for the Gg′/Tg, with the Gg′ conformer the most stable form. Additionally, the infrared spectrum of the gas, and Raman spectrum of the liquid phase are reported. The structural parameters, conformational stabilities, barriers to internal rotation and fundamental frequencies have been obtained from ab initio calculations utilizing different basis sets at the restricted Hartree–Fock or with full electron correlation by the perturbation method to second order. The theoretical results are compared to the experimental results when appropriate. Combining the ab initio calculations with the microwave rotational constants, r₀ adjusted parameters have been obtained for the three 2-haloethanols (F, Cl and Br) for the Gg′ conformers.     

Thermal degradation of biodegradable edible films based on xanthan and starches from different sources

Films based on xanthan/wheat starch and xanthan/maize starch were prepared in different proportions and analysed in terms of thermal stability in relation to the degradation reaction in an inert atmosphere. The main gaseous decomposition products were identified by infrared spectroscopy. Xanthan was found to be less thermally stable than starch from different sources. The starch addition to xanthan induced an increase in the film thermal stabilities. The thermal degradation mechanism of xanthan starts with scission of the side chain groups with subsequent scission of the main chain. Starches from maize and wheat presented a constant mechanism of thermal degradation. The proportion of xanthan/starch (50/50) presented a synergistic behaviour which may be associated with changes in the mechanism of the thermal degradation process. The FTIR spectra of the gaseous products during thermal degradation of xanthan showed a broad absorption in the 2750–3300 cm⁻¹ region, probably indicating decomposition of β-d-mannopyranosyl groups, present in xanthan side chains. For pure starches, absorptions related to alcohol O–H stretching (3500–3750 cm⁻¹), CO stretching of CO₂, CO and carbonyl compounds (2361, 2177 and 1743 cm⁻¹, respectively) were observed. For xanthan/starch mixtures (50/50) the same compounds as those for the pure polymer degradation were evolved. However, a shift of the CO to higher wavenumber values indicates that new carbonyl compounds are being formed due to changes in the thermal degradation mechanism.     

Spectroscopic and structural analysis of Ca substituted La orthoferrite

Samples of orthoferrites La_1−xCa_xFeO₃ (0.15≤x≤0.45) were synthesized by double sintering ceramic technique. X-ray diffraction and infrared spectroscopy experiments were carried out and discussed for the investigated samples. The data showed the formation of single-phase orthorhombic structure of space group Pbnm. The FTIR spectra were performed in the region (1200–200 cm⁻¹). Four main absorption bands were present with some side bands and shoulders in the range (1200–400 cm⁻¹). Another four bands were appeared in the range (400–200 cm⁻¹). The positions, intensities and values of the absorptions bands vary depending on the Ca content in the samples. The first absorption band appeared at about 920 cm⁻¹ was assigned to the La–O stretching vibration.     

Novel flow injection-fluorometric method for the determination of trace silicate and its application to ultrapurified water analysis

A highly sensitive fluorescence quenching method for the determination of silicate based on the formation of an ion associate between molybdosilicate and Rhodamine B (RB) in nitric acid medium was developed. A flow injection system coupled with a fluorescence detector was used for the measurement of fluorescence intensity at 560 and 580 nm as excitation and emission wavelengths, respectively. The calibration graph for Si showed a linear range of 0.1–5 ng cm⁻³ with correlation coefficient of 0.9999, and the detection limit of 0.06 ng cm⁻³. The proposed method was successfully applied to the determination of silicate in ultrapurified water with satisfactory results.     

FTIR investigation of the conformational properties of the cyanide bound human hemoglobin

Infrared spectra at 4 cm⁻¹ resolution of the cyanide ligated human methemoglobin (Hb-CN) were examined in the C---N stretching region. The FTIR spectra of hemoglobin ligated with the various isotopomeric forms of the cyanide ion support the existence of three conformational states for Hb-CN. In potassium phosphate buffer at pH of 7.5, the three bands were observed at 2116, 2122 and 2127 cm⁻¹ for natural abundance Hb-CN. These bands shift to 2086, 2091 and 2095 cm⁻¹ for Hb-¹²C¹⁵N and 2073, 2077 and 2081 cm⁻¹ for Hb-¹³C¹⁴N. Two extra bands have been identified in the IR spectra of solid Hb-CN in KBr pellets. The peaks persist in the pH range between 3.5 and 10.5 with small changes in frequency and intensity. The appearance of several C---N stretching bands is consistent with C---N vibrators residing in different environment and support the hypothesis that Hb-CN assumes multiple conformers under the conditions studied.     

Solvent impregnated hollow fibre for a selective preconcentration of Pb(II) in an on-line determination by flame atomic absorption spectrometry

A solvent impregnated hollow fibre (SIHF) module has been developed for the preconcentration of lead by using bis(2-ethylhexyl) phosphoric acid (DEHPA) dissolved in kerosene as extractant. The module has been designed for an on-line determination of trace amounts of lead(II) at mg l⁻¹ (ppm) level by flame atomic absorption spectrometry (FAAS).

The SIHF system is based on the metal liquid–liquid distribution between aqueous solutions of different acidity and the mentioned organic solution. The highest enrichment factor of Pb(II) was determined at pH=4.0 using a formic acid/formiate buffer solution.

Preconcentration experiments were carried out at low lead(II) concentration (mg l⁻¹ level) by using the SIHF module. This study includes the influence of hydrodynamic and chemical conditions on the loading and elution of Pb(II) on the SIHF, i.e., flow rate through the fibres, acidity of the eluent (as nitric acid concentration) and the chemical nature of the acid used in the elution. Breakthrough curves were determined for different sampling flow rates, 0.54 ml min⁻¹ was selected to minimise the loading volume of Pb(II) sample. 0.1 M nitric acid was chosen as eluent solution, and perchloric acid also shows appropriate elution characteristics. The degree of concentration obtained for Pb(II) are of 10 fold the original concentration. The quantification limit for Pb(II) achieved with this preconcentration system is 0.17 mg l⁻¹.

The results obtained indicate that the SIHF system can be applied for on-line determination of trace amounts of lead(II) by FAAS.     

Novel CO2 selectively permeating membranes containing PETEDA dendrimer

Pentaerythrityl tetraethylenediamine (PETEDA) dendrimer was synthesized from pentaerythrityl tetrabromide and ethylenediamine. Its molecular structure was characterized by elemental analysis, Fourier transform infrared resonance (FT-IR) and hydrogen nuclear magnetic resonance (¹H NMR) spectroscopy. The composite membranes for selectively permeating CO₂ were prepared by using PETEDA-PVA blend polymer as the active layer and polyethersulfone (PES) ultrafiltration membrane as the support layer and their permselectivity was tested by pure CO₂ and CH₄ gases and the gas mixture containing 10 vol.% CO₂ and 90 vol.% CH₄, respectively. For pure gases, the membrane containing 78.6 wt% PETEDA and 21.4 wt% PVA in the blend has a CO₂ permeance of 8.14 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity of 52 at 143.5 cmHg feed gas pressure. While feed gas pressure is 991.2 cmHg, CO₂ permeance reaches 3.56 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ and CO₂/CH₄ selectivity is 19. For the gas mixture, the membrane has a CO₂ permeance of 6.94 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 33 at 188.5 cmHg feed gas pressure, and a CO₂ permeance of 3.29 × 10⁻⁵ cm³ (STP) cm⁻² s⁻¹ cmHg⁻¹ with a CO₂/CH₄ selectivity of 7.5 at a higher feed gas pressure of 1164 cmHg. A possible gas transport mechanism in the composite membranes is proposed by investigating the permeating behavior of pure gases and the gas mixture and analyzing possible reactions between CO₂/CH₄ gases and the PETEDA-PVA blend polymer. The effect of PETEDA content in the blend polymer on permselectivity of the composite membranes was investigated, presenting that CO₂ permeance and CO₂/CH₄ selectivity increase and CH₄ permeance decreases, respectively with PETEDA content. This is explained by that with increasing PETEDA content, the carrier content increases, and the crystallinity and free volume of the PETEDA-PVA blend decrease that were confirmed by the experimental results of X-ray diffraction spectra (XRD) and positron annihilation lifetime spectroscopy (PALS).     

The rovibrational analysis of the high-resolution IR spectrum of CD2HF below 1200 cm: an interacting tetrad of vibrational levels

The spectrum of CD₂HF was measured by high-resolution interferometric Fourier-transform IR (FTIR) spectroscopy (apodised instrumental band with:0.004 cm⁻¹ fwhm) between 800 and 1200 cm⁻¹ covering the four lowest fundamentals. A complete rotational analysis using a semi-automatic assignment procedure yields accurate band centres (ν₉: 912.2028 cm⁻¹, ν₆:964.4994 cm⁻¹, ν₅: 1050.5104 cm⁻¹, ν₄: 1093.8632 cm⁻¹) and a complete set of first-order Coriolis coupling constants. The most important couplings occur between ν₉ and ν₆ (ξ_a= 1.069 cm⁻¹, ξ_c= −0.3535 cm⁻¹) and between ν₅ and ν₄ (ξ_b= −0.80606 cm⁻¹). The analysis was guided by and compared with results from our ab initio calculations for Coriolis constants and transition moments using CADPAC at TZP/MP2 level.     

A dense oxygen separation membrane with a layered morphologic structure

A configuration of dense mixed ionic and electronic conducting (MIEC) membrane with layered morphological structure for oxygen separation, which combines the benefits of high oxygen permeation flux of cobalt-based membrane, high chemical stability of iron-based perovskite and high mechanical strength of thick membrane, was studied. The membrane is normally composed of two layers; each layer is a dense MIEC oxide. The substrate layer is a thick dense membrane with high oxygen permeability but relatively lower chemical stability. The feasibility of dense thick Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF5582) membrane as the substrate layer and Ba_0.5Sr_0.5Co_0.2Fe_0.8O_3−δ (BSCF5528) as the thin-film layer was mainly experimentally investigated. Both the BSCF5582 and the BSCF5528 show the same cubic perovskite structure and the similar lattice constant with no detrimental reaction products formed. By optimizing fabrication parameters of a simple dry pressing process, dual-layered membrane, free of cracks, was successfully fabricated. The oxygen permeation flux of a dual-layered membrane with the thin-film BSCF5528 layer facing to the sweep gas reached 2.1 mL cm⁻² min⁻¹ [STP] (1.56 × 10⁻⁶ mol cm⁻² s⁻¹) at 900 °C, which is about 3.5 times higher than that of the BSCF5528 membrane (0.6 mL cm⁻² min⁻¹, [STP] (4.46 × 10⁻⁷ mol cm⁻² s⁻¹) under the same conditions.     

A novel method for the spectrophotometric determination of nitrite in water

A rapid, simple, selective and sensitive method for the spectrophotometric determination of nitrite in water has been developed and optimum reaction conditions along with other analytical parameters have been evaluated. Nitrite reacts with barbituric acid in acidic solution to give the nitroso derivative, violuric acid. At analytical wavelength of 310 nm, Beer's law is obeyed over the concentration range 0.00–3.22 ppm of nitrite. The molar absorptivity is 15330 ± 259.7 (95%) with pooled standard deviation of 355.57 and R.S.D. of 2.32%. As well as the method is sensitive (2.99 × 10⁻³ μg NO₂ cm⁻²) and selective, it tolerates most of the potential interferents. It has been successfully applied to nitrite determination in natural waters by use of a calibration graph with determination limit of 1.66 μg NO₂ in 100 mL working solution corresponding to minimum 9.5 ppb NO₂–N in water samples. Lower concentrations of nitrite (3.0 μg NO₂/L sample) is precisely analyzed by using the method of dilution with sample, with R.S.D. of lower than 0.5%. The results were compared with standard N-(1-naphtyl)ethylenediamine dihydrochloride method and very good agreement between the data was observed. The method can easily be applied in the field.     

Indirect determination of ascorbic acid by solid-phase spectrophotometry

Solid-phase spectrophotometry (SPS) technique, in the visible region, was used for the spectrophotometric determination of ascorbic acid based on the reducing effect on iron(III) ion, followed by formation of the iron(II)-ferrozine chelate. The chelate is easily sorbed on a dextran-type anion-exchange gel and the absorbance of the resin at 567 and 800 nm, packed in a 1 mm cell, is measured directly. The apparent molar absorptivity using 100 ml of sample was 2.1×10⁷ l mol⁻¹ cm⁻¹ and it allowed the determination of ascorbic acid in the range 5–90 ng ml⁻¹; the detection limit was 0.91 ng ml⁻¹ and the RSD 0.91% for a concentration of 50 ng ml⁻¹ of ascorbic acid (n=10). The proposed method permits a highly sensitive and selective determination of ascorbic acid without any preconcentration and it has been satisfactorily applied for its determination in fruit juices, pharmaceuticals, urine and conservative liquids.     

Intramolecular hydrogen bonding. Spectroscopic and theoretical studies of vibrational transitions in dibenzoylmethane enol

The vibrational structure of the title compound (DBM) was investigated by FTIR spectroscopy in liquid solutions, by FTIR linear dichroism (LD) measurements, and by Raman spectroscopy. The results were supported by the application of theoretical model calculations and analyzed with particular attention to the possible origin of the broad, very strong, and irregularly shaped absorbance band observed in the 1700–1400 cm⁻¹ region. The orientation factors derived from the observed LD data indicate that rotational dynamics of the phenyl groups do not contribute significantly to the broadening of the band. The position of the two sharp Evans transmission windows near 1580 and 1500 cm⁻¹ is unaffected by deuteration of the reactive protons in DBM. The transmissions coincide with prominent peaks in the Raman spectrum and can be assigned to combinations of phenylic modes (9a, 18a) with low IR intensity, but large Raman scattering activity.     

High pressure performance of thin Pd–23%Ag/stainless steel composite membranes in water gas shift gas mixtures; influence of dilution, mass transfer and surface effects on the hydrogen flux

The hydrogen permeation and stability of tubular palladium alloy (Pd–23%Ag) composite membranes have been investigated at elevated temperatures and pressures. In our analysis we differentiate between dilution of hydrogen by other gas components, hydrogen depletion along the membrane length, concentration polarization adjacent to the membrane surface, and effects due to surface adsorption, on the hydrogen flux. A maximum H₂ flux of 1223 mL cm⁻² min⁻¹ or 8.4 mol m⁻² s⁻¹ was obtained at 400 °C and 26 bar hydrogen feed pressure, corresponding to a permeance of 6.4 × 10⁻³ mol m⁻² s⁻¹ Pa^−0.5. A good linear relationship was found between hydrogen flux and pressure as predicted for rate controlling bulk diffusion. In a mixture of 50% H₂ + 50% N₂ a maximum H₂ flux of 230 mL cm⁻² min⁻¹ and separation factor of 1400 were achieved at 26 bar. The large reduction in hydrogen flux is mainly caused by the build-up of a hydrogen-depleted concentration polarization layer adjacent to the membrane due to insufficient mass transport in the gas phase. Substituting N₂ with CO₂ results in further reduction of flux, but not as large as for CO where adsorption prevail as the dominating flow controlling factor. In WGS conditions (57.5% H₂, 18.7% CO₂, 3.8% CO, 1.2% CH₄ and 18.7% steam), a H₂ permeance of 1.1 × 10⁻³ mol m⁻² s⁻¹ Pa^−0.5 was found at 400 °C and 26 bar feed pressure. Operating the membrane for 500 h under various conditions (WGS and H₂ + N₂ mixtures) at 26 bars indicated no membrane failure, but a small decrease in flux. A peculiar flux inhibiting effect of long term exposure to high concentration of N₂ was observed. The membrane surface was deformed and expanded after operation, mainly following the topography of the macroporous support.     

Conformational studies of cyclopropylmethyl isocyanate from temperature dependent FT-IR spectra of xenon solutions and ab initio calculations

Variable temperature (−55 to −100 °C) studies of the infrared spectra (3200 to 100 cm⁻¹) of cyclopropylmethyl isocyanate, c-C₃H₅CH₂NCO, dissolved in liquefied xenon, have been carried out. The infrared spectra (gas and solid) as well as the Raman spectrum of the liquid have been recorded from 3200 to 100 cm⁻¹. By analyzing six conformer pairs in xenon solutions, an enthalpy difference of 193 ± 19 cm⁻¹ (2.31 ± 0.23 kJ/mol) was obtained with the gauche–cis rotamer (the first designation indicates the orientation of the CNCO group with respect to the three-membered ring, the second designation indicates the relative orientation of the NCO group with respect to the bridging CC bond) the more stable form and the only form present in polycrystalline solid. The abundance of the cis–trans conformer present at ambient temperature is 16 ± 1%. The potential function governing the conformational interchange has been obtained from B3LYP/6-31G(d) calculations and the two-dimensional potential has been obtained. From MP2 ab initio calculations utilizing various basis sets with diffuse functions, the gauche–cis conformer is predicted to be more stable by 223 to 269 cm⁻¹, which is consistent with the experimental results. However, without diffuse functions the predicted conformational energy differences are much smaller (77–166 cm⁻¹). Similar diffuse function dependency affects density functional theory calculations by the B3LYP method to a lesser extent. A complete vibrational assignment for the gauche–cis conformer is proposed and several fundamentals for the cis–trans conformer have been identified. The structural parameters, dipole moments, conformational stability, vibrational frequencies, infrared intensities and Raman activities have been predicted from ab initio calculations and r₀ structural parameters are estimated. These experimental and theoretical results are compared to the corresponding quantities of some similar molecules.     

High-field EPR investigation of a series of mononuclear Mn(II) complexes doped into Zn(II) hosts

The five-coordinate mono-halide mononuclear Zn(II) complexes [Zn(tpa)X]⁺ (tpa = tris(2-pyridylmethyl)amine; X = I ([Zn(tpa)I]I; 1a), Br ([Zn(tpa)Br](ZnBr₄)_0.5; 2a) and Cl ([Zn(tpa)Cl](ZnCl₄)_0.5; 3a)) and the six-coordinate mononuclear complex [Zn(tpa)(NCS)₂] (4a) have been synthesized and characterized by X-ray crystallography. The [Zn(tpa)X]⁺ complexes doped with the corresponding [Mn(tpa)X₂] complexes (X = I (1b), Br (2b) and Cl (3b)) have been synthesized and their electronic properties investigated by multifrequency high field EPR (HF-EPR) (95–285 GHz). The magnetically diluted conditions allow the determination of the hyperfine coupling constant A (A = 68.10⁻⁴ cm⁻¹ for 1b–3b). The zero-field splitting parameters (D and E) found for 1b–3b are comparable to those found for neat samples of the [Mn(tpa)X₂] complexes (1b: D = 0.635 cm⁻¹, E/D = 0.189; 2b: D = 0.360 cm⁻¹, E/D = 0.192; 3b: D = 0.115 cm⁻¹, E/D = 0.200). The efficacy of using multifrequency EPR under dilute conditions to precisely determine spin Hamiltonian parameters is discussed.     

Simple flow-injection system for the simultaneous determination of nitrite and nitrate in water samples

A novel spectrophotometric reaction system was developed for the determination of nitrite as well as nitrate in water samples, and was applied to a flow-injection analysis (FIA). The spectrophotometric flow-injection system coupled with a copperised cadmium reductor column was proposed. The detection was based on the nitrosation reaction between nitrite ion and phloroglucinol (1,3,5-trihydroxybenzene), a commercially available phenolic compound. Sample injected into a carrier stream was split into two streams at the Y-shaped connector. One of the streams merged directly and reacted with the reagent stream: nitrite ion in the samples was detected. The other stream was passed through the copperised cadmium reductor column, where the reduction of nitrate to nitrite occurred, and the sample zone was then mixed with the reagent stream and passed through the detector: the sum of nitrate and nitrite was detected. The optimised conditions allow a linear calibration range of 0.03–0.30 μg NO₂⁻-N ml⁻¹ and 0.10–1.00 μg NO₃⁻-N ml⁻¹. The detection limits for nitrite and nitrate, defined as three times the standard deviation of measured blanks are 2.9 ng NO₂⁻-N ml⁻¹ and 2.3 ng NO₃⁻-N ml⁻¹, respectively. Up to 20 samples can be analyzed per hour with a relative standard deviation of less than 1.5%. The proposed method could be applied successfully to the simultaneous determination of nitrite and nitrate in water samples.