Determination of nitrogen in hydrolyzed protein formulations by continuous vapour phase FTIR

An on-line system with vapour generation (VG) and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of free ammonium and organic nitrogen in agrochemical formulations containing hydrolyzed proteins. Commercial samples were digested, in batch mode, with sulphuric acid and the obtained solution was alkalinized on-line to transform the NH₄⁺ to NH₃ that was continuously monitored by FTIR. Free ammonium was determined in the same system after simple dilution of undigested samples with water. Different gas phase separators were assayed in order to introduce gaseous NH₃ into a home made IR gas cell of 10 cm pathlength, where the corresponding FTIR spectra were acquired by accumulating 10 scans per spectrum. The 967.0 cm⁻¹ band was used for the quantification of ammonia. The figures of merit of the proposed method involve a linear range up to 100 mg L⁻¹, a limit of detection (3σ) of 1.4 mg L⁻¹ of N, a limit of quantification (10σ) of 4.8 mg L⁻¹ of N, a precision (R.S.D.) of 3.0% for 10 replicate determinations of a 10.0 mg L⁻¹ of N and a sample measurement frequency of 60 h⁻¹. The method was successfully applied to the determination of free ammonium and total N in commercial amino acid formulations and results compare well with those obtained by the Kjeldhal method.     

Sequential injection methodology for carbon speciation in bathing waters

A sequential injection method (SIA) for carbon speciation in inland bathing waters was developed comprising, in a single manifold, the determination of dissolved inorganic carbon (DIC), free dissolved carbon dioxide (CO₂), total carbon (TC), dissolved organic carbon and alkalinity. The determination of DIC, CO₂ and TC was based on colour change of bromothymol blue (660 nm) after CO₂ diffusion through a hydrophobic membrane placed in a gas diffusion unit (GDU). For the DIC determination, an in-line acidification prior to the GDU was performed and, for the TC determination, an in-line UV photo-oxidation of the sample prior to GDU ensured the conversion of all carbon forms into CO₂. Dissolved organic carbon (DOC) was determined by subtracting the obtained DIC value from the TC obtained value. The determination of alkalinity was based on the spectrophotometric measurement of bromocresol green colour change (611 nm) after reaction with acetic acid. The developed SIA method enabled the determination of DIC (0.24–3.5 mg C L⁻¹), CO₂ (1.0–10 mg C L⁻¹), TC (0.50–4.0 mg C L⁻¹) and alkalinity (1.2–4.7 mg C L⁻¹ and 4.7–19 mg C L⁻¹) with limits of detection of: 9.5 μg C L⁻¹, 20 μg C L⁻¹, 0.21 mg C L⁻¹, 0.32 mg C L⁻¹, respectively. The SIA system was effectively applied to inland bathing waters and the results showed good agreement with reference procedures.     

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.     

Flow analysis-hydride generation-Fourier transform infrared spectrometric determination of antimony in pharmaceuticals

In this work, a flow analysis system with hydride generation and Fourier transform infrared (FTIR) spectrometric detection has been developed for the determination of antimony in pharmaceuticals. The method is based on the on-line mineralization/oxidation of the organic antimonials present in the sample and pre-reduction of Sb(V) to Sb(III) with K₂S₂O₈ and KI, respectively; prior to the stibine generation. The gaseous SbH₃ is separated from the solution in a gas phase separator, and transported by means of a nitrogen carrier into a short pathway (10 cm) IR gas cell, where the corresponding FTIR spectrum is acquired by accumulating 3 scans in a continuous mode. The 1893 cm⁻¹ band was used for the quantification of the antimony. The procedure is carried out in a closed system, which reduces sample handling and makes possible the complete automation of the antimony determination. The figures of merit of the proposed method (linear range: 0-600 mg l⁻¹, limit of detection (3σ)=0.9 mg l⁻¹, limit of quantification (10σ)=3 mg Sb l⁻¹, precision (R.S.D.) less than 1% and sample frequency=28 h⁻¹), are appropriate for the designed application. Furthermore, precise and accurate results were found for the analysis of different antimonial pharmaceutical samples, indicating that the methodology developed represents a valid alternative for the determination of antimony in pharmaceuticals, which could be suitable for the routine control analysis.     

A new tool for inorganic nitrogen speciation study: simultaneous determination of ammonium ion, nitrite and nitrate by ion chromatography with post-column ammonium derivatization by Nessler reagent and diode-array detection in rain water samples

The paper presents a new method for a simultaneous determination of inorganic nitrogen species in the oxidized (NO₂⁻, NO₃⁻) and reduced (NH₄⁺) form in rain water samples. The method is based on a system of nitrogen species separation employing ion exchange and diode-array detection. The ions are separated in a strong ion-exchanger, nitrites and nitrates are determined directly at 208 and 205 nm, respectively, while the ammonium ions are determined in the column hold-up time after a post-column derivatization by the Nessler reagent, at 425 nm. The use of a diode-array detector permits a simultaneous identification of the inorganic nitrogen species in 8 min. The detection limits obtained are: NO₂⁻, 0.1 mg L⁻¹; NO₃⁻, 0.05 mg L⁻¹; NH₄⁺, 1 mg L⁻¹. The method proposed has been successfully used for speciation analysis of inorganic nitrogen in precipitation.     

Multi-pumping flow system for the determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples

A multi-pumping flow system (MPFS) for the spectrophotometric determination of dissolved orthophosphate and dissolved organic phosphorus in wastewater samples is proposed. The determination of orthophosphate is based on the vanadomolybdate method. In-line ultraviolet photo-oxidation is employed to mineralise organic phosphorus to orthophosphate prior to detection. A solenoid valve allows the deviation of the flow towards the UV-lamp to carry out the determination of organic phosphorus.Calibration was found to be linear up to 20 mg P L⁻¹, with a detection limit (3s_b/S) of 0.08 mg P L⁻¹, an injection throughput of 75 injections h⁻¹ and a repeatability (R.S.D.) of 0.6% for the direct determination of orthophosphate. On the other hand, calibration graphs were linear up to 40 mg P L⁻¹, with a detection limit (3s_b/S) of 0.5 mg P L⁻¹, an injection throughput of 11 injections h⁻¹ and a repeatability (R.S.D.) inferior to 2.3% for the procedures involving UV photo-oxidation.     

A sensitive spectrophotometric method for determination of carbon tetrachloride with the aid of ultrasonic decolorization of methyl orange

A sensitive method for carbon tetrachloride (CCl₄) determination has been developed with the aid of ultrasonic oxidation decolorization of methyl orange (MO). It is found that the ultrasonic oxidation decolorization rate of MO can be significantly promoted by adding a little amount of CCl₄. The increased ultrasonic decolorization rate of MO is strongly dependent on the concentration of CCl₄ added, and a linear correlation is observed between the amount of CCl₄ and the decolorization rate of MO in the ultrasonic oxidation process. Thus, the CCl₄ determination is transformed to a simple and direct determination of the decoloration extent of MO solution at a given concentration. As an indirect spectrophotometric determination of CCl₄, the new method is sensitive and easy of operation with a maximum wavelength of 508 nm, molar absorptivity of 3.83 × 10⁴ L mol⁻¹ cm⁻¹, and a Sandell sensitivity of 7.96 × 10⁻³ μg cm⁻². Under optimized conditions, Beer's law is obeyed in the range of 0.4-20 mg L⁻¹ of CCl₄ (DL = 0.19 mg L⁻¹, r = 0.9996). The concentrations of CCl₄ in several practical samples have been determined satisfactorily by using this method.     

Catalytic activity of iron hexacyanoosmate(II) towards hydrogen peroxide and nicotinamide adenine dinucleotide and its use in amperometric biosensors

Hydrogen peroxide and nicotinamide adenine dinucleotide (NADH) may be determined amperometrically using screen-printed electrodes chemically modified with iron(III) hexacyanoosmate(II) (Osmium purple) in flow injection analysis (FIA). The determination is based on the exploitation of catalytic currents resulting from the oxidation/reduction of the modifier. The performance of the sensor was characterized and optimized by controlling several operational parameters (applied potential, pH and flow rate of the phosphate buffer). Comparison has been made with analogous complexes of ruthenium (Ruthenium purple) and iron (Prussian blue). Taking into account the sensitivity and stability of corresponding sensors, the best results were obtained with the use of Osmium purple. The sensor exhibited a linear increase of the amperometric signal with the concentration of hydrogen peroxide in the range of 0.1-100 mg L⁻¹ with a detection limit (evaluated as 3σ) of 0.024 mg L⁻¹ with a R.S.D. 1.5% for 10 mg L⁻¹ H₂O₂ under optimized flow rate of 0.4 mL min⁻¹ in 0.1 M phosphate buffer carrier (pH 6) and a working potential of +0.15 V versus Ag/AgCl. Afterwards, a biological recognition element - either glucose oxidase or ethanol dehydrogenase - was incorporated to achieve a sensor facilitating the determination of glucose or ethanol, respectively. The glucose sensor gave linearity between current and concentration in the range from 1 to 250 mg L⁻¹ with a R.S.D. 2.4% for 100 mg L⁻¹ glucose, detection limit 0.02 mg L⁻¹ (3σ) and retained its original activity after 3 weeks when stored at 6 °C. Optimal parameters in the determination of ethanol were selected as: applied potential +0.45 V versus Ag/AgCl, flow rate 0.2 mL min⁻¹ in 0.1 M phosphate buffer carrier (pH 7). Different structural designs of the ethanol sensor were tested and linearity obtained was up to 1000 mg L⁻¹ with a maximum R.S.D. of 5.1%. Applications in food analysis were also examined.     

Detoxification of antimony by selenium and their interaction in paddy rice under hydroponic conditions

Antimony (Sb) contamination has become a growing concern in recent years. Strategies for reducing Sb contamination and its related health risks are urgently desired. This study was conducted to explore the possibility of selenium (Se) detoxification on Sb toxicity in paddy rice in order to find a feasible method to reduce the health risk of Sb pollution. Seedlings of paddy rice were exposed to 5 mg L⁻¹ Sb (KSbC₄H₄ O₇·1/2H₂O), in the presence of Se (Na₂SeO₃) at 0.1, 1, 5 mg L⁻¹ in culture solution, with no Sb and Se addition as the control. Paddy rice took up Sb greatly and the highest Sb contents measured among all treatments in this experiment in the leaves, stems and roots were 65.5, 298.5 and 195.7 mg kg⁻¹, respectively. Without Sb addition in the solution, single exposure to 0.1 mg L⁻¹ Se remarkably reduced the malondialdehyde (MDA) formation in paddy rice,demonstrating the beneficial effect of Se at low dosages. The addition of 5 mg L⁻¹ Sb was found to generate toxicity to paddy rice, showing as decreased biomass and increased leaf MDA content in paddy rice, while addition of 1 mg L⁻¹ Se mitigated the toxicity of Sb, as seen with the decreased leaf MDA content and increased biomass, indicating antidotal role of Se to Sb. In addition, the presence of 0.1, 1, 5 mg L⁻¹ Se generally decreased the accumulation of Sb in the leaves, stems and roots in paddy rice. Toxicity was also seen when paddy rice was exposed to single Se at 1 and 5 mg L⁻¹ levels, however, 5 mg L⁻¹ Sb addition was found to decrease the contents of Se in the leaves/stems whereas increased them in roots, accompanied with decreased MDA contents and increased biomass in paddy rice, indicating a possible detoxification role of Sb to Se too. Therefore, Sb, although toxic, could also be an antitoxin to Se in paddy rice at certain condition. Our results showed that Se could alleviate Sb toxicity efficiently in paddy rice through two effects as antagonism and antioxidation.     

A sequential injection system for indirect spectrophotometric determination of lactic acid in yogurt and fermented mash samples

A suitable non-enzymatic method is presented as an alternative to the lactic acid determination in yogurt and fermented mash samples. The oxidative conversion of lactic acid by Ce⁴⁺ to CO₂ was performed in a sequential injection system with a heating coil set at 45 °C. A gas diffusion unit was coupled to the flow system for promoting the permeation of CO₂, which was collected into a bromothymol blue solution (pH 8.4), used as indicator solution for the spectrophotometric determination (619 nm). Simplicity in operation, low reagent consumption, low cost and ruggedness are some remarkable characteristics of the proposed system. Base line drift was < 0.005 h^− 1. A linear range from 20.0 to 100.0 mg L^− 1 lactic acid was obtained (r² = 0.998), and the detection and quantification limits were estimated as 0.158 mg L^− 1 and 1.6 mg L^− 1, respectively. The sampling rate was 22 h^− 1, with a consumption of 0.04 g Ce⁴⁺ per determination. Interferences of matrix components were not detected. Samples of yogurt and sugar cane fermented mash products were analyzed, and no significant difference at 95% confidence level was observed when comparing the proposed method with HPLC analysis.     

Dissolved oxygen amperometric sensor based on layer-by-layer assembly using host-guest supramolecular interactions

The development of a simple, efficient and sensitive sensor for dissolved oxygen is proposed using the host-guest binding of a supramolecular complex at a host surface by combining a self-assembled monolayer (SAM) of mono-(6-deoxy-6-mercapto)-β-cyclodextrin (βCDSH), iron (III) tetra-(N-methyl-4-pyridyl)-porphyrin (FeTMPyP) and cyclodextrin-functionalized gold nanoparticles (CDAuNP). The supramolecular modified electrode showed excellent catalytic activity for oxygen reduction. The reduction potential of oxygen was shifted about 200 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare gold electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves probably 4-electrons with a rate constant (k_obs) of 7 × 10⁴ mol⁻¹ L s⁻¹. A linear response range from 0.2 up to 6.5 mg L⁻¹, with a sensitivity of 5.5 μA L mg⁻¹ (or 77.5 μA cm⁻² L mg⁻¹) and a detection limit of 0.02 mg L⁻¹ was obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation was 3.0% for 10 measurements of a solution of 6.5 mg L⁻¹ oxygen.     

Gas chromatographic separation of PCB and OCP by photocatalytic degradation

A photocatalytic degradation method was developed for polychlorobiphenyl (PCB) and organochloride pesticide (OCP) discrimination and quantification. A mixture of Aroclor 1260 and p,p′-DDT was irradiated at 254 nm by UV lamp (40 W) in the presence of TiO₂ (30 mg mL⁻¹ non-aqueous solution). Comparison of gas chromatograms showed that p,p′-DDT signals decreased significantly after irradiation, while Aroclor 1260s chromatograms did not show any difference before and after irradiation. Detection limits were 0.30 mg L⁻¹ and 0.15 mg L⁻¹ for p,p′-DDT and Aroclor 1260, respectively. The method was applied to spiked egg samples, the recoveries were found as 72% for DDT and 82.01% for Aroclor 1260.     

Spectrophotometric determination of carbon tetrachloride via ultrasonic oxidation of iodide accelerated by dissolved carbon tetrachloride

Ultrasonic oxidation of iodide was investigated in the presence of carbon tetrachloride (CCl₄). The ultrasonic oxidation of potassium iodide led to formation of iodine and then I₃⁻ in the presence of excess iodide, and the generated I₃⁻ shows strong UV absorption with a molar absorptivity of 2.31 × 10⁴ L mol⁻¹ cm⁻¹ at the maximum absorption wavelength of 351 nm. The ultrasonic oxidation of iodide was found to be significantly promoted by a small addition of CCl₄, and it was further found that the generation rate was increased with the amount of CCl₄ added. This can be used to analyze the level of CCl₄ dissolved in aqueous solutions. Under optimum conditions, the concentration of generated iodine (or its absorption at 351 nm) was found to correlated linearly with the concentration of CCl₄ in the range of 0.2-50 mg L⁻¹ (detection limit = 0.09 mg L⁻¹, R² = 0.999). As an alternative indirect spectrophotometric method of CCl₄ determination, the proposed method was successfully applied to determine the concentrations of CCl₄ in several practical samples, showing merits of being sensitive and simple of operation.     

A highly sensitive amperometric sensor for oxygen based on iron(II) tetrasulfonated phthalocyanine and iron(III) tetra-(N-methyl-pyridyl)-porphyrin multilayers

The development of a highly sensitive sensor for oxygen is proposed using a glassy carbon (GC) electrode modified with alternated layers of iron(II) tetrasulfonated phthalocyanine (FeTsPc) and iron(III) tetra-(N-methyl-pyridyl)-porphyrin (FeT4MPyP). The modified electrode showed excellent catalytic activity for the oxygen reduction. The reduction potential of the oxygen was shifted about 330 mV toward less negative values with this modified electrode, presenting a peak current much higher than those observed on a bare GC electrode. Cyclic voltammetry and rotating disk electrode (RDE) experiments indicated that the oxygen reduction reaction involves 4 electrons with a heterogenous rate constant (k_obs) of 3 × 10⁵ mol⁻¹ L s⁻¹. A linear response range from 0.2 up to 6.4 mg L⁻¹, with a sensitivity of 4.12 μA L mg⁻¹ (or 20.65 μA cm⁻² L mg⁻¹) and a detection limit of 0.06 mg L⁻¹ were obtained with this sensor. The repeatability of the proposed sensor, evaluated in terms of relative standard deviation (R.S.D.) was 2.0% for 10 measurements of a solution of 6.4 mg L⁻¹ oxygen. The sensor was applied to determine oxygen in pond and tap water samples showing to be a promising tool for this purpose.     

Sensitive and ultra-fast determination of arsenic(III) by gas-diffusion flow injection analysis with chemiluminescence detection

A novel chemiluminescence gas-diffusion flow injection system for the determination of arsenic(III) in aqueous samples is described. The analytical procedure involves injection of arsenic(III) samples and standards into a 0.3 mol L⁻¹ hydrochloric acid carrier stream which is merged with a reagent stream containing 0.2% (w/v) sodium borohydride and 0.015 mol L⁻¹ sodium hydroxide. Arsine, generated in the combined carrier/reagent donor stream, diffuses across the hydrophobic Teflon membrane of the gas-diffusion cell into an argon acceptor stream and then reacts with ozone in the flow-through chemiluminescence measuring cell of the flow system. Under optimal conditions, the method is characterized by a wide linear calibration range from 0.6 μg L⁻¹ to 25 mg L⁻¹, a detection limit of 0.6 μg L⁻¹ and a sample throughput of 300 samples per hour at 25 mg L⁻¹ and 450 samples per hour at 25 μg L⁻¹.     

Hybrid sequential injection-flow injection manifold for the spectrophotometric determination of total sulfite in wines using o-phthalaldehyde and gas-diffusion

A new automated spectrophotometric method for the determination of total sulfite in white and red wines is reported. The assay is based on the reaction of o-phthalaldehyde (OPA) and ammonium chloride with the analyte in basic medium under SI conditions. Upon on-line alkalization with NaOH, a blue product is formed having an absorption maximum at 630 nm. The parameters affecting the reaction - temperature, pH, ionic strength, amount concentration and volume of OPA, amount concentration of ammonium chloride, flow rate and reaction coil length - and the gas-diffusion process - sample and HCl volumes, length of mixing coil, donor flow rate - were studied. The proposed method was validated in terms of linearity (1-40 mg L⁻¹, r = 0.9997), limit of detection (c_L = 0.3 mg L⁻¹) and quantitation (c_Q = 1.0 mg L⁻¹), precision (s_r = 2.2% at 20 mg L⁻¹ sulfite, n = 12) and selectivity. The applicability of the analytical procedure was evaluated by analyzing white and red wine samples, while the accuracy as expressed by recovery experiments ranged between 96% and 106%.     

Optimization of chemical and instrumental parameters in hydride generation laser-induced breakdown spectrometry for the determination of arsenic,antimony, lead and germanium in aqueous samples

A laser induced breakdown spectrometry hyphenated with on-line continuous flow hydride generation sample introduction system, HG-LIBS, has been used for the determination of arsenic, antimony, lead and germanium in aqueous environments. Optimum chemical and instrumental parameters governing chemical hydride generation, laser plasma formation and detection were investigated for each element under argon and nitrogen atmosphere. Arsenic, antimony and germanium have presented strong enhancement in signal strength under argon atmosphere while lead has shown no sensitivity to ambient gas type. Detection limits of 1.1 mg L⁻¹, 1.0 mg L⁻¹, 1.3 mg L⁻¹ and 0.2 mg L⁻¹ were obtained for As, Sb, Pb and Ge, respectively. Up to 77 times enhancement in detection limit of Pb were obtained, compared to the result obtained from the direct analysis of liquids by LIBS. Applicability of the technique to real water samples was tested through spiking experiments and recoveries higher than 80% were obtained. Results demonstrate that, HG-LIBS approach is suitable for quantitative analysis of toxic elements and sufficiently fast for real time continuous monitoring in aqueous environments.     

A flow injection procedure based on solenoid micro-pumps for spectrophotometric determination of free glycerol in biodiesel

A flow system designed with solenoid micro-pumps is proposed for fast and greener spectrophotometric determination of free glycerol in biodiesel. Glycerol was extracted from samples without using organic solvents. The determination involves glycerol oxidation by periodate, yielding formaldehyde followed by formation of the colored (3,5-diacetil-1,4-dihidrolutidine) product upon reaction with acetylacetone. The coefficient of variation, sampling rate and detection limit were estimated as 1.5% (20.0 mg L⁻¹ glycerol, n = 10), 34 h⁻¹, and 1.0 mg L⁻¹ (99.7% confidence level), respectively. A linear response was observed from 5 to 50 mg L⁻¹, with reagent consumption estimated as 345 μg of KIO₄ and 15 mg of acetylacetone per determination. The procedure was successfully applied to the analysis of biodiesel samples and the results agreed with the batch reference method at the 95% confidence level.     

Reversed flow injection spectrophotometric determination of chlorate

An interfacing has been developed to connect a spectrophotometer with a personal computer and used as a readout system for development of a simple, rapid and sensitive reversed flow injection (rFI) procedure for chlorate determination. The method is based on the oxidation of indigo carmine by chlorate ions in an acidic solution (dil. HCl) leading to the decrease in absorbance at 610 nm. The decrease in absorbance is directly related to the chlorate concentration present in the sample solutions. Optimum conditions for chlorate were examined. A linear calibration graph over the range of 0.1-0.5 mg L⁻¹ chlorate was established with the regression equation of Y = 104.5X + 1.0, r² = 0.9961 (n = 6). The detection limit (3σ) of 0.03 mg L⁻¹, the limit of quantitation (10σ) of 0.10 mg L⁻¹ and the RSD of 3.2% for 0.3 mg L⁻¹ chlorate (n = 11) together with a sample throughput of 92 h⁻¹ were obtained. The recovery of the added chlorate in spiked water samples was 98.5 ± 3.1%. Major interferences for chlorate determination were found to be BrO₃⁻, ClO₂⁻, ClO⁻ and IO₃⁻ which were overcome by using SO₃²⁻ (as Na₂SO₃) as masking agent. The method has been successfully applied for the determination of chlorate in spiked water samples with the minimum reagent consumption of 14.0 mL h⁻¹. Good agreement between the proposed rFIA and the reference methods was found verified by Student's t-test at 95% confidence level.     

Batch and hydrodynamic monitoring of vitamin C using novel periodate selective sensors based on a newly synthesized Ni(II)-Schiff bases complexes as a neutral receptors

A highly selective membrane electrodes based on a two newly synthesized nickel (II) Schiff bases, [NiL¹] and [NiL²] where L¹ and L² are N,N/bis(salicylaldehyde)4,5-dimethyl-1,2-phenylenediamine (H₂L¹) and N,N/bis(salicylaldehyde)4,5-dichloro-1,2-phenylenediamine (H₂L²) were used as a neutral carrier ionophores for static and hydrodynamic potentiometric mode of operations for the determination of periodate. Under static mode of operation, the sensors displayed a near-Nernstian slope of −66.1 ± 0.8 and −59.9 ± 1.1 mV decade⁻¹ of activity and detection limits to 5.2 × 10⁻⁶ and 7.3 × 10⁻⁶ mol L⁻¹ for the sensors based on [NiL¹] and [NiL²], respectively. Under hydrodynamic mode of operation (FIA), the slope of the calibration plot, limit of detection, and working linear range were −71.1 mVdecade⁻¹ of activity, 7.3 × 10⁻⁶ and 1.0 × 10⁻⁵ to 1.0 × 10⁻³ mol L⁻¹, respectively. The response time of the sensors in whole concentration ranges was very short (<10 s). The response of the sensors was independent on the pH range of 3-8. A tubular version was further developed and coupled to a flow injection system for ascorbic acid (AA) determination in beverages and pharmaceutical preparations. This approach was achieved by selecting a 50-cm reactor and an overall flow of 3 mL min⁻¹, and injecting volume 100 μL of AA standards in a 1.0 × 10⁻⁴ mol L⁻¹ IO₄⁻ solution. Under these conditions, a linearity range of 2-13 μg mL⁻¹, with a slope of 4.97 mV (mg/L)⁻¹ (r² = 0.9995), detection limit 0.9 mg L⁻¹ and a reproducibility of ±1.1 mV (n = 5) was recorded. This simple and inexpensive flow injection analysis manifold, with a good potentiometric detector, enabled the analysis of ∼50 samples h⁻¹ without requiring pretreatment procedures. An average recovery of 98.8% and a mean standard deviation of 1.3% were obtained.