Determination Of Nitrate In Water Research Articles

In Situ Determination of Nitrate in Water Using Fourier Transform Mid-Infrared Attenuated Total Reflectance Spectroscopy Coupled with Deconvolution Algorithm.

Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectroscopy has been used to determine the nitrate content in aqueous solutions. However, the conventional water deduction algorithm indicated considerable limits in the analysis of samples with low nitrate concentration. In this study, FTIR-ATR spectra of nitrate solution samples with high and low concentrations were obtained, and the spectra were then pre-processed with deconvolution curve-fitting (without water deduction) combined with partial least squares regression (PLSR) to predict the nitrate content. The results show that the typical absorption of nitrate (1200−1500 cm−1) did not clearly align with the conventional algorithm of water deduction, while this absorption was obviously observed through the deconvolution algorithm. The first principal component of the spectra, which explained more than 95% variance, was linearly related to the nitrate content; the correlation coefficient (R2) of the PLSR model for the high-concentration group was 0.9578, and the ratio of the standard deviation of the prediction set to that of the calibration set (RPD) was 4.22, indicating excellent prediction performance. For the low-concentration group model, R2 and RPD were 0.9865 and 3.15, respectively, which also demonstrated significantly improved prediction capability. Therefore, FTIR-ATR spectroscopy combined with deconvolution curve-fitting can be conducted to determine the nitrate content in aqueous solutions, thus facilitating rapid determination of nitrate in water bodies with varied concentrations.

Highly sensitive modified glassy carbon sensor based on TDAN for nitrate detection in real water

Glassy carbon electrodes modified with a plasticized PVC membrane including tetradodecyl ammonium nitrate (TDAN) and two different plasticizers [bis(2-etheylhexyl) sebacate (DOS) and dibutyl phthalate (DBP)]. TDAN is a quaternary ammonium salt, used in nitrate-selective field-effect transistor membrane, and it is applied as an ionophore for sensor development. Membranes were prepared as sensing matrix for nitrate detection through the intensity of its reduction peak using cyclic voltammetry. Under optimum conditions, the detection limits of nitrate obtained with TDAN + DOS and TDAN + DBP, are 10–6 mol/dm3 and 10–9 mol/dm3, respectively. As a result, the developed sensors based on TDAN + DOS and TDAN + DBP matrices demonstrate satisfactory quantified amounts in determination of nitrate in water where the measured values were less than 0.57 × 10–7 mol/dm3 and 0.73 × 10–10 mol/dm3, respectively.

A new thin film modified glassy carbon electrode based on melaminium chloride pentachlorocuprate(II) for selective determination of nitrate in water

A new electrochemical thin film glassy carbon sensor for nitrate detection based on a copper complex, namely melaminium chloride pentachlorocuprate (H2mela)ClCuCl5 (mela = melamine), as a novel ionophore in plasticized polyvinyl chloride matrix was elaborated. The title complex was synthesized and characterized using FT-IR spectroscopy and single-crystal X-ray diffraction. To improve the sensitivity, the optimal pH value was evaluated and the effect of plasticizer was performed using three different plasticizing solvent mediators: dioctyl sebacate, dibutyl phthalate, and o-nitrophenyl octyl ether. The optimum performance was observed at pH 4 with the membrane incorporating dioctyl sebacate as a plasticizer. Cyclic voltammetry and square wave voltammetry were used to characterize the (H2mela)[CuCl5]Cl-GC sensor with a potential between 0.3 and 1 V. This sensor was characterized by a wide linear range from 1.2 × 10−10 M to 1.2 × 10−7 M, a low limit of detection of 1.2 × 10−10 M and low response time less than 1 min. This proposed sensor gave good results in the determination of nitrate in water and, therefore, can be used successfully in real samples.

A sensitive and simple modified zeolitic carbon paste electrode for indirect voltammetric determination of nitrate

Carbon paste electrode (CPE) was modified and used for indirect determination of nitrate in aqueous solution based on the decrease in the peak current of Fe(II) redox system in the presence of nitrate. The modification of CPE was done by Fe(II)-exchanged clinoptilolite nanoparticles (Fe(II)-NClin). The electrochemical impedance spectroscopy (EIS) results showed the best charge transfer for Fe(II)-NClin/CPE with respect to raw CPE and the modified CPE with the raw NClin sample (NClin/CPE). To study the effects of more influencing experimental variables (such as modifier%, solution pH, and step potential and amplitude) in square wave voltammetry and reducing the numbers of experiments, experimental design was applied by response surface methodology (RSM). The optimal run was obtained at pH 3.35, amplitude = 335 mV, modifier% = 15, and step potential = 25 mV. Under optimum conditions, the current response of Fe(II)-NClin/CPE was inversely proportional to NO3− in the concentration range from 80 to 1100 μmol L−1 of nitrate ions with a detection limit of 5.4 ± 0.2 μmol L−1 and quantization limit of 18.1 ± 0.3 μmol L−1 nitrate. The proposed electrode has a good sensitivity to nitrate anions about 90 nA (μmol/L)−1 nitrate (1.5 nA μg−1 nitrate). The proposed electrode showed good capability for determination of nitrate in water and meat products as real samples.

Direct DOC and nitrate determination in water using dual pathlength and second derivative UV spectrophotometry

UV spectrophotometry is largely used for water and wastewater quality monitoring. The measurement/estimation of specific and aggregate parameters such as nitrate and dissolved organic carbon (DOC) is possible with UV spectra exploitation, from 2 to multi wavelengths calibration. However, if nitrate determination from UV absorbance is known, major optical interferences linked to the presence of suspended solids, colloids or dissolved organic matter limit the relevance of UV measurement for DOC assessment. A new method based on UV spectrophotometric measurement of raw samples (without filtration) coupling a dual pathlength for spectra acquisition and the second derivative exploitation of the signal is proposed in this work. The determination of nitrate concentration is carried out from the second derivative of the absorbance at 226 nm corresponding at the inflexion point of nitrate signal decrease. A short optical pathlength can be used considering the strong absorption of nitrate ion around 210 nm. For DOC concentration determination the second derivative absorbance at 295 nm is proposed after nitrate correction. Organic matter absorbing slightly in the 270–330 nm window, a long optical pathlength must be selected in order to increase the sensitivity. The method was tested on several hundred of samples from small rivers of two agricultural watersheds located in Brittany, France, taken during dry and wet periods. The comparison between the proposed method and the standardised procedures for nitrate and DOC measurement gave a good adjustment for both parameters for ranges of 2–100 mg/L NO3 and 1–30 mg/L DOC.

Spreadsheet for designing valid least-squares calibrations: A tutorial

Instrumental methods of analysis are used to define the price of goods, the compliance of products with a regulation, or the outcome of fundamental or applied research. These methods can only play their role properly if reported information is objective and their quality is fit for the intended use. If measurement results are reported with an adequately small measurement uncertainty both of these goals are achieved. The evaluation of the measurement uncertainty can be performed by the bottom-up approach, that involves a detailed description of the measurement process, or using a pragmatic top-down approach that quantify major uncertainty components from global performance data. The bottom-up approach is not so frequently used due to the need to master the quantification of individual components responsible for random and systematic effects that affect measurement results. This work presents a tutorial that can be easily used by non-experts in the accurate evaluation of the measurement uncertainty of instrumental methods of analysis calibrated using least-squares regressions. The tutorial includes the definition of the calibration interval, the assessments of instrumental response homoscedasticity, the definition of calibrators preparation procedure required for least-squares regression model application, the assessment of instrumental response linearity and the evaluation of measurement uncertainty. The developed measurement model is only applicable in calibration ranges where signal precision is constant. A MS-Excel file is made available to allow the easy application of the tutorial. This tool can be useful for cases where top-down approaches cannot produce results with adequately low measurement uncertainty. An example of the application of this tool to the determination of nitrate in water by ion chromatography is presented.

A Palladium-Tin Modified Microband Electrode Array for Nitrate Determination

A microband electrode array modified with palladium-tin bimetallic composite has been developed for nitrate determination. The microband electrode array was fabricated by Micro Electro-Mechanical System (MEMS) technique. Palladium and tin were electrodeposited successively on the electrode, forming a double-layer structure. The effect of the Pd-Sn composite was investigated and its enhancement of catalytic activity and lifetime was revealed. The Pd-Sn modified electrode showed good linearity (R2 = 0.998) from 1 mg/L to 20 mg/L for nitrate determination with a sensitivity of 398 μA/(mg∙L−1∙cm2). The electrode exhibited a satisfying analytical performance after 60 days of storage, indicating a long lifetime. Good repeatability was also displayed by the Pd-Sn modified electrodes. The results provided an option for nitrate determination in water.

Study of Effect of Interferent in the Determination of Nitrate in Water

Water quality assessment has become a challenge for the scientific community. Nitrate is one of important parameters, which contributes in quality assessment. In this paper, UV spectroscopic technique is employed for quantitative determination of nitrate in water at its characteristic wavelength ∼ 200nm, using spiked samples with known nitrate concentration in deionised water. The detection range for nitrate using this technique is 0.2ppm - 4ppm. Since nitrate detection is hindered by the presence of interferents viz. dissolved organic matter, nitrite, hexavalent chromium and surfactant, herein, we discuss the effect of non-ionic surfactant, TritonX 100, on determination of nitrate in water. The range of non-ionic surfactant (TritonX 100) is taken from 1 ppm-20ppm whereas cationic and anionic surfactant is not taken into consideration because of their null effect on nitrate determination in water.

Method for Nitrate Determination in Water in the Presence of Nitrite

Method for Nitrate Determination in Water in the Presence of Nitrite

Photo-induced flow-injection determination of nitrate in water

A sensitive flow-injection method for the chemiluminescent determination of ultra-low concentration of nitrate in water is presented. Nitrate is on-line photolytically converted to peroxynitrite by absorption of UV light inside of 60 mm long quartz capillary (i.d. 530 µm, o.d. 720 µm). Peroxynitrite is subsequently determined by the chemiluminescent reaction with luminol. The detection limit of nitrate is 7 × 10−10 M (S/N = 3). The linear range of the method is 2 × 10−9–1 × 10−5 M nitrate. The interference of nitrite is eliminated by its conversion to nitrogen after mixing of sample with a solution of sulfamidic acid. Other common anions do not interfere. The interference of cations is eliminated by passing the sample through a cation-exchange column. The FIA procedure allows analysing of 15 samples per hour. The method was applied to the determination of nitrate in various real water samples. The results are in good agreement with a reference ion chromatographic method.

Detailed Validation of a Method for the Determination of Nitrate in Water by UV/Vis Spectroscopy

Detailed Validation of a Method for the Determination of Nitrate in Water by UV/Vis Spectroscopy

Determination of Nitrate in Water by HPLC

We established a method fordetermination of nitrate in water by High Performance Liquid Chromatography(HPLC). The sample was analysed by HPLC-ADA and was quantitated by externalstandard method after being simply processed. This methd has the advantages ofhigh separation efficiency and fast analysis. The experiment result showed thatthe linearly dependent coefficient was0.994, the recovery rate was between 98.7%～105.7%,the relative standard deviation（RSD）wasless than 2.1 %, and the lowest detectable limit is 0.01ng (S/N=1.6).

Integrated flow analysis platform for the direct detection of nitrate in water using a simplified chromotropic acid method

This work describes the first use of a direct nitrate analyser using chromotropic acid. A simplified chromotropic acid method eliminating several steps previously associated with this method is employed in the platform. In a sulphuric acid medium, chromotropic acid reacts with nitrate ions and produces a characteristic yellow colour associated with an absorbance band in the visible region (λmax = 430 nm). The modified method allows for nitrate determination over the linear range 0.9–80 mg L−1 nitrate with a limit of detection of 0.73 μg L−1 nitrate. Validation was achieved by analysing water samples from various sources including groundwater, trade effluent and drinking water by the modified method and by ion chromatography. The method was implemented on a flow analysis platform incorporating a paired emitter–detector diode (PEDD) as the optical detector. An excellent correlation coefficient of 0.993 was obtained between the modified method and ion chromatography. The modified chromotropic acid method represents a rapid, simple, low cost technique for the direct determination of nitrate in water.

A New Cadmium Reduction Device for the Microplate Determination of Nitrate in Water, Soil, Plant Tissue, and Physiological Fluids

A reusable catalytic reductor consisting of 96 copperized-cadmium pins attached to a microplate lid was developed to simultaneously reduce nitrate (NO3-) to nitrite (NO2-) in all wells of a standard microplate. The resulting NO2- is analyzed colorimetrically by the Griess reaction using a microplate reader. Nitrate data from groundwater samples analyzed using the new device correlated well with data obtained by ion chromatography (r2 = 0.9959). Soil and plant tissue samples previously analyzed for NO3- in an interlaboratory validation study sponsored by the Soil Science Society of America were also analyzed using the new technique. For the soil sample set, the data are shown to correlate well with the other methods used (r2 = 0.9976). Plant data correlated less well, especially for samples containing low concentrations of NO3-. Reasons for these discrepancies are discussed, and new techniques to increase the accuracy of the analysis are explored. In addition, a method is presented for analyzing NO3- in physiological fluids (blood serum and urine) after matrix modification with Somogyi's reagent. A protocol for statistical validation of data when analyzing samples with complex matrixes is also established. The simplicity, adaptability, and low cost of the device indicate its potential for widespread application.

Single interface flow system with potentiometric detection for the determination of nitrate in water and vegetables

In this work a single interface flow system (SIFA) with potentiometric detection was for the first time implemented and applied to the determination of nitrate in waters and plant extracts. The analytical potential of the SIFA system was exploited not only to transport the sample towards detection but also to carry out, in a reproducible and automated way, the tasks associated with sample pre-treatment, namely ionic strength, pH adjustment and interfering species suppression. The advantageous aspects of combining a SIFA system with potentiometry with enhanced simplicity, ease of implementation and automation were further discussed and emphasised. The obtained results showed relative deviations lower than 5%, for both types of samples, with sampling rates of about 40 h −1. In addition, an innovative and straightforward process for constructing plastic membrane ion selective electrodes with a tubular configuration able to be coupled to flow-based analytical systems is also proposed. The developed approach, consisting of assembling the electrode inside a flow tubing connector is very simple to implement, robust, particularly adequate to be combined with flow methodologies and maintains all dynamic and analytical characteristics exhibited by previous assembling processes.

The use of one-shot sensors with a dedicated portable electronic radiometer for nitrate measurements in aqueous solutions

A simplified procedure for the in situ determination of nitrate in waters is presented based on ionophore–chromoionophore one-shot sensors measured in a simple form by a portable radiometer designed by us. The colour change in the sensing film is detected by measuring the transmitted intensity with a solid state radiometer. A light-emitting diode (LED), with a dominant wavelength of 660 nm, was used as the illumination source. Negative feedback for LED bias and thermal correction were included to improve system stability. The procedure is based on the use of one-shot sensors pretreated with NaOH and the measurement of an absorbance ratio as analytical parameter. The one-shot sensors are used directly without any prior conditioning and the absorbance is measured with the portable radiometer before and after equilibration with the sample. The results obtained show that the procedure has good sensitivity with a range between 0.002 and 1000 mM using a sigmoidal calibration function, and a precision around 4% expressed as the logarithm of the nitrate concentration. The performance of the optical one-shot sensor was tested for the analysis of nitrate in different types of natural water (tap, river, well and sea), validating the results against a reference procedure.

Conductometric nitrate biosensor based on methyl viologen/Nafion ®/nitrate reductase interdigitated electrodes

A highly sensitive, fast and stable conductometric enzyme biosensor for determination of nitrate in water is reported for the first time. The biosensor electrodes were modified by methyl viologen mediator mixed with nitrate reductase (NR) from Aspergillus niger by cross-linking with glutaraldehyde in the presence of bovine serum albumin and Nafion ® cation-exchange polymer. The process parameters for the fabrication of the enzyme electrode and various experimental variables such as pH, the enzyme loading and time of immobilization in glutaralaldehyde vapor were investigated with regard to their influence on sensitivity, limit of detection, dynamic range and operational and storage stability. The biosensor can reach 95% of steady-state conductance value in about 15 s. Linear calibration in the range of 0.02 and 0.25 mM with detection limits of 0.005 mM nitrate was obtained with a signal-to-noise ratio of 3. When stored in 5 mM phosphate buffer (pH 7.5) at 4 °C, the sensor showed good stability over 2 weeks.

Disposable Receptor-Based Optical Sensor for Nitrate

A new optical absorption-based disposable sensor for nitrate is described. The nitrate-sensitive element is a bicyclic cyclophane receptor next to a suitable pH-sensitive lipophilic dye immobilized in a plasticized polymeric membrane. The rigid amide-based receptor with C3 symmetry controls the anion selectivity pattern of the optical element. The optical selectivity coefficients obtained for nitrate over a variety of naturally occurring anions in natural waters meet the requirements for the determination of nitrate in waters. The disposable sensor responds to nitrate rapidly-the typical response time is 5 min-and reversibly over a wide dynamic range (26 microM-63 mM) with sensor-to-sensor reproducibility (relative standard deviation, RSD, 3.68%, as log aNO3-, at the medium level of the range and RSD 1.39% for repeated measurements with the same sensor). The performance of the optical disposable sensor was tested for the analysis of nitrate in different types of natural waters (river, well, spring), validating results against a reference procedure. The proposed method is quick, inexpensive, selective, and sensitive and uses only conventional instrumentation.

Spectrophotometric Determination of Nitrate with a Single Reagent

A spectrophotometric procedure for determination of nitrate in water, soil extracts, and a variety of other sample types is described using one reagent solution which is easily prepared and stored. Sample and equipment requirements are minimal. Reduced chemical hazard, simplicity, and versatility represent improvements over existing methods. Limit of detection is 0.01 µg N mL−1 (0.72 μM ) or less, depending on the matrix.

Determination of Nitrate in Water Containing Dissolved Organic Carbon by Ultraviolet Spectroscopy

Direct measurement of ultraviolet (UV) light absorption by nitrate in the 200–205 nm wavelength band offers a reliable, accurate and rapid method of nitrate determination in natural waters. However, UV light is also strongly absorbed by organic matter at these wavelengths. A two-wavelength approach was adopted and evaluated for the correction of absorbance that organic matter might have contributed. The measurements were made at 205 nm and 300 nm. The relationship between absorbance at 205 nm and 300 nm due to organic matter was incorporated into traditional nitrate calibration curve to make allowance for the organic matter contribution. The method developed has a detection limit of 0.04 mg NO3-N dm−3 and is capable of determining nitrate concentration in the range of 0.08 – 4.0 mg NO3-N dm−3. In terms of accuracy and reproducibility, the method compares well with the hydrazine-reduction method, with matching precision (1.14% over the concentration range) and accuracy (± 2%). This two-wavelength approach based method is rapid, low-cost and does not require any reagents or treatment, and is suitable for waters with dissolved organic carbon (DOC) concentration of up to 20-mg dm−3.