Reaction Of Nitrite Research Articles

Nitrogen isotopic fractionations during nitric oxide production in an agricultural soil

Abstract. Nitric oxide (NO) emissions from agricultural soils play a critical role in atmospheric chemistry and represent an important pathway for loss of reactive nitrogen (N) to the environment. With recent methodological advances, there is growing interest in the natural-abundance N isotopic composition (δ15N) of soil-emitted NO and its utility in providing mechanistic information on soil NO dynamics. However, interpretation of soil δ15N-NO measurements has been impeded by the lack of constraints on the isotopic fractionations associated with NO production and consumption in relevant microbial and chemical reactions. In this study, anoxic (0 % O2), oxic (20 % O2), and hypoxic (0.5 % O2) incubations of an agricultural soil were conducted to quantify the net N isotope effects (15η) for NO production in denitrification, nitrification, and abiotic reactions of nitrite (NO2-) using a newly developed δ15N-NO analysis method. A sodium nitrate (NO3-) containing mass-independent oxygen-17 excess (quantified by a Δ17O notation) and three ammonium (NH4+) fertilizers spanning a δ15N gradient were used in soil incubations to help illuminate the reaction complexity underlying NO yields and δ15N dynamics in a heterogeneous soil environment. We found strong evidence for the prominent role of NO2- re-oxidation under anoxic conditions in controlling the apparent 15η for NO production from NO3- in denitrification (i.e., 49 ‰ to 60 ‰). These results highlight the importance of an under-recognized mechanism for the reversible enzyme NO2- oxidoreductase to control the N isotope distribution between the denitrification products. Through a Δ17O-based modeling of co-occurring denitrification and NO2- re-oxidation, the 15η for NO2- reduction to NO and NO reduction to nitrous oxide (N2O) were constrained to be 15 ‰ to 22 ‰ and −8 ‰ to 2 ‰, respectively. Production of NO in the oxic and hypoxic incubations was contributed by both NH4+ oxidation and NO3- consumption, with both processes having a significantly higher NO yield under O2 stress. Under both oxic and hypoxic conditions, NO production from NH4+ oxidation proceeded with a large 15η (i.e., 55 ‰ to 84 ‰) possibly due to expression of multiple enzyme-level isotopic fractionations during NH4+ oxidation to NO2- that involves NO as either a metabolic byproduct or an obligatory intermediate for NO2- production. Adding NO2- to sterilized soil triggered substantial NO production, with a relatively small 15η (19 ‰). Applying the estimated 15η values to a previous δ15N measurement of in situ soil NOx emission (NOx=NO+NO2) provided promising evidence for the potential of δ15N-NO measurements in revealing NO production pathways. Based on the observational and modeling constraints obtained in this study, we suggest that simultaneous δ15N-NO and δ15N-N2O measurements can lead to unprecedented insights into the sources of and processes controlling NO and N2O emissions from agricultural soils.

Study on Complete Antigen Synthesis of Promazine Hydrochloride

To explore the method of complete antigen synthesis of promazine hydrochloride. Based on the analysis of the molecular structure and immunogenicity of promazine hydrochloride, complete antigen was synthesized by mixed anhydride method,under the condition of excess acid, the diazotization reaction of nitrite and p-aminobenzoic acid produces diazosalt, diazonium salt reacts with promazine hydrochloride; Triethylamine and isobutyl chloroformate form a mixed anhydride, promazine hydrochloride complete antigen was synthesized by amino ligation of mixed anhydride and carrier protein bovine serum albumin (BSA), complete antigen synthesis was identified by ultraviolet spectroscopy, the characteristic absorption peaks of promazine hydrochloride, bovine serum albumin and synthetic promazine hydrochloride complete antigen were analyzed. The peak wavelength of the synthesized complete antigen, promazine hydrochloride and bovine serum albumin is different, the complete antigen synthesis of promazine hydrochloride was proved successful. The results of this study provided a basis for the rapid detection of promazine hydrochloride residues in animal-derived food by immunoassay.

Carcinogenic effects of N-nitroso compounds in the environment

N-nitroso compounds (NOC) are produced by the acid catalyzed reaction of nitrite with certain nitrogen compounds. The gastrointestinal tract (GI) is the main site for the formation of reactive nitrogen species (RNS). Bacteria present on the GI tract surface reduced the dietary nitrate or nitrite into Nitric oxide NO and other related compounds. The clinical sign of NOC carcinogenicity varies according to species, dose, and route of administration. Humans are exposed to preformed N-nitroso compounds and endogenous NOC via the environmental food chain. Several NOC are potential human carcinogens, including DENA and NDMA, but evidence from population studies is inconsistent.

GC-MS approach revealing hidden nitrite reactions in hemolysate using 18O-labelled nitrite and cysteine-based thiols

In erythrocytes, nitric oxide (NO) and its autoxidation product nitrite undergo multiple reactions with hemoglobin species to form nitrate, Fe-nitrosyl hemoglobin (HbFe(II)NO), S-nitrosohemoglobin (HbCysβ93SNO), and other intermediates including nitrito-methemoblobin HbFe(III)ONO, nitro-methemoblobin HbFe(III)NO2 and nitrous anhydride (N2O3). Here, we report a stable-isotope dilution GC-MS assay that allows studying reactions of nitrite in hemolysate. The method is based on the use of 18O-labelled nitrite in combination with l-cysteine or N-acetyl-l-cysteine ethyl ester and GC-MS measurement of unlabelled and labelled nitrite and nitrate species. This approach reveals reactions that are hidden at physiological nitrite concentrations.

Electrochemical Sensor for the Detection of Nitrite Based on PEDOT and Hollow Gold - Palladium Nanoparticles

Nitrites are chemical compounds commonly used as additives in food industry, especially to improve organoleptic properties of meat and prevent its degradation. According to the World Health Organization, nitrite concentrations exceeding 3 mg/L in drinking water and wastewater are hazardous for the environment and human health [1]. Nitrites can react with hemoglobin and form methemoglobin which blocks oxygen transport and generates cyanosis in infants. Also, N–nitroso compounds, potentially carcinogenic products, can be formed by the reaction of nitrites with amines [1]. For those reasons, monitoring the level of nitrite in water is extremely important.Nitrite ions are traditionally detected and quantified by colorimetry, chemiluminescence and chromatographic and spectrophotometric techniques. However, these techniques are time consuming, require complex devices or the pretreatment of the samples to prevent interferences and moreover, imply the use or the production of some toxic reagents. Electrochemical sensors based on nanomaterials like graphene, metal nanoparticles and conducting polymers have also been used for the detection of nitrite [2,3]; however, to the authors´ best knowledge, sensors based on PEDOT and hollow bimetallic nanoparticles have not been tested as potential material for this purpose.In this work, hollow AuPd nanoparticles were produced by galvanic replacement from cobalt cores. The nanoparticles were analyzed by SEM, EDX and TEM/STEM. Results revealed the hollow structure of the nanoparticles (size 30-45 nm, Fig. 1). It was confirmed that they contain Au and Pd. EDX was performed to evaluate the elemental profile through the nanoparticle. Hollow AuPd nanoparticles, previously centrifuged and resuspended in water, were co-deposited from a solution of the monomer EDOT, the surfactant SDS, LiClO4 at potentiostatic conditions. The analytical performance of the composite material for the detection of nitrite was evaluated by differential pulse voltammetry (Fig. 2) in the range of 50 to 250 µM. The sensitivity of the sensor was 0.04 +/-0.01 µA µM-1.[1] World Health Organization, Guidelines for Drinking – water Quality. (2017) 398pp. Available from: https://www.ncbi.nlm.nih.gov/books/NBK442376/[2] Fu L., Yu S., Thompson L. And Yu A. RSC Adv. 5 (2015) 40111.[3] Li G., Xia Y. Tian Y., Wu Y., Liu J., He Q. and Chen D. J. Electrochem. Soc. 166(12) (2019) B881. Figure 1

Voltammetric determination of nitrites in meat products after reaction with ranitidine producing 2-methylfuran cation

A completely new voltammetric method has been developed for the determination of nitrites in meat products. This highly selective electroanalytical method utilizes a specific reaction of nitrites with ranitidine in an acidic environment to form an electroactive NDMA and 2-methylfuran cation with the corresponding side chain in the fifth position. A cathodic reduction at −0.210 V of 2-methyl-2H-furan-3-one at GCE covered with a thin layer of ERGO and adsorbed SDBS surfactant was preferred to anodic oxidation of NDMA at +0.8 V due to the desired selectivity. For evaluation using peak height, two linear ranges from 6.2 to 125 μmol L−1 and from 150 to 300 μmol L−1 nitrites characterized by R2 of 0.9991 and 0.9963 with a detection limit of 1.89 μmol L−1 nitrites were found, respectively. If the peak-area-based evaluation is preferred, only one linear dependence described by a regression equation Apc(µAV) = 0.0079c (µmol L−1) − 0.0442 with the R2 of 0.9996 will be obtained. The verification of voltammetric method was carried out using a comparison with a spectrophotometric Griess Reagent Kit (G-7921) in the analysis of the model sample and various meat products.

Preparation and Characterization of Self-Dispersing Phthalocyanine Blue 15:4 Pigment for Dyeing of Wool Textiles

A self-dispersing pigment was produced by a diazonium coupling reaction; the pigment reacted with aromatic diazonium salts which were generated by the reaction of p-aminobenzene sulfonic acid and sodium nitrite. The surface of the pigment particles was negatively charged due to sulfonic acid groups on the pigment surface. The pigment particle size and zeta potential were, respectively, 134.5 nm and −45.4 mV at neutral pH. The wool surface was positively charged by adjusting the pH; then the anionic self-dispersing pigment dyed the cationic wool. The results show that self-dispersing pigment can adhere well without a binder, and that the K/S value is closely related to pH, dyeing time, and the amount of pigment. The color fastness of the wool was good and the light fastness of the wool was grade 5, which is better than acid dyes. Self-dispersing pigments are potential candidates for dyeing high-weather-resistance textiles.

Analytical Chemistry Optical Chemosensor for Spectrophotometric Determination of Nitrite in Wastewater

AbstractAn easy, sensitive, and rapid spectrophotometric method has been documented for determining nitrite (NO2−) in water and wastewater. To detect and adsorb harmful nitrite ions from wastewater efficiently; a stable optical nanosensor was manufactured by immobilization of 1‐Naphthylamine (1‐NA) over mesoporous silica nanospheres (MSNs). The determination of nitrite was based on the reaction of nitrite with the optical sensor (1‐NA chemosensor) and forming diazonium salt which was subsequently coupled with N‐(1‐Naphthyl) ethylenediamine dihydrochloride (NED) to form a stable brownish azo dye. The dye shows an absorption maximum at 457 nm. The optimal conditions for the reaction and the analytical parameters were evaluated. The method has been designed by controlling the acidity, the quantity of reagents required and the amount of tolerance of certain ions. The range of linearity was found to be 0.108‐10.8 μM of nitrite. The nitrite identification detection limit and quantitation limit are 0.106 μM and 0.353 μM, respectively. The performance of the chemosensor in extracting the NO2− ions was tested. According to the Langmuir isotherms, the adsorption pattern was highly competent, where the removal capacity for NO2− ion was 156.0 mg/g by the chemosensor. Some cations and anions have been identified as the competing ions; these ions were not affected on the NO2− ion in both detection and adsorption processes.

Spectrophotometric analysis of selected metal ions using microwave assisted in situ complexation

ABSTRACTA novel spectrophotometric method has been developed for the analysis of cadmium, cobalt, copper, iron and lead. This method is based on microwave-assisted in-situ complexation of metals ions with a ligand formed by the reaction of phenol, sodium nitrite and streptomycin in an acidic medium. The method was applied for the analysis of a variety of real samples including pharmaceuticals and industrially important products such as batteries. In this work, the wavelength for each of the metal complexes was scanned in the range of 400–800 nm. Each of this reaction was carried out in acidic medium; however, the amount of acid was found to vary with variation in the nature of metal ions. The optimum pH was 2.8 for iron, 6.5 for lead, 5.0 for copper, 5.5 for cobalt and 5.6 for cadmium. Keeping in view the difference in coordination number and difference in reactivity of metals, each of the reagents such as phenol, sodium nitrite and streptomycin were optimised for each of the metals separately. All experimental conditions such as optimum concentration of reagents and microwave heating time were optimised. It was observed that the optimum concentration of phenol is 8.99 mg/L for cadmium, cobalt and iron while that for lead and copper was 7.99 mg/L and 3.99 mg/L, respectively. The amount of sodium nitrite was found the same for each of the metals. In case of streptomycin, the optimum concentrations for each of cadmium and cobalt were found to be 0.988 mg/L and that for lead and iron were 1.498 mg/L, and 0.499 mg/L for cobalt. The limit of detection for each cadmium, cobalt, copper, iron and lead were found 0.0242, 0.0105, 0.1915, 0.1018 and 0.0185 mg/L, respectively. The limit of quantification for cadmium, cobalt, copper, iron and lead were determined as 0.0806, 0.0349, 0.6382, 0.3394 and 0.0615 mg/L, respectively. The developed method was successfully applied for the determination of selected metals in real samples.

A highly selective chromogenic probe for the detection of nitrite in food samples

A rapid, sensitive, and highly selective method for determining nitrite in food has been developed. This method is based on the reaction of nitrite with the amino group of 3,3,5,5-tetramethylbenzidine (TMB) to form a diazonium salt, and then the diazonium salt and glucosamine hydrochloride are coupled to each other to form an orange compound. The optimal conditions for maximum color and other analytical parameters were studied. A colorimetric method for nitrite detection has been developed with an outstanding correlation coefficient (R2 = 0.9944), a wide linear range (1–75 μM) and 0.73 μM limit of detection (at S/N = 3) for nitrite ions. This method was successfully applied to the determination of nitrite in a variety of foods and gave recoveries in the range between 100.16% and 103.07%, demonstrating that the accuracy, reliability and potential application of this assay for monitoring nitrite in foods.

Carbonic anhydrase II does not regulate nitrite-dependent nitric oxide formation and vasodilation.

Although it has been reported that bovine carbonic anhydrase CAII is capable of generating NO from nitrite, the function and mechanism of CAII in nitrite-dependent NO formation and vascular responses remain controversial. We tested the hypothesis that CAII catalyses NO formation from nitrite and contributes to nitrite-dependent inhibition of platelet activation and vasodilation. The role of CAII in enzymatic NO generation was investigated by measuring NO formation from the reaction of isolated human and bovine CAII with nitrite using NO photolysis-chemiluminescence. A CAII-deficient mouse model was used to determine the role of CAII in red blood cell mediated nitrite reduction and vasodilation. We found that the commercially available purified bovine CAII exhibited limited and non-enzymatic NO-generating reactivity in the presence of nitrite with or without addition of the CA inhibitor dorzolamide; the NO formation was eliminated with purification of the enzyme. There was no significant detectable NO production from the reaction of nitrite with recombinant human CAII. Using a CAII-deficient mouse model, there were no measurable changes in nitrite-dependent vasodilation in isolated aorta rings and in vivo in CAII-/- , CAII+/- , and wild-type mice. Moreover, deletion of the CAII gene in mice did not block nitrite reduction by red blood cells and the nitrite-NO-dependent inhibition of platelet activation. These studies suggest that human, bovine and mouse CAII are not responsible for nitrite-dependent NO formation in red blood cells, aorta, or the systemic circulation.

Synthesis and characterization of nitro-functionalized hydroxyl-terminated polybutadiene using N-iodosuccinimide

A convenient, inexpensive and highly efficient one-pot procedure of synthesizing nitro-functionalized hydroxyl-terminated polybutadiene (Nitro-HTPB) is reported by the reaction of hydroxyl-terminated polybutadiene (HTPB) and sodium nitrite in the presence of N-iodosuccinimide in EG–EtOAc–H2O at 60 °C for 24 h. The investigation of the effective parameters on the synthesis of Nitro-HTPB such as amounts of reactants, temperature and reaction time indicated that in the optimum reaction conditions, the nitration HTPB backbone is restricted to 6.7% of double bonds until the outstanding physical and chemical properties of HTPB are retained. The Nitro-HTPB was characterized by FTIR, 1H NMR, 13C NMR, DSC and TGA. The polymer showed good thermal stability, yield of 93%, viscosity of 14.2 Pa.s−1, number average molecular weight of 2730 gmol−1 and hydroxyl value of 34 mg KOH per g.

The Effectiveness of Dipstick for the Detection of Urinary Tract Infection.

Background The balance between the choices of UTI diagnostic tools in most primary care settings has been settled for by the more rapid, less labour-intensive dipstick. This study aimed to evaluate the effectiveness of dipstick for diagnosing UTI. Method A total of 429 urine samples were collected from patients suspected of UTI; cultured on cysteine-lactose-electrolyte-deficient (CLED) agar, blood agar, and MacConkey agar; and incubated at 37°C overnight. Urine cultures with bacteria count ≥105 cfu/ml were classified as “positive” for UTI. A dipstick was used to screen for the production of nitrite (NIT) and leucocyte esterase (LE), following the manufacturer's instructions. Biochemical reactions of nitrite and leucocyte esterase > “trace” were classified as “positive.” A quantitative urine culture was used as the gold standard. Results The highest sensitivity value and negative predictive value were recorded for the combined “NIT+ or LE+” dipstick results. The highest specificity value, positive predictive value, positive likelihood ratio, and negative likelihood ratio were recorded for “nitrite-positive and leucocyte esterase-positive” results. Combined “nitrite-positive or leucocyte-positive” result was relatively the best indicator for accurate dipstick diagnosis, with AUC = 0.7242. Cohen's kappa values between dipstick diagnosis and quantitative culture were <0.6. Conclusion Combined performance of nitrite and leucocyte esterase results appeared better than the solo performance of nitrite and leucocyte esterase. However, little confidence should be placed on dipstick diagnosis; hence, request for quantity culture should be encouraged in the primary healthcare settings.

Magnetic solid-phase extraction and a portable photocolourimeter using a multi-colour light emitting diode for on-site determination of nitrite

In this study, a new, simple, cheap, fast method for on-site determination of trace amount of nitrite in atmospheric liquids and surface water is suggested. The proposed method is based on a combination of magnetic solid phase extraction with a designed portable photometer based on light-emitting diodes. The colour reaction of nitrite was carried out with 4-nitroaniline in acidic medium and then coupled with naphth-1-ol in alkaline medium to form an azo product. The reaction and extraction conditions (e.g., acidity for diazotization and alkalinity for naphth-1-ol coupling, and other reagent concentrations, amount of sorbent, desorption solvent type and volume, etc.) were optimized. Under the optimal conditions, the calibration graph was linear in the range of 0.01–0.3 mg L−1 with the limit of detection (LOD) of 0.0013 mg L−1. The enhancement factor was about 110. Relative standard deviations (RSDs) for the extraction of 0.03 and 0.1 mg L−1 of nitrite were obtained 2.49% and 5.34% for five replicates, respectively. The proposed method was able to analyse nitrite ion in water samples with satisfactory recovery ranged from 87% to 103%.

Promotive effect of H2O on low-temperature NO reduction by CO over Pd/La0.9Ba0.1AlO3-

Abstract For future removal of NOx by catalysts, low-temperature NO reduction is desired. Results confirmed that a drastic improvement of catalytic activity by H2O on NO–CO–O2 reaction over Pd/La0.9Ba0.1AlO3-δ catalyst at the low temperature of 473 K or below. In a humidified condition, NO reaction with CO on Pd/La0.9Ba0.1AlO3-δ proceeded without being affected by competitive adsorption of NO and CO, whereas that on Pd/Al2O3 was inhibited by strong adsorption of CO on a Pd surface. From in-situ DRIFTS measurements, results showed that nitrite species on the support react with CO adsorbed onto Pd at the periphery of Pd particles and that carbonate species accumulated on Pd/La0.9Ba0.1AlO3-δ are removed rapidly in a humidified condition. Although NO reduction proceeds dominantly on the Pd surface in a dry condition, supplied steam promotes desorption of the surface carbonate to advance the reaction of nitrite with CO for de-NOx in a humidified condition. This mechanism occurs specifically on Pd/La0.9Ba0.1AlO3-δ by virtue of the lattice oxygen and oxygen vacancy on La0.9Ba0.1AlO3-δ.

First real-time isotopic characterisation of N2O from chemodenitrification

Chemodenitrification can be a substantial abiotic source of nitrous oxide (N2O) in soil. The isotopic signature of N2O from this process could support source partitioning, but it is currently unknown in sufficient detail. In this study, we determined the isotopic composition of N2O, produced by the reaction of nitrite (NO2−) with lignin, four lignin derivatives, and three types of soils, online with a quantum cascade laser absorption spectrometer (QCLAS). We present the first dataset of continuous measurements of δ15Nbulk (δ15Nbulk ≡ (δ15Nα + δ15Nβ)/2), δ18O, and site preference (SPN2O, SPN2O ≡ δ15Nα − δ15Nβ) of N2O from chemodenitrification in both chemical assays and soils. Considerable amounts of N2O were produced by chemical reduction of NO2−, indicating that chemodenitrification could dominate N2O emission in NO2−-rich environments. The values of SPN2O varied by more than 20‰ in the reactions of sodium nitrite with organic substances. Contrary to the common assumption that SPN2O values are constant for a distinct N2O source process, our results reveal a considerable shift in SPN2O over time for most experiments. The large SPN2O variability might be explained by the multiple pathways with hyponitrous acid or nitramide as N2O precursors. These findings provide important new information to improve our understanding about the dependency of N2O isotopic signatures on N2O production processes.

Solvent stir bar microextraction technique with three-hollow fiber configuration for trace determination of nitrite in river water samples.

In this work, trace determination of nitrite in river water samples was studied using solvent stir bar microextraction system with three-hollow fiber configuration (3HF-SSBME) as a preconcentration step prior to UV-Vis spectrophotometry. The obtained results showed that the increase in the number of solvent bars can improve the extraction performance by increasing the contact area between acceptor and sample solutions. The extraction process relies on the well-known oxidation-reduction reaction of nitrite with iodide excess in acidic donor phase to form triiodide, and then its extraction into organic acceptor phase using a cationic surfactant. Various extraction parameters affecting the method were optimized and examined in detail. Detection limit of 1.6μgL-1 and preconcentration factor of 282 can be attained after an extraction time of 8min under the optimum conditions of this technique. The proposed method showed a linear response up to 1000μgL-1 (r2 = 0.996) with relative standard deviation values less than 4.0%. The accuracy of the developed method was assessed using the Griess technique. Finally, the proposed method was successfully employed for quantification of nitrite in river water samples (Ghezelozan, Zanjan, Iran).

Dicopper μ-Oxo, μ-Nitrosyl Complex from the Activation of NO or Nitrite at a Dicopper Center.

Treatment of a dicopper(I,I) complex with nitric oxide produces a dicopper μ-oxo, μ-nitrosyl complex [LCu2(μ-O)(μ-NO)]2+, representing the first structurally characterized μ-oxo, μ-nitrosyl metal complex. This compound can also be synthesized from the reaction of nitrite with an [LCuIICuI]3+ synthon. Full characterization of the thermal-sensitive [LCu2(μ-O)(μ-NO)]2+ complex with IR, EPR, and X-ray crystallography suggests a localized mixed-valent CuIII, CuII, O2-, NO- formulation. The [Cu2(μ-O)(μ-NO)]2+ core efficiently oxidizes exogenous substrates, such as phosphine, cyclohexadienes, and isochroman to afford phosphine oxide, benzene, and 1-isochromanone. Since both nitrite and nitric oxide are proposed oxidants in denitrifying methane oxidation, the oxidative reactivity of [Cu2(μ-O)(μ-NO)]2+ core is potentially relevant to anaerobic methane oxidation observed in methanotrophic archaea.

Abiotic Formation of Humic-Like Substances through Freezing-Accelerated Reaction of Phenolic Compounds and Nitrite.

A previously unknown abiotic humification pathway which is highly accelerated in frozen solution containing phenolic compounds and nitrite was investigated and proposed. The production of humic-like acids (HLA) and fulvic-like acids (FLA) was observed in the frozen solution (-20 °C) whereas it was negligible in aqueous solution (20 °C). Inorganic nitrogen was transformed into organic nitrogen during the humification process. Mass spectrometry (MS) and elemental analyses, including pyrolysis-GC/MS and FT-ion cyclotron resonance/MS, showed that humification products (HLA and FLA) have chemical structures and compositions similar to nature humic substances. The enhanced humification reaction could be attributed to the freeze-concentration effect, whereby nitrite ions in the unfrozen grain boundary region are transformed into nitrosonium ions which oxidize phenols to phenolic radicals. Confocal Raman microscopy confirmed that catechol and nitrite ions are preferentially concentrated at the ice grain boundary and electron paramagnetic resonance spectroscopic analysis of catechol/nitrite solution detected the phenolic radicals only in frozen solution, not in aqueous solution. The freezing-induced generation of phenolic radicals should lead to the formation of humic-like substances through polymerization. This study identifies and proposes a new humic formation pathway that might work as a model abiotic "bottom-up" mechanism in frozen environmental conditions.

Determination of Nitrite in Processed Meat Using Digital Image Method and Powdered Reagent

A novel analytical approach for the rapid determination of nitrite in processed meat was developed. A yellow to reddish orange colored spots from chrysoline resorcinol azo dye created and photographed using the digital image based (DIB) method. The spots resulted from the reaction of nitrite with a powdered reagent consists of a ground solid mixture of sulfanilic acid and resorcinol. Quantification of nitrite was obtained using ImageJ software containing RGB color model. The limit of detection (LOD), quantification (LOQ) and the linear analytical range were 0.5, 1.7 mg L-1 and 2.0-60 mg L-1 (R = 0.990), respectively. Also, using the dissolved spot (DS) method followed by a spectrophotometric measurement afforded a LOD, LOQ and linear analytical range of 0.04 and 1.3 mg L-1 and 1.5-80 (R = 0.993), respectively. The developed methods were applied to the determination of nitrite residue in commercial chicken sausages, luncheon meat, luncheon chicken, and luncheon turkey and beef samples with satisfied accuracy. The results obtained by the DIB and DS methods were compared to the official AOAC 973.31 method and showed no significant differences. The corresponding Pearson correlation coefficients (R2) for spiked beef extract are 0.994 and 0.997, respectively.