Ion chromatographic determination of trace iodate, chlorite, chlorate, bromide, bromate and nitrite in drinking water using suppressed conductivity detection and visible detection

Debugging periodate oxidation of cellulose: Why following the common protocol of quenching excess periodate with glycol is a bad idea

Periodate oxidation of cellulose to produce "dialdehyde cellulose" (DAC) has lately received increasing attention in sustainable materials development. Despite the longstanding research interest and numerous reported studies, there is still an enormous variation in the proposed preparation and work-up protocols. This apparently reduces comparability and causes reproducibility problems in DAC research. Two simple but prevalent work-up protocols, namely glycol quenching and filtration/washing, were critically examined and compared, resulting in this cautionary note. Various analytical techniques were applied to quantify residual iodine species and organic contaminations from quenching side reactions. The commonly practiced glycol addition cannot remove all oxidising iodine compounds. Both glycol and the formed formaldehyde are incorporated into DAC's polymeric structure. Quenching of excess periodate with glycol can thus clearly be discouraged. Instead, simple washing protocols are recommended which do not bear the risk of side reactions with organic contaminants. While simple washing was sufficient for mildly oxidised celluloses, higher oxidised samples were more likely to trap residual (per)iodate, as determined by thiosulfate titration. For work-up, simple washing with water is proposed while determining potential iodine contaminations after washing with a simple colorimetric test and, if needed, removal of residual periodate by washing with an aqueous sodium thiosulfate solution.

The Novel Polymethacrylate Based Hydrophilic Stationary Phase for Ion Chromatography

Ion chromatography is widely used as a useful and powerful tool for the analysis of anionic and cationic components found in waters and aqueous media. The performance and selectivity of ion chromatography are based on the stationary phase column packed material. In this study, it is aimed to develop new column material with quaternary ammonium functional group based on monodisperse polymeric particles for ion chromatography and to investigate their chromatographic performance. For the analysis of inorganic anions by ion chromatography, new stationary phases macroporous monodisperse particles based on 3-chloro-2-hydroxy propylmethacrylate-co-ethylene dimethacrylate are obtained as column packing material. 3-chloro-2-hydroxy propylmethacrylate and ethylene glycol dimethacrylate are transformed to porous monodisperse particle form by using glycidyl methacrylate as the seed latex and ethyl benzene as the porogen solvent via micro-suspension polymerization technique. Then macroporous monodisperse particles surface is functionalized by triethylamine so strong anion exchange is obtained for ion chromatography packing material. A series of stationary phases prepared from polymer particles containing different amounts of porogen solvent were tested. The results show that column packing material is successful to separate inorganic anions mixture such as F−, Cl−, NO2−, Br−, NO3− by using the carbonate and bicarbonate solutions as mobile phases.

Simultaneous Quantification of Commonly Used Counter Ions in Peptides and Active Pharmaceutical Ingredients by Mixed Mode Chromatography and Evaporative Light Scattering Detection

In academia and industry, the analysis of counter ions in small molecules and synthetic peptides represents a great challenge. Due to the frequent use of salt forms and the application of a wider range of counter ions in pharmaceutically used substances, simple and generic methods for quantification are required. Especially, the analysis of trifluoracetic acid (TFA) in synthetic peptides is of high interest. Quantification of TFA is needed to assess the content and safety of synthetic peptides and for the interpretation of functional assay results, respectively. In here, a full quantitative mixed mode high performance liquid chromatography based method coupled to evaporative light scattering detection is presented. Finally, 14 positively and negatively charged counter ions were simultaneously quantified within 30 minutes. The method was validated in terms of specificity, accuracy, precision, limit of quantification, sample stability and carry over as proposed by the International Council of Harmonization. In order to prove the applicability of the procedure, small molecules reference substances and synthetic peptides were analyzed, respectively. The obtained results indicated a successful determination of counter ions in small molecules and differences to expected concentrations of prepared peptide solutions. Furthermore, an unexpectedly high content of sodium was observed for synthetic peptides.

Determining Potassium Bromate in the Inhalable Aerosol Fraction in Workplace Air with Ion Chromatography

Background

The article presents the results of studies performed in order to develop a new method of airborne potassium bromate(V) determination at workplaces.

Methods

The method is based on a collection of the inhalable fraction of potassium bromate(V) using the IOM Sampler, then extraction of bromates with deionized water and chromatographic analysis of the obtained solution. The analysis was performed using ion chromatography with conductometric detection. The tests were performed on a Dionex IonPac®AS22 analytic column (250 × 4 mm, 6 μm) with AG22 precolumn (50 × 4 mm 11 μm).

Results

The method provides for potassium bromate(V) determination within the concentration range of 0.043 ÷ 0.88 mg/m³ for an air sample of 0.72 m³ in volume, i.e., 0.1–2 times the exposure limit value as proposed in Poland. The method was validated in accordance with PN-EN 482. The obtained validation data are as follows: measuring range: 3.1–63.4 μg/mL, limit of detection (LOD) = 0.018 μg/mL and limit of quantification (LOQ) = 0.053 μg/mL. The developed method has been tested in the work environment, on laboratory employees having contact with potassium bromate(V).

Conclusion

The analytical method allowed the determination of the inhalable fraction of airborne potassium bromate(V) at workplaces and can be used to assess occupational exposure.

Selective and sensitive determination of bromate in bread by ion chromatography-mass spectrometry

Potassium bromate is a food additive used as "flour improver" in the baking industry. Bromate is considered a carcinogenic and nephrotoxic substance. Thus, the bromate concentration must be carefully monitored in flour products. We developed a method for a selective and sensitive determination of bromate in flour that uses ion chromatography coupled with single quadrupole mass spectrometry (IC -MS). A recently introduced high-capacity anion-exchange column was used to separate bromate from matrix anions. Six commercial flour and flour products including homemade bread baked using flour containing potassium bromate, were analyzed. The method showed good precision with RSDs <0.2%, and <5% (n = 8), for retention time and peak area respectively. Bromate recoveries from flour samples ranged from 86 to 110%. The limits of detection and quantitation of bromate in the prepared solution were 0.10 µg/L and 0.34 µg/L, respectively, which corresponded to 5 µg/kg and 17 µg/kg in bread.

A fluorimetric nitrite biosensor with polythienothiophene-fullerene thin film detectors for on-site water monitoring

A novel fluorimetric sensor for highly sensitive nitrite detection on the site is presented in this study. The proposed on-chip approach comprises the use of integrated polymer photodetectors to detect light from fluorescence reactions with a diaminofluorescein probe. The detectors were prepared with a heterostructured nanofilm of polythieno[3,4-b]thiophene/benzodithiophene and (6,6)-phenyl-C₇₁-butyric-acid methyl-ester as a photoactive layer. Prior to fluorimetric detection, the quality of the spin-coated photoactive layer was characterized via nano-morphology and current-density measurements. Nitrite assays were conducted on a poly(methyl methacrylate) microchannel chip, to which polythienothiophene-C₇₁ based detectors were aligned. Results of signal-to-noise ratio determination have indicated a detection limit below 0.55 μM, lower than the 0.1 mg L^-1 maximum limit of operation in recirculating aquaculture systems for farming Atlantic salmon Salmo salar. An increase of the nitrite concentration to toxic levels may therefore be possible to detect. The fluorimetric sensor exhibited good linearity over three orders of magnitude and acceptable detection reproducibility, which confirmed its analytical value. Further tests revealed great promise of the integrated biosensor device for detecting nitrite in aquaculture-relevant samples with high precision. The approach reported hereby may provide impetus to in situ analytical tools for monitoring water quality at aquaculture facilities, the food industries or water monitoring stations.

Soil available phosphorus content drives the spatial distribution of archaeal communities along elevation in acidic terrace paddy soils

Archaea play crucial roles in geochemical cycles and influence the emission of greenhouse gases in acidic soils. However, little is known about the distribution pattern of total archaeal diversity and community composition with increasing elevation, especially in acidic agricultural ecosystems. Terraces, characterized by vertical climate changes and unique hydrological properties, are "natural experiments" to explore the spatial distribution of microorganisms along elevation in paddy soils. Here we investigated the diversity and structure of soil archaeal communities in nine increasingly elevated acidic paddy soils of the Yunhe terrace, China. Archaeal communities were dominated by Methanomicrobia of Euryarchaeota (38.5%), Group 1.1a-associated cluster (SAGSCG-1) of Thaumarchaeota (22.0%) and Subgroup-6 (previously described as crenarchaeotal group 1.3b) of Bathyarchaeota (17.8%). The archaeal phylotype richness decreased with increasing elevation. Both the species richness and phylogenetic diversity of the archaeal communities were significantly negatively correlated with soil available phosphorus (AP) content according to linear regression analyses. The archaeal communities differed greatly between soils of increasing elevation, and were roughly clustered into three groups, mostly in relation to AP contents. A variation partitioning analysis further confirmed that edaphic factors including the content of AP (17.1%), nitrate (7.83%), soil organic carbon (4.69%), dissolved organic carbon (4.22%) and soil pH (4.07%) shaped the archaeal community. The variation of soil properties were probably induced by elevation. The co-occurrence network indicated a modular structure of the archaeal community. Overall, our results emphasized that soil AP content was the best predictor of archaeal diversity and community structure, and the impacts of elevation on soil archaeal communities were not diminished by long-term rice cultivation, although minor compared with the effects of soil properties.

Electroanalytical Sensing of Bromides Using Radiolytically Synthesized Silver Nanoparticle Electrocatalysts

Monitoring bromides (Br^-) is of crucial importance since bromates, potential human carcinogens, are formed during ozonation of water containing bromides in concentrations >100 μg L^-1. Within this study, silver (Ag) and four carbon-supported Ag catalysts were synthesized by the γ-radiation method and their morphology and structure examined using transmission electron microscopy, X-ray diffraction, and UV-Vis analysis. The nanocatalysts were tested for Br^- sensing in aqueous media using cyclic voltammetry. All five Ag materials exhibited electroactivity for sensing of Br^- ions, with pure Ag catalyst giving the best response to Br^- ions presence in terms of the lowest limit of detection. Sensing of bromides was also explored in tap water after addition of bromides suggesting that herein prepared catalysts could be used for bromides detection in real samples. Furthermore, sensing of other halogen ions, namely, chlorides and iodides, was examined, and response due to chloride presence was recorded.

Determination of chlorate, perchlorate and bromate anions in water samples by microbore reversed-phase liquid chromatography coupled to sonic-spray ionization mass spectrometry

RATIONALE

Sonic-spray ionization mass spectrometry (SSI-MS) has recently been shown to provide similar mass spectra to those generated by electrospray ionization mass spectrometry for a wide range of compounds, i.e. from small inorganic species to peptides, proteins and numerous other biomolecules. However, limited information about this new ionization technique, such as sensitivity, limit of detection and quantification accuracy, has been reported. In particular, its coupling to liquid chromatography needs further development and assessment, along with the introduction of a broad range of applications.

METHODS

A high-efficiency glass pneumatic nebulizer, used for decades for sample introduction in atomic spectrometry, was used for the SSI-MS analysis of chlorate (ClO₃^- ), perchlorate (ClO₄^- ) and bromate (BrO₃^- ) anions, following their separation using reversed-phase microbore high-performance liquid chromatography and tandem mass spectrometry (MS/MS) operated in selected reaction monitoring mode.

RESULTS

The developed and optimized microbore HPLC/SSI-MS/MS technique exhibited low limits of detection: 5.3 ng L^-1 for chlorate, 10 ng L^-1 for perchlorate and 33.7 ng L^-1 for bromate, and provided reliable and accurate measurements of chlorate concentrations in water samples as demonstrated when comparing it with Ion Chromatography-Conductivity Detection (IC-CD), the benchmark technique for ion quantitation.

CONCLUSIONS

This is the first time that the use of HPLC/SSI-MS/MS has been reported for the detection and quantitation of chlorate, perchlorate and bromate in water samples. In addition, the exceptionally low LODs achieved using SSI render the technique competitive with the established and dominating electrospray ionization technique. Here, we have demonstrated that a commercially available high-efficiency glass pneumatic nebulizer can also be used, without any further modification, as an efficient gas-phase ion source. Copyright © 2017 John Wiley & Sons, Ltd.

Comparative metabolic profiling of the lipid-producing green microalga Chlorella reveals that nitrogen and carbon metabolic pathways contribute to lipid metabolism

Microalgae are a promising feedstock for biofuel production. Microalgal metabolic pathways are heavily influenced by environmental factors. For instance, lipid metabolism can be induced by nitrogen-limiting conditions. However, the underlying mechanisms of lipid biosynthesis are unclear. In this study, we analyzed the global metabolic profiles of three genetically closely related Chlorella strains (C1, C2, and C3) with significant differences in lipid productivity to identify the contributions of key metabolic pathways to lipid metabolism. We found that nitrogen obtained from amino acid catabolism was assimilated via the glutamate-glutamine pathway and then stored as amino acids and intermediate molecules (particularly proline, alanine, arginine, succinate, and gamma-aminobutyrate) via the corresponding metabolic pathways, which led to carbon-nitrogen disequilibrium. Excess carbon obtained from photosynthesis or glycolysis was re-distributed into carbon-containing compounds, such as glucose-6-phosphate, fructose-6-phosphate, phosphoenolpyruvate, lactate, citrate, 3-hydroxybutyrate, and leucine, and then diverted into lipid metabolism for the production of storage lipids via the gamma-aminobutyrate pathway, glycolysis, and the tricarboxylic acid cycle. These results were substantiated in the model green alga Chlamydomonas reinhardtii by analyzing various mutants deficient in glutamate synthase/NADH-dependent, glutamate synthase/Fd-dependent, glutamine synthetase, aspartate aminotransferase, alanine aminotransferase, pyruvate kinase, and citrate synthase. Our study suggests that not only carbon but also nitrogen assimilation and distribution pathways contribute to lipid biosynthesis. Furthermore, these findings may facilitate genetic engineering efforts to enhance microalgal biofuel production.

Formation of iodinated trihalomethanes during UV/chloramination with iodate as the iodine source

Iodinated trihalomethanes (I-THMs) are a group of emerging disinfection by-products with high toxicity, and iodide (I(-)) as well as iodinated organic compounds are expected to be their iodine sources. Nevertheless, in this study, iodate (IO3(-)) was proven to be a new iodine source of I-THM formation during UV/chloramination. In the iodate-containing waters (without any other iodine sources), I-THM formation increased with the increase of UV dose, IO3(-) and NH2Cl concentrations. With the increase of Br(-)/IO3(-) molar ratio, I-THM formation (especially for the brominated species) increased. Besides, NOM species could affect I-THM formation from IO3(-) during UV/chloramination. Fulvic acid could promote IO3(-) phototransformation to I(-) but humic acid impeded the production of I(-) during UV irradiation. Under realistic drinking water treatment conditions (DOC = 5.0 mg-C/L, IO3(-) = 12.7 μg-I/L, UV dose = 50 mJ/cm(2), NH2Cl = 5 mg-Cl2/L), CHCl2I was detected as 0.17 μg/L using solid-phase microextraction method, and the production rate of I-THMs from IO3(-) was about 7% of that from I(-).

Effective Biological DeNOx of Industrial Flue Gas by the Mixotrophic Cultivation of an Oil-Producing Green Alga Chlorella sp. C2

Nitrogen oxides (NOx) are the components of fossil flue gas that result in the most serious environmental concerns. We previously showed that the biological removal of NOx by microalgae appears superior to traditional treatments. This study optimizes the strategy for the microalgal-based DeNOx of flue gas by fed-batch mixotrophic cultivation. By using actual flue gas fixed salts (FGFS) as the nitrogen supply, the mixotrophical cultivation of the green alga Chlorella sp. C2 with high NOx absorption efficiency was optimized in a stepwise manner in a 5 L bioreactor and resulted in a maximum biomass productivity of 9.87 g L(-1) d(-1). The optimized strategy was further scaled up to 50 L, and a biomass productivity of 7.93 g L(-1) d(-1) was achieved, with an overall DeNOx efficiency of 96%, along with an average nitrogen CR of 0.45 g L(-1) d(-1) and lipid productivity of 1.83 g L(-1) d(-1). With an optimized mixotrophical cultivation, this study further proved the feasibility of using Chlorella for the combination of efficient biological DeNOx of flue gas and microalgae-based products production. Thus, this study shows a promising industrial strategy for flue gas biotreatment in plants with limited land area.

The large-scale distribution of ammonia oxidizers in paddy soils is driven by soil pH, geographic distance, and climatic factors

Paddy soils distribute widely from temperate to tropical regions, and are characterized by intensive nitrogen fertilization practices in China. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in soil nitrification, but little is known about their biogeographic distribution patterns in paddy ecosystems. Here, we used barcoded pyrosequencing to characterize the effects of climatic, geochemical and spatial factors on the distribution of ammonia oxidizers from 11 representative rice-growing regions (75–1945 km apart) of China. Potential nitrification rates varied greatly by more than three orders of magnitude, and were significantly correlated with the abundances of AOA and AOB. The community composition of ammonia oxidizer was affected by multiple factors, but changes in relative abundances of the major lineages could be best predicted by soil pH. The alpha diversity of AOA and AOB displayed contrasting trends over the gradients of latitude and atmospheric temperature, indicating a possible niche separation between AOA and AOB along the latitude. The Bray–Curtis dissimilarities in ammonia-oxidizing community structure significantly increased with increasing geographical distance, indicating that more geographically distant paddy fields tend to harbor more dissimilar ammonia oxidizers. Variation partitioning analysis revealed that spatial, geochemical and climatic factors could jointly explain majority of the data variation, and were important drivers defining the ecological niches of AOA and AOB. Our findings suggest that both AOA and AOB are of functional importance in paddy soil nitrification, and ammonia oxidizers in paddy ecosystems exhibit large-scale biogeographic patterns shaped by soil pH, geographic distance, and climatic factors.

Evaluation of an oil-producing green alga Chlorella sp. C2 for biological DeNOx of industrial flue gases

NOx, a significant portion of fossil fuel flue gases, are among the most serious environmental issues in the world and must be removed in an additional costly gas treatment step. This study evaluated the growth of the green alga Chlorella sp. C2 under a nitrite-simulated NOx environment and the removal rates of actual flue gas fixed salts (FGFSs) from Sinopec's Shijiazhuang refinery along with lipid production. The results showed that nitrite levels lower than 176.5 mM had no significant adverse effects on the cell growth and photosynthesis of Chlorella sp. C2, demonstrating that this green alga could utilize nitrite and NOx as a nitrogen source. High concentrations of nitrite (88.25-176.5 mM) also resulted in the accumulation of neutral lipids. A 60% nitrite removal efficiency was obtained together with the production of 33% algae lipids when cultured with FGFS. Notably, the presence of nitrate in the FGFS medium significantly enhanced the nitrite removal capability, biomass and lipid production. Thus, this study may provide a new insight into the economically viable application of microalgae in the synergistic combination of biological DeNOx of industrial flue gases and biodiesel production.

Polymeric optical sensors for selective and sensitive nitrite detection using cobalt(III) corrole and rhodium(III) porphyrin as ionophores

Cobalt(III) 5,10,15-tris(4-tert-butylphenyl) corrole with a triphenylphosphine axial ligand and rhodium(III) 5,10,15,20-tetra(p-tert-butylphenyl) porphyrin are incorporated into plasticized poly(vinyl chloride) films to fabricate nitrite-selective bulk optodes via absorbance measurements. The resulting films yield sensitive, fast and fully reversible response toward nitrite with significantly enhanced nitrite selectivity over other anions including lipophilic anions such as thiocyanate and perchlorate. The selectivity patterns differ greatly from the Hofmeister series based on anion lipophilicity and are consistent with selectivity obtained with potentiometric sensors based on the same ionophores. The optical nitrite sensors are shown to be useful for detecting rates of emission of nitric oxide (NO) from NO releasing polymers containing S-nitroso-N-acetyl-DL-penicillamine.

A novel ion chromatography cycling-column-switching system for the determination of low-level chlorate and nitrite in high salt matrices

A novel ion chromatography cycling-column-switching system was developed for the determination of chlorate and nitrite in high salt matrices. The simple system included a pump, two valves, a single eluent, and a conductivity detector. Both online pre-concentration and matrix elimination were achieved by this method. The target anions were eluted from the concentrator column to the analytical columns circularly. Chloride matrix was then eliminated completely. The method was applied to the determination of low-level chlorate and nitrite in the chloride matrix. Our experimental results demonstrated that this system is of advantages such as high sensitivity, facile automation and simple sample pretreatment, which might be a promising approach for environmental researches and food control.

Sensitive and robotic determination of bromate in sea water and drinking deep-sea water by headspace solid-phase micro extraction and gas chromatography-mass spectrometry

A robotic method has been established for the determination of bromate in sea water and drinking deep-sea water. Bromate in water was converted into volatile derivative, which was measured with headspace solid-phase micro extraction and gas chromatography-mass spectrometry (HS-SPME GC-MS). Derivatization reagent and the HS-SPME parameters (selection of fibre, extraction/derivatization temperature, heating time and; the morality of HCl) were optimized and selected. Under the established conditions, the detection and the quantification limits were 0.016 μg L(-1) and 0.051 μg L(-1), respectively, and the intra- and inter-day relative standard deviation was less than 7% at concentrations of 1.0 and 10.0 μg L(-1). The calibration curve showed good linearity with r(2)=0.9998. The common ions Cl(-), NO(3)(-), SO(4)(2-), HPO(4)(2-), H(2)PO(4)(-), K(+), Na(+), NH(4)(+), Ca(2+), Mg(2+), Ba(2+), Mn(4+), Mn(2+), Fe(3+) and Fe(2+) did not interfere even when present in 1000-fold excess over the active species. The method was successfully applied to the determination of bromate in sea water and drinking deep-sea water.

Ultra trace determination of bromate in mineral water and table salt by liquid chromatography-tandem mass spectrometry

A liquid chromatography-tandem mass spectrometry method (LC-MS/MS) was developed in order to determine the bromate in mineral water and table salt. The following optimum conditions for the LC-MS/MS detection were established: derivatization reagent (300 mg/L of 2,6-dimethylaniline), acidity (0.2M HCl), reaction temperature (30 °C) and heating time (20 min). The formed derivative was directly injected in the LC system without extraction or purification procedures. In the established conditions, the method was used to detect bromate in mineral water and table salt. The limit of detection and limit of quantification of bromate in mineral water were 0.02 μg/L and 0.07 μg/L, respectively, and those of table salt were 0.07 μg/kg and 0.23 μg/kg, respectively. The 17 common ions did not interfere even when present in 1,000-fold excess over the bromated ion of 10.0 μg/L. The accuracy was in a range of 92-104% and the assay precision was less than 9% in the table salt. The method was successfully applied to determine bromate in mineral water and table salt.

Determination of iodate in food, environmental, and biological samples after solid-phase extraction with Ni-Al-Zr ternary layered double hydroxide as a nanosorbent

Nanostructured nickel-aluminum-zirconium ternary layered double hydroxide was successfully applied as a solid-phase extraction sorbent for the separation and pre-concentration of trace levels of iodate in food, environmental and biological samples. An indirect method was used for monitoring of the extracted iodate ions. The method is based on the reaction of the iodate with iodide in acidic solution to produce iodine, which can be spectrophotometrically monitored at 352 nm. The absorbance is directly proportional to the concentration of iodate in the sample. The effect of several parameters such as pH, sample flow rate, amount of nanosorbent, elution conditions, sample volume, and coexisting ions on the recovery was investigated. In the optimum experimental conditions, the limit of detection (3s) and enrichment factor were 0.12 μg mL(-1) and 20, respectively. The calibration graph using the preconcentration system was linear in the range of 0.2-2.8 μg mL(-1) with a correlation coefficient of 0.998. In order to validate the presented method, a certified reference material, NIST SRM 1549, was also analyzed.

Low-level bromate analysis in drinking water by ion chromatography with optimized suppressed conductivity cell current followed by a post-column reaction and UV/Vis detection

In the present work, a high capacity anion exchange column was used to efficiently and simultaneously separate traces of oxyhalide disinfection byproducts (DBP) anions and bromide by an ion chromatography system followed by a post-column reaction (PCR). The PCR generates in situ hydroiodic (HI) acid from the excess of potassium iodate that combines with bromate from the column effluent to form the triiodide anion detectable by UV/Vis absorbance at 352 nm. The suppressed conductivity cell current was optimized at 70 mA, with a flow rate of 1.0 mL/min and a 9 mM carbonate eluent. Its performance was investigated on a trace-level determination of bromate in ozonated municipal and bottled drinking water. Based on ozonated municipal drinking water matrix, the method detection limit of 0.27 μg BrO(-)(3)/L was evaluated with the Method Quantification Limit (MQL) of 0.89 μg BrO(-)(3)/L. However, in ultrapure water, a MDL of 0.015 μg BrO(-)(3)/L and a MRL of 0.052 μg BrO(-)(3)/L were achieved. The recovery for spiked municipal samples was in the range of 90%-115%.

A simple and sensitive spectrophotometric method for the determination of trace amounts of nitrite in environmental and biological samples using 4-amino-5-hydroxynaphthalene-2,7-disulphonic acid monosodium salt

A very simple, sensitive, fairly selective and rapid spectrophotometric method for the determination of trace amounts of nitrite has been described. This method is based on the diazotized intramolecular coupling of electrophilic diazonium cation with the phenolic group of 4-amino-5-hydroxynaphthalene-2,7-disulphonic acid monosodium salt (AHNDMS) in a phosphate buffer solution of pH 7.5. The cyclic product has a purple color with maximum absorbance at 560nm and is stable for 6h. Optimum reaction conditions and other important analytical parameters for the maximum color development were established. Beer's law was found to obey for nitrite in the concentration range of 0.1-1.6microgml(-1) with molar absorptivity of 2.6x10(4)lmol(-1)cm(-1) and Sandell's sensitivity of 0.0075microgml(-1). The effect of interfering ions on the determination is described. The recommended method was applied for the determination of nitrite in different water, soil and human saliva samples. The performance of the recommended method was evaluated in terms of Student's t-test and variance ratio F-test, which indicated the significance of proposed method over the reference method.

Sensitive spectrophotometric methods for the assessment of nitrite in water sample

Two spectrophotometric methods have been developed for the determination of nitrite using dapsone (DAP) with alpha-naphthol and 4-amino-5-hydroxynapthalene-2,7-disulphonic acid monosodium salt (AHNDMS) as chromogenic reagents with maximum absorbance wavelength at 540 and 520 nm respectively. For the method that utilizes dapsone with alpha-naphthol (DAP-alpha-naphthol), the beer's law range is obeyed between 0.05-0.8 microg ml(-1) with molar absorptivity of 5.749 x 104 l mol(-1) cm(-1). The second method that uses dapsone with AHNDMS (DAP-AHNDMS), the beer's law is valid over the range 0.2-1.4 mug ml(-1) and molar absorptivity 2.44 x 104 l mol(-1) cm(-1). The common interfering ions in the analytical procedures have been studied. This proposed methods are reliable, reproducible and have been successfully applied to determine nitrite in various water sources of environmental interest.