Addition Of Hypochlorite Research Articles

A PET based colorimetric/fluorescent dual-signal probe for selective detection of hypochlorite in real water samples

As a potent oxidizing agent, hypochlorite is pervasive across various terminal disinfection processes, including water treatment, household blenching and medical sterilization. Thus, the specific visualization identification of hypochlorite in real water samples is crucial for assessing water quality safety and pollutant toxicity. Herein, a novel turn-on colorimetric/fluorescent dual-signal probe AMXM based on 6‑methoxy-2,3-dihydro-1H-xanthene-4-carboxaldehyde scaffold has been successfully designed and synthesized for highly selective and sensitive detection of ClO− in real water sample. Upon the addition of hypochlorite, the solution's color visibly changes from red to yellow to the naked eye, and a strong yellowish green fluorescence is observed under UV light at 365 nm. AMXM demonstrates an excellent linear response (R2 = 0.9922), with a low detection limit of 56.2 nM, and is unaffected by other potential interfering substances. The mechanism of AMXM’s response to hypochlorite ions was confirmed through 1H NMR spectroscopy and density functional theory (DFT) calculations. Furthermore, AMXM was successfully applied to paper test strips and used for the quantitative determination of hypochlorite ions in four real water samples.

Sustainable urban water management: Evaluating two pilot-scale advanced decentralized treatment systems for removal of organic contaminants of emerging concern in reclaimed groundwater

The rapid growth of population and the effects of climate change have placed unprecedented pressure on urban water supplies and pollution control. Consequently, it is essential to explore new local water resources in water-strained areas. To this end, this work focuses on evaluating pollutant removal effectiveness of decentralized treatment systems for groundwater reclamation. Two pilot-scale treatment trains, Treatment Line 1 (L1) and Treatment Line 2 (L2), which use membrane-free (with granulated activated carbon as the main process) or membrane-based (with reverse osmosis as the primary technology), were compared for their effectiveness in reducing concentrations of organic contaminants of emerging concern (CECs). Additionally, the effect of sodium hypochlorite addition for biofilm control on the contaminant removal performance was also examined. Results from the analysis of nearly 120 trace organic compounds (only 21 were detected in the raw water) showed that L2 significantly overperformed L1. Furthermore, the addition of a pre-chlorination step did not improve the removal performance. Regarding trace organic compounds, L1 without pre-chlorination averaged an overall good removal performance (94 ± 12%). However, Irbesartan, gemfibrozil and gabapentin showed moderate removals (50–90%) and Valsartan was poorly removed (<50%). After pre-chlorinating L1, the overall removal performance decreased (86 ± 20%). Nearly one third of the target contaminants showed moderate removal (50–90%), with Irbesartan and Valsartan exhibiting poor attenuations (<50%), highlighting that negatively-charged compounds were challenging to eliminate. In contrast, L2 exhibited very high removals (>99%) on all studied trace organic contaminants regardless of pre-chlorination. Our study also identified several indicator compounds to monitor CEC removal. Finally, considering the trade-offs between cost and final water use (non-potable), L1-based schemes with intermittent pre-chlorination could be the preferred implementation option. The results of this work will offer valuable insights into decentralized treatment systems, assisting decision-makers in choosing suitable approaches for sustainable urban water management.

Ratiometric fluorescent probe with AIE characteristics for hypochlorite detection and biological imaging

It is very important and highly valuable to detect ClO− in samples and living cells with accuracy and speed. In this work, a novel fluorescent probe NA was prepared from 4-bromo-1,8-naphthalic anhydride by acylation reaction and Suzuki coupling reaction and used for the detection of ClO−. Thiomethyl serves as the recognition group for probe NA, while naphthalimide serves as fluorescent chromophore. The probe exhibited an extremely pronounced blue shift from yellow to blue fluorescence within 1 min after the addition of hypochlorite (ClO−). The probe demonstrates high sensitivity to ClO− with a limit of detection (LOD) of 1.22 µM. Also, probe NA demonstrates excellent selectivity and immunity to interference. Additionally, simple fluorescent test strips containing probe NA were prepared in this study, enabling rapid detection of ClO− in water samples. And NA had been effectively used to image endogenous and exogenous ClO−fluorescence in living cells. The results suggest that probe NA has significant potential for portable detection and biological applications.

Electrochemically synthesized green fluorescent carbon dots for quantitation of hypochlorite and carbendazim.

Green emission carbon dots (CDs) electrochemically prepared from 2,6-pyridinedicarboxylic acid and o-phenyl-enediamine were applied separately for the quantitation of hypochlorite and carbendazim. The characteristic and optical properties of the CDs were studied through fluorescence, UV-vis absorption, X-ray photoelectron spectroscopy, and transmission electron microscopy. The synthesized CDs were mainly 0.8-2.2 nm in size, with an average size of 1.5 nm. The CDs exhibited green luminescence centered at 520 nm when excited by 420 nm light. The green emission of the CDs is quenched after the addition of hypochlorite, mainly through the redox reaction between hypochlorite and hydroxyl groups on the CDs surface. Furthermore, the hypochlorite-induced fluorescence quenched can be prevented in the presence of carbendazim. The sensing approaches exhibit good linear ranges of 1-50 μM and 0.05-5 μM for hypochlorite and carbendazim, respectively, with low detection limits of 0.096 and 0.005 μM, respectively. Practicalities of the luminescent probes were separately validated by the quantitation of the two analytes in real sample matrix with recoveries ranging from 96.3 to 108.9% and the relative standard deviation values below 5.51%. Our results show the potential of the sensitive, selective, and simple CD probe for water and food quality control.

Hydrometallurgical Processing of Chalcocite Tailing Sample for Extraction of Copper

Objective: To recover the copper remained in tailing sample of chalcocite due to its hazardous impact on biota, in addition to the fact that primary sources are becoming scare and they are of high economic values. Methods: In order to recover copper from tailing, herein, hydrochloric acid leaching followed by the selective precipitation of copper has been studied. The parameters like acid concentration (1.0-2.5M), sodium hypochlorite addition dosage (0.5-5.0M), temperature (25-55°C), time (1-9h), agitation speed (180-360rpm) and pulp density (2-14 wt./vol.%) were varied to determine the optimum condition of leaching. Results: According to experimental findings, metal-chloro complexes were effectively synthesized by the addition of 0.5M hydrogen peroxide with 1.5M hydrochloric acid solution at 45°C, 3h of leach time and 260rpm that yielded approximately 99% of copper into the leach liquor. Afterward, the leach liquor was treated for recovery of copper salt by adding a 300g/L solution of sodium hydroxide, precipitating Cu(OH)2. Conclusion: The current research potentially contributes to both ecologically and economically through the hydrometallurgical processing of tailing sample for extraction of copper.

Environmental impacts of the widespread use of chlorine-based disinfectants during the COVID-19 pandemic.

Chlorinated disinfectants are widely used in hospitals, COVID-19 quarantine facilities, households, institutes, and public areas to combat the spread of the novel coronavirus as they are effective against viruses on various surfaces. Medical facilities have enhanced their routine disinfection of indoors, premises, and in-house sewage. Besides questioning the efficiency of these compounds in combating coronavirus, the impacts of these excessive disinfection efforts have not been discussed anywhere. The impacts of chlorine-based disinfectants on both environment and human health are reviewed in this paper. Chlorine in molecular and in compound forms is known to pose many health hazards. Hypochlorite addition to soil can increase chlorine/chloride concentration, which can be fatal to plant species if exposed. When chlorine compounds reach the sewer/drainage system and are exposed to aqueous media such as wastewater, many disinfection by-products (DBPs) can be formed depending on the concentrations of natural organic matter, inorganics, and anthropogenic pollutants present. Chlorination of hospital wastewater can also produce toxic drug-derived disinfection by-products. Many DBPs are carcinogenic to humans, and some of them are cytotoxic, genotoxic, and mutagenic. DBPs can be harmful to the flora and fauna of the receiving water body and may have adverse effects on microorganisms and plankton present in these ecosystems.Supplementary InformationThe online version contains supplementary material available at 10.1007/s11356-021-18316-2.

Simultaneous Detection of Hypochlorite and Singlet Oxygen by a Thiocoumarin-Based Ratiometric Fluorescent Probe.

The development of fluorescent probes derived from thiocarbonyl compounds for reactive oxygen species has been actively pursued in recent years. However, a better understanding of the optical response behaviors of thiocarbonyl compounds toward reactive oxygen species remains a challenge. Along with this, further studies to overcome the limitation of a single emission channel and aggregation-caused quenching features of thiocarbonyl-based fluorescent probes are highly desirable. Due to the important role of hypochlorite and singlet oxygen in biological processes and their common coexistence in living systems with frequent intertransformations, the design of a fluorescent probe that can recognize both hypochlorite and singlet oxygen is of great interest. Herein, a thiocarbonyl-based ratiometric fluorescent probe (Fcoum-S) for simultaneous detection of hypochlorite and singlet oxygen in aqueous solution and living cells was designed and synthesized. Upon the addition of hypochlorite in Fcoum-S solution (phosphate-buffered saline, 10 mM, pH 7.4, 10% acetonitrile), a ratiometric fluorescence response was observed via a specific hypochlorite-promoted desulfurization reaction with a good linear relationship between the ratio of fluorescence intensities at 526 and 602 nm (I 526nm/I 602nm) and the hypochlorite concentrations (a low detection limit of 0.15 μM). Furthermore, upon green light irradiation, Fcoum-S was efficiently desulfurized to its oxo analogue (Fcoum-O) by in situ generated singlet oxygen, leading to a significant change in fluorescence. Fcoum-S could work well in an aqueous medium owing to the high reactivity of the thiocarbonyl group and the aggregation-induced emission characteristics. More importantly, Fcoum-S could target mitochondria and was successfully utilized for fluorescence imaging of mitochondrial hypochlorite/singlet oxygen in live cells. This work provides a molecular design guideline for further exploring thioketone derivatives as fluorescent probes.

A Flexible Chemosensor Based on Colorimetric and Fluorescent Dual Modes for Rapid and Sensitive Detection of Hypochlorite Anion.

A flexible chemosensor has been developed based on colorimetric and fluorescent dual modes using tetraphenylethylene-centered tetraaniline (TPE4A) for rapid and sensitive detection of hypochlorite anion. The fluorescent probe TPE4A exhibits a unique aggregation-induced emission (AIE) character which is proved by a blue shift of the fluorescent peak from 544 to 474 nm with the water equivalents increasing. With the addition of hypochlorite in solution, the absorbance of the probe changes and the responding fluorescence color can be observed to change from light green to purple. The detection limit of hypochlorite is 1.80 × 10−4 M in solution, and the visual detection limit is 1.27 µg/cm2 with the naked eye for the flexible paper-based chemosensor. The proposed flexible chemosensors show a good selectivity and sensitivity which has great potential for effective detection of hypochlorite anions without any spectroscopic instrumentation.

A procedure for removal of cyanuric acid in swimming pools using a cell-free thermostable cyanuric acid hydrolase.

Cyanuric acid (CYA) is used commercially for maintaining active chlorine to inactivate microbial and viral pathogens in swimming pools and hot tubs. Repeated CYA addition can cause a lack of available chlorine and adequate disinfection. Acceptable CYA levels can potentially be restored via cyanuric acid hydrolases (CAH), enzymes that hydrolyze CYA to biuret under mild conditions. Here we describe a previously unknown CAH enzyme from Pseudolabrys sp. Root1462 (CAH-PR), mined from public databases by bioinformatic analysis of potential CAH genes, which we show to be suitable in a cell-free form for industrial applications based upon favorable enzymatic and physical properties, combined with high-yield expression in aerobic cell culture. The kinetic parameters and modeled structure were similar to known CAH enzymes, but the new enzyme displayed a surprising thermal and storage stability. The new CAH enzyme was applied, following addition of inexpensive sodium sulfite, to hydrolyze CYA to biuret. At the desired endpoint, hypochlorite addition inactivated remaining enzyme and oxidized biuret to primarily dinitrogen and carbon dioxide gases. The mechanism of biuret oxidation with hypochlorite under conditions relevant to recreational pools is described.

Determination of Hypochlorite via Fluorescence Change from Blue to Green Based on 4-(1H-imidazo [4,5-f] [1,10]-phenanthrolin-2-yl) Benzaldehyde Oxime.

The new design strategy will provide the possibility for preparing a dynamic sensor by employing the inhibition of C = N isomerization. In this work, the functional probe 4-(1H-imidazo [4,5-f] [1,10]-phenanthrolin-2-yl) benzaldehyde oxime (compound 4) has been synthesized and such molecule gives rise to blue emission. Due to the incorporation of hypochlorite, the oxime group can be oxidized to the structure of aldehyde. As a result, the molecular motif exhibits sharp emission change from blue to green due to the addition of hypochlorite with enough sensitivity and selectivity (detection limit = 53 nM, linear range 0.5-8.0 µM). It has also been used for monitoring ClO- by employing solution color change and the absorption signal difference could effectively rule out the effects of interference species. To our knowledge, it will be the first case of a highly selective hypochlorite sensor derived from oxime isomerization reaction based on phenanthroline backbone.

A thiourea-based fluorescent chemosensor for bioimaging hypochlorite

A thiourea-based fluorescent turn-off chemosensor FHC was developed for recognizing hypochlorite. With the addition of hypochlorite to FHC, FHC displayed a specific desulfurization reaction of the thiourea group followed by the fluorescent quenching response. The fluorescent turn-off response of FHC to hypochlorite was very fast to finish within a few seconds. Detection limit of hypochlorite was determined to be 0.43μM. FHC can be applied for the bioimaging of hypochlorite in both HeLa cells and zebrafish. Response process of FHC to hypochlorite, via the desulfurization of the thiourea moiety, was demonstrated, based on 1H NMR titrations, ESI-mass, fluorescent and UV–vis titrations and DFT calculations.

Surface modification and flotation improvement of ilmenite by using sodium hypochlorite as oxidant and activator

In this study, we have developed a novel method for ilmenite activation. Sodium hypochlorite was used as an oxidant and surface modifier to promote ilmenite flotation. And it has successfully been performed valence transitions of iron atoms on the ilmenite surface, thereby enhancing the action activity between the surface sites of ilmenite and sodium oleate. Eventually the surface Fe3+ content increased from 42.15 to 63.79%. Oxidation by sodium hypochlorite increased the amount of Fe3+ on the ilmenite surface by 21.64% and improved the ilmenite recovery to 95%, while the maximum recovery of ilmenite without sodium hypochlorite addition was only 85%. The activation mechanism of ilmenite by sodium hypochlorite was studied by batch flotation, Zeta potential measurement, X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and reaction thermodynamic analysis. The results of potential measurement show that sodium hypochlorite made the Zeta potentials of ilmenite–sodium oleate system more negative mainly due to the enhanced adsorption effect between them. FTIR results indicate that more prominent absorption peak of iron oleate appeared in the FTIR spectrum of ilmenite treated with sodium oleate after sodium hypochlorite oxidation. XPS analyses suggest that more Fe2+ on ilmenite surface supplied electrons to the oxidant and formed more Fe3+. Reaction thermodynamic analyses also show that compared with Fe2+, Fe3+ was more likely to interact with oleate ions and formed more stable species. In summary, sodium hypochlorite can activate ilmenite and improve its flotation.

Enhanced thallium(I) removal from wastewater using hypochlorite oxidation coupled with magnetite-based biochar adsorption

The development of efficient and regenerable adsorbent coupled with advanced oxidation for enhanced thallium (Tl) removal has been a recent focus on wastewater treatment. In this study, a magnetite-based biochar derived from watermelon rinds was synthesized and used as a sustainable adsorbent and catalyst for hypochlorite oxidation and removal of Tl(I) from wastewater. The addition of hypochlorite substantially enhanced the Tl(I) removal under normal pH range (6–9). Maximum Tl adsorption capacity of 1123 mg/g was achieved, which is 12.3% higher than the highest value previously reported. The magnetic biochar can be regenerated using 0.1 mol/L HNO3 solution for elution in only 5 min, with a Tl desorption efficiency of 78.9%. The Tl removal efficiency was constantly higher than 98.5% during five consecutive recycle tests, indicating the effective reuse performance of the adsorbent. Oxidation, surface precipitation, pore retention and surface complexation were the main mechanisms for Tl(I) removal. The re-dissolution of Tl compounds and ion exchange of Tl cations with proton were the main mechanisms for adsorbent regeneration. Given the fast oxidation rate, high adsorption capacity, steady reusability and facile separability, this magnetic biochar-hypochlorite technique is a promising means for Tl(I) removal from wastewater. The catalytic hypochlorite oxidation induced by the magnetic biochar has also great potential to the effective removal of other pollutants.

Ratiometric fluorescent sensor based oxazolo-phenazine derivatives for detect hypochlorite via oxidation reaction and its application in environmental samples

In this work, we designed and synthesized a ratiometric fluorescent sensor (POC) based phenazine derivative which can specifically detect hypochlorite (detection limit equals to 8.9 × 10−7 M) in DMSO/H2O (3:7, v/v) solution. With addition of hypochlorite to the solution of POC, hypochlorite broken π-π stacking of POC, and then oxidizes sulfur atoms in phenazine groups to sulfoxide, which resulted in the fluorescent color changed from blue to yellow. Job's plot showed that binding stoichiometry of POC with ClO− was 2:1. In addition, POC could be used to real-time detect hypochlorite in environment samples, and the naked eyes detection limit reached up to 7 × 10−5 M.

Nanomolar colorimetric hypochlorite sensor in water.

Hypochlorous acid is present in several biological systems and plays a pivotal role in bioprocesses. The acid also finds application in industrial and synthetic spheres. The ecological toxicity of elevated hypochlorite concentrations in aqueous media has been thoroughly documented. As a consequence, there is a pressing need to develop quantitative and qualitative methods for the detection of hypochlorite in water. In this regard, nanomolar detectable, non-toxic and intensely coloured probes based on commercially available dyes such as Fuchsin basic, Methyl violet, Acid red-1, and Trypan blue have been successfully applied for hypochlorite detection in fully aqueous media. In all of these cases, specific and selective naked eye sensing of hypochlorite was achieved. As a rule of thumb, the addition of hypochlorite to a dye solution results in discoloration. The sensing mechanism follows an oxidative chemodosimetric approach and UV-Vis, as well as NMR titration experiments, support the oxidative cleaving of the molecular framework even in the presence of hypochlorite in trace amount (>1 nM). Furthermore, probes are subjected towards real-sample analysis of daily use water which contains bleaching agent and found to be promising in strip test too. Limits of detection of the dyes Fuchsin basic, Methyl violet, Acid red-1 and Trypan blue are 0.86 nM, 2.97 nM, 2.31 nM and 30 μM respectively. These dyes are promising analytical tools for the detection of hypochlorite.

Membrane Bioreactors Used for Treatment of Food Industry Effluents

Effluents from the food industry determine pollution problems due to high COD and BOD concentrations. Compared to other industrial divisions, food industry requires large amounts of water. In this study, MBR was based on submerged hollow fibers membranes functioning by low vacuum. Two phases of bioreactor treatment were carried out with different HRTs (2-8) and (2-24) hours. Sixteen water samples collected from the influent and the effluent of the bioreactor during the two phases. NaOCl compound was added during the backwashing process for all tests, and the same compound was added with mixed liquid for the second test at period 24 hour of aeration. The samples were tested for twelve water quality tests: temperature, Dissolved Oxygen, pH, Turbidity, Total Suspended Solids, Mixed Liquor Suspended Solids, Chemical Oxygen Demand, Biochemical Oxygen Demand, Nitrate Nitrogen, Ammonium Nitrogen, Total Phosphate, and Ortho Phosphate. The results indicated that the bioreactor system can be used efficiently to treat industrial wastewater from the food industry. The efficiency of the technology was evaluated with sodium hypochlorite addition to removing the adherent bacteria on the surface area of hollow fibers. The results showed that the bioreactor under the conditions of the second phase was excellent in removing Turbidity, TSS, COD, and BOD5 with a removal efficiency 99.96%, 89.52%, 93.56%, and 99.36% respectively, when added 82 ml of NaOCl in the bioreactor tank, and was a good removing of TP, and Ortho-P with removal efficiency 60.76% and 48.95% respectively. Otherwise, a negative effect of NaOCl on both of NO3-N and NH4-N was obtained in term of removal where the minimum removal efficiency was observed when adding 82 ml of NaOCl under the conditions of the second phase.

Chlorine toxicity to Navicula pelliculosa and Achnanthes spp. in a flow-through system: The use of immobilised microalgae and variable chlorophyll fluorescence

Chlorination is a widely used antifouling method for freshwater and marine applications. Chlorine added to seawater reacts to form oxidants that are toxic to biofouling organisms. Further, the oxidants that result are short-lived, but may nevertheless affect non-target species in waterbodies receiving the antifouling effluent. This study evaluated the toxicity of chlorinated seawater (e.g. following sodium hypochlorite addition) on two different species of marine benthic diatoms (Achnanthes spp., and Navicula pelliculosa), which are representative of microphytobenthos communities – an important component in coastal habitats that may be exposed to chlorinated seawater. To evaluate the growth inhibition over a 72 h period, algae were immobilised in alginate beads and exposed to different levels of chlorination in a flow through system. Growth rates and physiological condition of the microalgae were evaluated using a Fast Repetition Rate fluorometer (FRRf). To determine whether alginate influenced the sensitivity of algal response, studies were also conducted in a static test system (without renewal of test solutions) using both free cells and immobilised cells with initial chlorine added to achieve a similar range of concentrations as those used in the flow-through study. Within the first hour of the exposure period there was an indication that, for both species, the free algal cells in the static system were more sensitive to exposure to chlorinated seawater than were alginate-immobilised cells in the flow through system. Immobilised cells in a static system with a single addition of chlorine were also less sensitive to chlorination than free algal cells. However, for periods of 24 h or more due to decay of TRO in the static system the exposure of immobilised algae in the flow through system had a greater impact and hence lower effect concentrations. For the flow-through studies Achnanthes spp. was the most sensitive after 72 h exposure with a potential no effect concentration EC10 value of 0.02 mg l−1 as Cl2 equivalents expressed as total residual oxidants (TRO) compared 0.04 mg l−1 TRO for N. pelliculosa. Immobilisation of algal cells in alginate was found to be an effective means of determining the impact of chlorination and is likely to be effective for other non-persistent substances. Based on the data produced, the extent and significance of ecological effects of chlorination upon algal species typical of microphytobenthos are likely to be limited providing discharges comply with a maximum allowable concentration of 0.01 mg l−1 TRO at the edge of an agreed mixing zone.

Hypochlorite-Mediated Modulation of Photoinduced Electron Transfer in a Phenothiazine-Boron dipyrromethene Electron Donor-Acceptor Dyad: A Highly Water Soluble "Turn-On" Fluorescent Probe for Hypochlorite.

A highly water-soluble phenothiazine (PTZ)-boron dipyrromethene (BODIPY)-based electron donor-acceptor dyad (WS-Probe), which contains BODIPY as the signaling antennae and PTZ as the OCl- reactive group, was designed and used as a fluorescent chemosensor for the detection of OCl- . Upon addition of incremental amounts of NaOCl, the quenched fluorescence of WS-Probe was enhanced drastically, which indicated the inhibition of reductive photoinduced electron transfer (PET) from PTZ to 1 BODIPY*; the detection limit was calculated to be 26.7 nm. Selectivity studies with various reactive oxygen species, cations, and anions revealed that WS-Probe was able to detect OCl- selectively. Steady-state fluorescence studies performed at varied pH suggested that WS-Probe can detect NaOCl and exhibits maximum fluorescence in the pH range of 7 to 8, similar to physiological conditions. ESI-MS analysis and 1 H NMR spectroscopy titrations showed the formation of sulfoxide as the major oxidized product upon addition of hypochlorite. More interestingly, when WS-Probe was treated with real water samples, the fluorescence response was clearly visible with tap water and disinfectant, which indicated the presence of OCl- in these samples. The in vitro cell viability assay performed with human embryonic kidney 293 (HEK 293) cells suggested that WS-probe is non-toxic up to 10 μm and implicates the use of the probe for biological applications.

Oxidation of phenothiazine based fluorescent probe for hypochlorite and its application to live cell imaging

New phenothiazine appended BODIPY derivative has been synthesized and characterized for the determination of hypochlorite in live cells. The fluorescent probe has exhibited 72 fold fluorescence enhancement upon addition of hypochlorite over other reactive oxygen species. Further, the studies proved that the probe has ability to detect the hypochlorite even at extremely low level (4.1 nM). Having less cytotoxicity and negligible auto-fluorescence, the probe was successfully used to monitor external addition and internal secretion of hypochlorite in RAW 264.7 cells.

Characterization of enalapril and ranitidine chlorination by-products by liquid chromatography/high-resolution mass spectrometry and their toxicity evaluation

Due to its low cost, its capability for disinfection and oxidation, chlorination using gaseous chlorine or hypochlorite salts, has also been commonly applied in water treatment plants for oxidation and disinfection purposes. Little is known about the identity and toxicity of by-products resulting from the chlorination of pharmaceutical micropollutants, such as enalapril (ENA) and ranitidine (RAN). ENA and RAN chlorination by-products were characterized in this study by high-performance liquid chromatography coupled to high-resolution mass spectrometry (HPLC/HRMS) and their toxicity were assessed by MTT assay. Chlorination experiments with ENA and RAN solutions (10 mg L-1) indicate degradation efficiencies of 100% for both compounds after only 5 min of exposure to chlorine at concentration of 9.53 mg Cl2 L-1. On the other hand mineralization rates were lower than 3%, thereby indicating there was accumulation of degradation by-products in all experiments. Mass spectrometric analysis revealed, at all times of reaction after the addition of hypochlorite, the presence of 1-(2-((4-(chlorophenyl)-1-ethoxy-1-oxobutan-2-yl)amino)propanoyl)pyrrolidine-2-carboxylic acid (enalapril by-product) and N-chloro-N-(2-(((chloro-5-((dimethylamino)methyl)furan-2-yl)methyl)sulfinyl)ethyl)-N-methyl-2-nitroethene 1,1-diamine (ranitidine by-product). Despite the formation of oxidized chlorinated by-products in all chlorination assays, the treated solutions were nontoxic to HepG2 cells by the MTT assay. It has been observed that chlorination (10 mg L-1, 5 min) of ENA and RAN solutions exhibited high degradation efficiencies of the target compounds and low mineralization rates. Based on the mass spectrometry data, the routes for ENA and RAN successive oxidation by chlorine has been proposed.