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In this study, a method was developed for the simultaneous determination of volatile phenols, cyanides, anionic surfactants and ammonia nitrogen in drinking water using a flow analyzer. The samples were first distilled at 145°C. The phenol in the distillate then reacts with basic ferricyanide and 4-aminoantipyrine to form a red complex, which is measured colorimetrically at 505 nm. The cyanide in the distillate then reacts with chloramine T to form cyanochloride, which then forms a blue complex with pyridinecarboxylic acid, which is measured colorimetrically at 630 nm. Anionic surfactants react with basic methylene blue to form a compound which is extracted with chloroform and washed with acidic methylene blue to remove interfering substances. Blue compounds in chloroform were determined colorimetrically at 660 nm. In an alkaline environment with a wavelength of 660 nm, ammonia reacts with salicylate and chlorine in dichloroisocyanuric acid to form indophenol blue at 37 °C. At mass concentrations of volatile phenols and cyanides in the range of 2–100 µg/l, the relative standard deviations were 0.75–6.10% and 0.36–5.41%, respectively, and the recovery rates were 96.2–103.6% and 96.0-102.4%. %. Linear correlation coefficient ≥ 0.9999, limits of detection 1.2 µg/L and 0.9 µg/L. Relative standard deviations were 0.27–4.86% and 0.33–5.39%, and recoveries were 93.7–107.0% and 94.4–101.7%. At a mass concentration of anionic surfactants and ammonia nitrogen 10 ~ 1000 μg / l. Linear correlation coefficients were 0.9995 and 0.9999, detection limits were 10.7 µg/l and 7.3 µg/l, respectively. There were no statistical differences compared to the national standard method. The method saves time and effort, has a lower detection limit, higher accuracy and accuracy, less contamination, and is more suitable for analysis and determination of large volume samples.
Volatile phenols, cyanides, anionic surfactants and ammonium nitrogen1 are markers of organoleptic, physical and metalloid elements in drinking water. Phenolic compounds are fundamental chemical building blocks for many applications, but phenol and its homologues are also toxic and difficult to biodegrade. They are emitted during many industrial processes and have become common environmental pollutants2,3. Highly toxic phenolic substances can be absorbed into the body through the skin and respiratory organs. Most of them lose their toxicity during the detoxification process after entering the human body, and then excreted in the urine. However, when the body’s normal detoxification capabilities are exceeded, excess components can accumulate in various organs and tissues, leading to chronic poisoning, headache, rash, skin itching, mental anxiety, anemia, and various neurological symptoms 4, 5, 6,7. Cyanide is extremely harmful, but widespread in nature. Many foods and plants contain cyanide, which can be produced by some bacteria, fungi or algae8,9. In rinse-off products such as shampoos and body washes, anionic surfactants are often used to facilitate cleansing because they provide these products with the superior lather and foam quality that consumers seek. However, many surfactants can irritate the skin10,11. Drinking water, groundwater, surface water and wastewater contain nitrogen in the form of free ammonia (NH3) and ammonium salts (NH4+), known as ammoniacal nitrogen (NH3-N). The decomposition products of nitrogen-containing organic matter in domestic wastewater by microorganisms mainly come from industrial wastewater such as coking and synthetic ammonia, which form part of the ammoniacal nitrogen in water12,13,14. Many methods, including spectrophotometry15,16,17, chromatography18,19,20,21 and flow injection15,22,23,24 can be used to measure these four contaminants in water. Compared to other methods, spectrophotometry is the most popular1. This study used four dual-channel modules to simultaneously evaluate volatile phenols, cyanides, anionic surfactants, and sulfides.
An AA500 continuous flow analyzer (SEAL, Germany), an SL252 electronic balance (Shanghai Mingqiao Electronic Instrument Factory, China), and a Milli-Q ultrapure water meter (Merck Millipore, USA) were used. All chemicals used in this work were of analytical grade, and deionized water was used in all experiments. Hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, chloroform, ethanol, sodium tetraborate, isonicotinic acid and 4-aminoantipyrine were purchased from Sinopharm Chemical Reagent Co., Ltd. (China). Triton X-100, sodium hydroxide and potassium chloride were purchased from Tianjin Damao Chemical Reagent Factory (China). Potassium ferricyanide, sodium nitroprusside, sodium salicylate and N,N-dimethylformamide were provided by Tianjin Tianli Chemical Reagent Co., Ltd. (China). Potassium dihydrogen phosphate, disodium hydrogen phosphate, pyrazolone and methylene blue trihydrate were purchased from Tianjin Kemiou Chemical Reagent Co., Ltd. (China). Trisodium citrate dihydrate, polyoxyethylene lauryl ether and sodium dichloroisocyanurate were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (China). Standard solutions of volatile phenols, cyanides, anionic surfactants, and aqueous ammonia nitrogen were purchased from the China Institute of Metrology.
Distillation Reagent: Dilute 160 ml of phosphoric acid to 1000 ml with deionized water. Reserve buffer: Weigh out 9 g of boric acid, 5 g of sodium hydroxide and 10 g of potassium chloride and dilute to 1000 ml with deionized water. Absorption Reagent (renewed weekly): Accurately measure 200 ml stock buffer, add 1 ml 50% Triton X-100 (v/v, Triton X-100/ethanol) and use after filtration through a 0.45 µm filter membrane. Potassium ferricyanide (renewed weekly): Weigh 0.15 g of potassium ferricyanide and dissolve it in 200 ml of reserve buffer, add 1 ml of 50% Triton X-100, filter through a 0.45 µm filter membrane before use. 4-Aminoantipyrine (renewed weekly): Weigh 0.2 g of 4-aminoantipyrine and dissolve in 200 ml of stock buffer, add 1 ml of 50% Triton X-100, filter through a 0.45 µm filter membrane.
Reagent for distillation: volatile phenol. Buffer solution: Weigh out 3 g potassium dihydrogen phosphate, 15 g disodium hydrogen phosphate and 3 g trisodium citrate dihydrate and dilute to 1000 ml with deionized water. Then add 2 ml of 50% Triton X-100. Chloramine T: Weigh 0.2 g of chloramine T and dilute to 200 ml with deionized water. Chromogenic reagent: Chromogenic reagent A: Completely dissolve 1.5 g of pyrazolone in 20 ml of N,N-dimethylformamide. Developer B: Dissolve 3.5 g of hisonicotinic acid and 6 ml of 5 M NaOH in 100 ml of deionized water. Mix Developer A and Developer B before use, adjust pH to 7.0 with NaOH solution or HCl solution, then dilute to 200 ml with deionized water and filter for later use.
Buffer solution: Dissolve 10 g sodium tetraborate and 2 g sodium hydroxide in deionized water and dilute to 1000 ml. 0.025% methylene blue solution: Dissolve 0.05 g of methylene blue trihydrate in deionized water and make up to 200 ml. Methylene blue stock buffer (renewed daily): dilute 20 ml of 0.025% methylene blue solution to 100 ml with stock buffer. Transfer to a separating funnel, wash with 20 ml of chloroform, discard the used chloroform and wash with fresh chloroform until the red color of the chloroform layer disappears (usually 3 times), then filter. Basic Methylene Blue: Dilute 60 ml filtered methylene blue stock solution to 200 ml stock solution, add 20 ml ethanol, mix well and degas. Acid methylene blue: Add 2 ml of 0.025% methylene blue solution to approximately 150 ml of deionized water, add 1.0 ml of 1% H2SO4 and then dilute to 200 ml with deionized water. Then add 80 ml of ethanol, mix well and degas.
20% polyoxyethylene lauryl ether solution: Weigh out 20 g of polyoxyethylene lauryl ether and dilute to 1000 ml with deionized water. Buffer: Weigh out 20 g of trisodium citrate, dilute to 500 ml with deionized water and add 1.0 ml of 20% polyoxyethylene lauryl ether. Sodium salicylate solution (renewed weekly): Weigh 20 g of sodium salicylate and 0.5 g of potassium ferricyanide nitrite and dissolve in 500 ml of deionized water. Sodium dichloroisocyanurate solution (renewed weekly): Weigh 10 g of sodium hydroxide and 1.5 g of sodium dichloroisocyanurate and dissolve them in 500 ml of deionized water.
Volatile phenol and cyanide standards prepared as solutions of 0 µg/l, 2 µg/l, 5 µg/l, 10 µg/l, 25 µg/l, 50 µg/l, 75 µg/l and 100 µg/l, using 0.01 M sodium hydroxide solution. Anionic surfactant and ammonia nitrogen standard were prepared using deionized water 0 µg/L, 10 µg/L, 50 µg/L, 100 µg/L, 250 µg/L, 500 µg/L, 750 µg/L and 1000 mcg/l. solution.
Start the cooling cycle tank, then (in order) turn on the computer, sampler and power to the AA500 host, check that the piping is connected correctly, insert the air hose into the air valve, close the pressure plate of the peristaltic pump, put the reagent piping into clean water in the middle. Run the software, activate the corresponding channel window and check if the connecting pipes are securely connected and if there are any gaps or air leaks. If there is no leakage, aspirate the appropriate reagent. After the baseline of the channel window becomes stable, select and run the specified method file for discovery and analysis. Instrument conditions are shown in Table 1.
In this automated method for the determination of phenol and cyanide, samples are first distilled at 145 °C. The phenol in the distillate then reacts with basic ferricyanide and 4-aminoantipyrine to form a red complex, which is measured colorimetrically at 505 nm. The cyanide in the distillate then reacts with chloramine T to form cyanochloride, which forms a blue complex with pyridinecarboxylic acid, which is measured colorimetrically at 630 nm. Anionic surfactants react with basic methylene blue to form compounds which are extracted with chloroform and separated by a phase separator. The chloroform phase was then washed with acidic methylene blue to remove interfering substances and separated again in a second phase separator. Colorimetric determination of blue compounds in chloroform at 660 nm. Based on the Berthelot reaction, ammonia reacts with salicylate and chlorine in dichloroisocyanuric acid in an alkaline medium at 37 °C to form indophenol blue. Sodium nitroprusside was used as a catalyst in the reaction, and the resulting color was measured at 660 nm. The principle of this method is shown in Figure 1.
Schematic diagram of a continuous sampling method for the determination of volatile phenols, cyanides, anionic surfactants and ammoniacal nitrogen.
The concentration of volatile phenols and cyanides ranged from 2 to 100 µg/l, linear correlation coefficient 1.000, regression equation y = (3.888331E + 005)x + (9.938599E + 003). The correlation coefficient for cyanide is 1.000 and the regression equation is y = (3.551656E + 005)x + (9.951319E + 003). Anionic surfactant has a good linear dependence on the concentration of ammonia nitrogen in the range of 10-1000 µg/L. The correlation coefficients for anionic surfactants and ammonia nitrogen were 0.9995 and 0.9999, respectively. Regression equations: y = (2.181170E + 004)x + (1.144847E + 004) and y = (2.375085E + 004)x + (9.631056E + 003), respectively. The control sample was continuously measured 11 times, and the limit of detection of the method was divided by 3 standard deviations of the control sample per the slope of the standard curve. The detection limits for volatile phenols, cyanides, anionic surfactants, and ammonia nitrogen were 1.2 µg/l, 0.9 µg/l, 10.7 µg/l, and 7.3 µg/l, respectively. The detection limit is lower than the national standard method, see Table 2 for details.
Add high, medium, and low standard solutions to water samples free of traces of analytes. Intraday and interday recovery and accuracy were calculated after seven consecutive measurements. As shown in Table 3, the intraday and intraday volatile phenol extractions were 98.0-103.6% and 96.2-102.0%, respectively, with relative standard deviations of 0.75-2.80% and 1. 27-6.10%. The intraday and interday cyanide recovery was 101.0-102.0% and 96.0-102.4%, respectively, and the relative standard deviation was 0.36-2.26% and 2.36-5.41%, respectively. In addition, the intraday and interday extractions of anionic surfactants were 94.3–107.0% and 93.7–101.6%, respectively, with relative standard deviations of 0.27–0.96% and 4.44–4.86%. Finally, intra- and inter-day ammonia nitrogen recovery was 98.0–101.7% and 94.4–97.8%, respectively, with relative standard deviations of 0.33–3.13% and 4.45–5.39%, respectively. as shown in Table 3.
A number of test methods, including spectrophotometry15,16,17 and chromatography25,26, can be used to measure the four pollutants in water. Chemical spectrophotometry is a newly researched method for detecting these pollutants, which is required by national standards 27, 28, 29, 30, 31. It requires steps such as distillation and extraction, resulting in a long process with insufficient sensitivity and accuracy. Good, bad accuracy. The widespread use of organic chemicals can pose a health hazard to experimenters. Although chromatography is fast, simple, efficient, and has low detection limits, it cannot detect four compounds at the same time. However, non-equilibrium dynamic conditions are used in chemical analysis using continuous flow spectrophotometry, which is based on the continuous flow of gas in the flow interval of the sample solution, adding reagents in appropriate ratios and sequences while completing the reaction through the mixing loop and detecting it in the spectrophotometer, previously removing air bubbles. Because the discovery process is automated, samples are distilled and retrieved online in a relatively closed environment. The method significantly improves work efficiency, further reduces detection time, simplifies operations, reduces reagent contamination, increases the sensitivity and detection limit of the method.
The anionic surfactant and ammonia nitrogen were included in the combined test product at a concentration of 250 µg/L. Use the standard substance to convert the volatile phenol and cyanide to the test substance at a concentration of 10 µg/L. For analysis and detection, the national standard method and this method were used (6 parallel experiments). The results of the two methods were compared using an independent t-test. As shown in Table 4, there was no significant difference between the two methods (P > 0.05).
This study used a continuous flow analyzer for the simultaneous analysis and detection of volatile phenols, cyanides, anionic surfactants and ammonia nitrogen. The test results show that the sample volume used by the continuous flow analyzer is lower than the national standard method. It also has lower detection limits, uses 80% fewer reagents, requires less processing time for individual samples, and uses significantly less carcinogenic chloroform. Online processing is integrated and automated. The continuous flow automatically aspirates reagents and samples, then mixes through the mixing circuit, automatically heats, extracts and counts with colorimetry. The experimental process is carried out in a closed system, which speeds up analysis time, reduces environmental pollution, and helps ensure the safety of experimenters. Complicated operation steps such as manual distillation and extraction are not needed22,32. However, instrument piping and accessories are relatively complex, and test results are influenced by many factors that can easily cause system instability. There are several important steps you can take to improve the accuracy of your results and prevent interference with your experiment. (1) The pH value of the solution should be taken into account when determining volatile phenols and cyanides. The pH must be around 2 before it enters the distillation coil. At pH > 3, aromatic amines can also be distilled off, and the reaction with 4-aminoantipyrine can give errors. Also at pH > 2.5, the recovery of K3[Fe(CN)6] will be less than 90%. Samples with a salt content of more than 10 g/l can clog the distillation coil and cause problems. In this case, fresh water should be added to reduce the salt content of the sample33. (2) The following factors may affect the identification of anionic surfactants: Cationic chemicals can form strong ion pairs with anionic surfactants. Results may also be biased in the presence of: humic acid concentrations greater than 20 mg/l; compounds with high surface activity (eg other surfactants) > 50 mg/l; substances with strong reducing ability (SO32-, S2O32- and OCl- ); substances that form colored molecules, soluble in chloroform with any reagent; some inorganic anions (chloride, bromide and nitrate) in wastewater34,35. (3) When calculating ammonia nitrogen, low molecular weight amines should be taken into account, since their reactions with ammonia are similar, and the result will be higher. Interference may occur if the pH of the reaction mixture is below 12.6 after all reagent solutions have been added. Highly acidic and buffered samples tend to cause this. Metal ions that precipitate as hydroxides at high concentrations can also lead to poor reproducibility36,37.
The results showed that the continuous flow analysis method for the simultaneous determination of volatile phenols, cyanides, anionic surfactants and ammonia nitrogen in drinking water has good linearity, low detection limit, good accuracy and recovery. There is no significant difference with the national standard method. This method provides a fast, sensitive, accurate and easy-to-use method for the analysis and determination of a large number of water samples. It is especially suitable for detecting four components at the same time, and the detection efficiency is greatly improved.
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Post time: Feb-22-2023