Determination of quaternary ammonium salts in seawater by UV-spectrophotographyLi Yahong *, Hou Chunyang, Wu Jie, Chen ChongThe inst. of Seawater Desalination and Multipurpose Utilization, SOA, Tianjin (300192)E-mail: flyllyh@Abstract: Water treatment agent quaternary ammonium salts has been applied widely as an effective biocide in marine Red-Tide control and cooling seawater systems. The paper researched on the reliability of determination of quaternary ammonium salts in seawater by UV-spectrophotography. The UV spectrum scanning showed that the different concentration seawater is non-interference on the largest absorption peak of quaternary ammonium salts. The calibration curves of quaternary ammonium salts were linear(r=0.999) indistilled water and seawater. Three linear regression equation is consistent (SE=6.51%(1N),SE=12.61%(2.5N)). Therefore, the standard curve of D.W. solution is suitable for determination of quaternary ammonium salts in seawater. The method is simple and reliable, which can be used to effectively monitor appliance and discharge of quaternary ammonium salts in marine environment and cooling seawater systems.Keywords: UV- spectrophotography, seawater, quaternary ammonium salts1IntroductionQuaternary ammonium salts(QAS)，a cationic surfactant, is an effective biocide in industrial water and wastewater treatment and marine Red-Tide control, which can change the permeability of bacterial cytoplasm membrane, cause the cell material exosmosis, hinder its metabolism and kill bacterium finally. In recent years, with seawater utility technologies' development and application, water treatment agent QAS has been widely used in seawater utility. In order to protect marine environment, effectively monitor of the content in seawater utility systems, and scientifically guide on applying and discharging, it is necessary to establish an effective quantitative method for determination of the QAS content in seawater.QAS has the characteristic absorption peak in the ultra-violet spectrograph area and shows linear correlation between concentration and absorption at 263 nm wavelength. The method showed better precision and stability in analyzing medical disinfectants benzalkonium bromide [1-3].The paper studied on interference of seawater and the reliability of determination of quaternary ammonium salts in seawater by UV-spectrophotography.2Instruments and MaterialsUltraviolet spectrophotometer (UV2102，Unico(Shanghai) Instrument Co., Ltd); Quaternary ammonium salt standard comparison (purity≥99.0%, Fluka); TS-781 (Tianjin chemical research & design institute), 1227 (Tianjin Biaomian chemical auxiliary reagent factory); Seawater (Tangku purifies treatment plant), Distilled water.3Methods and ResultsThese instructions apply to everyone, regardless of the formatter being used.-1-3.1Wavelength scanThe seawater quality has regional difference. Concentrated seawater in seawater utility systems is different from seawater in marine. Distilled water as a reference, the ultraviolet scanning of seawater with different concentration ratio and QAS standard comparison were conducted in the range of 200nm~300nm. Figure 1 showed that the absorption wavelength of different concentration ratio seawater was at 212nm or 221nm. QAS has a few of ultraviolet absorption peaks, respectively at 224nm, 254nm, 258nm, 263nm and 269nm. The absorption of QAS at 258nm or 263nm wasn’t interfered by seawater.From Fig1, QAS’s maximum absorption spectra was at 258nm identical with Yan’s report on benzalkonium bromide [1,2], but not coincide with most literatures reporting in 262~263nm[3,4]. The wavelength of 263nm was selected in the following experiments.Fig1: The UV spectrum scanning of seawater and quaternary ammonium salts3.2Effect of seawater on QASs determent by UV-spectrophotography3.2.1Stability experimentThe absorption of QAS comparison solution of 250mg/L was detected respectively at 263nm after 0h, 2h and 16h at the room temperature. The result showed that QAS solution was stable in 16h and RSD was 0.19%.3.2.2 Calibration curveQAS comparison was weighed precisely by 0.1000g to prepare 100mg/L standard comparison solution respectively with distilled water and aseptic seawater. The absorption at 263nm was detected respectively with distilled water and aseptic seawater as reference. The calibration curves had good linear relation. The standard curve prepared by distilled water in the range from 0mg/L to 100mg/L was linear with r=0.9997; the linear ranges of seawater solution were 0mg/L～50mg/L, with r=0.999.Fig2: The calibration curves of quaternary ammonium salts-2-Table1: The linear regression equation of quaternary ammonium saltsLINEAR REGRESSION EQUATION CORRELATION COEFFICIENT Distilled water C = 472.37A - 0.5848 0.9997（ｎ=10）1N Seawater C = 501.67A - 0.167 0.9995（ｎ=5）2.5N Seawater C = 525.21A+ 0.2277 0.9989（ｎ=5）Two QAS seawater calibration curves (Y) were compared with that of distilled water (X) by relative deviation (SE%=︱Y-X︱/X) to evaluate the consistency of three calibration curves with the allowance error scope 1/4 as standard. Figure 3 indicated that the relative deviation between the linear equations increased with the seawater concentration ratio (1~2.5N) increasing in the range from 10 mg/L to 50mg/L. Comparison between 1N seawater curve and distilled water one, the average relative deviation（SE）was 6.51% and was12.61% to 2.5N seawater curve, below 1/4, which imply that three linear regression equations were consistent.The seawater concentration ratio was below 2.5N normally in cooling seawater technology with current engineering, therefore, the method was reliable directly calculating the content of QAS in seawater based on the calibration curve of distilled water.3.2.3 Average recovery rateThe average recovery experiment was similarly used to evaluate the reliability of the calibration curve by distilled water. QAS solution of 40mg/L was prepared respectively with distilled water and sea water of different concentration ratio and the absorption was measured at 263nm. The results was perfect with the average recovery of 94.95% and RSD 1.9% according to the linear regression equation C = 472.37A - 0.5848, which indicated that it was reliable to determinate the content of QAS in seawater of different concentration ratio by C = 472.37A - 0.5848.Fig4: The average recovery of quaternary ammonium salts in seawater with different concentration rate-3-3.3Determination of two water treatment reagent QAS from marketTwo water treatment reagent QAS were bought from market as experimental samples. The samples solutionof 1000mg/L was prepared respectively with distilled water and seawater and determinated by sodium tetraphenylboron method（HG/T2230-2006）and UV-spectrophotography. From table2, we can see that themethod of UV- spectrophotography was also reliable with the relative deviation of less 1.24% compared withsodium tetraphenylboron method.Table2: Contents of quaternary ammonium salts by sodium tetraphenylboron method and UV- spectrophotographyWATER TREATMENT REAGENT QASFROM MARKETMETHODTS-781 1227Sodium tetraphenylboron method 35.6 49.0UV- spectrophotography 36.04 48.79SE% 1.240.43 4DiscussionBear's law was obeyed for 0 mg/L ~50mg/L of QAS in complex seawater and 0 mg/L ~100mg/L in distilledwater at 263nm and the correlation coefficient was 0.999.The calibration curve by distilled water was suitable for the quantitative analysis of QAS in seawater bydifferent concentration ratio. The average recovery was perfect and the result precision of QAS’sUV-spectrophotography wasn’t interfered by seawater. The linear range of 0 mg/L ~100mg/L can meet toreal engineering need. Obviously, compared with ones by seawater with different quality in different detectedsystems, it was also reliable and more simply that the calibration curve by distilled water was applied directlyto determinate the content of QAS in seawater. The UV-spectrophotography method became more flexibleand convenient when the calibration curve by distilled water can be used directly for determination of theQAS content in seawater in marine environment and cooling seawater.References[1] Yan Zhenyu, Jiang Xinmin, Wang Chaohui. (2000) Determination of liqour benzalkori bromidum contents by Bmethod in UV spectrum Chinese Journal of Modern Applied Pharmacy,17(2):132-134(in Chinese)[2] Lu Xiao-Ying, Long Zi-Jin. (2002) Determination of 0.1％ benzalkonium bromide solotion content by ultravioletspectrophotometry Anhu Medial Pharma J 6(2):50-51(in Chinese)[3] Tu Jinlang, Rao Dan, Huang Xiaofang et al. (2001) Determination of benzalkonium bromide solotion content byultraviolet spectrophotometry Journal of Guiyang Medical College 26(2):177(in Chinese)[4] Pan Jianyu，Yin Pinghe，Zhao Ling et al. (2003) Spectrophotometer detection of benzalkonium bromideconcentration in seawater Chinese Journal of Applied Ecology 14(7):1203-1204(in Chinese)-4-。