基于顺序注射分析的海水亚硝酸盐快速检测方法研究

A Study of Fast Detection of Nitrite in Seawater Based on Sequential Injection Analysis

为实现海水亚硝酸盐的快速检测,使测量过程更适用于在线监测,对前期已有的顺序注射分析技术进行了优化,结合自主研制的Z型高灵敏度液芯波导样品池和多适应环管器,基于分光光度检测方法,在不完全显色反应的基础上,建立了一种海水亚硝酸盐快速全自动检测方法。进样技术中高精度注射泵与多通道选择阀配合,顺序吸入样品和试剂至储液盘管后,再反推至混合盘管,期间发生不完全显色反应,并最终由注射泵将显色混合溶液缓推过Z型液芯波导样品池,同步流动检测溶液吸光度变化,结合朗伯比尔定律最终获取待测亚硝酸盐溶液浓度。为达到稳定且快速分析的目的,分析了测量方法中几个关键参数,如不完全显色反应时间、检测时流速和盐度对测量结果的影响,寻求最佳的技术及参数组合。不完全显色反应研究结果表明,在10～60s显色时间范围内,吸光度检测结果的相对标准误差(RSD)均不超过1.64%,说明10～60s的显色时间对本方法无影响,因此选择10s作为快速检测方法的显色反应时间。通过对不同流速情况下样品检测结果的分析发现,流速过快会导致检测不稳定,过慢则不利于快速分析,选择吸光度测量较为稳定的10,11.6,13和15μL·s-1四个流速,对测量结果的稳定性和重复性进行分析,结果表明,上述四个流速下的线性效果都很好,因此,选择最快的15μL·s-1作为该方法的检测流速。为验证该方法对盐度的敏感性,以适应淡水和大范围海水为出发点,研究分析了0～35盐度范围内,三种不同浓度(150,250,350μg·L-1)亚硝酸盐溶液的吸光度变化情况,得到的RSD分别为1.39%,2.03%和1.28%,证明盐度对本方法的吸光度测量基本无影响。对80,150和250μg·L-1亚硝酸盐标准溶液平行测定11次得到的RSD分别为2.13%,1.07%和1.83%,说明本方法精密度较好。通过对空白样品进行10次平行样测量,计算得到本方法检出限为37μg·L-1(约0.5μmol·L-1)。为验证本方法的可信度,利用该快速检测方法和《海洋调查规范》标准测量方法对同一批次亚硝酸盐标准溶液制作标准曲线,二者的R2均大于0.999,对同一浓度样品两种方法得到的测量结果数据拟合线性回归方程为y=1.046 1x-0.005 7,R2=0.999 6,说明两种检测方法结果高度一致,更进一步验证了该研究快速测量方法的可行性和可靠性。亚硝酸盐快速检测方法测样速率高达50样·h-1,与传统的人工检测和流动注射分析方法相比,亚硝酸盐的测量耗时从十几分钟缩短到1min左右,检测分析过程中样品和试剂消耗量极少,测量过程重复性好,整个测量过程全自动进行,操作更为简单智能,避免了人工介入带来的误差,使得基于分光光度的营养盐要素在线及原位检测系统更加小巧、快速和低耗,更适用于现场在线及长时间序列监测,具有很广的应用范围和较好的应用前景。

An automatic fast determination method of nitrite in seawater was developed by optimizing the previous self-research of sequential injection analysis(SIA),combining our self-developed Z-type liquid waveguide capillary cell(LWCC)flow cell and tubing-looper,using spectrophotometry and incomplete chromogenic reaction to accomplish the automatic fast determination and make its measurement process more suitable for in-situ analysis and monitoring.The heart of the injection technology is a highprecision syringe pump and a multiposition valve(MVP).Cooperating with MVP,the syringe pump inhales samples and reagents in a holding coil in sequence,and then reversely pushes the mixed solution to the mixing coil and an incomplete chromogenic reaction occurred during this period.The syringe pump finally slowly pushes the mixed solution through the Z-type LWCC flow cell,meanwhile,the absorbance changes of flow solution is detected by a spectrometer,and the nitrite concentration of sample is acquired with Lambert-Beer law.Several key parameters of the fast detection method,such as incomplete chromogenic reaction time,flow rate of mixed solution during detection and salinity were analyzed for stable and fast analysis purposes.The study on the incomplete chromogenic reaction shows that the relative standard deviations(RSDs)of absorbance measurement results are all less than 1.64%within 10~60sreaction time,indicating the chromogenic reaction time of 10~60shas no effect on the fast detection method,therefore,10 sis selected as the fast detection method chromogenic reaction time.The research of mixed solution’s flow rate during detection shows that the flow rate has a large effect on the absorbance detection.Rapid flow rate influences the detection instability,and slow flow rate is not conducive to the fast detection.The stability and repeatability of absorbance measurement results are analyzed under the speeds of 10,11.6,13 and 15μL·s^-1,which are relatively stable on absorbance measurement on the basis of experimental verification.The analysis results indicate that the linearity under the above four flow rates are all good,so the fastest speed 15μL·s^-1 is selected for the fast detection method.The absorbance changes of three different concentrations of nitrite(150,250,350μg·L^-1)in the 0~35salinity range are analyzed to verify the sensitivity of this fast detection method to salinity and the adaptation to freshwater and the wide range of seawater.The RSDs are 1.39%,2.03%and 1.28%respectively,indicating that salinity has no effect on this method.The RSDs measured of parallel 80,150,and 250μg·L^-1 nitrite standard solutions for 11 times are 2.13%,1.07%and 1.83%respectively,indicating that this fast detection method has a good precision.The detection limit of this method acquired by taking 10 parallel samples of blank samples is37μg·L^-1(about 0.5μmol·L^-1).In order to verify the credibility,the standard curves of same batch nitrite standard solutions are made by using the fast detection method in this paper and the standard method in"Specifications for oceanographic survey".The R2 of above two methods are both greater than 0.999,and the linear regression equation of the measurement data obtained by the two methods of same concentration sample is y=1.046 1x-0.005 7with the R2=0.999 6,which shows that the results of the two methods are highly consistent,further verifying the feasibility and reliability of the fast detection method in this paper.The determination rate of this method is up to 50samples·hour-1.Compared with the traditional manual detection method and flow injection analysis method,the nitrite fast detection method in this paper shortens the time-consumed from a dozen minutes to a minute or so,reduces the sample and reagents consumption in the entire detection process.The fast detection method has a good repeatability,and the whole measurement process is fully automated,and the operation is simpler and more intelligent,which avoids the error caused by manual intervention and makes the nutrients online and in-situ detection system based on spectrophotometry more compact,fast and low-consumption,which is more suitable for in-situ and long time monitoring.The fast detection method in this paper is applicable to other seawater nutrients as long as it is slightly adjusted,having a wide range of applications and good application prospects.