EGTA滴定法测定海水Ca^(2+)浓度精度评估及其在近海海域实测的必要性  

Precision of EGTA titration on seawater Ca ^(2+) concentrationand the necessity for actual measurement in offshore waters

作　　者：张锗 边海珍 任宏伟[1] 胡玉斌 ZHANG Zhe;BIAN Haizhen;REN Hongwei;HU Yubin(Institute of Marine Science and Technology,Shandong University,Qingdao 266237,China)

机构地区：[1]山东大学海洋研究院,山东青岛266237

出　　处：《应用海洋学学报》2023年第3期514-519,共6页Journal of Applied Oceanography

基　　金：国家重点研发计划“全球变化及应对专项”(2020YFA0608304);广东省基础与应用基础研究基金(2021B1515120080);山东大学青年学者未来计划(2018WLJH43)。

摘　　要：海水Ca^(2+)浓度是计算碳酸钙饱和度的重要参数之一,通常由海水钙盐比值计算得出,但该方法在受多种因素影响的近海海域可能不适用。本研究开展了EGTA自动电位滴定法对不同盐度海水Ca^(2+)浓度测定精度和准确度的研究,探究“盐效应”对Ca^(2+)浓度测定可能存在的影响,并比较了近海养殖区海水实测Ca^(2+)浓度与通过钙盐比估算值的差异。研究表明:(1)EGTA自动电位滴定法测定不同盐度海水Ca^(2+)浓度精度较高,在各个盐度条件下,5次平行测定的标准偏差为0.001~0.006 mmol/kg,精度均优于0.1%;(2)在盐度20.00~34.62范围内,Ca^(2+)的实测值与通过钙盐比值计算所得的相对误差为-0.043%~0.023%,准确度在±0.05%内;(3)不同盐度海水样品Ca^(2+)浓度的实测值与理论值基本吻合,电位滴定法测定Ca^(2+)浓度不存在“盐效应”问题;(4)受陆源输入过程的影响,近海(烟台牟平养殖区)表层及底层海水Ca^(2+)的实测值比按钙盐比值的计算值分别高出0.360 mmol/kg和0.333 mmol/kg,表明利用钙盐比值估算法不适用于近海海水中Ca^(2+)浓度,通过实测Ca^(2+)浓度计算近海海水碳酸钙饱和度可以更准确评估近海酸化的程度。Seawater Ca ^(2+)concentration is one of the important parameters for calculating calcium carbonate saturation,which is usually derived from seawater calcium-salinity ratio,but this may not be applicable in offshore waters because of influences of many factors.In this study,the accuracy and precision of Ca ^(2+)concentration determined by automatic potentiometric titration at different salinities were investigated and the potential influence of the“salt effect”was evaluated.The difference between the measured Ca ^(2+)concentration and the estimated value by seawater calcium-salinity ratio in the offshore mariculture area was compared.The results showed that:(1)the precision of Ca ^(2+)concentration determined by automatic potentiometric titration was high at different salinities,with the standard deviations of five replicate determinations ranging from 0.001 to 0.006 mmol/kg,which were better than 0.1%.(2)In the salinity range of 20.00-34.62,the relative errors between the measured and calculated values based on the calcium-salinity ratio of Ca ^(2+)were-0.043%-0.023%,which were within±0.05%.(3)The measured and calculated values of Ca ^(2+)concentration in seawater samples at different salinities agreed with each other,indicating that there was no“salt effect”.(4)The measured values of surface and bottom seawater Ca ^(2+)concentration in Muping Marine Ranching were higher than the calculated ones i.e.0.360 mmol/kg and 0.333 mmol/kg,respectively,which might result from the impact of riverine input.Therefore,calculating the calcium carbonate saturation of offshore seawater by measured Ca ^(2+)concentration can more accurately assess the extent of offshore acidification.

关 键 词：海洋化学 近海海水 海洋酸化 钙盐比 钙离子 电位滴定法 

分 类 号：P734[天文地球—海洋化学]