| Total Alkalinity(TA),one of the four parameters of the marine carbonate system,is a measure of buffering capacity of seawater.The community of ocean carbon cycle and acidification requires TA data with high temporal and spatial resolution.The underway TA analyzer is a useful tool to obtain TA data of high spatial resolution.However,the existing analyzers cannot meet the requirements of related marine scientific research and have few practical applications.As a result,this study modified our previously developed Underway Analyzer for Total Alkalinity(UA-TA)to improve its performance and standardized the assembly procedures and performance testing methods of the analyzer.The obtained results are as follows:Improvements have been made with the appearance,internal structure,components,circuits and software of the analyzer.The results show that:(1)The improved UA-TA has a concise and beautiful appearance,a reasonable internal structure and a good thermostat effect,and is more compact;(2)The improvement of the optical path,flow path components and circuits promotes the stability and reliability of the analyzer and expands its functions;(3)The improved software has a friendly interface and simplifies the data processing process,which increases the automation level of this analyzer.The modified UA-TA has been tested in the laboratory frequently,and the results show:(1)The linearity of the analyzer’s working curve is excellent with a linear correlation coefficient(R2)above 0.9995.(2)The precision of the analyzer has been significantly improved.A precision of ±0.21 μmol/kg(n=7)was obtained in a consecutive measurement of one sample in one hour,a precision of ±0.44 μmol/kg(n=165)was obtained in a consecutive measurement of one sample in one day.(3)The accuracy is improved.Evaluated with the standard sample,its accuracy is-0.09±0.51μmol/kg,and evaluated with the Gran titration method,its accuracy is-0.95±1.25μmol/kg.(4)The agreement between two analyzers is-1.70±0.90μmol/kg.(5)There is no obvious drift after 15 days of continuous operation.The improved UA-TA has been tested many times on the research vessels and the shore-based marine station.The results show:(1)The analyzer can run stably and smoothly in the real marine environment for more than 1 month.(2)The accuracy of the analyzer obtained in the field testes is ±0.30～0.60 μmol/kg,but the field accuracy needs further evaluation.In short,the improved analyzer is comparable in precision,accuracy and stability to the commercially available analyzer.Based on the results obtained during the improvement,this study summarized the assembly steps and testing methods and compiled standard operation protocols to provide guidance for the manufacture and inspection of the analyzer.These protocols will ensure the performance of the analyzer and lay a foundation for the application of the analyzer.In addition,a simple method for purifying bromocresol green(BCG)based on liquid-liquid extraction has been developed.The test results showed that the purity of BCG increased from 96.9%to 99.7%when it was purified,and the performance of the analyzer was significantly improved after using the purified BCG. |
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