Simplified seawater alkalinity analysis: Use of linear array spectrometers

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• 作者：Yao ; Wensheng ; Byrne ; Robert H.
• 刊名：Deep Sea Research Part I: Oceanographic Research Papers
• 出版年：1998
• 出版时间：August, 1998
• 年：1998
• 卷：45
• 期：8
• 页码：1383-1392
• 全文大小：478 K

文摘

Modified spectrophotometric procedures are presented for the determination of seawater total alkalinity using rapid scan linear array spectrometers. Continuous monitoring of solution pH allows titrations to be terminated at relatively high pH, whereby excess acid terms are very small. Excess acid concentrations are quantified using the sulfonephthalein indicators, bromocresol green and bromocresol purple. The outlined spectrophotometric procedures require no thermal equilibration of samples. Using bromocresol green, solution pH_T ([H⁺]_T in moles per kg of solution) is given as: Formula Not Shown − log(1 − 0.001005S) and R(25) = R(t){1 + 0.00909(25 − t)}, where 29 ≤ S ≤ 37, 13°C ≤ t ≤ 32°C, and R(t) is the absorbance ratio (A₆₁₆/A₄₄₄) at temperature t and salinity S. Using bromocresol purple, the solution pH_T is given as pH_T = 5.8182 + 0.00129(35 − S) + log((R(25) − 0.00381)/(2.8729 − 0.05104R(25))) and R(25) = R(t){1 + 0.01869(25 − t)}, where 29 ≤ S ≤ 37, 13°C ≤ t ≤ 32°C, and R(t) = A₅₈₉/A₄₃₂. Alkalinity measurements using bromocresol purple had a precision on the order of 0.3 μmol kg^−1 and were within 0.3-0.9 μmol kg^−1 of the alkalinities of certified seawater reference materials.