Sequential extraction of P components (SEDEX) in sediment core M157_41-03, off Namibia@en

A 5-step sequential extraction scheme modified after Ruttenberg (1992), Schenau and De Lange (2000) and Küster-Heins et al., (2010) was used for the speciation of particulate P. Approximately 125mg freeze-dried sediment sample was successively washed with 25 ml of (1) 2 M NH4Cl (pH 7; 4 h; repeat 8 to 10 times), (2) CDB (citrate-dithionite-bicarbonate) buffer solution (pH 7.5; 8 h), (3) 1M sodium acetate buffer solution (pH 4; 6 h), (4) 1 M HCl (24 h) and (5) 1 M HCl (24 h) after ignition for 3 hours at 550 °C. The extracted P components include biogenic P in fish scales, bones and teeth that are mainly composed of hydroxyapatite (PHydap) from step 1, iron-bound P (PFe) from step 2, authigenic apatite (PAuthigenic) from step 3 typically corresponding to carbonate fluorapatite, detrital P (PDetrital) from step 4 and organic P (Porg) from step 5. The sum of these fractions gives the total P content (Ptotal). The P concentration of the solutions was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) with a precision of < 5 %.本研究采用了经Ruttenberg(1992)、Schenau与De Lange(2000)以及Küster-Heins等人(2010)改良的五步连续萃取方案，用于颗粒态磷（particulate P）的形态分级分析。称取约125 mg冻干沉积物样品，依次采用25 mL如下试剂进行萃取：(1) 2 mol/L 氯化铵（NH₄Cl，pH=7，萃取4 h，重复8~10次）；(2) 柠檬酸钠-连二亚硫酸钠-碳酸氢钠（CDB，citrate-dithionite-bicarbonate）缓冲液（pH=7.5，萃取8 h）；(3) 1 mol/L 乙酸钠（sodium acetate）缓冲液（pH=4，萃取6 h）；(4) 1 mol/L 盐酸（HCl，萃取24 h）；(5) 样品经550 ℃灼烧3 h后，再用1 mol/L 盐酸（HCl）萃取24 h。萃取得到的磷组分包括：第1步萃取的以羟基磷灰石（hydroxyapatite）为主要成分的鱼鳞、骨骼及牙齿中的生物源磷（PHydap）；第2步萃取的铁结合态磷（PFe）；第3步萃取的通常对应碳酸盐氟磷灰石（carbonate fluorapatite）的自生磷灰石（PAuthigenic）；第4步萃取的碎屑态磷（PDetrital）；第5步萃取的有机磷（Porg）。各分级组分的含量之和即为总磷含量（Ptotal）。采用电感耦合等离子体光学发射光谱法（inductively coupled plasma optical emission spectrometry, ICP-OES）测定萃取液中的磷浓度，测定精度小于5%。