Chemometrics-assisted cross injection analysis for simultaneous determination of phosphate and silicate

This work presents a novel method for simultaneous spectrophotometric determination of phosphate and silicate by using a cross injection analysis (CIA) coupled with the use of partial least squares (PLS) for data evaluation. The detection principle is based on the well-known <i>‘molybdenum blue’</i> method. The molybdate ions in the presence of stannous chloride in acidic medium give phosphomolybdenum blue and silicomolybdenum blue as products. In this work, all the liquids, including sample and reagents were simultaneously introduced into a CIA platform by using two peristaltic pumps for controlling the x-channel and y-channel flow which was automatically manipulated by using in-house control board. Crossflow provides sufficient mixing inside the platform prior detection of the absorption spectra of blue complexes in the wavelength of 400–900 nm. Since spectra of the blue colour product of phosphate and silicate are resemblant, these two analytes therefore reciprocally interfere with one another. This results in difficulty in simultaneous analysis of phosphate and silicate. In this work, PLS was utilised as assistor of CIA system for simultaneous analysis of phosphate and silicate using molybdenum blue reaction without using any modification of reagents and addition of selective masking agent. The calibration ranges are 0.1–6 mgP L⁻¹ and 5–100 mgSi L⁻¹ for phosphate and silicate, respectively. By using CIA coupled with PLS for data evaluation, the analysis of two analytes was achieved within 1.5 min with only single injection. The developed system was applied to natural water samples and the system was validated with the conventional methods. By statistical paired <i>t</i>-test, there was no evidence of significant difference at 95% confidence level (<i>t</i>_stat = 2.28, <i>t</i>_critical = 2.31 and <i>t</i>_stat = 0.62, <i>t</i>_critical = 2.31 for phosphate and silicate, respectively). This implied that the chemometrics-assisted CIA system was successfully developed for simultaneous spectrophotometric determination of phosphate and silicate.

本研究提出一种全新方法，可结合交叉注射分析（cross injection analysis, CIA）与偏最小二乘（partial least squares, PLS）进行数据解析，实现磷酸盐与硅酸盐的同时分光光度测定。该检测原理基于经典的钼蓝法：在酸性介质且氯化亚锡存在的条件下，钼酸根离子会生成磷钼蓝与硅钼蓝两种产物。本研究中，通过两台蠕动泵分别控制x通道与y通道的流体流量，并借助自研控制板实现自动操控，将包括样品与试剂在内的所有液体同步引入CIA平台。交叉流可在平台内部实现充分混合，随后在400~900 nm波长范围内检测蓝色配合物的吸收光谱。由于磷酸盐与硅酸盐生成的蓝色产物光谱相似，两种分析物会相互产生干扰，这给二者的同时分析带来了困难。本研究将PLS作为CIA系统的辅助工具，无需对试剂进行任何改性或添加选择性掩蔽剂，即可依托钼蓝反应实现磷酸盐与硅酸盐的同时分析。磷酸盐与硅酸盐的校准范围分别为0.1~6 mgP·L⁻¹与5~100 mgSi·L⁻¹。通过将CIA与PLS数据解析相结合，仅需单次进样即可在1.5分钟内完成两种分析物的检测。所开发的系统已应用于天然水样检测，并通过传统方法完成了系统验证。经配对t检验，在95%置信水平下未发现显著差异（磷酸盐的t统计量=2.28，临界t值=2.31；硅酸盐的t统计量=0.62，临界t值=2.31）。这表明，依托化学计量学辅助的CIA系统已成功实现磷酸盐与硅酸盐的同时分光光度测定。