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Modeling Methylene Blue Aggregation in Acidic Solution to the Limits of Factor Analysis

机译:在因素分析极限下模拟酸性溶液中的亚甲基蓝聚集

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Methylene blue (MB~+), a common cationic thiazine dye, aggregates in acidic solutions. Absorbance data for equilibrated solutions of the chloride salt were analyzed over a concentration range of 1.0 × 10~(-3) to 2.6 × 10~(-5) M, in both 0.1 M HCl and 0.1 M HNO_3. Factor analyses of the raw absorbance data sets (categorically a better choice than effective absorbance) definitively show there are at least three distinct molecular absorbers regardless of acid type. A model with monomer, dimer, and trimer works well, but extensive testing has resulted in several other good models, some with higher order aggregates and some with chloride anions. Good models were frequently indistinguishable from each other by quality of fit or reasonability of molar absorptivity curves. The modeling of simulated data sets demonstrates the cases and degrees to which signal noise in the original data obscure the true model. In particular, the more mathematically similar (less orthogonal) the molar absorptivity curves of the chemical species in a model are, the less signal noise it takes to obscure the true model from other potentially good models. Unfortunately, the molar absorptivity curves in dye aggregation systems like that of methylene blue tend to be sufficiently similar so as to lead to the obscuration of models even at the noise levels (0.0001 ABS) of typical benchtop spectrophotometers.
机译:亚甲基蓝(MB〜+)是一种常见的阳离子噻嗪染料,在酸性溶液中聚集。在浓度为1.0×10〜(-3)至2.6×10〜(-5)M的0.1 M HCl和0.1 M HNO_3中,分析了氯化盐平衡溶液的吸光度数据。原始吸光度数据集的因子分析(通常比有效吸光度更好)是确定的,至少有三种不同的分子吸收剂,与酸类型无关。具有单体,二聚体和三聚体的模型可以很好地工作,但是广泛的测试已经产生了其他几个好的模型,其中一些具有更高阶的聚集体,有些具有氯阴离子。好的模型之间常常因拟合质量或摩尔吸收率曲线的合理性而彼此无法区分。模拟数据集的建模演示了原始数据中的信号噪声掩盖了真实模型的情况和程度。特别地,模型中化学物质的摩尔吸收率曲线在数学上越相似(正交性越小),则将真实模型与其他潜在良好模型相混淆所需的信号噪声就越少。不幸的是,染料聚集系统(如亚甲基蓝)的摩尔吸收率曲线趋于足够相似,即使在典型台式分光光度计的噪声水平(0.0001 ABS)下,也会导致模型模糊。

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