Modeling Methylene Blue Aggregation in Acidic Solution to the Limits of Factor Analysis
Modeling Methylene Blue Aggregation in Acidic Solution to the Limits of Factor Analysis
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DOI：
10.1021/ac303271m
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发表时间：
2013-01-15
影响因子：
7.4
通讯作者：
Vander Griend, Douglas A.
中科院分区：
文献类型：
--
作者：
Golz, Emily K.;Vander Griend, Douglas A.
亚甲蓝（MB+）是一种常见的阳离子噻嗪染料，在酸性溶液中聚集。在0.1 M HCl和0.1 M HNO 3中，在1.0 x 10（-3）至2.6 x 10（-5）M的浓度范围内分析氯化物盐平衡溶液的吸光度数据。原始吸光度数据集的因子分析（分类上比有效吸光度更好的选择）明确显示，无论酸类型如何，至少有三种不同的分子吸收剂。具有单体、二聚体和三聚体的模型工作良好，但广泛的测试产生了其他几个良好的模型，一些具有更高阶的聚集体，一些具有氯离子。好的模型往往无法通过拟合质量或摩尔吸光系数曲线的合理性来区分。模拟数据集的建模展示了原始数据中的信号噪声掩盖真实模型的情况和程度。特别是，模型中化学物质的摩尔吸光率曲线在数学上越相似（正交性越小），从其他潜在的好模型中模糊真实模型所需的信号噪声就越少。不幸的是，染料聚集系统中的摩尔吸光系数曲线，如亚甲蓝的摩尔吸光系数曲线，往往是足够相似的，从而导致模糊的模型，即使在典型的台式光谱仪的噪声水平（0.0001 ABS）。
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 x 10(-3) to 2.6 x 10(-5) M, in both 0.1 M HCl and 0.1 M HNO3. 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.