Controlling and monitoring the residual activity of QACs is critical for maintaining safe yet effective levels of these agents in the environment. This study investigates the utility of bromophenol blue (BPB) as a safe, rapid and user-friendly indicator to detect in situ residual QACs dried on hard, non-porous surfaces, as well a means to assess their antimicrobial efficacy. At pH 7, BPB has a purple color which turns blue upon its complexation with QACs such as didecyldimethylammonium chloride (DDAC). BPB itself has no antimicrobial properties up to 400 ppm. Within the range of 0 - 400 ppm, BPB color change was tied to specific DDAC antimicrobial performances with a detection threshold of 100 ppm. BPB concentration and application volume could be adjusted such that a color shift from purple to blue correlated with a set percent reduction (>99.9%) in test bacteria (S. aureus and K.aerogenes). The BPB solutions developed in this study yielded similar color shifts on polycarbonate and stainless steel surfaces and did not cross-react with chemical ingredients commonly found in sanitizers and disinfectant products. Overall, this study suggests that BPB provides a simple solution to safely monitor the post application level and biocidal activity of residual dried QACs on surfaces.

中文翻译：

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干燥表面残留季铵化合物的比色检测和使用溴酚蓝的抗菌活性预测

控制和监测 QAC 的残留活性对于维持环境中这些试剂的安全有效水平至关重要。本研究调查了溴酚蓝 (BPB) 作为一种安全、快速和用户友好的指示剂的效用，用于检测在坚硬、无孔表面上干燥的原位残留 QAC，以及评估其抗菌功效的方法。在 pH 值为 7 时，BPB 呈紫色，与 QAC（如二癸基二甲基氯化铵 (DDAC)）络合后变为蓝色。BPB 本身不具有高达 400 ppm 的抗菌特性。在 0 - 400 ppm 范围内，BPB 颜色变化与特定 DDAC 抗菌性能相关，检测阈值为 100 ppm。可以调整 BPB 浓度和应用量，使颜色从紫色转变为蓝色与设定的减少百分比 (>99. 9%）在测试细菌（S. aureus 和 K.aerogenes）中。本研究中开发的 BPB 溶液在聚碳酸酯和不锈钢表面上产生了类似的颜色变化，并且不会与消毒剂和消毒剂产品中常见的化学成分发生交叉反应。总的来说，这项研究表明，BPB 提供了一种简单的解决方案，可以安全地监测表面残留干燥 QAC 的后施用水平和杀菌活性。