ph indicator

Bromothymol Blue 是 pH 指示剂，在测定弱酸弱碱时使用，在酸性条件下为黄色，在碱性条件下为蓝色。

Methyl orange is a pH indicator frequently. It is used in titration because of its clear and distinct colour variance at different pH values.

Quin-2 is a high-affinity fluorescent calcium indicator (Kd = 115 nM for calcium). It displays high selectivity for calcium, as it is not affected by sodium gradients, membrane potential, or intracellular pH. High affinity probes like quin-2 are ideal for monitoring low levels of calcium, as are found in resting cells. Loadings of up to 2 mM quin-2 are without serious toxic effects, so quin-2 may be used to buffer intracellular calcium transients. Excitation emission maxima for quin-2 are 339 and 492 nm, respectively.

Methyl yellow（Solvent Yellow 2）为pH指示剂，该化合物在pH低于4.0时显红色，高于4.0时转为黄色。

alpha-Naphtholphthalein 是一种指示剂，在 pH 6 时为浅黄色，随着 pH 增加逐渐呈现明显的颜色变化，变为浅绿-绿-蓝色。alpha-Naphtholphthalein 可浸入棉混纺织物中，用于开发伤口 pH 监测医疗用品（如医用纱布、病服和压缩绷带等）。

Bromophenol blue sodium是pH值指示剂，pH值为3.0时为黄色，pH值为4.6时为蓝色。Bromophenol blue sodium还用作跟踪染料，监测琼脂糖凝胶电泳和聚丙烯酰胺凝胶电泳的过程。

Methyl red hydrochloride 是一种偶氮染料，用作 pH 指示剂。在 pH 值 4.4 时呈红色，而在 pH 值 6.0 时为黄色。

Litmus 是一种 pH 指示剂，当 pH 值为 4.5 时呈红色，而在 pH 值为 8.3 时呈蓝色。