Department of Chemistry and Chemical Engineering, Queens University Belfast, David Keir Building, Stranmillis Road, Belfast, BT9 5AG, UK.
Analyst. 2019 Oct 21;144(20):5947-5952. doi: 10.1039/c9an01507h. Epub 2019 Sep 25.
A colourimetric vacuum air pressure indicator is described, based on the very low level of CO in air. The indicator uses the pH indicator dye, ortho-cresolphthalein, OCP, which is violet coloured in its deprotonated form and colourless when protonated. When the violet coloured OCP anion is ion-paired with the tetrabutylammonium cation, the product is readily dissolved in a non-aqueous solution containing the polymer ethyl cellulose to create an ink which, when cast and allowed to dry, responds to levels of CO well below that in air, i.e.≪0.041%; the indicator's halfway colour changing point is at 0.062 atm of air at 22 °C, which is interesting in that in food vacuum packaging the pressure in the pack is usually ca. 0.04 atm. The indicator can be used as a qualitative and quantitative indicator of vacuum air pressure. The latter requires the use of digital photography, coupled to RGB colour analysis, in the analysis of the indicator's colour. As with most CO indicators, the indicator's response is temperature sensitive, with ΔH = 78 ± 5 kJ mol. The indicator's 90% response and recovery times to a cycle of vacuum and air are 16.2 and 2.7 min, respectively. The efficacy of the indicator as a vacuum-package integrity indicator for food packaging is illustrated and other potential applications are discussed briefly. This is the first reported example of an ink-based, inexpensive, colourimetric vacuum air pressure indicator.
一种比色真空气压指示器，基于空气中非常低的 CO 水平。该指示器使用 pH 指示剂染料邻甲酚酞，OCP，在去质子化形式下呈紫色，质子化时呈无色。当紫色的 OCP 阴离子与四丁基铵阳离子形成离子对时，产物很容易溶解在含有聚合物乙基纤维素的非水溶液中，形成一种墨水，当浇注并干燥时，对远低于空气中的 CO 水平（即≪0.041%）作出响应，指示剂的半变色点在 22°C 时的空气为 0.062 个大气压，这很有趣，因为在食品真空包装中，包装内的压力通常约为 0.04 个大气压。该指示剂可用作真空气压的定性和定量指示剂。后者需要使用数字摄影，结合 RGB 颜色分析，来分析指示剂的颜色。与大多数 CO 指示剂一样，该指示剂的响应对温度敏感，ΔH = 78 ± 5 kJ mol。该指示剂对真空和空气循环的 90%响应和恢复时间分别为 16.2 和 2.7 分钟。该指示剂作为食品包装完整性的真空包装指示剂的功效进行了说明，并简要讨论了其他潜在应用。这是首例基于墨水的、廉价的、比色真空气压指示剂的报告。
