A Simple Constant‐Force Pocket Probe

A constant‐force pocket probe is constructed by application of a constant‐force spring. This is wound on two cylinders in reverse‐winding mode. As the distance to the probe top is constant, a constant force is obtained. Very little experience is needed to master the rotating of the handle while using the probe

Potentiometric detection of creatinine in the presence of nicotine: Molecular recognition, sensing and quantification through multivariate regression

Systematic errors in the calix [4] pyrrole-based potentiometric detection of creatinine have been observed in heavy smokers. This work further characterizes the interactions between the nicotinium cation and the cavitand as well as the resulting interference produced during the potentiometric detection. It is found that the nicotinium cation binds the electronic rich aromatic cavity defined by the pyrrole rings of the receptor's cone conformation with an estimated binding constant higher than 10 124\u202fM 121 in methylene chloride. On the other hand, the creatininium cation is preferentially included in the hydrophobic aromatic cavity of the ionophore by establishing hydrogen bond interactions with the pyrrole NHs groups. Potentiometric calibrations confirmed the detection of the nicotinium cation at neutral and acidic pH, respectively. Due to the lower pka of creatinine, a methodology to quantify creatinine in presence of nicotine by using an array of three sensors at two pH values is proposed. A partial least square regression was performed and reported recoveries of 103% with a standard deviation of 20%. The improved determination of creatinine was therefore discussed. This approach represents a step forward in the development of effective approaches to improve the measurement of creatinine in decentralized settings