It is said that the Ion Selective Electrodes method, a direct potentiometric approach, is often employed in laboratories to analyze various biological fluids. What are the potential issues and limitations that one could run across when using this strategy? Given that it was regarded as one of those routine tests performed in the laboratory environment, how frequent can these issues occur?
Good day, Ms. Ma. Nicole Cresencio Samillano ! Indeed ISE is one of the most used method in the laboratory because of its ease and efficiency. However, here are the issues or limitations you may encounter when using ISE:
- Effects of interference from other ions in the solution
- Effects of the ionic strength of the solution
- Potential drift during a sequence of measurement
You should also keep in mind that ISE is not ion specific. Meaning, the electrode used in ISE can be more specific to an interfering ion compared to the ion you are aiming to measure. ISE is best used when interfering ions are in trace amounts only. You should also keep in mind that the ionic strength of the solution can reduce the measured activity related to the true concentration when subjected to high concentration. Additionally, the effect of potential drift can easily be seen if a series of standard solutions are repeatedly measured over a period of time.
For more details, you may visit this reference link: Guide to ISE Measurements, Chap. 6) LIMITATIONS and CONSTRAINTS on the application of ISE measurements. (n.d.). https://www.nico2000.net/Book/Guide7.html#:~:text=The%20three%20main%20limitations%20on,during%20a%20sequence%20of%20measurements
ISE analyzers come in two flavors: Indirect, where the sample is diluted before analysis and direct, where it is not diluted. Indirect ISE is less affected by interfering things and the results are proportional to the mass concentration of ions. Direct ISE measures the thermodynamic activity of ions and better reflects their biological effect but the calibration of direct ISE:s is more complicated.