What Is an Ion Analyzer?
Ion Analyzer is a general term for devices that measure various ions.
While ion counters generally refer to devices that measure ions in the air, ion analyzers include specialized devices such as mineral-specific ion analyzers and devices that measure ion concentrations in aqueous solutions.
However, as a general interpretation, except in specialized fields, ion counters and Ion Analyzers are nearly synonymous. Therefore, this article describes devices that measure ion concentrations exclusively for minerals and in aqueous solutions.
Uses of Ion Analyzers
Ion Analyzers are used to measure the concentration of ions around minerals that contain radioactive materials. Ion Analyzers dedicated to minerals are used in such cases. Mineral-specific ion analyzers are unaffected by air flow, and can make stable measurements with little variation from one measurement to the next. Applications for mineral ion measurement include research, investigation of new construction materials, and the creation of mineral bracelets.
In addition to minerals, Ion Analyzers are also used to measure ion concentrations in aqueous solutions. Ion Analyzers are used, for example, to control the concentration of impurities emitted from wastewater facilities or in product development (e.g., Ag+) when using materials containing ions.
Principle of Ion Analyzer
The mineral-specific type detects radiation emitted from minerals and converts it to ionic content. Commercially available types take several tens of seconds after the object to be measured is placed under the analyzer, and display the average number of ions detected during that time. Due to the measurement principle, it is not possible to measure minerals that do not emit radiation.
The principle of measuring ion concentrations in aqueous solution originated in high-performance ion-exchange chromatography, which was first published in 1975. Although the field is relatively young, a wide variety of detection methods have been developed in just a few decades. Currently, the most common commercially available instrument is the absorbance spectrophotometric method, which can be miniaturized.
There are three types of absorbance spectrophotometers (UV Analyzers), which are used depending on the UV absorption or non-absorption of the sample’s ions:
1. Direct UV Method
The direct UV method uses an eluent with no or low UV absorption to measure sample ions with UV absorption.
2. Indirect UV Method
The indirect UV method is used to analyze sample ions with no UV absorption using eluents with UV absorption.
3. Post-Column Reaction IAS Method
In the post-column reaction IAS method, sample ions are separated and mixed with a reaction reagent to convert them to UV-absorbing compounds before detection.
The direct UV and indirect UV methods are relatively easy to use, while the post-column reaction single-absorption spectrophotometry is not suitable for general use due to the time and effort required to prepare the sample separately.
Other Information on Ion Analyzers
1. Measurement Range of Ion Analyzers
Ion Analyzers can measure ion concentrations in the range of 10-1 to 10-7 mol/L. However, since the measurement range varies depending on the type and structure of the ion electrode, it is necessary to establish a standard using a standard solution before measuring samples.
2. Influence of External Factors on Ion Measurement
When measuring ions, the following five external factors influence the measurement:
pH (potential of hydrogen) Factor
Depending on the type and structure of the ion electrode, the pH of the sample may affect the components of the ion response, causing the ion electrode to dissolve or the electrode potential to change. In addition, the sensitivity of the ion electrode may be reduced or the calibration curve may shift in parallel due to the effect of pH.
Therefore, the pH range over which ion measurements can be performed should be considered limited. The sample pH range over which ion measurements can be made generally narrows as the target ion concentration decreases.
Temperature Factor
The potential gradient measured by an ion electrode is affected by the temperature of the sample itself. Therefore, the liquid temperature of the reference standard solution and the liquid temperature of the sample must be equal. If the liquid temperatures of the reference solution and the sample differ, the measurement results will be affected.
Agitation Factor
The state of agitation of the sample solution has an effect on the electrode potential, response time of the measurement results. Therefore, the sample must be stirred at a constant speed that does not adversely affect the measurement itself.
Light Factor
Some ion electrodes are affected by light, which changes the potential of the electrode and affects the measurement results. Therefore, when measuring ion electrodes that are affected by light, light must be shielded using a light-shielding beaker.
Coexistent Ion Factor
Ion electrodes are highly ion selective, but there is no ion electrode that is unaffected by all ions. Therefore, the influence of coexisting ions on the ion electrode should be considered, and measures should be implemented to avoid such influence as much as possible.