## 4 Applications of Piezoelectric Materials in Analytical Chemistry
### Solution Measurement  
Nickel dimethylglyoxime has been utilized as a coating by [PERSON] and [PERSON] [155] to detect ammonia in solution. By Utilizing the hydrophobic membranes between both the sample solution as well as the crystal, the effects of moisture were reduced. Alternately, the crystal was moved to the sampling chamber after being allowed to establish equilibrium over a sample of the distilled water. A signal of -135 Hz was produced by 0.15 M of ammonia in water. Up to a value of 0.45 M ammonia, the calibration curve was linear. Sulfur dioxide was determined in the ppb range under identical circumstances utilizing quadrol as the coating. Piezoelectric crystals have been utilized by [PERSON] and colleagues [160; 161] to detect cyanide in solution. AT crystals cut to 9 MHz gold electrodes with silver plating were utilized. An original investigation either used dihydrogen phosphate-borate or a borate-hydroxide buffer to maintain a consistent volume of a sample or a standard solution at pH 9.6. In a water bath, the solution was maintained at a consistent temperature of 25 \({}^{\circ}\)C. For the analysis, the crystal, whose frequency was already determined, was submerged inside this solution for about 15 min while being agitated at 430 rpm. After being removed, the crystal was cleaned with acetone and water before being immersed in a steady stream of 30 \({}^{\circ}\)C air. The frequency was determined after 1 minute. According to reports, cyanide measurement has a linear range from 10\({}^{-7}\) M to 10\({}^{-5}\) M. Ethylenediaminettetraacetic acid (EDTA) was used to remove the cation interferences that formed complexes with cyanide. A preliminary investigation into the utilization of the piezoelectric quartz crystals to evaluate the rate of microbial or fungal growth on their surface was published in Down [162]. The study was unable to quantify any significant alterations brought on by the expansion of these biological systems. It was believed that cells grew very slowly and that the cell membrane was broken by high-frequency vibrations. [PERSON] and [PERSON] [163] used an oscillator equipped with transistors to develop a technique for the determination of the silver concentration in the solution. It was found that this form of oscillator had a much lower frequency drift than an integrated circuit oscillator, which has previously been reported [164]. Silver concentration in solution is measured using a three-electrode deposition system that includes a platinum-plated gold electrode as that of the cathode, a coiled platinum wire as the anode, and a silver chloride as the reference electrode. The test solution is mixed with 1 \(\times\) 10\({}^{-3}\) M EDTA to create a stable combination with the intervening ions in the solution. Mercury (II) was deposited on the electrode even in the presence of EDTA; however, a technique was established for both silver and mercury in the solution. After 10 min of electrodeposition, the silver response was linear, ranging from 10\({}^{-6}\) M to 3 \(\times\) 10\({}^{-5}\) M and from 2 \(\times\) 10\({}^{-7}\) M to 1 \(\times\) 10\({}^{-6}\) M after 1 h.  
[PERSON] and colleagues [165] devised a sensitive method for the determination of iodide in the solution utilizing a silver-plated piezoelectric crystal. First, 11.2 mL (approximately 0.38 oz)/min of a blank solution containing reagent is delivered through the cell until the crystal's frequency has stabilized (F1). The blank solution containing the reagent is added to the cell till the crystal reaches equilibrium (F2) after the sample or the standard solution has been running through it for precisely five minutes. The frequency change (AF), i.e., F = F1 \(-\) F2 is proportionate to the concentration of iodide. A 0.01 M of ammoniacal buffer solution having pH 9.4 containing 2 mM of sodium thiosulfate can then be passed through the cell for over 30 s at 50 Hz to remove the deposited iodide from the electrode (F). At least 30 determinations can be performed before the electrode must be replotted.