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86 PCB007 MAGAZINE I APRIL 2018 brated for any size power supply using a 50 mv shunt. A unit can be built for less than $5 or purchased. Electro-Analytical Techniques (Voltammetric) To perform a typical plating bath analysis, a small volume of sample solution (10−100 mi- croliters) is added to a test cell containing 10 milliliters of a supporting electrolyte solution and three specialized test electrodes. Instru- mentation controls the electrical potential of the working electrode, with respect to that of the reference electrode. If, because of the ap- plied potential, components of the test solu- tion are reduced or oxidized, a current will be measured between the working electrode and counter-electrode. When the appropriate meth- od is applied, different bath components are oxidized or reduced, and the current response is propor- tional to the concentration of the substance being oxi- dized or reduced. The con- centration of a given compo- nent is determined by com- paring the sample response to that of one or more stan- dard solutions of known concentration. Multi-com- ponent analysis is per- formed by scanning the ap- plied potential while record- ing the current responses of the sample. Voltammetric methods employing a con- tinuously renewed mercury drop are formally classified as polarography. Employing scanning or pulse potentials in voltam- metry can determine copper and formaldehyde in electro- less copper, the gold(I) and gold(III) in gold baths, nick- el and cobalt levels in hard gold deposits, tin, lead, sul- fonic acid, and proprietary additives in solder plating baths. The four common techniques of electro- analytical methods are: 1. Voltammogram (square wave voltammetry): measures current as a function of potential. 2. Polarography: voltammetry at the dropping mercury electrode. 3. Differential Pulse Polarography (DPP): forces species in solution to lose or gain electrons, i.e., oxide or reducer; measured versus a reference electrode. DPP determines concentration of species by measuring limiting current. Limiting current determined by concentration in solution. 4. Cyclic stripping voltammetry (CVS): A series of forward and reverse voltage Table 4: Application of the Agilent DAS for PCB chemical analysis compared to the older techniques of titration and atomic absorption spectrophotometer [2,3] . (Source: Printed Circuit Plating Bath Process Control-Part II, Metal Finishing Magazine, March 1985.)