Differential Pulse Voltammetry Explained
Learn what differential pulse voltammetry is.
Explore the mechanism of differential pulse voltammetry.
Find out how to build a differential pulse voltammetry circuit.
Too salty. Too bland. Those are the two common complaints from the kids when I tried making their favorite chicken broth. Now, if you know anything about Asian cooking, there’s never a strict level of measurement of how much salt should go into the broth. Moms and even professional cooks always go by experience.
After my last failed chicken broth, I decided to take baby steps when adding the salt. I tried sampling the broth after each half teaspoon to get the perfect taste. Guess what? It works. I guess that’s why differential pulse voltammetry follows a similar concept when used in analyzing chemical reactions.
What Is Differential Pulse Voltammetry?
Voltammetry refers to methods of asserting a varying level of voltages across electrodes and measuring the resulting current that flows through the electrolytes. Samples are taken over a certain period to establish the relationship of voltage potentials (E), current (i), and time (t).
There are a few types of voltammetry techniques, which contrast with each other based on the variance of voltage-level patterns that are applied. Differential pulse voltammetry, specifically, is a type of linear sweep voltammetry, or staircase voltammetry, where a series of pulses is applied to the electrode with sequential increasing baseline voltage. The system samples the current right before the next pulse is applied.
Below, you’ll see how the increasing baseline voltage of differential pulse voltammetry pulses derives from staircase voltammetry in appearance:
Voltage pulses for differential pulse voltammetry
Differential pulse voltammetry is preferred because its differential nature helps to minimize the effect of background charging current during analysis. The short pulses make the technique highly sensitive, which gives it the accuracy advantage of at least one part-per-billion during an analysis.
The highly-sensitive nature of differential pulse voltammetry makes it a useful chemical analysis method in real-life scientific applications, such as this published study, where it was found to be effective in separating tocopherols from commercial fish oil.
Now that we understand what differential pulse voltammetry is, we’ll take a look at the mechanism of it and the parts that make up the setup.
The Mechanism of Differential Pulse Voltammetry
Three-electrodes setup is commonly used for differential pulse voltammetry.
The setup of a differential pulse voltammetry mechanism involves at least two electrodes: a working electrode (WE) and a counter electrode (CE). The voltage pulses are transmitted by the counter electrode while the working electrode measures the resulting current. A third electrode, the reference electrode (RE), is often included to control the voltage of the counter electrode.
The pulses sent by the working electrode are usually between 10ms - 100ms with a gradual increment of 10 mV to 100 mV. As the pulse falls back to the incremental baseline voltage, there’s a typical idle time of 1-2 s so that the auxiliary electrode only picks up Faradaic current instead of charging current.
Next, we’ll take our knowledge of understanding differential pulse voltammetry and its mechanism and apply that to building a circuit.
How to Build A Differential Pulse Voltammetry Circuit
Differential pulse voltammetry is an effective chemical analytical method, but it heavily depends on the electronics at its core for its accuracy. The circuit of a differential pulse voltammetry consists of the following:
The potentiostat is made up of op-amps. It integrates the counter electrode, working electrode, and reference electrode to provide the required pulses and sample the current. Do note that the potentiostat, itself, does not generate the pulses but shifts the voltage of the pulses in accordance with the provided offset level.
A potentiostat connects electrodes in differential pulse voltammetry.
DAC and ADC
The digital-to-analog converter (DAC) converts the digital value of the step voltage to an analog signal for the control amplifier. The value is increased gradually for subsequent pulses. In a real-life setup, there could be a margin of error between the desired voltage and the applied voltage. In such cases, a feedback sensing circuit is used to measure and adjust the DAC value.
Now, the goal of the differential pulse voltammetry is to measure the resulting current and you’ll need an analog-digital converter (ADC) for that. It converts the analog measurement into digital values, which are then used for further analysis.
To generate the pulses, you’ll need a microcontroller with the pulse width modulation (PWM) functionality. A 32-bit microcontroller is preferable, as the pulse duty cycle needs to be considerably small. The microcontroller sends the pulse to the potentiostat, transmits the required offset voltage to the amplifier, and measures the current from the working electrode.
When designing a differential pulse voltammetry circuit, it helps to use an advanced PCB design software. Allegro PCB Editor allows you to set strict DRC rules for both analog and digitals signals in the circuit to build the best, functional circuit needed for your voltammetry sampling.
If you’re looking to learn more about how Cadence has the solution for you, talk to us and our team of experts.