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Table of Contents

Optical Platform Colorimetry (EVAL-CN0503-ARDZ)

Colorimetry can be used to determine the concentration of materials in a solution based on its absorbance. One application of colorimetry is pH measurement with the aid of a coloring reagent. This document details the steps in setting up the EVAL-CN0503-ARDZ for pH measurement.

General Description/Overview

The EVAL-CN0503-ARDZ is a four-channel optical platform capable of fluorescence, absorbance and scattering measurements. The two middle channels/light paths are only capable of absorbance and 180-degree scattering measurements. This demo uses the two paths for absorbance measurements for two different light wavelengths.

Measuring pH using colorimetry involves using a chemical reagent or indicator. Different indicators exhibit different color and light absorbance behavior. Some indicators break down into different ions which also exhibit different properties which is why the solution has very different color hues at the ends of the pH range. For this demo we will be using bromothymol blue from either a prepared solution or the API pH Test Kit. Bromothymol blue separates into a weak acid (HIn) and a conjugate base (In). HIn has high absorbance to 430nm light while In has high absorbance at 615nm light. The demo will use light sources with these two wavelengths for the two middle channels.

While bromothymol blue exhibits the most change in color in the 6 to 8 pH range, buffer solutions with known pH solutions can be used to set up the measurement/calibration curve. The demo uses the CN0503 GUI and details steps to set-up the pH measurement curve using a spreadsheet.

Demo Requirements

The following is a list of items needed in order to replicate this demo.

  • EVAL-CN0503-ARDZ, completely assembled (see Hardware User Guide)
  • EVAL-ADICUP3029 with firmware (see Software User Guide)
  • Host computer with software (see Quick Setup Guide)
  • Bromothymol blue or API pH Test Kit (https://apifishcare.com/product/ph-test-kit)
  • pH Buffer Solutions (Optional for calibration)
  • Common household chemicals for testing

Setting the EVAL-CN0503-ARDZ

Before starting with these steps, please check the Hardware User Guide for the steps to assembling the EVAL-CN0503-ARDZ. Additionally, please check the Software User Guide for the steps in setting up the firmware and the Quick Setup Guide for running the software. This demo assumes that you already have an assembled board with a working firmware already programmed on the EVAL-ADICUP3029 and a ready-to-run software in the host computer.

Configure the onboard jumper shunt connection as below:

Jumper Header Setting
LD2SEL and LD3SEL Set to VARD
IOSEL Set to ARD
P1.8V Shorted
  1. Connect the 430nm LED Board and the 615nm LED Board to LED2 and LED3, respectively.
  2. Connect the EVAL-ADICUP3029 to the EVAL-CN0503-ARDZ and connect a microUSB-to-USB cable from the board to the host computer.
  3. Run the software (using python scripts or the executable)
  4. Select the correct COM Port of the device and connect (see Software User Guide for help)
  5. Load the configuration file for pH Measurement ()
  6. Configure the settings for path 2 and 3 with the desired name, set wavelengths to 430 and 615, respectively, and select measurement type: absorption for both.
  7. Add empty cuvette/s (or filled with distilled water) to path 2 and path 3 and click Optimize LED for each path. This properly sets the LED current in these paths so that the light intensity is close to 50%.
  8. Click OK and on the main window select optical path 2 and display mode ARAT.
  9. Click on Start Measurement and note the average value on the graph. Remember the empty cuvette or distilled water sample should still be in the path. The average value will be used as the baseline ratio for this path.
  10. Click on Stop Measurement (Repeat the two previous steps for path 3) then, click on the settings icon on the top right corner to bring back the settings and click on Advanced to bring up the another window.
  11. In the “Enter a direct command” text field, type “DEF1 RATB <average value>” for path 2 and “DEF2 RATB <average value>” for path3, then press Send Command. Replace the <average value> to the value you have noted earlier.
  12. Optionally, you can write pH to the primary unit field of path 2 and path 3. These are just labels and are not necessary.
  13. Click Okay here and on the settings window to go back to the main.
  14. Remove the empty cuvette/s or distilled water sample/s. The device is now ready to measure pH.
  15. Place a prepared cuvette with the test sample to either path 2 and path 3. Check the Preparing Test Sample section on how to prepare a cuvette with the test sample and indicator.
  16. Select either path 2 or path 3, set display mode to INS1, and press Start Measurement. By default the system was configured to use the measurement curve shown below. Check the Setting Measurement Curve section on how to set your own using spreadsheets and the advanced settings

Preparing Test Samples

Generating a Measurement Curve

resources/eval/user-guides/circuits-from-the-lab/cn0503/colorimetry.1617613092.txt.gz · Last modified: 05 Apr 2021 10:58 by Angelo Nikko Catapang

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