3 Ways to Improve the Accuracy of Your Colorimeter
Colorimeters are used in the field because they produce more accurate readings than titrations or color-matching methods. They are also often used in accounts requiring higher precision because the stakes are higher. Improper treatment could cause higher nonconformance costs (equipment failure or higher energy costs), wasted chemical (in contracts), and eventually loss of contracts. But, is it the device alone that assures accurate test results, or are there more factors in play? Here are three important things to keep in mind:
1.) Time: The chemists who develop the colorimeter methods carefully evaluate the times needed for “optimum color development.” In certain tests, wait times are required to allow the indicator to react with the analyte, and much work goes into making certain those times are accurate. If the exact wait times are not adhered to, the outcome will be inconsistent test results. Colorimeter users need to follow the directions to a T.
2.) Glassware: The differences in sample cell quality can be greater than the stated margin of error for a method. Most of the time users do not perform a test with “matched” sample cells which greatly reduce the error associated with differences in sample cells. Matched sample cells can cost much more than unmatched cells, and if you break one matched cell (I am guilty of breaking glassware in the field) you need to buy a new set. So what can you do in the meantime? When I was in the field I used one sample cell whenever possible for both the blank and the prepared sample; chlorine testing is a great example. This one-cell method will not always work — for instance if you’re running multiple samples for iron — but if you want to save time, the expense of buying new glassware, and improve your accuracies, employ this method whenever possible.
3.) Calibration: Is your colorimeter calibrated for each wavelength it uses? Great question! I have talked to so many colorimeter users who say they do not check their device’s calibration — ever! I have also talked to users who buy standards to check only one or two of the wavelengths, but what about the other two to four wavelengths? To assure your test results are accurate, it’s essential that you check the calibration of your colorimeter on a regular basis. Of course you could always send the device back to the manufacturer each year to have it calibrated, but what do you do while it’s gone? What about the cost for this service? Your best option is to use standards that allow you to test each wavelength in the field. For maximum confidence and economics, make sure your supplier has that option available to you.
Colorimeters are great tools, but, like any analyzer, they need to be used properly and maintained well.
