By Marianne R. Metzger

There are literally of testing options for the average water treatment dealer. So which one do we use and why?

Performing some analysis to get a general idea of water quality should be a standard practice. If it’s not, perhaps you should explore other career opportunities.

Many professionals will employ onsite testing, laboratory analysis or a combination of both. Let’s face it–you cannot fix a problem if you do not know the identity or scope of the problem.

An accurate water analysis is crucial to designing the correct water treatment system. Many water treatment professionals utilize testing kits that are colorimetric, meaning that the specific color or color intensity will indicate the level of the contaminant being analyzed.

There are several different kinds of colorimetric tests. Each has its advantages and disadvantages.

Card testing

The easiest color change test has its color standards printed on a card. With these tests, the reagent is added to the sample or the test strip is dipped into the sample, which causes a color change. The color is then compared to the chart provided, which shows different colors or intensities for the various ranges of concentration.

These tests are often used because they are easy to perform and economical. However, there are some issues with accuracy, starting with the printed color charts.

Printed color charts cannot imitate the characteristics of an aqueous sample, so matching is basically an educated guess. Printing quality can also be an issue, depending on how close the printed colors come to the target colors. The challenge also is if the manufacturer can consistently achieve the same color from press run to press run.

How well the printed standard holds up with constant use and in different environments is another concern. When performing the test, there is the possibility of getting the chart wet, which can ruin a chart if it is not printed on waterproof paper or at least laminated.

These charts only provide a range of colors and not an exact result, so more accurate analysis may be needed based upon treatment needs. If running an alkalinity test using a strip and it is determined the reading is between 40 and 80 mg/L, it may be that a maximum range level of 100 mg/L needs to be achieved.

This test does not indicate how much chemical needs to be added to achieve desired results. Further analysis is needed that can give a definitive result.

Liquid color comparator

Another color change test utilizes a liquid color comparator, which is more accurate because the colors actually mimic aqueous samples. With this method, reagent can be added to the sample and compared to the multiple color standards usually housed in a handheld comparator.

These comparators can be much like pool testing kits, which have the sample reservoir right next to the color comparator. The comparator can also be a wheel that is turned to compare the various ranges to the sample.

These are economical, portable and affordable to use. They do not create the same variation problems as do printed color charts, but there may be problems with fading colors when utilizing more economical versions. Higher end units will guarantee liquid standards do not fade over time, so it may be worth the investment.

The biggest problem with these tests, along with the printed charts, is that some variability in results will occur based upon the person who is reading them. Every person can interpret color differently.

It is also estimated that six to eight percent of the population has red-green deficiencies in their vision, which obviously can skew color-based results. If color-blindness is a concern, a colorimeter should be considered.

Colorimeter usage

Color change tests can be done through the use of a colorimeter. It operates much like the other methods in that it adds appropriate reagent that produces a color change.

The sample is then placed into a meter where the color is read by measuring the absorbance of a solution at a specified wavelength of light. Colorimeters can be purchased to perform a single analysis or one that can perform a variety of tests.

Colorimeters provide an actual level of the contaminant being analyzed rather than a range, which is helpful in determining treatment options. Colorimeters can be portable for field use or they can be benchtop units for use in laboratories.

Depending on the analysis desired, these can be relatively inexpensive. The more sophisticated the colorimeter, the more expensive it can be.

Keep in mind that once the colorimeter is chosen, reagents need to be continually purchased from the manufacturer, an on-going expense. While one manufacturer may offer colorimeters at a discounted price, reagent cost may be greater in the long run. Titration color change methods can use droppers, laboratory burettes, digital tritrators or direct-read micro burettes. These tests use various color indicators that can slowly add to the sample until the desired color change takes place.

Based upon the amount of indicator added, the amount of the contaminant being tested can be calculated. There are many titration methods available, including analysis for contaminants such as hardness, alkalinity, chlorine and dissolved oxygen.

The droppers are the least expensive method, while burettes and digital titrators can be more expensive but also more accurate. Regardless, these titration methods offer another easy-to-use test method that can be relatively inexpensive.

Methods and standards

Once the best testing method is determined, familiarity with the testing method is needed. Testing which is performed on the same sample under the same conditions may not yield identical results. This is attributed to unavoidable random errors that are present in all testing procedures.

Accuracy of the testing method is affected by repeatability. Repeatability refers to how often the testing method can be used to get the same result–or nearly the same–using similar analysis and instruments.

In order to ensure repeatable results, standards need to be utilized. Standards are samples with a known concentration of the analyte in question.

If running a test for iron using a colorimeter, purchase a standard for iron. From that standard several samples can be prepared with different concentrations by diluting the original standard.

It is suggested that at least two samples for each concentration level should be made. The analyst should then be able to run various samples, getting results that are at or close to the known concentration.

This may take some practice because variations can occur from the slightest difference in running the analysis, such as the length of time a sample is mixed from the way the sample is mixed. Once repeatability with the testing method is achieved, greater confidence can be achieved in running some unknown samples to obtain results.

Skewing results

Some test methods using color change are susceptible to interferences, which can skew results. Many colorimetric tests can be affected by turbidity of the water.

Turbidity refers to cloudiness or discoloration of the water. This cloudiness or discoloration can interfere with a color change making the results inaccurate.

Highly turbid water can be filtered to yield a more accurate analysis. When analyzing samples of unknown quality, there is the potential for a variety of contaminants that could be present and affect results.

If an unexpected result is achieved, instruments may need to be calibrated or additional steps need to be performed in the analysis to reduce interference. Chlorine can sometimes interfere with certain methods, but the interference can be reduced by adding a dechlorinating agent such as sodium thiosulfate, sodium sulfite or sodium bisulfite. It is important to know which method is followed by the test kit being used in order to determine the possible interferences and plan appropriately.

Most water treatment professionals utilize some type of onsite analysis to help in determining treatment needs or sizing equipment. It is important to choose the method that will work best for the determined needs.

The more that familiarity with testing methods is increased, the better chance there is of producing an accurate analysis. Thoroughly studying the testing instructions and performing the analysis until comfort with the procedure is achieved will lead to more accurate results.

Tests can give idea of the problem and how bad it is. Because of the possibility of operator error, the same person should do the ongoing tests. Once a problem is detected, it’s a good idea to have a lab analysis to determine the most appropriate solution and treatment required and frequency.)

References

  1. Holmes-Farley, Randy. “Reef Alchemy: A Comparison of pH Calibrations,” Reef Keeping an Online Magazine, February 2005.
  2. http://www.reefkeeping.com/issues/2005-02/rhf/index.php
  3. Eaton, Andrew F., et al, Standard Methods for Examination of Water and Waste Water, 20th Edition, pages 2-26, 2-27
  4. McGowan, Wes, Harrison, Joseph E. Water Processing Residential, Commercial, Light Industrial, Third Edition, Water Quality Association, 2000.
  5. Adams, Thomas. A2LA Guide for Measurement of Uncertainty in Testing, July 24, 2002

About the author

Marianne R. Metzger is GPG Business Unit Manager for National Testing Laboratories, Ltd in Cleveland, OH. Metzger has a Bachelor’s Degree in environmental geology and political science from Case Western Reserve University of Cleveland, OH. She most recently worked for Accent Control Systems as a Sales Engineer, after previously spending more than a decade at National Testing Laboratories in a variety of positions, including customer service, technical support and Business Group Manager. Metzger can be reached by phone at (800) 458-3330, Ext 223, or by e-mail at mmetzger@NTLLABS.com.

 

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