Healthy Water, Healthy People Testing Kit Support



FAQ’s for Healthy Water, Healthy People
Advanced Water Quality Testing Kit #8

General

What is standard adjust? Should I use it?
Standard adjust is a feature on the DR/850 colorimeter that allows you to adjust the accuracy of the instrument. This is done by measuring a solution of known concentration, called a standard solution. If the displayed result does not match that of the standard concentration, you can use the standard adjust feature to adjust the displayed result so that it does display the exact concentration. This adjusts the calibration curve that is in the instrument software.

Calibration of the instrument at the factory is very accurate, however some methods have more variability due to user technique and reagent variability. Standard adjust is recommended for those methods, such as nitrate and sulfate, for the best accuracy.

What is the difference between standard adjust and user calibration?
Standard adjust maintains the shape of the factory calibration curve but adjusts the whole curve using one standard solution so that the instrument reads the exact value of the standard. Typical limits for calibration curve adjustment are 10-20%. These limits ensure that if a standard solution were prepared incorrectly, the instrument would reject the adjustment.

User calibration puts an entirely new calibration curve into the instrument and does not have rejection limits if standards are prepared incorrectly.

How do I use the single parameter standards?
The simplest way to use one of these standards is to use the standard in place of the sample and run the test as usual. Where a test procedure says to measure a portion of sample into a sample cell, add the standard solution to the cell instead, and follow the rest of the steps in the procedure.

If the result is close to the specified standard concentration, you can be confident that your instrument and reagents are working correctly and that you are performing the test correctly.

What is a reagent blank and when do I need to use one?
A reagent blank is a correction for any color that is due to the reagents alone and not to the parameter being measured. To measure the reagent blank, run the test using distilled or deionized water in place of the sample. Subtract this reagent blank value from all sample results.

The reagent blank value for most tests is usually very small, but can be higher for some tests such as high range nitrate. A correction for reagent blank is most important when sample results are low, because the blank will comprise a larger proportion of the sample concentration.

What is the difference between deionized, demineralized, and distilled water? Does it matter which one I use?
Each type of water is purified to remove contaminants and all can be used with these kits. Deionized and demineralized water are the same thing and are purified using ion-exchange resins. When water passes over the resin, contaminants in the water stick to the resin. Trace amounts of organic matter can come from the resin, but that will not interfere with these tests.

Distilled water is purified using a distillation process, which is an excellent way to remove contaminants. The quality of distilled water found in grocery stores can vary, however, so it is a good idea to try a different brand if results are questionable.

How do I use the demineralizer bottle?
Fill the bottle with tap water and invert to mix. This water can then be used wherever deionized or distilled water is needed. When all of the beads turn yellow, that means the resin is saturated and it is time to replace it.

Are the digital titrator delivery tubes disposable?
Delivery tubes can be reused again and again. Remove them from the cartridge and rinse with distilled water before storing or changing to a different cartridge. A squirt bottle works well for this. Before reusing, be sure to prime the solution from the cartridge through the tube.

How do I use the Test Yes packets?
Open a Test Yes packet and dissolve in 1 liter of distilled water. Use this solution as the sample and run the test as usual (add the reagent/s and wait the reaction time if specified.) You will get a positive, although unknown, result using this solution for alkalinity, chlorine, hardness, nitrate, and phosphate.

Can these tests be run on seawater?
All tests in this kit except for nitrate and manganese can be run on seawater samples.

Alkalinity

After I added the phenolphthalein, the sample did not turn pink, what should I do?
This is common and will happen whenever the starting pH of the sample is less than 8.3. This means that there is no phenolphthalein alkalinity in the sample. Continue with the test by adding the bromcresol-green methyl red indicator and titrate to the endpoint for total alkalinity.

My sample turns light pink when I add the bromcresol-green methyl red indicator, not a blue-green color, what is wrong?
If chlorine is in the sample, it will bleach the indicator. Start with a fresh sample and add one drop 0.1 N sodium thiosulfate per 100 mL sample to remove chlorine. Then begin the test as usual.

I cannot see the endpoint color very well. What can I do?
You can use a pH tester instead of the colored indicators and stop the titration at the endpoint pH (see Table 2 in the procedure for specific endpoint pH values.) Do not filter the sample if it is turbid, because filtering may alter the results.

How do I know which pH endpoint to titrate to (from Table 2 in the procedure) when I don’t know the alkalinity of my sample?
If you have test strips, you can use them to estimate the alkalinity level and use that level for your endpoint pH. If you don’t have test strips, use an endpoint of 4.5 initially, and then repeat the test with a fresh sample using the range that most closely matches your first result.

Biological Oxygen Demand (BOD) and Dissolved Oxygen (DO)

What happens if I have an air bubble in my BOD bottle?
If there is an air bubble in the bottle used to measure dissolved oxygen, the DO result will be higher than it actually is. This will make the final calculation for BOD incorrect. If the bottle that is incubated has a bubble, there will be more oxygen available to the sample than there should be, and results will also be incorrect.

Does the order in which I add the manganous sulfate and alkaline iodide-azide powder pillows affect the test results?
It is best to add the manganous sulfate first and then the alkaline iodide-azide.

My final DO is always zero. What can I do?
Note that the result in this case is not initial – final DO. You can only say that the result is greater than the initial – final DO difference, because there is no way to know how much more oxygen the sample would have consumed if more oxygen had been available. You can start over and dilute your sample with distilled water, for instance one part sample to one part distilled water, to try and get a final DO concentration that is not zero. Then multiply the initial – final DO difference by the dilution factor to get the BOD result.

How does this modified procedure compare to the Standard Methods procedure?
The Standard Methods BOD procedure is more complicated and involves making sample dilutions, adding microorganisms and nutrients, and incubating at a carefully controlled temperature of 20 oC (68 oF) for 5 days. There are also specific instructions for cleaning the bottles and preparing dilution water that is not contaminated. The procedure in your kit is simplified and therefore the results will not match those from the Standard Methods procedure.

What is Standard Methods?
Standard Methods is a reference book used for water testing in all drinking water and wastewater plants. It contains step-by-step procedures that are to be followed for measuring all aspects of water quality.

How can I use the BOD glucose plus glutamic acid standard solution?
This standard solution should only be used with the Standard Methods procedure because you must add microorganisms and nutrients, make dilutions, and incubate for 5 days at a carefully controlled temperature to get the correct result.

Chlorine

What is the difference between free and total chlorine?
Free chlorine refers to both hypochlorous acid (HOCl) and the hypochlorite (OCl-) ion or bleach, and is commonly added to water systems for disinfection. If ammonia is present, chlorine will combine with the ammonia and form compounds known as combined chlorine, also called chloramines.

Total chlorine is the sum of free chlorine and combined chlorine. The level of total chlorine will always be higher than or equal to the level of free chlorine.

Free chlorine is typically measured in drinking water disinfection systems to find whether the water system contains enough disinfectant. Typical levels of free chlorine in drinking water are 0.2 – 2.0 mg/L Cl2, though levels can be as high as 5.0 mg/L.

Total chlorine is typically measured to determine the total chlorine content of treated wastewater, often for discharge purposes.

I am getting positive results and I’m sure there is no chlorine in my sample. Could there be an interference?
Other oxidants such as those listed in the procedure can interfere with the chlorine test. When measuring total chlorine, keep the sample covered in the sample compartment during the reaction time, because sunlight can react with the DPD indicator and cause a false positive.

I’m not getting any results. How can I tell if this test is working correctly?
Open a Test Yes packet and dissolve in 1 liter of distilled water. Pour 10 mL of this solution into the sample cell and run the test as usual (add the DPD and wait the reaction time if using the total chlorine test.) You will get a positive result using this solution.

For greater accuracy, you can use a sample of known chlorine concentration, called a chlorine standard solution. Run the test using the standard solution in place of your sample. If your result is close to the concentration of the standard solution, you can be sure that your reagents and instrument are working properly, and that you are performing the test correctly. Chlorine standard solutions must be diluted using distilled water before use.

Conductivity

How often do I have to calibrate the tester?
For the best results, calibrate the tester every day that you use it to be sure it is reading correctly.

Which conductivity standard should I use for calibration?
Choose a standard that has a conductivity that is similar to the conductivity of your samples. If you do not know what the approximate conductivity of your samples will be, start with the 1000 uS/cm standard. If you find that your samples have a much higher or lower conductivity than this standard, choose a standard with a different conductivity for future calibrations.

How do I store the tester?
Rinse the electrode with distilled water and store dry with the cap on.

Hardness

My sample turns a purplish color and never turns blue no matter how much EDTA I add. What is wrong?
This is an indication that your sample contains an interfering metal. Try repeating the test using a smaller sample volume. This may dilute the interfering metal to a level at which it does not interfere. If this does not help, follow the suggestions in the interference section of the procedure.

Won’t the deionized water added to my Erlenmeyer flask after adding the sample affect my results?
The total amount of hardness in the flask will not change after the deionized water is added. The EDTA will react with this amount of hardness whether it is diluted or not, therefore the additional deionized water will not affect the results. A total volume of 100 mL ensures that the sample is buffered consistently and that the indicator has the same concentration from one sample to the next.

How exact does the 2mL of Hardness 1 buffer solution have to be?
This volume is not critical. Using the eyedropper that comes with the bottle of Hardness 1 buffer is an adequate way to measure this volume.

Iron

What is total iron?
Iron can exist in water in several different forms, such as ferrous iron (Fe2+), ferric iron (Fe3+), complexed iron, in which iron is bound with various chemicals such as EDTA, and iron oxides, such as rust. Total iron includes all of these forms. Ferrous iron is soluble in water and is typically found in ground water. Once exposed to air, ferrous iron quickly oxidizes to ferric iron.

Iron can enter a water system by leaching natural deposits and from industrial wastes, effluents from pickling operations or acidic mine drainage. Iron in domestic water supply systems stains laundry and porcelain, and can cause a bitter or astringent taste at only 0.1 mg/L ferrous and 0.2 mg/L ferric iron.

Do I have to run a digestion on the sample in order to get accurate results?
Digestion is the best way to know for sure that you are measuring all of the iron in the sample. However, if a sample is not digested, the FerroVer reagent will still measure all of the soluble forms and most of the insoluble forms of iron in the sample. To be sure, try a digestion and compare the results with an undigested portion of the same sample.

Manganese

What is total manganese?
Manganese can exist in water in several different oxidation states, from Mn2+ to Mn7+. Total manganese includes all of these oxidation states. Manganese in natural waters rarely exceeds 1 mg/L, but levels of only 0.1 mg/L can cause an objectionable taste and stains on laundry and on plumbing fixtures.

Do I have to run a digestion on the sample in order to get accurate results?
Digestion is the best way to know for sure that you are measuring all of the manganese in the sample. It is also an excellent way to clean up the sample if there is a fair amount of organic matter that causes turbidity or color. To be sure, try a digestion and compare the results with an undigested portion of the same sample.

I get very different results using 2 different DR/850 instruments, why is this?
Be sure both instruments show Mn in the display. If they don’t, press the conc key until they both show Mn. Although the test measures manganese, the result can be displayed as permanganate (MnO4-), or potassium permanganate (KMnO4), by a molecular weight conversion. The conversion from manganese to permanganate is 2.16, and from manganese to potassium permanganate is 2.88.

Nitrate

When I repeat the test on the same sample, I get different results. What is wrong?
This is likely due to the way the sample is shaken after the NitraVer5 or NitraVer6 reagent has been added. It is important to be consistent when shaking the sample, and it may be necessary to change the shaking time. The longer and more vigorously the sample is shaken, the higher the result. To find what the best shaking time is, run the test with a nitrate standard solution instead of your sample. If your results are lower than expected, repeat the test by increasing the shaking time by 30 seconds or 1 minute until your results are close to the concentration of the standard. If your results using the standard are higher than expected, reduce the shaking time. Then use that shaking time for all your samples. Remember to measure and subtract the reagent blank when using the standard solution. When you receive a new lot of NitraVer reagent, you may need to adjust the shaking time again.

My results are suddenly 4 times what they usually are, what might be causing this?
This may be due to the form of nitrate that is displayed on the instrument. The default form is NO3-N, which is nitrate as nitrogen, and is a common way to report results to regulatory agencies. If you press the conc key, the displayed result will change to NO3, and the previous result will be multiplied by the molecular weight conversion between nitrogen and nitrate, which is 4.43. Be sure to record your results using the same form for consistency.

How do I dispose of cadmium waste from the NitraVer reagents?
It is important to follow hazardous waste regulations for disposal of waste from this test. Federal regulations may be superseded by state and local regulations, so it is important to check with a regulatory agency in your area for disposal instructions. The Environmental Protection Agency maintains a hotline where you can find local regulatory contact information; this hotline is 800-424-9346.

I’m not getting any results. How can I tell if this test is working correctly?
Open a Test Yes packet and dissolve in 1 liter of distilled water. Pour 10 mL of this solution into the sample cell and run the test as usual (add the reagents and wait the reaction time.) You will get a result using this solution.

For greater accuracy, you can use a sample of known nitrate concentration, called a nitrate standard solution. Run the test using the standard solution in place of your sample. If your result is close to the concentration of the standard solution, you can be sure that your reagents and instrument are working properly, and that you are performing the test correctly.

pH

How often do I have to calibrate?
For the best results, calibrate the tester every day that you use it to be sure it is reading correctly.

Which buffers should I use for calibration?
Two buffers should be used for calibration of a pH tester. If the expected pH of the sample is below 7, use pH 4 and 7 buffers. If the expected pH is above 7, use pH 7 and 10 buffers.

How should I store the tester?
During everyday use between sample measurements, store the electrode in either a pH 4 or 7 buffer solution. If storing for several weeks, rinse the electrode with distilled water and store dry. After long-term storage, let stand in pH 4 or 7 buffer solution for 30 minutes before using.

Phosphate

I don’t have 1:1 HCl for cleaning glassware. Is there anything else I can use?
You can also use the 5.25N sulfuric acid, or dissolve a PhosVer3 packet in 10 mL of distilled water and let the glassware soak for a few minutes in that. Rinse well with distilled water after cleaning.

Why do I have to multiply my results for total phosphorus by 1.2?
This factor corrects for the increase in volume from adding sulfuric acid and sodium hydroxide to the sample. After 2 mL of sulfuric acid plus 2 mL sodium hydroxide are added to the sample, the volume changes from 25 mL to 29 mL. The dilution factor = 29 ÷ 25, or 1.2.

In the traditional digestion procedure, the sample is boiled and much of the sample evaporates. Distilled water is added at the end so that the final volume is exactly 25 mL, therefore no multiplication factor is required.

I’m comparing my results with another group and my results are 3 times higher. What is wrong?
Most likely you are comparing results that are not in the same chemical form. The default form that is displayed on the DR/850 is PO43-, which is phosphorus as phosphate. Many labs report phosphorus as mg/L P, which has a concentration that is approximately 1/3 the concentration as PO43-.

The same amount of color is measured in the test regardless of which form is used, but when this color is converted to concentration, different conversions are used for the different forms. The conversion to mg/L PO43- uses the weight of PO43-, whereas the conversion to mg/L P uses the weight of P, which is approximately 1/3 the weight of PO43-.

If you press the conc key on the DR/850, the displayed result will change to P and P2O5. Be sure to record your results using the same form for consistency.

I’m not getting any results. How can I tell if this test is working correctly?
Open a Test Yes packet and dissolve in 1 liter of distilled water. Pour 10 mL of this solution into the sample cell and run the test as usual (add the PhosVer3 and wait the reaction time.) You will get a positive result using this solution.

For greater accuracy, you can use a sample of known phosphate concentration, called a phosphate standard solution. Run the test using the standard solution in place of your sample. If your result is close to the concentration of the standard solution, you can be sure that your reagents and instrument are working properly, and that you are performing the test correctly.

Sulfate

Why is a User Calibration recommended for this test? Is it necessary?
Rather than measuring a color, this test measures the amount of turbidity that forms in the sample, which typically leads to more scatter and less reproducibility in the results. The amount of turbidity formed can vary with sample mixing and with the size of the particles in the SulfaVer4 reagent. The instrument is calibrated at the factory using accurate methods, however newer lots of SulfaVer4 may change the calibration. A user calibration is not necessary for testing samples for sulfate, however it may give more accurate results.

Can I use the Standard Adjust feature rather than a User Calibration?
Yes, you can add the SulfaVer4 to a 50 mg/L standard solution and adjust the reading to display 50 mg/L if it displays a result that is higher or lower than 50 mg/L. This will also adjust the calibration curve and is less time-consuming than a user calibration.

Suspended Solids

What is the difference between suspended solids and turbidity?
Both are a measure of the amount of particles in water, however suspended solids measures the amount of particles by weight, and turbidity measures the effect that the particles have on the degree of clarity or cloudiness of a water sample. The most accurate way to measure suspended solids is to filter the sample, dry the filter paper, and weigh the amount of solids on the filter paper.

Turbidity

What is the difference between NTU, FTU, and FAU?
NTU stands for Nephelometric Turbidity Unit and indicates that the instrument is measuring scattered light from the sample at a 90-degree angle from the incident light. This type of measurement is always made in a turbidimeter.

FTU stands for Formazin Turbidity Units and indicates calibration with formazin primary standards, however it does not specify how the instrument measures the sample. FAU or Formazin Attenuation Units indicates that the instrument is measuring the decrease in transmitted light through the sample at an angle of 180 degrees to the incident light. This type of measurement is not considered a valid turbidity measurement by most regulatory agencies.

The turbidity units NTU, FTU, and FAU are all based on calibrations using the same formazin primary standards. Therefore when a formazin standard is measured, the value for each of these units will be the same, however the value on samples may differ significantly.

What is the best way to measure turbidity? Will my results using the DR/850 be accurate?
A turbidimeter is the best instrument to use for measuring turbidity. The DR/850 will not measure the turbidity of clear samples accurately, however it can be used to compare relative turbidities of cloudy samples.

Do I have to use deionized water as a blank?
It is important to use water of very low turbidity for the blank. Using deionized or distilled water will ensure that the water used for the blank is clean.

 

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