Laboratory

Phosphorus Monitoring Alternatives can Save Time and Improve Precision and Accuracy

By: Dean Falkner

Phosphorus monitoring alternatives can save time and improve precision and accuracy.

There are options in performing the phosphorus test that can make your life easier, save time, and can actually help improve the accuracy and precision of your test results.  If it seems too simple, consider the statistics associated with this test procedure:

            Curve Correlation Coefficient:  0.99985-0.99999  

            Limit of detection:  0.003 mg. P/l

Things that you might want to consider employing in performing phosphorus analyses:

Reagent dispensing with pipeters: Another step adding to the time to run the phosphorus test is pH neutralization.  Adjustable pipeters can quickly deliver the exact same volume of acid to the samples prior to digestion.  That consistency results in the neutralizing being similar for every sample.  Another pipeter can be used to quickly dispense a volume of hydroxide (just a few drops less than what’s needed to neutralize the sample).  The final hydroxide addition can be added with just a few drops.

Another pipeter can be used to deliver the necessary combined reagent.

Nessler Tubes (or test tubes):  Low form Nessler Tubes measure/contain 50 ml.  They can fit in a rack and into an autoclave for digestion.   The sample can be added to the tube, acid and persulfate added, then put a sheet of aluminum foil over the rack before autoclaving.  The aluminum foil prevents any condensate from the autoclave to enter the tubes.

The final mixing is completed by covering each tube with “Parafilm” and thoroughly mixing each tube.

By completing each test in a single tube, there is no issue of spilling or complete sample transfer.  As a result, the test precision of the test is improved. 

Sample Digestion:  The digestion can be completed by boiling the samples, heat in a commercially available block digester, or autoclaving the sample.  Each are legitimate methods to digest the sample.  From my perspective, boiling down samples is time consuming compared to the block digester or autoclave.  The autoclave was a good option, because it didn’t require the purchase of a block digester and the ongoing costs of supplies.  Simply set the autoclave for “liquids”, …load the autoclave and work on other things.  Open the door after the temperature is down to 90 C and complete the analysis.

Replace the spectrophotometer 1 cm path length tube holder with a 5 cm cell holder:  The longer the light path in the spectrophotometer, the more absorbance will be measured for any sample.

The increased absorbance is beneficial in lowering the limit of detection for the phosphorus test.

ASTM’s Ascorbic Acid Procedure:  American Society of Testing & Materials had a slightly different approach to the combined reagent.  The test has the sulfuric acid, ammonium molybdate, and antimony potassium tartrate and water in a single solution that can be stored for a year.  Adding 0.5 mg of ascorbic acid to 100 ml of the solution completes the combined reagent.

Call Dean to arrange a demonstration or to get questions answered at 262.225.7298.

Monitoring Humidity In Lab for Weight Measurements

By: Kurt Birkett

Muggy summer days can be a real problem with accurate weighing. We have placed a humidity gauge atop our balance to keep a heads up for high humidity days. On these days we also keep indicating desiccant inside the balance to keep the reading stable. Our desiccator has a built in humidity gauge also that lets us know when the desiccant needs recharging. It is important to act quickly when transferring from dessicator to balance and record the reading within 5 -10 seconds. If your lab has humidity control, consider yourself fortunate but for most of us we need to take the extra dedication to achieve accurate measurements.

More Time Saving Equipment for the Lab

By: Dean Falkner - Sheboygan Wastewater Treatment Plant

Process control monitoring can be done daily with the use of a test kit for orthophosphate. Monitoring the orthophosphate concentration in composite and grab samples with these simple kits is cheap, easy, and monitors the form of phosphorus controlled by chemical addition anyway. It takes only 5 to 10 minutes. The kits are available by many sources, including Hach.

Total phosphorus testing can be done much easier with changes in the glassware used. The common practice is to put samples in ehrlenmeyer flasks, add reagents and autoclave, neutralize, transfer, and then do color development. The glassware takes a lot of space and the transferring process invites errors.

An alternate approach takes advantage of clinical lab procedures that really are not expensive. The change relies on the use of pre-calibrated 50 ml. test tubes ie. nessler tubes.

1. The sample is added to the numbered tube along with acid (for preservation). The tubes sit in a rack...holding up to 40 tubes. This makes it easy to batch run a week's worth of samples in even one of the smaller autoclaves. The weekly batch also helps bring quality assurance samples in a "realistic level".
2. Prior to digestion, the tubes get the persulfate dispensed with an automatic dispenser. We opted for the use of ammonium persulfate, because we can dissolve it in water and use the dispenser. After that, we cover the rack with aluminum foil and autoclave.
3. After digestion, water is added to bring the volume up to 15 to 20 ml. Then phenolphthalein is added and the sample neutralized as normal. We do use a test-tube shaker to speed-up the mixing....and avoid any unnecessary splashing...which would lead to error.
4. The neutralized samples get combined reagent added with an automatic dispenser. After that, they are diluted to the 50 ml mark with the distilled water. Final mixing is done by covering the tubes with parafilm...then shake mixing.
5. Sample concentrations are measured as normal. This system works well with the use of ortho-P test kits. The daily information is gained with the test kit for operation staff. The total P monitoring meets the State's requirements. The process does work great for us. HOWEVER, PLEASE TRY THE IDEA OUT WHILE YOU FOLLOW YOUR EXISTING APPROACH!!!!

Saving Costs on Lab Purchases

By: Dean Falkner - Sheboygan Wastewater Treatment Plant

Lab purchases are typically done from the catalog of any given laboratory supply house. The implication is that you will have to pay the standard price for any given item....just like ordering from a Whitney or Overton's catalog. The thing is....price is often negotiable.

Ways you can help control lab costs include:

1. Put together a list of all laboratory supplies and equipment you're likely to need in the next year. List the catalog numbers and source with the items and the number you'll need. Be sure to include any major lab equipment purchases...including field DO meters or incubators. Then, send the list out to the various chemical suppliers for quotes on the total package AND ASK FOR A FUTURE PURCHASE DISCOUNT STRUCTURE.
2. If you want to keep things simple, ask the supplier that you're working with whether you are being given a "government discount". Many of the suppliers have established "standard discounts" that you may get...just by asking for them.
3. Check with the person responsible for purchasing whether they have information on the "Wisconsin's Discount Structure" that addresses purchases from computers to lab supplies to .....
4. If you're at a small community with minimal purchasing needs...maybe a few communities could put together a larger list of supplies to use for bidding. Agree up front where the material should be shipped and how the bill will be paid.

Time Saving Equipment for the Lab

By: Dean Falkner - Sheboygan Wastewater Treatment Plant

Pipetting is a traditional element of any lab operation. It's done for everything from BOD tests to phosphorus tests. The only problems with pipets are:

They always have to be cleaned.

Without a pipet bulb (pipetting by mouth) is hazardous.

Using a pipet bulb of some sort takes time.

It does take attention to detail to do a good, accurate job.

Consider the clinical alternatives of various auto-pipetors with disposable tips. The tips are throw away. They are reproducable even with a hang-over, and they're safe for the employee using it. There are costs for the tips....but consider the cost for broken pipets, pipet washers & rinsers, the hazards of acid cleaning solutions, etc.....

Some of the auto-pipetors are capable of being adjustable...to meet your needs for BOD & phosphorus volumes.