SD900 Sampler Cheat Sheet

Customers continually tell us how easy they find the SD900 controller to program their sampling collection. Here's a quick set up for a time-based program collecting composite 200mL samples hourly over a 24 hour period.

Effects of Sample Temperature When Measuring pH

I don’t need to worry about sample temperature when measuring pH. My measurement is temperature compensated right? Yes, but...

It’s happened to most analysts and operators at some point, certainly to anyone who routinely needs to take measurements in climates with weather and temperature extremes. A pH meter/probe is calibrated in the relatively warm 25 degrees Celsius (25°C) lab or plant atmosphere, which must then measure the pH of a solution at a much lower temperature, say 1°C. T he probe goes in and begins its lengthy process of drifting until it stabilizes, sometimes 30 minutes or more. What’s going on with the pH measurement at this point? The simple answer is that, as long as the instrument has some means of correcting for the temperature, the signal from the temperature sensor is fed into the pH meter so that it can accurately determine pH value of the sample at that temperature. An automatic temperature correction (ATC) takes the temperature and compensates for the change in the electrode’s output due to the effect that the temperature has on the electrode. But there is another pH change that occurs with a temperature change that relates to the hydrogen ion activity in the solution.

The actual pH of the sample can change with temperature due to changes in ionization of compounds as well as hydrogen ion activity. ATC does not correct for this sort of temperature influence, but will only correct for the change in the output of the electrode—not for the change in the actual solution pH. Temperature will also affect the glass membrane's impedance. For each 8° below 25°C, the specified impedance approximately doubles. Depending on the original impedance of the glass membrane, the meter will have to handle a higher impedance at a lower temperature.

Sometimes, the temperature differences are impossible to avoid, and you have to do the best you can with what you’ve got. But if you have the ability to calibrate the pH probe in buffers that are closer to the temperature of the sample, you’re assured that you will achieve a more precise reading.

Using AccuVac Ampules—4 Easy Steps

1. Collect the sample in a beaker or other open container.
   
   
2. Break the tip off the ampule with either of these methods:
   
   • Use the optional AccuVac Snapper
   
   • Place the ampule tip well below the sample surface and break the tip off
     against the beaker wall. The break must be far enough below the surface
     to prevent air from being drawn in as the level of the sample drops.
   
   
3. Secure an ampule cap over the tip of the ampule. Invert the ampule several times to dissolve the reagent. The cap protects from broken glass and provides a grip for inserting and removing the ampule from the cell holder. Wipe the ampule with a lint-free cloth to remove fingerprints.
   • Note: Without the cap, the liquid will stay in the ampule when inverted. DO NOT place
     fingers over broken glass!
   
   
4. Insert the ampule into the sample cell holder and read the results directly.
   
   

Better Results for ULR Silica in the Lab

When trying to measure ppb levels of silica, any contamination can be the cause of false high readings. By taking a few extra steps, one can minimize the chances of false high readings.

1. Plastic Containers for All Analysis
   Use plastic containers for all analysis and storage because glass can contaminate the sample with silica. Small bottles or flasks with screw-type closures work well. This includes graduated cylinders, flasks for mixing, etc.
   
   
2. Cleanliness of All Containers and Lab Apparatus
   All containers used in this test must be cleansed thoroughly to remove any traces of silica. Clean containers by normal means (do not use phosphate detergents), then rinse with high quality deionized water of low-level silica concentration. Soak for 10 minutes with a 1:50 dilution of Molybdate 3 Reagent in low-level silica water. Rinse repeatedly with either low-level silica water or the sample before use. Keep containers tightly closed when not in use. Fill the Pour-Thru Cell with this same mixture of Molybdate 3 and water, and let stand for several minutes before use. Rinse with low-level silica water.
   
   
3. Cleaning the Pour-Thru Cell
   The Pour-Thru Cell may accumulate a buildup of colored products, especially if the reacted solutions are allowed to stand in the cell for long periods after measurement. Remove the color by rinsing with a 1:5 dilution of ammonium hydroxide, followed by several deionized water rinses. Cover the Pour-Thru Cell when it is not in use so debris from the environment does not get into the pour-thru cell.