1. Should I buy commercial Glucose/Glutamic acid standard?
The most accurate, dependable way to ensure your GGA’s meet criteria is to make your own, however many labs use and obtain good results with commercial GGA standard. Commercial GGA solution may be purchased through your lab supply company and is a very useful tool to save time. Keep in mind, GGA is a food source for the bacteria, so if the bottle becomes contaminated, and you are depending on a certain amount of food source to be available to meet criteria, you could miss the mark. Always have reagent grade Glucose and L-Glutamic acid on hand to run against the commercial solutions when in question.
2. How do I make my own Glucose/Glutamic acid standard?
To make your own GGA standard:
- Dry reagent grad Glucose and L-Glutamic acid in an oven at 103° C for 1 hour
- Cool in a desiccator and keep there until used
- On the day of the test set up, weigh out exactly 150mg of Glucose and 150mg of L-Glutamic acid to a liter of DI water or Distilled
- Pour into a beaker and stir for 15 minutes to completely dissolve the solution
- Distribute the GGA solution into the bottles by using a volumetric pipette, paying close attention to bringing the bottom of the meniscus to the top of the 6ml line.
NOTE: Make sure all reagents have not exceeded their expiration dates prior to use. Also make sure your desiccator or vacuum is functioning correctly.
3. What are the acceptable Glucose-Glutamic acid values?
According to Standard Methods, Glucose-Glutamic acid values should be in the range of 198 ± 30.5 mg/l.
4. When setting up the Glucose-Glutamic acid test, what volume of PolySeed solution was inoculated into each BOD5 bottle?
We recommended add 4.0 mls of PolySeed seed solution to each BOD5 bottle containing the Glucose-Glutamic acid.
5. How many Glucose-Glutamic acid tests should be set-up?
We recommend that you test at least three Glucose-Glutamic acid dilutions.
6. How important is time and temperature in regards to the GGA test?
It is important that the Glucose-Glutamic acid seeded preparations are read within 2 hours. In the event that the preparations are not read immediately, they should be placed at 20ºC until the time of reading.