Quanti-Tray Questions and Answers
Are Quanti-Tray and Quanti-Tray/2000 US EPA-approved?
Yes. US EPA has stated in writing that Quanti-Tray and Quanti-Tray/2000 can be used for compliance testing. Quanti-Tray approval letters from US EPA are available on request.
How do Quanti-Tray and Quanti-Tray/2000 compare to other standard methods?
Quanti-Tray provides a wider counting range than and comparable accuracy to membrane filtration (MF).
| Method |
Lower Counting Range/100 mL |
Upper Counting Range/100 mL |
| Quanti-Tray |
‹1 |
200 |
| Quanti-Tray/2000 |
‹1 |
2,419 |
| 5-Tube MPN |
‹1.1 |
16 |
| 10-Tube MPN |
‹1.1 |
23 |
| Membrane Filtration |
‹1 |
80 |
Are Quanti-Tray and Quanti-Tray/2000 trays sterile?
Yes, the trays are gas sterilized using ethylene oxide. A certificate indicating sterility is included with each box.
What is the shelf life of Quanti-Tray and Quanti-Tray/2000?
The shelf life of Quanti-Tray and Quanti-Tray/2000 is up to three years from date of manufacture. When storing opened bags of trays, fold over the opened end of the bag and seal with tape.
Does the temperature of the sealer affect the organisms that may be in the water sample?
No, the short time period that the tray is in the sealer will not harm the bacteria. The temperature in the wells will not increase more than 5°C during sealing.
Sometimes a few of the wells are not completely filled, what impact will that have on interpreting results?
Empty wells do not affect the test interpretation as long as the entire sample is in the tray. The effect on the Most Probable Number (MPN) table is statistically insignificant. An empty or partially filled well is interpreted the same way as a full well.
Can the trays be stacked in the incubator?
Yes. Quanti-Trays can be stacked as high as desired. Use caution not to block the airflow in the incubator.
How is Quanti-Tray interpreted when using Colilert® or Colilert®-18?
Use the Quanti-Tray® Comparator (#WQTC) or Quanti-Tray®/2000 Comparator (#WQT2KC) as a reference. Any color or fluorescence equal to or greater than the comparator is considered positive.
Some Colilert and Colilert-18 positive wells are darker than others. How does this affect interpretation?
Color intensity is a reflection of the different metabolic rates and final concentrations of the coliforms and E. coli in the different wells. Any yellow color or fluorescence in the sample well equal to or greater than the Quanti-Tray or Quanti-Tray/2000 Comparator is considered positive.
How do you interpret fluorescent wells that are not yellow when using Colilert or Colilert-18?
To determined the presence of E. coli, wells must be yellow and fluoresce. A fluorescent well, which is not yellow, is not an E. coli positive well.
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