Algal indicators: analytical methods, detection limits, and holding times - USEPA/SuRGE GitHub Wiki
Background
- Region 10 collected samples for chlorophyll a (chla) analysis. All samples were extracted in CIN. Analysis of the extract was conducted at CIN or BSA contract laboratory.
- Beginning in 2020, an additional sample was collected for phycocyanin. All chla and phycocyanin samples collected >=2020 are analyzed at ORD's Narragansett Laboratory.
- Beginning in 2020, a sample was collected for microcystin and analyzed ORD's Narragansett Laboratory.
Detection Limits
Analyte detection limits are difficult to pin down because they are dependent upon the volume of water that was passed through the filter. CIN has established a minimum detection limit of 9 ug_l of chla in the raw extract (not in the sample water). readChlorophyllR10_2018.R includes code to flag any sample with < 9 ug_l of chla in the raw extract. We do not have sufficient data to identify detection limit violations from other laboratories.
See email from Jeff Hollister on 6/9/2025 for microcystin reporting and detection limits.
Analyte Names and Units
Please note that the analyte names and units used below are consistent with the SuRGE chemistry data objects, but may differ from those in the data files provided by the laboratories. See Wiki page Chemistry units, names, and data sources for the official list of analyte names and units to be used in the SuRGE data objects.
Table
| Analyte | Analyte Container and volume | Analytical method | Year | Detection limit | Reporting limit | Preservation and Holding times | Lab |
|---|---|---|---|---|---|---|---|
| chla | Water collected in opaque 1L HDPE bottle. Filtrate collected on Glass Fiber filter within 24 hours and wrapped in foil. | ORD SOP: J-WECD-WMB-SOP-1942-0. Acetone extraction. | 2018 | 9 ug/L in extract | not reported | Filter is stable at -80 oC for 60 days. Filtrate stable for 11 months at -80 oC. | CIN |
| chla | Water collected in opaque 1L HDPE bottle. Filtrate collected on Glass Fiber filter within 24 hours and wrapped in foil. | ORD SOP: J-ACESD-MAB-SOP-1425-0. Acetone extraction. | >= 2020 | not reported | not reported | 60 days @ -20C | NAR |
| phycocyanin | Water collected in opaque 1L HDPE bottle. Filtrate collected on Glass Fiber filter within 24 hours and wrapped in foil. | ORD SOP: J-ACESD-MAB-SOP-1425-0. Acetone extraction. | >= 2020 | not reported | not reported | not reported | NAR |
| microcystin | 30 mL glass bottle | ELISA | >= 2020 | 0.1 ug/L | 0.15 ug/L | freeze @ -20C | NAR |