Phosphate standard dilutions
Below are methods for preparing 5 mL phosphate standards in three different concentration ranges. Adjust volumes as necessary for preparing larger volumes (e.g. 10 mL or 100 mL of standards).
- Low range: 0 - 5 ppm e.g. Ascorbic acid, Hach PhosVer3, API test kit
- Mid-range: 0 - 30 ppm e.g. Ascorbic acid method, API test kit
- High range: 0 - 90 ppm e.g.Vanadate-Molybdate Method
In each case, the first step is preparing a working stock by diluting a commercially available phosphate standard. This working stock is then diluted further resulting in a set of 8 phosphate concentrations (plus a distilled water blank).
In addition to the equipment listed on the appropriate phosphate assay page, you will also need the following equipment and reagents if you plan to collect phosphate calibration data:
- 1,000 ppm PO4 (330 ppm P) Phosphate standard, Labchem Cat # LC18570-1
- 100 mL volumetric flask for preparing the working stock
- 5 mL (or 10 mL) sample tubes
- Distilled water
Low range (0.00 - 5.00 ppm PO4)
- Prepare a 5 ppm PO4 working stock: 0.50 mL of the 1,000 ppm standard in 100 mL distilled water in volumetric flask. Fill to the line with distilled water.
| Tube |
PO4 concentration (ppm) |
Volume of 5 ppm working stock (mL) |
Volume of distilled water (mL) |
|---|
| 1 |
0.000 |
0.000 |
5.00 |
| 2 |
0.625 |
0.625 |
4.375 |
| 3 |
1.250 |
1.250 |
3.75 |
| 4 |
1.875 |
1.875 |
3.125 |
| 5 |
2.500 |
2.500 |
2.50 |
| 6 |
3.125 |
3.125 |
1.875 |
| 7 |
3.750 |
3.750 |
1.25 |
| 8 |
4.375 |
4.375 |
0.625 |
| 9 |
5.000 |
5.000 |
0.00 |
Mid range (0.00 - 30 ppm PO4)
- Prepare a 30 ppm PO4 working stock: 3 mL of the 1,000 ppm standard in 100 mL distilled water in volumetric flask. Fill to the line with distilled water.
| Tube |
PO4 concentration (ppm) |
Volume of 30 ppm working stock (mL) |
Volume of distilled water (mL) |
|---|
| 1 |
0.00 |
0.000 |
5.00 |
| 2 |
3.75 |
0.625 |
4.375 |
| 3 |
7.50 |
1.250 |
3.75 |
| 4 |
11.25 |
1.875 |
3.125 |
| 5 |
15.00 |
2.500 |
2.50 |
| 6 |
18.75 |
3.125 |
1.875 |
| 7 |
22.50 |
3.750 |
1.25 |
| 8 |
26.25 |
4.375 |
0.625 |
| 9 |
30.00 |
5.000 |
0.00 |
High range (0.00 - 90 ppm PO4)
- Prepare a 90 ppm PO4 working stock: 9 mL of the 1,000 ppm standard in 100 mL distilled water in volumetric flask. Fill to the line with distilled water.
| Tube |
PO4 concentration (ppm) |
Volume of 90 ppm working stock (mL) |
Volume of distilled water (mL) |
|---|
| 1 |
0.00 |
0.000 |
5.00 |
| 2 |
11.25 |
0.625 |
4.375 |
| 3 |
22.50 |
1.250 |
3.75 |
| 4 |
33.75 |
1.875 |
3.125 |
| 5 |
45.00 |
2.500 |
2.50 |
| 6 |
56.25 |
3.125 |
1.875 |
| 7 |
67.50 |
3.750 |
1.25 |
| 8 |
78.75 |
4.375 |
0.625 |
| 9 |
90.00 |
5.000 |
0.00 |
