Stabilised formazin composition, method of preparation and diluent for formazin composition
A stabilised aqueous formazin composition comprises 100 parts by weight water; up to 0.03 parts by weight formazin polymer; 0.4 to 5 parts by weight hexamethylenetetramine; and a buffer composition, wherein the buffer composition is adjusted to maintain a pH of the formazin solution in a range between 8.4 and 10. The stabilised formazin composition has a turbidity of 400 NTU or less. A diluent for preparing the stabilised formazin composition from a formazin stock composition is provided, wherein the diluent comprises hexamethylenetetramine in a concentration of between 4 and 50 g/l and a buffer composition adjusted to a pH of the diluent in a range of from 8.4 to 10.
1. A stabilised aqueous formazin composition having a turbidity of 400 NTU or less, said composition comprising:
100 parts by weight water;
up to 0.03 parts by weight formazin polymer;
0.4 to 5 parts by weight hexamethylenetetramine; and
a buffer composition,
wherein the buffer composition is adjusted to a pH of the formazin composition in a range of from 8.4 to 10.
2. The composition of claim 1 , wherein said hexamethylenetetramine is present in an amount of 0.4 to 4 parts by weight.
3. The composition of claim 1 wherein the buffer composition is selected from the group consisting of ammonium buffers, phosphate buffers and borate buffers.
4. The composition of claim 3 wherein the buffer composition comprises a dihydrogen phosphate salt and sodium hydroxide.
5. The composition of claim 3 wherein the buffer composition comprises a borate salt and hydrogen chloride.
6. The composition of claim 1 wherein the buffer composition is present in a concentration effective to provide a buffer capacity of at least 1 percent.
7. The composition of claim 1 wherein the formazin composition has a buffer capacity of 1 to 15 percent.
8. The composition of claim 1 wherein the formazin composition has a turbidity of 100 NTU or less, and comprises up to about 0.0075 parts by weight of the formazin polymer.
9. A method for preparing a stabilised aqueous formazin composition having a turbidity of 400 NTU or less and a pH in the range of from 8.4 to 10, comprising the steps of:
providing an aqueous diluent comprising hexamethylenetetramine in a concentration of between 4 and 50 g/l and a buffer composition adjusted to a pH of the diluent in a range of from 8.4 to 10; and
mixing the diluent to an aqueous formazin stock composition having a turbidity of greater than 400 NTU, to obtain the stabilised aqueous formazin composition having an NTU of 400 or less.
10. The method of claim 9 , wherein the diluent is free of sulfate ions.
11. The method of claim 9 wherein the buffer composition is selected from the group consisting of ammonium buffers, phosphate buffers and borate buffers.
12. The method of claim 11 wherein the buffer composition comprises a dihydrogen phosphate salt and an alkali metal hydroxide.
13. The method of claim 11 wherein the buffer composition comprises a borate salt and hydrogen chloride.
14. The method of claim 9 wherein the diluent has a buffer capacity of 1 to 15 percent.
15. The method of claim 9 wherein the formazin composition is exposed to UV radiation for disinfection.
16. A diluent solution comprising hexamethylenetetramine in a concentration of between 4 and 50 g/l and a buffer composition adjusted to a pH of the diluent solution in a range of from 8.4 to 10.
17. The composition of claim 1 where the buffer composition is adjusted to the pH of the formazin composition in the range of from 8.4 to 9.
18. The composition of claim 2 , wherein the hexamethylenetetramine is present in the amount of 0.4 to 3 parts by weight.
19. The process of claim 9 wherein the buffer composition is adjusted to the pH of the diluent in the range of from 8.4 to 9.
20. The diluent solution of claim 16 wherein the buffer composition is adjusted to the pH of the diluent solution in the range of from 8.4 to 9.