Chemical indicator compositions, indicators and methods

1. A chemical indicator composition comprising:

a) a bismuth (III) compound comprising at least one organic group which includes 2 to 20 carbon atoms;

b) elemental sulfur; and

c) a reducing agent selected from the group consisting of ascorbic acid and its derivatives, tocopherols, gallates, t-butyl hydroquinones, napthylamines, polyphenols, and combinations thereof; and

d) a compound which makes the composition alkaline when exposed to water vapor at an elevated temperature.

2. The composition of claim 1 , wherein the reducing agent is present in at least 1 wt. % based on the total weight of the composition and at no more than 5 wt. % based on the total weight of the composition.

3. The composition of claim 1 , wherein the compound which makes the composition alkaline has a solubility in water at 20° C. of more than 5 gram per 100 cubic centimeters of water.

4. The composition of claim 1 , wherein the compound which makes the composition alkaline when exposed to water vapor at an elevated temperature is present at no more than 4 wt % based on the total weight of the composition.

5. The composition of claim 1 , wherein the bismuth compound and the elemental sulfur are present in a weight ratio of not more than 2:3 and not less than 0.5:3; and wherein the elemental sulfur and the compound which makes the composition alkaline are present in a weight ratio of not more than 1:1 and not less than 1:5.

6. The composition of claim 1 , further comprising a dye which causes the color of the composition in the presence of steam to become black; wherein without the dye, the color of the composition in the presence of steam would be brown.

7. The composition of claim 1 , wherein the bismuth compound is bismuth subsalicylate.

8. The composition of claim 1 , wherein the compound which makes the composition alkaline is selected from the group consisting of sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, and sodium phosphate, or a combination thereof.

9. A chemical indicator composition comprising:

a) a bismuth (III) compound comprising at least one organic group which includes 2 to 20 carbon atoms;

b) elemental sulfur; and

c) a compound which makes the composition alkaline when exposed to water vapor at an elevated temperature and is selected from the group consisting of potassium carbonate, potassium bicarbonate, and sodium phosphate.

10. A method of determining the effectiveness of a steam sterilization process, the method comprising:

providing a chemical indicator comprising the chemical indicator composition of claim 1 ;

placing the chemical indicator in a steam sterilization chamber;

exposing the chemical indicator to steam at a temperature of at least 121° C.; and

determining an optical density of the chemical indicator.

11. A chemical indicator comprising a substrate and the chemical indicator composition of claim 1 coated on at least a portion of a major surface of the substrate.

12. The chemical indicator of claim 11 , wherein the substrate is coated with or impregnated with a saturant.

13. The chemical indicator of claim 11 , further comprising a saturant layer covering the chemical indicator composition.

14. The chemical indicator of claim 13 , further comprising a barrier layer covering the saturant layer and the substrate.

15. The chemical indicator of claim 11 , further comprising an adhesive layer covering at least a portion of a second major surface of the substrate opposite chemical indicator composition.

16. The composition of claim 1 , wherein the reducing agent facilitates formation of sulfide groups that react with the bismuth (III) compound to darken the color of the indicator composition upon exposure to steam.

17. The composition of claim 1 , wherein the reducing agent is selected from the group consisting of tocopherols, napthylamines, polyphenols, and combinations thereof.

18. The composition of claim 1 , wherein the reducing agent is selected from ascorbic acid and its derivatives, and combinations thereof.

19. A chemical indicator composition comprising:

a) a bismuth (III) compound comprising at least one organic group which includes 2 to 20 carbon atoms;

b) elemental sulfur;

c) a compound that makes the composition alkaline when exposed to water vapor at an elevated temperature; wherein the compound has a solubility in water at 20° C. of more than 5 grams/100 ml; and

d) a reducing agent selected from the group consisting of tocopherols, napthylamines, polyphenols and combinations thereof.