Reagent for detection and assessment of free chlorine in aqueous solution

1. A heat dried reagent composition for use in detecting and/or assessing free chlorine in an aqueous solution, the composition comprising:

i) an indicator comprising N,N-diethyl-p-phenylenediamine (DPD) in an amount sufficient to detect and/or assess 0.01 to 20 parts per million (ppm) free chlorine in an aqueous reaction solution;

ii) an anionic or nonionic surfactant;

iii) ethylenediaminetetraacetic acid (EDTA);

iv) trehalose;

and

v) a pH 6-7 buffer in an amount sufficient to obtain a pH of 5.5 to 7.5 in the aqueous reaction solution;

wherein the composition is dry.

2. The heat dried reagent composition of claim 1 , wherein the buffer is selected from the group consisting of: phosphate-borate; imidazole; bis-tris; citrate; malonic acid; malate; MES; and phosphate.

3. The heat dried reagent composition of claim 1 , wherein the buffer is phosphate-borate.

4. The heat dried reagent composition of claim 1 , wherein the surfactant comprises a surfactant selected from the group consisting of sodium (C 14 -C 16 ) olefin sulfonate; isopropylamine dodecylbenzene sulfonated, branched; sodium cholate; sodium dioctyl sulfosuccinate: sodium methyl oleoyl taurate; sodium polyoxyethylene(1) lauryl sulfate; octyl phenol ethoxy ethoxylated 2,4,7,9-tetramethyl 5 decyn-4,7-diol; and any combination thereof.

5. The heat dried reagent composition of claim 1 , wherein the surfactant comprises sodium (C 14 -C 16 ) olefin sulfonate.

6. The heat dried reagent composition of claim 1 , wherein:

i) DPD in an amount that will result in 10 parts per million (ppm) to 1000 ppm in an aqueous reaction solution;

ii) the surfactant in an amount that will result in 30 ppm to 600 ppm in the aqueous reaction solution;

iii) ethylenediaminetetraacetic acid (EDTA) in an amount that will result in 22 ppm to 912 ppm in the aqueous reaction solution;

iv) trehalose in an amount that will result in 225 ppm to 7500 ppm in the aqueous reaction solution;

and

v) the pH 6-7 buffer in an amount that will result in a 1 mM to 100 mM buffer concentration in the aqueous reaction solution.

7. A method of assessing free chlorine in an aqueous sample, comprising:

combining an aqueous sample of interest with a heat dried reagent composition of claim 1 to form a reaction solution,

measuring light absorbance of the reaction solution at a wavelength between 490 to 555 nanometers, and

converting the light absorbance measurement to a free chlorine amount using a standard curve.

8. The method of claim 7 , wherein the heat dried reagent composition is present in an analysis chamber of a device comprising at least one such chamber, and the aqueous sample of interest is introduced into the analysis chamber comprising the composition to form the reaction solution.

9. The method of claim 8 , wherein the light absorbance is measured within 20 to 60 seconds after the formation of the reaction solution.

10. The method of claim 9 , wherein the light absorbance is measured at a wavelength between 490 nm to 530 nm.

11. The method of claim 7 , wherein the aqueous sample of interest is added to the heat dried reagent composition to form the reaction solution having a final volume of 40 microliters to 1 milliliter.

12. A method of detecting free chlorine in an aqueous sample, comprising:

combining an aqueous sample of interest with a heat dried reagent composition of claim 1 to form a reaction solution, and

observing the color of the reaction solution,

wherein a pink color in the reaction solution is indicative of free chlorine in the aqueous sample of interest.

13. A method of preparing a heat dried reagent composition for use in detecting and/or assessing free chlorine in an aqueous solution, the method comprising:

drying a volume of an aqueous reagent precursor solution comprising:

i) an indicator comprising N,N-diethyl-p-phenylenediamine (DPD) in an amount sufficient to detect and/or assess 0.01 to 20 parts per million (ppm) free chlorine in an aqueous reaction solution;

ii) a pH 6-7 buffer in an amount sufficient to obtain a pH of 5.5 to 7.5 in the aqueous reaction solution;

iii) an anionic or nonionic surfactant;

iv) ethylenediaminetetraacetic acid (EDTA);

and

v) trehalose;

wherein the drying is performed at a temperature from about 50° C. to about 105° C. for a sufficient time to obtain a dry composition.

14. The method of claim 13 , wherein the volume of the aqueous reagent precursor solution is from about 5 microliters to about 150 microliters.

15. The method of claim 14 , wherein the drying is performed at from about 70° C. to about 95° C.

16. The method of claim 15 , wherein the volume of the aqueous reagent precursor solution is from about 5 microliters to about 50 microliters.

17. The method of claim 13 , further comprising, prior to the drying step, the step of aliquoting the aqueous reagent precursor solution into an analysis chamber of a device comprising as least one such chamber.

18. The method of claim 13 , wherein the heat dried reagent composition comprises:

i) DPD in an amount that ill result in 10 parts per million (ppm) to 1000 ppm in an aqueous reaction solution;

ii) the surfactant in an amount that will result in 30 ppm to 600 ppm in the aqueous reaction solution;

iii) ethylenediaminetetraacetic acid (EDTA) in an amount that will result in 22 ppm to 912 ppm in the aqueous reaction solution,

iv) trehalose in an amount that will result in 225 ppm to 7500 ppm in the aqueous reaction solution;

and

v) the pH 6-7 buffer in an amount that will result in a 1 mM to 100 mM buffer concentration in the aqueous reaction solution.

19. The method of claim 18 , wherein the aqueous reagent precursor solution is about 5 to 30 fold more concentrated than the concentration of the aqueous reaction solution.