REAGENTS

1. Curcumin
2. Oxalic Acid
3. Absolute Ethyl Alcohol
4. 1000 ppm B - certified, NIST traceable standard.

STANDARDS

1. Stock Solution
   1. 10 ppm B - pipet 10 mL of 1000 ppm B standard into a 1 liter volumetric flask. Dilute to volume with deionized water and mix well. Store in a plastic bottle.
2. Instrument Calibration Standards - pipet the designated mL of 10 ppm B stock solution into 100 mL volumetric flasks. Dilute to volume with deionized water and mix well. Store in plastic bottles.

Standard #	Stock Solution mL	Final Concentration ppm
1	0.10	1.00
2	0.20	2.00
3	0.30	3.00
4	0.40	4.00
5	0.50	5.00

CURCUMIN - OXALIC ACID SOLUTION

Dissolve 0.04 g curcumin and 5.0 g oxalic acid in 100 mL absolute ethyl alcohol. Store in a cool, dark place for up to 48 hours.

EXTRACTION PROCEDURE

Follow the hot water boron extraction procedure given on page 19.

COLOR DEVELOPMENT PROCEDURE

1. Pipet 2 mL of extract into a plastic beaker.
2. Add 4 mL of curcumin - oxalic acid solution and mix well.
3. Evaporate on a hot water bath at 55 C until dry.
4. Continue heating on the hot water bath 15 minutes after the extracts appear to be dry.
5. Cool and add 25 mL of absolute ethyl alcohol.
6. Filter using Whatman #1 paper.
7. Read on a colorimeter or spectrophotometer set at 545 nm.
8. Prepare instrument calibration standards in the same manner.

REFERENCE

1. Naftel. J. A. 1939. Colorimeter micro-determination of boron by the curcumin- acetate solution method. Anal. Chem. 25:1264-1267.