Methods for detection of chloral hydrate in dichloroacetic acid

1. A method of preparing an oligonucleotide, comprising:

providing a support-bound nucleotide comprising a 5′-hydroxyl group;

coupling an additional nucleoside to said support-bound nucleoside, said additional nucleoside comprising a 5′-hydroxy protecting group and a 3′-functional group capable of linking to said 5′-hydroxyl group;

selecting dichloroacetic acid having a chloral hydrate concentration of less than 15ppm; and

removing said 5′-hydroxy protecting group in the presence of said dichloroacetic acid.

2. The method of claim 1 , wherein said dichloroacetic acid has a chloral hydrate concentration of less than 10 ppm.

3. The method of claim 1 , wherein said dichloroacetic acid has a chloral hydrate concentration of less than 5 ppm.

4. The method of claim 1 , wherein said dichloroacetic has a chloral hydrate concentration of less than 1 ppm.

5. The method of claim 1 , further comprising taking a nuclear magnetic resonance spectrum of said dichloroacetic acid and integrating a nuclear magnetic resonance peak associated with a CH proton of chloral hydrate.

6. A method of removing a 5′-hydroxyl protecting group during an oligonucleotide synthesis, comprising: selecting dichloroacetic acid having a chloral hydrate concentration of less than 15 ppm; and

contacting a 5′-hydroxyl protecting group of an oligonucleotide with said dichloroacetic acid.

7. The method of claim 6 , further comprising determining whether a nuclear magnetic resonance spectrum of said dichloroacetic acid includes a nuclear magnetic resonance peak associated with a CH proton of chloral hydrate.

8. A method comprising:

testing dichloroacetic acid for the presence of chloral hydrate;

determining the chloral hydrate concentration in said dichloroacetic acid is less than 15 ppm; and

contacting a 5′-hydroxy protecting group of an oligonucleotide with said dichloroacetic acid under conditions effective to remove said protecting group.

9. The method of claim 8 , further comprising

coupling a nucleoside to said 5′-hydroxy protecting group, said nucleoside comprising a 3′-functional group capable of linking to said 5′-hydroxyl group.