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 nucleotide, said additional nucleotide comprising a 5′-hydroxy protecting group and a 3′-functional group capable of linking to said 5′-hydroxyl group;

providing a solvent that comprises said dichloroacetic acid in an amount of at least 3% by volume, and said dichloroacetic acid having a chloral hydrate concentration of less than 15 ppm; and

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

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 , wherein said solvent comprises dichloroacetic acid in an amount of at least 10% by volume and having a chloral hydrate concentration of less than 15 ppm.

6. The method of claim 5 , wherein said dichloroacetic acid has a chloral hydrate concentration of less than 10 ppm.

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

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

9. The method of claim 1 , wherein said solvent is selected from the group consisting of acetonitrile, benzene, cyclohexane, pentane, hexane, toluene, cycloheptane, methylcyclohexane, heptane, ethylbenzene, m-, o-, or p-xylene, octane indane and nonane.

10. The method of claim 9 , wherein said solvent is toluene.

11. A method of removing a 5′-hydroxyl protecting group during an oligonucleotide synthesis, comprising:

providing a solvent that comprises said dichloroacetic acid in an amount of at least 3% by volume, and said 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.

12. 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;

providing a solvent that comprises said dichloroacetic acid in an amount of at least 3% by volume; and

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

13. The method of claim 12 , further comprising:

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