We Claim:
1. An improved process for the preparation of Dalteparin sodium, which
comprises the steps of:
(a) depolymerising heparin sodium with sodium nitrite of 2.5 to 3.5% by weight in the presence of an acid,
(b) reducing the product obtained in step (a) with < 2.0 mole equivalents of a reducing agent to obtain crude Dalteparin sodium,
(c) isolating the crude Dalteparin sodium obtained in step (b),
(d) stirring the crude product obtained in step (c) in a solvent mixture to obtain precipitate of Dalteparin sodium,
(e) dissolving the precipitate obtained in step (d) in water and subjecting to ultra-violet irradiation at 254 nm wavelength and 4 to 40W power for a time period of 10 seconds to 8 minutes and
(f) lyophilizing the solution obtained in step (e) in presence of alcohol to obtain Dalteparin sodium in free powder form.

2. The process as claimed in claim 1, wherein the depolymerisation is carried out at a pH in the range of 2.0 to 4.0.
3. The process as claimed in claim 1, wherein the acid is hydrochloric acid, acetic acid or sulphuric acid.
4. The process as claimed in claim 1, wherein the reducing agent is sodium borohydride, potassium borohydride or lithium borohydride.
5. The process as claimed in claim 1, wherein the reduction is carried out at room temperature for a period of about 1.0 to 3.0 hours.
6. The process as claimed in claim 1, wherein the lyophilization is carried out by adding alcohol to the Dalteparin sodium solution obtained in step (e).
7. The process as claimed in claim 6, wherein the alcohol is at a concentration of and 5 to 15 % by volume relative to the water used in step (e).
8. The process as claimed in claim 6 or claim 7, wherein alcohol is ethanol.
9. An improved process for the preparation of Dalteparin sodium, which comprises the steps of:

(a) depolymerizing an aqueous solution of heparin sodium with sodium nitrite of 2.5 to 3.5% by weight in the presence of hydrochloric acid at a pH of 2 to 4 and at a temperature of 5 to 10°C,
(b) reducing the product obtained in step (a) with 1.5 to 2.0 equivalents of sodium borohydride to obtain crude Dalteparin sodium,
(c) isolating the crude Dalteparin sodium obtained in step (b),
(d) stirring the crude product obtained in step (c) in a solvent mixture to obtain precipitate of Dalteparin sodium,
(e) dissolving the precipitate obtained in step (d) in water and subjecting to ultra-violet irradiation at 254 nm wavelength and 4 to 40W power for a time period of 10 seconds to 8 minutes and
(f) lyophilizing the solution obtained in step (e) in presence of alcohol to obtain Dalteparin sodium in pure powder form and with N-NO content within limits.
10. An improved process for the preparation of Dalteparin sodium comprising the steps of:
(a) depolymerising an aqueous solution of heparin sodium with aqueous sodium nitrite solution of 2.5 to 3.1% by weight relative to heparin sodium in the presence of hydrochloric acid at a pH of 2 to 4 and at a temperature of 5 to 10°C,
(b) reducing the product obtained in step (a) with 1.5 to 2.0 equivalents of sodium borohydride to obtain crude Dalteparin sodium,
(c) isolating the crude Dalteparin sodium obtained in step (b),
(d) stirring the crude product obtained in step (c) in a solvent mixture to obtain precipitate of Dalteparin sodium,
(e) dissolving the precipitate obtained in step (d) in water and subjecting to ultra-violet irradiation at 254 nm wavelength and 4 to 40W power for a time period of 10 second to 8 minutes and
(f) lyophilizing the solution obtained in step (e) in presence of alcohol to obtain of Dalteparin sodium in free powder form,

wherein the process does not involve any chromatographic purification
step. 11. The process as claimed in any of the claims 1-10, wherein the UV irradiation is carried out in a continuous photochemical reactor integrated with one or more UV lamps.