dextran is a polysaccharide polymer of formula ( c 6 h 10 o 5 ) n composed exclusively of a - d - gluconpyranosyl units linked predominately α - 1 - 6 and obtained by the action of bacteria grown on a sucrose substrate by methods well - known in the art . native dextrans usually have high molecular weight . lower molecular weight dextrans are prepared by partial depolymerization of the native dextrans by methods known in the art , such as treatment with mineral acid . a dextran obtained by partial depolymerization of such a native dextran may be further modified , as for example by partial reduction using sodium borohydride or catalytic hydrogenation , or by oxidation . the term &# 34 ; dextran &# 34 ; as used herein is intended to include dextran , reduced dextran , and oxidized dextran . treatment of unmodified dextran with mild oxidizing agents such as sodium or potassium periodate introduces carboxyl groups on the terminal glucose unit . optionally , the terminal glucose unit may be oxidized to carboxylic groups using , for example , bromine , sodium hypobromite , sodium bromite , sodium hypochlorite or sodium chlorite . in one embodiment of the invention , dextran is dissolved in water and oxidized by treatment with between about 0 . 4 and about 0 . 6 parts per weight ( ppw ) 5 % aqueous sodium hypochlorite , followed by between about 0 . 10 and about 0 . 15 ppw of aqueous sodium hydroxide . the oxidation is best carried out at ambient temperature ( about 15 ° to about 35 ° c .). a representative dextran contemplated for use in the present invention is a partially depolymerized dextran having a molecular weight of between about 1 , 000 and about 10 , 000 , preferably between about 3 , 000 and about 6 , 000 . in accordance with the foregoing , between about 1 and about 10 ppw of such a dextran are dissolved in water ( preferred dextrans being unoxidized or oxidized dextrans and oxidized dextrans being most preferred ). a particularly preferred embodiment of the process of the present invention utilizes between about 1 . 0 and about 1 . 5 ppw of oxidized dextran having a molecular weight of 5 , 000 to 6 , 000 . the aqueous dextran solution is then added with stirring to an aqueous solution of about 1 ppw of iron ( iii ), where the term &# 34 ; iron ( iii )&# 34 ; means trivalent hydrous ferric oxide . the iron ( iii ) solution is prepared by neutralizing a ferric salt with alkali . suitable ferric salts include any water - soluble salts which generate hydrous ferric oxide when treated with alkalis . representative salts include ferric chloride , ferric nitrate , ferric sulfate , ferric perchlorate , ferric acetate , ferric trichloroacetate , ferric citrate and the like , as well as double salts such as ferric ammonium sulfate or ferric ammonium citrate and the like . of the above salts , ferric chloride is particularly preferred . representative alkalis include the hyroxides and carbonates of sodium , lithium and potassium . the ferric salt may be neutralized by treatment with excess alkali , or may be formed in a two step process involving partial neutralization with alkali followed by addition of the dextran solution and additional alkali to achieve complete neutralization and complex formation . the iron ( iii ) solution is preferably prepared by adding between about 0 . 14 and about 0 . 24 ppw of aqueous sodium carbonate to an aqueous solution containing about 1 ppw of hydrated ferric chloride . after combining the aqueous iron ( iii ) and dextran solutions , the mixture is made basic by addition of between about 0 . 15 and about 0 . 25 ppw alkali , preferably sodium hydroxide . the mixture is then heated , preferably at between about 80 ° and about 100 ° c ., and stirred until complex formation is complete . when unoxidized dextran is used , gradual heating may be required to prevent formation of a heterogeneous mixture . the solution may then be acidified using solid , gaseous or liquid acid , preferably aqueous hydrochloric acid , to obtain a ph of between about 4 and about 5 . the solution may then be heated , preferably at between about 118 ° and about 135 ° c ., at a pressure of between about 10 and about 20 psi ( 68 and 138 kpa ). after cooling to ambient temperature , crystalline iron - dextran complex is obtained by adding the reaction solution to a water - miscible organic solvent in a solution - to - solvent ratio of about not less than 1 : 1 by volume , followed by filtration . representative solvents include methanol , ethanol , isopropanol , acetone and the like , with methanol being the most preferred solvent and ( when methanol is used ) the preferred ratio of aqueous iron - dextran solution to solvent being about 1 : 8 . to reduce solvent volume , the aqueous iron - dextran solution may be concentrated prior to addition to the solvent . the initially obtained crystalline iron - dextran may be washed with additional solvent prior to drying and storage . the process of the present invention will be better understood in connection with the following examples , which are intended solely as an illustration thereof . to a solution of molecular weight 5000 dextran ( 60 . 7 g ) in water ( 108 ml ) was added bleach ( 32 ml ) and 5 % aqueous sodium hydroxide ( 7 . 5 ml ). the solution was stirred for one hour and then was refrigerated for 17 hours . to a stirred solution of ferric chloride ( 60 g ) in water ( 300 ml ) was added , dropwise over 60 minutes , a solution of sodium carbonate ( 11 . 8 g ) in water ( 100 ml ), followed by the bleach - dextran solution . to the resulting solution was added a solution of sodium hydroxide ( 22 . 6 g ) in water ( 100 ml ) over a 60 minute period . the mixture was heated at 90 °- 100 ° c . for 90 minutes and then was cooled to ambient temperature and acidified with to ph 4 with hcl to give 907 g of iron - dextran solution . a 447 g aliquot was removed and concentrated to a volume of 160 ml and then was added with stirring to 1038 g of methanol . the resulting crystalline solid was collected by filtration and washed with methanol . the solid was slurried in methanol ( 173 g ), filtered , and dried to afford 15 . 63 g of iron - dextran powder . the material passed gel permeation chromatographic analysis . to a solution in water ( 70 ml ) of ferric chloride ( 24 . 0 g ) was added a solution of sodium carbonate ( 4 . 7 g ) in water ( 40 ml ) over an 80 - minute period . to the mixture was added a solution of dextran ( 27 . 3 g ) in water ( 70 ml ), followed by addition , over 40 minutes , of a solution of sodium hydroxide ( 9 . 0 g ) in water ( 110 ml ). the mixture was then added to methanol ( 350 ml ). the resulting solid was filtered , dissolved in water ( 150 ml ) and heated at 85 ° c . for 60 minutes . the mixture was cooled and added to methanol ( 100 ml ). the resulting solid was filtered and dried to afford 19 . 4 g of iron dextran powder . the material passed gel permeation chromatographic analysis . to a solution of molecular weight 5000 dextran ( 27 . 3 g ) in water ( 70 ml ) was added 2 . 25n aqueous sodium hydroxide ( 5 ml ); the resulting mixture was heated at 75 °- 80 ° c . for 30 minutes . the solution was cooled and added to a ferric solution prepared by treating a solution of ferric chloride ( 24 . 0 g ) in water ( 70 ml ) with 1 . 1n aqueous sodium carbonate ( 40 ml ). the resulting solution was heated to 80 °- 90 ° c ., cooled , and added to methanol ( 100 ml ) with stirring . the resulting crystalline solid was filtered and dried to give iron - dextran powder . the material passed gel permeation chromatographic analysis . to a 30 - gallon reactor containing a 25 ° c . solution under n 2 of ferric chloride hexahydrate ( 5 . 0 kg ) in degassed water ( 25 kg ) was added a solution of sodium carbonate ( 1 . 0 kg ) in water ( 8 . 3 kg ). the temperature was maintained at 20 °- 26 ° c . while stirring at 30 - 50 rpm during the addition . in a 50 - gallon reactor , dextran ( 5 . 2 kg ) was dissolved in water ( 9 . 1 kg ). to the dextran solution was added 5 % aqueous sodium hypochlorite ( 2 . 9 kg ) and after thorough mixing 10 % aqueous sodium hydroxide solution ( 0 . 7 kg ) was added . the solution was stirred until it did not react with ki starch paper . the oxidized dextran solution was then added to the ferric solution over 5 minutes while maintaining the temperature of the ferric solution at 23 °- 25 ° c . and stirring at 75 - 100 rpm . a solution of sodium hydroxide ( 2 . 0 kg ) in water ( 8 . 3 kg ) was added over a period of about one hour . the reaction mixture was then stirred for 90 minutes at 21 °- 26 ° c . and then was warmed to 85 °- 100 ° c . for 90 minutes . the reaction mixture was then cooled to 30 °- 40 ° c . and adjusted to ph 4 . 3 - 5 . 0 with hcl . the reaction mixture was then filtered and the filtrate was heated at 121 °- 130 ° c . in a sealed vessel for 80 - 90 minutes . the solution was concentrated to a volume of about 15 l and cooled to ambient temperature . the iron - dextran solution was then slowly added to 121 kg of methanol over about 60 minutes with vigorous stirring . a precipitate formed instantly . the solid was filtered and rinsed with methanol ( 120 kg ) and then was suspended in 64 kg of methanol . the suspension was stirred for 30 minutes . the solid was filtered and dried in vacuo at 85 ° c . to give 4 . 03 kg of iron - dextran powder . it is understood that the foregoing detailed description and accompanying examples are merely illustrative and are not to be taken as limitations upon the scope of the invention , which is defined solely by the appended claims and their equivalents . various changes and modifications to the disclosed embodiments will be apparent to those skilled in the art . such changes and modifications , including without limitation those relating to the materials and / or methods of use of the invention , may be made without departing from the spirit and scope thereof .