2.5. ASSAYS - DrugFuture

1 EUROPEAN PHARMACOPOEIA Iodine ASSAYS01/2008 ACID VALUEThe acid valueIAis the number that expresses, in milligramsthe quantity of potassium hydroxide required to neutralise thefree acids present in 1 g of the g of the substance to be examined, or thequantity prescribed, (mg),in50mLofamixtureofequalvolumes ofethanol (96 per cent) Randlight petroleum R3,previously neutralised M potassium Msodium hydroxide, unless otherwise specified, using mL ofphenolphthalein solution R1as indicator. If necessary, heat toabout 90 C to dissolve the substance to be examined. Whenthe substance to be examined has dissolved, titrate Mpotassium M sodium hydroxideuntil the pinkcolour persists for at least 15 s (nmL of titrant). When heatinghas been applied to aid dissolution, maintain the temperature atabout 90 C during the ESTER VALUEThe ester valueIEis the number that expresses in milligramsthe quantity of potassium hydroxide required to saponify theesters present in 1 g of the substance.

2 It is calculated from thesaponification valueISand the acid valueIA:01/2008 HYDROXYL VALUEThe hydroxyl valueIOHis the number that expresses inmilligrams the quantity of potassium hydroxide requiredto neutralise the acid combined by acylation in 1 g of AIntroduce the quantity of the substance to be examined shownin Table (mg) into a 150 mL acetylation flask fitted withan air condenser, unless another quantity is prescribed in themonograph. Add the quantity ofacetic anhydride solution R1stated in Table and attach the air valueIOHQ uantity of sample(g)Volume ofacetylating reagent (mL)10 - - - - - or or - - - the flask in a water-bath for 1 h keeping the level of thewater about cm above the level of the liquid in the the flask and allow to cool.

3 Add 5 mL ofwater Rthrough the upper end of the condenser. If a cloudinessappears add sufficientpyridine Rto clear it, noting thevolume added. Shake the flask and replace in the water-bathfor 10 min. Withdraw the flask and allow to cool. Rinse thecondenser and the walls of the flask with 5 mL ofalcohol R,previously neutralised tophenolphthalein solution M alcoholic potassium hydroxideusing mL ofphenolphthalein solution R1as indicator (n1mL Malcoholic potassium hydroxide). Carry out a blank test underthe same conditions (n2mL M alcoholic potassiumhydroxide).METHOD BIntroduce the prescribed quantity of the substance to beexamined (mg) into a perfectly dry 5 mL conical flask fittedwith a ground-glass or suitable plastic stopper and add mLofpropionic anhydride reagent to dissolve the substance.

4 Allow to stand for 2 h and its contents into a wide-mouthed 500 mL conicalflask containing mL of a 9 g/L solution ofaniline Rincyclohexane Rand 30 mL ofglacial acetic acid of the flask, allow to stand for 5 min, add mLofcrystal violet solution Rand titrate M perchloricaciduntil an emerald-green colour is obtained (n1mL M perchloric acid). Carry out a blank test under the sameconditions (n2mL M perchloric acid).To take account of any water present, determine this (ypercent) by the semi-micro determination of water ( ).The hydroxyl value is then given by the equation:01/2008 IODINE VALUET heiodinevalueIIis the number that expresses in grams thequantity of halogen, calculated as iodine, that can be fixed inthe prescribed conditions by 100 g of the the monograph does not specify the method to be used,method A is applied.

5 Any change from method A to method Bis AUnless otherwise prescribed, use the following quantities(Table ) for the valueIIQuantity of sample (g)less than - - - - than - the prescribed quantity of the substance to beexamined (mg) into a 250 mL flask fitted with a ground-glassstopper and previously dried or rinsed withglacial acetic acid R,and dissolve it in 15 mL ofchloroform Runless otherwiseprescribed. Add very slowly mL ofiodine bromidesolution R. Close the flask and keep it in the dark for 30 minunless otherwise prescribed, shaking frequently. Add 10 mL of a100 g/L solution ofpotassium iodide Rand 100 mL ofwater M sodium thiosulfate, shaking vigorously untilthe yellow colour is almost discharged. Add 5 mL ofstarchsolution Rand continue the titration adding M sodiumGeneral Notices (1) apply to all monographs and other texts137