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.

2 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. 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.

3 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. 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.

4 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.

5 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 ( ).

6 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. 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.

7 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