2.5.12. WATER: SEMI-MICRO DETERMINATION - …

1 EUROPEAN PHARMACOPOEIA Aluminium in adsorbed vaccines01/2008:20512corrected water : semi -MICRODETERMINATIONThe SEMI-MICRO DETERMINATION of water is based upon thequantitative reaction of water with sulphur dioxide andiodine in a suitable anhydrous medium in the presence of abase with sufficient buffering apparatus consists of a titration vessel with: 2 identical platinum electrodes; tight inlets for introduction of solvent and titrant; an inlet for introduction of air via a desiccant; a sample inlet fitted with a stopper or, for liquids, systems for introduction of dry nitrogen or foraspiration of solvents may also be titration is carried out according to the instrumentsupplier s instructions. Care is taken throughout thedetermination to avoid exposure of reagents and solvents toatmospheric moisture. The end-point is determined using2 identical indicator electrodes connected to an electricalsource that maintains between the electrodes either aconstant current or a constant voltage.

2 Where direct titrationis used (method A), addition of titrant causes either adecrease in voltage where constant current is maintained oran increase in current where constant voltage is maintained,until the end-point is reached. Instruments with automaticend-point detection are commonly To the titration vessel, addmethanol R,dried if necessary, or the solvent recommended by thesupplier of the titrant. Where applicable for the apparatusused, eliminate residual water from the measurement cellor carry out a pre-titration. Introduce a suitable amountofwaterinanappropriateform( water Ror a certifiedreference material) and carry out the titration, stirring forthe necessary time. The water equivalent is not less than80 per cent of that indicated by the supplier. Standardise thetitrant before the first use and at suitable intervals otherwise prescribed, use Method A.

3 Introduce into the titration vesselmethanol R,or the solvent indicated in the monograph or recommendedby the supplier of the titrant. Where applicable forthe apparatus used, eliminate residual water from themeasurement cell or carry out a pre-titration. Introduce thesubstance to be examined rapidly and carry out the titration,stirring for the necessary extraction B. Introduce into the titration vesselmethanol R,or the solvent indicated in the monograph or recommendedby the supplier of the titrant. Where applicable forthe apparatus used, eliminate residual water from themeasurement cell or carry out a pre-titration. Introduce thesubstance to be examined rapidly and in a suitable state ofdivision. Add an accurately measured volume of the titrant,sufficient to give an excess of about 1 ml or the prescribedvolume. Allow to stand protected from light for 1 min or theprescribed time, with stirring.

4 Titrate the excess of reagentusingmethanol Ror the prescribed solvent, containing anaccurately known quantity of The accuracy of the DETERMINATION with thechosen titrant must be verified for each substance to beexamined. The following procedure, given as an example, issuitable for samples containing mg of using the reagent/solvent system , sequential known amounts ofwater Rareadded in an appropriate form (at least 5 additions) and thecumulative water content determined after each the percentage recovery (r)ateachpointusingthefollowing expression:W1=amount of water added, in milligrams;W2=amount of water found, in the regression line of the cumulative waterdetermined against the water added. Calculate the slope (b),the intercept with they-axis (a) and the intercept of theextrapolated calibration line with thex-axis (d).Calculate the percentage mean recovery ().

5 Calculate thepercentage errors (e1ande2) using the following expressions:a=they-axisintercept,inmilli gramsofwater;d=thex-axisintercept,inmill igramsofwater;M= water content of the substance, in milligrams reagent/solvent system is considered to be acceptable if: ; bis between and (deviation per cent); is between per cent and per ALUMINIUM IN ADSORBEDVACCINESH omogenise the preparation to be examined and transfera suitable quantity, presumed to contain 5 mg to 6 mgof aluminium, to a 50 ml combustion flask. Add 1 ml ofsulphuric acid R, acid Rand some glassbeads. Heat the solution until thick, white fumes areevolved. If there is charring at this stage add a few moredrops ofnitric acid Rand continue boiling until the colourdisappears. Allow to cool for a few minutes, carefully add10 ml ofwater Rand boil until a clear solution is to cool, add ml ofmethyl orange solution Randneutralise withstrong sodium hydroxide solution R( mlto 7 ml).

6 If a precipitate forms dissolve it by adding, dropwise,sufficientdilute sulphuric acid R. Transfer the solution to a250 ml conical flask, rinsing the combustion flask with 25 mlofwater R. Add ml M sodium edetate,10mlofacetate buffer solution pH Rand a few glass Rand titrate the hot solution M coppersulphateuntil the colour changes to purplish-brown. Carryout a blank titration omitting the M sodium edetateis equivalent to mgof (1)applytoallmonographsandothertexts141