SOP on Reagents & Chemicals
Scope
To establish a system and guidelines for the preparation of Laboratory Reagent, Normal Solutions, Standardization and their Verification.
Chemical Reagent
Procedure
Chemical Reagent/Solutions are required for the undertaking the routine chemical analysis. For better accuracy, the chemical reagent/solutions should be prepared using pure chemicals of standard makes. Also it be ensured that they are stored in proper containers and are verified for their deterioration.
Preparation of Chemical Reagents
– Weigh the requisite quantity of the chemical depending upon the strength and volume of the reagent required.
– Transfer the weighed chemical to the volumetric flask with the help of distilled water.
– Add the additional distilled water to the volumetric flask, but do not make upto the volume.
– Allow the solution to cool to room temperature, make upto volume and shake well till the contents are evenly mixed.
– Transfer the solution to a dried reagent glass bottle, which has been previously washed with a solution of chromic acid.
– Affix the label on the bottle incorporating:
– Name of the reagent
– Strength of the reagent
– Date of preparation
– Date of validity/use before date
– The chemical reagent solution must be observed for its clarity, haziness/turbidity, fungal growth, suspended matter, sedimentation, crystallisation on regular intervals.
All solutions which show evidence of deterioration due to the above mentioned reasons must be discarded regardless of their date of preparation and validity.
Preparation of Normal Volumetric Solution
– Weigh the requisite quantity of the chemical required for the preparation of 0.05N/0.1N, 0.2N, 0.5N, 1N solutions. The quantity weighed should be very near to the weight required for the respective normality of solutions to be prepared.
– Transfer the weighed quantity of the chemical to the volumetric flask with the help of distilled water.
– Add additional distilled water to the volumetric flask, but do not make upto the volume.
– Allow the solution to cool to room temperature, make upto volume and shake till the contents are evenly mixed.
– Volumetric solutions shall be standardised by titration against a primary reference solution preferably of the same normality prepared in a similar way to determine the normality of the prepared solution.
– Solutions of primary standards, which are highly purified salts of AR/GR quality of known purity are prepared by accurately weighing exact requisite quantity and dissolving it to produce a specific volume.
i) The normality of the solution may be calculated from the general formula.
N1V1 = N2V2
ii) Alternatively the solution may be standardised by weighing an exact amount of the primary reference standard, dissolving in water and titrating it with the normal solution and calculating as follow.
Wt. of the primary Potency/Purity of the
Normality = standard in mgs x primary standard
Factor (in mg) x 1000
– Transfer the solutions of the standardised normal solution and the standard reference solution to the dried glass bottles, which have been previously washed with a solution of chromic acid.
– Affix the label on the bottle incorporating:
(i) Name of normal solution/standard reference solution
(ii) Assigned normality of the solution
(iii) Date of preparation
(iv) Date of validity/use before date
The solutions must be observed for its clarity, haziness/turbidity, fungal growth, suspended matter, sedimentation on regular intervals.
All the solutions which show evidence of deterioration due to the above mentioned reasons must be discarded regardless of their date of preparation.
The normal solutions prepared above are required to be re-checked for their assigned normality at regular intervals. In case the normal solutions are not consumed, before date their normality is verified against the standard normal solutions prepared and the normality calculated. The assigned normality is mentioned on the bottle alongwith the date of verification.
– Records shall be documented for each solution prepared, its assigned normality, volumes used in the determinations, calculations etc., if any.
Preparation of Standard Solutions of Elements – ANIONS/CATIONS
In the instrumental techniques, the determinations are undertaken with solutions having very small concentrates of the elements to be determined. The standard solutions which will be required for the analysis must also contain very small concentrations of the relevant elements and is rarely practical to prepare the standard solutions by weighing out directly the required substance. The usual practice therefore is to prepare stock solutions which may contain about 1000gmL-1 of the required element and then the working standard solutions are prepared by suitable dilution of the stock solution as and when required.
Solutions which contain less than 10gmL-1 are often found to deteriorate on standing owing to adsorption of the solute on the walls of the glass containers. In view of this standard solution in which the solute concentrations is of this order should not be stored for more than 1 to 2 days.
The stock solutions may be prepared by dissolving the standard reference materials, AR/GR certified chemicals or requisite quantity and diluting to a specific volume.
Affix the label on the bottle incorporating:
– Name of the standard solution
– Strength of the element
– Date of preparation
– Date of validity/use before date
The chemical reagent solution must be observed for its clarity, haziness/turbidity, fungal growth, suspended matter, sedimentation, crystallisation on regular intervals.
All solutions which show evidence of deterioration due to the above mentioned reasons must be discarded regardless of their date of preparation and validity.