Limit Tests Vis-A-Vis Quantitative Determinations

 LIMIT TESTS VIS-A-VIS QUANTITATIVE DETERMINATIONS 

In general, limit tests are quantitative or semi-quantitative tests particularly put forward to identify and control invariably small quantities of impurity that are supposed to be present in a pharmaceutical substance. Obviously the amount of any single impurity present in an official substance is usually small, and therefore, the normal visible-reaction-response to any test for that impurity is also quite small. Hence, it is necessary and important to design the individual test in such a manner so as to avoid possible errors in the hands of various analysts. It may be achieved by taking into consideration the following three cardinal factors, namely :

 

(a) Specificity of the Tests : A test employed as a limit test should imply some sort of selective reaction with the trace impurity. It has been observed that a less specific test which limits a number of possible impurities rather instantly has a positive edge over the highly specific tests.

 

Exmaple : Contamination of Pb2+ and other heavy metal impurities in Alum is precipitated by thioacetamide as their respective sulphides at pH 3.5.

 

(b) Sensitivity : The extent of sensitivity stipulated in a limit test varies widely as per the standard laid down by a pharmacopoeia. The sensitivity is governed by a number of variable factors having a common objective to yield reproducible results, for instance :

 

(i) Gravimetric Analysis : The precipitation is guided by the concentration of the solute and of the precipitating reagent, reaction time, reaction temperature and the nature and amount of other substance(s) present in solution.

 

(ii) Colour Tests : The production of visible and distinct colouration may be achieved by ascertain-ing the requisite quantities of reagents and reactants, time period and above all the stability of the colour produced.

 

(c) Personal Errors : In fact, the personal errors must be avoided as far as possible as explained.

Comments

Post a Comment

Popular posts from this blog

Volumetric Analysis

Image
  VOLUMETRIC ANALYSIS Volumetric analysis may be broadly defined as those analytical methods whereby the exact volume of a solution of known concentration actually consumed during the course of an analysis is considered as a measure of the amount of active constituent in a given sample under determination (assay).   1. THEORY   According to the  official method of analysis , hydrochloric acid can be determined by  first  weighing a given sample accurately, and  secondly , by adding carefully a solution of known strength of sodium hydroxide in the presence of an appropriate indicator unless and until the exact equivalent amounts of HCl and NaOH have undergone the following chemical reaction : Analyte (or Active Constituent)  is the chemical entity under assay   e.g. , HCl.   Titrant  is the solution of known strength (or concentration) employed in the assay   e.g. , NaOH.   Titration  is the process of adding and then actually measuring the volume of titrant consumed in the   assay. Thi
Read more

Gas Liquid Chromatography (GLC): Instrumentation

Image
  INSTRUMENTATION A gas chromatograph essentially comprises of  six  vital components, namely :   ( a ) Carrier Gas Regulator and Flow Meter,   ( b ) Sample Injection System,   ( c ) Separation Column,   ( d ) Thermal Compartment,   ( e ) Detectors,   ( f ) Recording of Signal Current, and   ( g ) Integrator.   These components shall be discussed briefly in the sections that follow : Figure 29.2, gives the sche-matic diagram of a standard GLC equipment showing the various parts : The sample is introduced into the vaporizer and enters the column along with the carrier gas at a constant flow through the detector oven. The reference sample also passes through the detector oven into the column which is maintained by column-oven heat control device. The detector picks up the signals of the sample as well as the reference substance one after the other which is duly amplified and the signal current recorded on a strip-chart recording device or other suitable means. After passing through the d
Read more

Description of the Drug or Finished Product - Pharmaceutical Chemicals: Management

  DESCRIPTION OF THE DRUG OR FINISHED PRODUCT   The description of a particular drug or finished product may essentially include the following details, namely :   ·                Brand Name of the Product   ·                Name of the Active Ingredient   ·                Strength of Active Igredient in Dosage Form   ·                Lot/Batch Number   ·                Date of Manufacture   ·                Date of Expiry   ·                Storage Conditions (if any)   ·                Separate Dosage for Adults and Children
Read more