Medical brain notes 14

  INTRODUCTION   The skill, knowledge, expertise and above all the degree of confidence involved in the ultimate result of an analyst is solely governed by the extent of accuracy and precision achieved by the analytical procedure  vis-a-vis  the possible sources of error that may be incorporated inadvertently. In fact, the quantitative   pharmaceutical analysis is not merely confined to just taking a random sample, performing a single assay quickly, and finally making a loud claim that the result so obtained cannot be challenged. Truly speaking an ideal analyst must have a total in-depth knowledge of the chemistry involved along with the  pros and cons  of interferences that may be caused due to the host of compounds, elements and ions besides adequate exposure and hands-on experience of the statistical distribution of values.   The terminology ‘error’ invariably refers to the difference in the numerical values between a measured value and the tru...

  CLASSIFICATION OF ERRORS The numerous uncertainties usually encountered in a chemical analysis give rise to a host of ‘errors’ that may be broadly categorised into  two  heads, namely :   ( i ) Determinate (systematic) Errors, and   ( ii ) Indeterminate (random) Errors.   It is pertinent to mention here that it becomes rather difficult at times to place a particular ‘error’ into one of the above mentioned categories ; however, the classification may prove to be beneficial with regard to study of the various analytical errors that crop up in the course of routine analysis.   1. DETERMINATE (SYSTEMATIC) ERRORS   These are errors that possess a definite value together with a reasonable assignable cause; however, in principle these avoidable errors may be measured and accounted for coveniently. The most important errors belonging to this particular class are :   ( a )  Personal Errors :  They are exclusively caused due to ‘personal eq...

  INTRODUCTION After accomplishing the thorough investigation of various aspects of possible ‘determinate errors’ and having applied the relevant corrections, it has been observed that the data thus generated not only show fluctuations but also are found to be random in nature. The powerful and effective technique of statistics may render such results, which scatter in a random manner, into a better form that may be employed intelligently. Besides, the specific statistical treatment of the calibration data, aided by pre-programmable calculators and micro-computers, very often yields a fairly accurate and more presentable determination of the graphs between absorbance and concentration than those produced manually.   STATISTICAL VALIDATION The statistical validation of analytical results will be discussed with regard to the following  six  as-pects individually, along with appropriate examples wherever possible, in the sections that follow :   ( i ) Statistical t...