How to establish quality control in a laboratory

1What is Internal Quality Control (IQC)?

IQC is one of a number of concerted measures that analytical chemists can take to ensure that the data produced in the laboratory are fit for their intended purpose. In practice, fitness for purpose is determined by a comparison of the accuracy achieved in a laboratory at a given time with a required level of accuracy. Internal quality control therefore comprises the routine practical procedures that enable the analytical chemist to accept a result or group of results as fit for purpose, or reject the results and repeat the analysis. As such, IQC is an important determinant of the quality of analytical data, and is recognized as such by accreditation agencies.

2 What is Control Material or QC sample?

Internal quality control is undertaken by the inclusion of particular reference materials into the analytical sequence, are called "control materials” or “QC samples”.

As the control materials are treated in exactly the same way as the test materials, they are regarded as surrogates that can be used to characterize the performance of the analytical system, both at a specific time and over longer intervals.

Ideally both the control materials and those used to create the calibration should be traceable to appropriate certified reference materials or a recognized empirical reference method. When this is not possible, control materials should be traceable at least to a material of guaranteed purity or other well characterized material. However, the two paths of traceability must not become coincident at too late a stage in the analytical process. For instance, if control materials and calibration standards were prepared from a single stock solution of analyte, IQC would not detect any inaccuracy stemming from the incorrect preparation of the stock solution.

3 Quality assurance:

All those planned and systematic actions necessary to provide adequate confidence that a product or service will satisfy given requirements for quality. IQC is a part of quality assurance.

4 Accuracy: 

Closeness of the agreement between the result of a measurement and a true value of the measured.

5Precision:

 Closeness of agreement between independent test results obtained under prescribed conditions.

6 Traceability:

 Property of the result of a measurement or the value of a standard whereby it can be related to stated references, usually national or international standards, through an unbroken chain of comparisons all having stated uncertainties

7Uncertainty of measurement:

Parameter, associated with the result of a measurement, which characterizes the dispersion of the values that could reasonably be attributed to the measured.

Establishing Control Values for QC samples.

Obtain minimum ten values for QC samples, by analyzing every day with average of minimum 2 duplicates.

Calculate Upper Warning Limit (UWL) and Lower Warning Limits (LWL).Normally UWL= (Standard deviation x 2) + Average of QC samples values. LWL= Average of QC samples values- (Standard deviation x 2)

Calculate Upper Control Limit (UCL) and Lower Control Limits (LCL).Normally UCL= (Standard deviation x 3) + Average of QC samples values. LCL= Average of QC samples values- (Standard deviation x 3).

1.       Monitor Quality of analysis through QC Chart.

Plot QC values in Excel sheet and make a chart, mark UWL, LWL, UCL, and LCL.

Now every day QC analysis with samples can monitored through QC chart.Example of QC chart given below.