Standards and Calibrators Lecture 4-1 PDF

Calibrators, standards and their purposes Lecture 4 By Dr Najwa Al Jahdhami Topics to be covered Calibration definition, its requirement and purpose. Calibrators replaced by standards, and their uses. Difference between control and standards. Metho...

Calibrators, standards and their purposes Lecture 4 By Dr Najwa Al Jahdhami Topics to be covered Calibration definition, its requirement and purpose. Calibrators replaced by standards, and their uses. Difference between control and standards. Method of Preparing working standard to generate a calibration curve. Calibration curve definition, purpose, and steps to construct it. Calibration, its requirement and purpose Calibration adjusts the output of an instrument (spirometer, gas analyzer) to match a known input. The calibration process requires a measurement standard. This measurement standard is a physical object, system or experiment that has a known true value. The goal of calibration is to minimize any measurement uncertainty by ensuring the accuracy of test equipment. Calibrators replaced by standards The term “calibration material” has generally replaced “standard”. So what are standards used for? 1. Validate the run. 2. Generate a calibration curve. Is there a difference between a control and a standard? Cont… Standard: adjust the output of the method. Control: Ensure that results in a patients sample is accurate. Note: Samples that are used as standards to calibrate the method, shouldn’t be used as controls to monitor the method. Standards used to generate a calibration curve Calibration standards are key to the analytical process. They are used to create the calibration curve and the better the calibration curve, the better the data. The process of making a calibration standards generally follows the process shown: Cont… https://andyjconnelly.wordpress.com/2017/03/06/preparation- of-calibration-standards/ Stock solution purpose A stock solution acts as an intermediate solution between a standard solution and your calibration standards. For example, if you are calibrating in the range 1-10ppm it will be difficult to measure out the very small amounts of 1000ppm standard required. To make life easier you will generally make a 100ppm stock solution first and then use that to prepare the calibration standards. It is not recommended to store any stock solution or standard. Cont… To calculate the amount of aqueous standard material required to prepare a solution you can use the following equation: where C = Concentration (ppm, kmol m−3, mol dm−3, etc.) and V = Volume (ml, dm, etc.) As an example, How to make 50ml of 5ppm calibration solution from a 100ppm standard (or stock) solution? Example of standard preparation by stock solution A technologist needs to prepare a standard curve for a total protein assay. The stock standard has a concentration of 10 g/dL. Four working standards were necessary with concentrations of 800 mg/dL, 600mg/ dL, 400mg/dL, and 200mg/dL and a total volume of 2ml each. Deionized water is used as the diluents. What is the technologist’s next step? Cont… What if you are given an unknown concentration sample, however the absorbance values of the standard and unknown is given, including the concertation of the standards calculated previously! How can you obtain the unknown concentration? Calibration Curve Calibration curve is a regression model used to predict the unknown concentrations of analytes of interest based on the response of the instrument to the known standards. Drawing a Calibration Curve What are the steps to construct a calibration curve? https://www.youtube.com/watch?v=aZ8cniOFVaE Exercise A total protein assay was performed using five standards, two quality control specimens, and six patients specimens. The absorbance values for each of the standards, quality control specimens and patient specimens are listed below, draw a standard curve and get the results of the QC and patient specimens. Sample Conc. in g/dL Absorbance Standard 1 3.0 0.195 Standard 2 4.5 0.290 Standard 3 7.5 0.480 Standard 4 15 0.960 QC level 1 0.270 QC level 2 0.440 Patient 1 0.580 Patient 2.0170 Patient 3 0.250 Patient 4 0.490 Patient 5 0.920 Patient 6 0.970