Validation Exercise in the Measurement of Iron - Lab Report Example

Validation Exercise in the Measurement of Iron Section A: Process of method validation Validation is the process of evaluating method performance anddemonstrating that it meets a particular requirement. Method validation is the means of ensuring and providing documentary evidence that methods are capable of consistently producing a result of the required quality. It makes use of a set of tests that test both the assumptions which the method is based and establish and document the performance characteristics of the method, therefore demonstrating whether the method is fit for a particular purpose. Typical performance characteristics include selectivity and specificity, precision, bias, accuracy, detection capability, linearity and working range, ruggedness. The process of method validation can be used when the method is new and has no previous performance history, when an established method is proved to be changing with time, when an established method is used in a different laboratory, with different analysts or with different equipment and also to demonstrate the equivalence between two methods. Section B: Standardised Tables of Results Table 1: Determination of Iron Ions in Solution using Atomic Absorption Spectroscopy Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Average conc. g/L 0.0232 2.1327 4.4706 0.1471 0.0609 0.1118 Molarity (M) 0.0004 0.0381 0.0798 0.0026 0.0011 0.0020 ppm 23.24 21.327 4470.6 147.06 60.88 111.76 Max (M) 0.44 0.165 0.076 0.034 0.105 0.019 Min (M) 0.035 0.052 0.076 0.032 0.102 0.019 Average (M) 0.21725 0.08625 0.076 0.033 0.1035 0.019 Std Dev 0.2085 0.0528 0.0014 0.0021 Form of Fe 3 3 2 2 2 3 Table 2: Determination of Concentration of Iron by Colorimetric Method Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Average Conc. g/l 0.0466 0.4872 0.4967 0.5225 0.148 0.5122 average Molarity (M) 0.00083 0.0087 0.0089 0.0093 0.0026 0.0091 average ppm 46.56 487.2 496.7 522.5 148 512.2 Max (M) 0.31 2.345 2.25 2.305 1.078 2.18 Min(M) 0.076 0.655 0.769 0.933 0.117 0.55 Average(M) 0.19804 1.7494 1.78285 1.8736 0.55519 1.83746 Std Dev 0.04762 0.36373 0.31661 0.37093 0.21672 0.31488 Form of Fe 3 3 2 2 2 3 Table 3: Determination of the Iron Concentration by Ion Exchange Chromatography. Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Avg. conc. g/L 0.0728 5.859 8.587 0.332 0.102 0.2568 Molarity (M) 0.0013 0.1046 0.1533 0.1533 0.0018 0.0046 ppm 72.795 5859.88 8587.63 331.955 102.42 256.755 Max 0.1273 6.1875 9.358 0.3976 0.1640 0.2818 Min 0.0464 5.662 6.888 0.2589 0.0635 0.2318 Average 0.0728 5.8599 8.5876 0.3319 0.1024 0.2568 Std Dev 0.0369 0.2278 1.1447 0.0653 0.0482 0.0234 Form of Fe 3 3 2 2 2 3 Table 4: Determination of Iron by REDOX Method CONC Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 Average g/l 9.352 16.68 21.28 13.5 Molarity (M) 0.167 0.298 0.38 0.241 ppm 9352 16680 21280 13500 Max 0.00067 4.05 2.185 1.429 Min 0.00067 0.0721 0.0032 0.00176 Average 0.00067 0.308 0.497 0.56011 Std Dev 0.849 0.791 0.762 Form of Fe 3 3 2 2 2 3 Section C: Critical Analysis of Results and Methods i. Specificity and Selectivity Selectivity of a method refers to the extent to which it can determine particular analyte(s) in a complex mixture without interference from other components in the mixture while specificity generally refers to a method that provides a response for a single analyte only (McCormack, 1987). In selectivity, a number of chemical components may or may not be distinguished from each other while in specificity, only one component is distinguished from the rest. In Atomic Absorption Spectropy, the absorbance of a single chemical component cannot be distinguished from that of a complex mixture; therefore, this method is not specific. For this method to work, the iron salt should not be contaminated with other ions therefore deionised water is used. In Redox and Ion Exchange Chromatography, the unknown component can be easily distinguished from the rest since making the processes to be specific. These methods are best used in contaminated ions. ii. Precision This expresses the degree of scatter between groups of measurements obtained from several samples of the same type under prescribed conditions. The higher the difference between values, the lower the precision and the lower the difference between values, the higher the range. In determination of concentration of iron ions by atomic absorption spectropy, the overall range between the maximum and minimum values is the least making it the most precise method compared to the others. The least precise method is the colorimetric method since it has the highest overall range. iii. Accuracy The accuracy of an analytical method is defined as the degree to which the determined value of analyte in a sample corresponds to a true value (Wismer, 1991). Accuracy may be determined by analysing a sample of known concentration and comparing the measured value to the true value. Comparing the four methods to the provided to the real composition of the samples, determination of concentration of iron ions by atomic absorption spectropy is the most accurate since the results obtained from this method deviate the least from the true values as compared to other methods. On the other hand, the redox method is the least accurate. iv. Detection Capability This is the ability of an analytical procedure to detect the lowest amount of an analyte. It is calculated by searching the lowest calibration standard which produces peak response corresponding to the analyte. The average response (R) and standard deviation are calculated, giving the formula as R + (3 * SD). After calculations from tables, atomic absorption spectropy is the most consistent method compared to the other methods. After calculating the detection capability for all the methods, we see that it detects the lowest amount of analyte. The results from Ion exchange chromatography are not consistent. This shows that it has the least capability of detecting an electrolyte. This means that the results from atomic absorption spectropy are to be trusted than those of ion exchange chromatography due to its consistence. v. Linearity and working range. Linearity is the ability of an analytical procedure to produce results which are proportional to the concentration of the analyte within a certain concentration range. It is established by visually inspecting a graph of analytical response against the analyte concentration. The results should not show significant deviation from linearity, that is the correlation coefficient. The correlation coefficient, r, should not be less than 0.99. Both colorimetric and atomic absorption spectropy methods are linear since they have correlation coefficients that are greater than 0.99 that is, 0.998 and 0.998 respectively. The working range is the interval between the upper and lower concentrations of analyte in a sample that has demonstrated that the analytical method has suitable levels of precision, accuracy and linearity. Atomic absorption spectropy has the most suitable levels of precision, accuracy and linearity hence its range is our working range. vi. Ruggedness The ruggedness of an analytical procedure is a measure of its capacity to remain unaffected by small, but deliberate variations in the method parameters and provides an indication of its reliability during normal usage (William, 1953). The results obtained from atomic absorption spectropy by different people at different times has less variations hence the ruggedness of this analytical method is low. This shows that this method is highly reliable in different circumstances. On the other hand, ionic exchange method has more variations making it highly rugged. This means that it is affected by small changes in the parameters. Therefore, it is not a reliable method. vii. Bias This is the difference between the calculated mean of the measurement results and an accepted reference value. It is a systematic error. Atomic absorption spectropy has the least bias compared to the other methods since the difference between the results and the real samples is the least. Ionic exchange has the highest bias since it has the greatest difference. Section D: Final Summary The most suitable method for analysis of the samples provided should have the highest selectivity, precision, accuracy, detection capability; it should be linear, should not be rugged and should also not be biased. From the tables and the analysis of the results, atomic absorption spectropy satisfies the above parameters better than the other methods; therefore, it is the most suitable method for the analysis of the provided samples. REFERENCES McCormack, A. (1987) Roach, Measurement, Statistics and Computation :Analytical Chemistry by Open learning.Chichester,UK:John Wiley and sons Inc. G.D. Christian (1994) Analytical Chemistry.5th Edition. New York, USA: John Wiley and sons Inc Hognness T.R. (1954) Qualitative analysis and chemical equilibrium. New York, USA: Holt publishers. William, P (1953) Qualitative analysis and analytical chemical separations. New York, USA: Macmillan publishers Wismer R.K. (1991) Qualitative Analysis and Ionic Equilibrium. New York, USA: Macmillan publishers. Blair, A.A. (1901) the chemical analysis of iron. Philadelphia, USA: Lippincott. Deiss, E., Seaton, R. and Oswald,W.B.(2010) The sampling and chemical analysis of iron and steel. South Carolina: USA: Nabu press. Read More