Validation Exercise in Measurement of Iron - Lab Report Example

VALIDATION EXERCISE IN MEASUREMENT OF IRON by Introduction Method validation procedure can be defined as the process through which analytical requirements of a laboratory analysis is defined, as well as the method in the question being confirmed in reference to the performance capabilities and the application requirements (Paul   and Helmut, 2005). More importantly, this study focuses on four analytical techniques that includes, Molecular Spectroscopy – Colorimetric assay, Volumetric - Redox Titration, Atomic Absorption Spectroscopy (AAS) – Flame AAS and Cation Exchange Chromatography – Equivalent Mineral Acidity (EMA) method. Mainly, during the validation procedure these parameters are assessed: precision, linearity, and accuracy. The precision represents the degree of concordance between the result and the reference value Atomic Absorption Spectroscopy (AAS) – Flame AAS Inherently, metal salts normally vaporize during high temperatures, and consequently result to gaseous metal ions which consist of nucleus with neutrons and protons that are surrounded by electrons in various energy levels. The energy levels at such a time are quantized since they have defined energies. More importantly, when energy of a precise wavelength is absorbed, then electrons can be promoted to empty orbital with energy E1 from filled orbital with level E0 such that The absorbed quantum hv = E1 – E0 During atomic absorption spectroscopy energy comes from a cluster of lamps that are fitted with a hollow cathode that is specific to the metal in question (Zabicky, 2009). Notably, it is the valence of electrons which are only promoted, and more importantly, the amount of energy that is absorbed is comparative to concentration of the gaseous ions. Methodology The experiment included dissolving a calculated amount of iron salt in 1000cm3 of de-ionized water to make a stock solution of 1000ppm of iron ions. Consequently, 25cm3 of this solution was diluted to 250cm3 to give a working standard of 100ppm. This was followed by use of this 100ppm standard to prepare a series of four or five more dilute standards in the range 0-10ppm. Subsequently, the absorbance of each standard and unknown were measured under identical conditions, a calibration curve constructed and concentration of Iron present in each sample determined. Molecular Spectroscopy – Colorimetric assay When determining iron (II) through calorimetric method while using phenanthroline, it forms octahedral complex that contains bidentate ligand 1, 10 phenathroline which is red in color. Moreover, when the absorbance of the solutions containing this elements is measured under controlled conditions, then the concentration of iron (II) can be determined. Notably, the corresponding complex created by iron (III) is pale blue in color. Since the complex formed by iron (III) does not depict an intense color as iron (II) complex, thereby creating sensitivity issues, hydroxylamime is added to the iron solution to convert all iron ions to iron (II), which produces better results. Consequently, using beer-lambert law, the calibration curve can be constructed and then taking advantage of y=mx, it is possible to calculate the unknown. Methodology Prepare a range of standard solutions of Iron (II) - phenanthroline complex as per the accompanying table. After mixing the standard iron solution, the buffer solution and the hydroxylamine hydrochloride allow about 15 minutes for the reduction of the iron(III) to iron(II) to occur before addition of the phenanthroline and water. Measure the absorbance of each solution at 510nm using solution 1 as reference. Use solutions 2-6 to plot a graph of absorbance against concentration. Check that the relationship is linear (i.e.Beer - Lambert law is obeyed). Use the graph to determine the concentration of iron in the sample. Ion exchange chromatography The process involves determination of total cations in water. This entails passing water that contains the dissolved ionized solids through cation exchanger, where all cations are removed, and they are replaced with hydrogen ions. Consequently, the alkalinity that is present in water is done away with, with neutral salts being converted to mineral acids. Then the effluent is titrated with 0.02 M NaOH, while using methyl orange indicator. REDOX The process will call for standardization of 0.02 M Potassium permanganate solution while using ammonium iron (II) sulphate. Actually, both manganese and iron are transition elements and they can exist in a number of states where electrons can either be gained or lost. The start of reaction between permanganate ion and iron (II) is signified where the purple color of permanganate ion turns to colourless. At the end when iron (II) will be turned to iron (III), the purple permanganate will then change to pink. This marks the end point. Discussion Atomic Absorption Spectroscopy (AAS) – Flame AAS The Fe concentration is determined Flame AAS by using the following equation: Total Fe (µg/g) = c x F/m0 (Rubinson, 1987). c is concentration of standard solution (µg/mL) F is the dilution factor, m0 = working quantity (g). During the validation procedure these parameters are assessed: precision, linearity, and accuracy. The precision represents the degree of concordance between the result and the reference value (Chung et. al., 2004). Linearity is assessed through graphical representation of the measured absorbance at λ = 510 nm. Linearity depicts the direct proportionality of the Fe concentration solution into the given range (0 - 10 µg/mL) with absorbance. The results are linear. Accuracy represents the agreement for the actual expected value with the measured value. Since it possible to get stock solution with different components, a number of samples were used for a better optimization of the results. Following this, the precision of flame AAS can be described through the recovery of iron content in the sample. Molecular Spectroscopy – Colorimetric assay This method involves measuring light absorbance by the samples, which is then compared to that of the standard solution. Therefore, the choice of the light wavelength is such that only iron will be responsible for the absorbance of light. From beer-lambert law, y = mx Where m is the gradient According to beer’s law, then m = Ec, where E = molar absorptivity and C = concentration According to Rubinson (1998), at λmax = 510, molar absorptivity = 11,100 L/mol-cm. Therefore, concentration = m/E Then Concentration = 197/11,100 0.0177 g/dm3 Linearity Volumetric – Redox Titration Solutions The concentration of the standard samples was as follows Conc Sample 1 Sample 2 Sample 3 Sample 4 Sample 5 Sample 6 g/L 0.056 4.48 4.48 0.224 0.056 0.224 Molarity (M) 0.001 0.08 0.08 0.004 0.001 0.004 ppm 56 4480 4480 224 56 224 Form of Fe Fe(III) Fe(III) Fe(II) Fe(II) Fe(II) Fe(III) Specificity Solutions of the unknown stock were prepared to make about six samples. These samples were titrated against standard reactants in a REDOX reaction to obtain the following results. titre volume 0.167 19.25313 2.445294 0.399375 calculated conc 0.00067 0.297759 0.461656 0.420408 Accuracy, precision and reproduction These were determined on the basis of determination of iron. The concentration of iron was determined through a cerometric method in accordance to this equation (Iwona and  Bernd, 2008). Lineality The graph represents a linear progression, despite the fact that it has high deviations. Concentration of iron salt (M) = no. of moles weighted out * 1000/ vol of solution made up. In this case M = mol * 1000/250 MnO4 : Fe2+ Volume used in titration (V) titre value : 25cm3 Molarity (M) ? : M Mole ratio, from eqn. 1 : 5 Formula = v * M/n = v * M/n Titre value * ?/1 = 25cm3 * M/5 Cation Exchange Chromatography – Equivalent Mineral Acidity (EMA) method The process involved preparation of a 25-30cm column of resin in a chromatography column. Consequently, 250cm3 of hydrochloric acid (2 mol dm-3 ) passed through the tube over about 30 minutes. The column was rinsed with deionised water until the effluent is just alkaline to screened methyl orange (Sivasankar, 2008). This made the resin to be ready for use. 50.0cm3 of the sample of water was passed under test through the column at a rate of 3-4cm3 per minute discarding the effluent. After this 50.0cm3 through the column was passed two times at approximately the same rate and collect the effluent separately, and titrate each with standard 0.02 mol dm-3 sodium hydroxide using screened methyl orange as indicator. Calculation of EMA and conversion to ppm of Fe present for different forms of Iron. Normal E.M.A. = V x M x 50 x 1000 Vl where V - volume of NaOH of molarity M for a volume Vl. Units - ppm of CaCO3 1 ppm = 1 mg/dm3 E.M.A – Equivalent Mineral Acidity is a measure of the number of H+ ions released from the surface of the ion exchange resin after exchange with other ions (Dulski, 1996). The reference measurement is that of a CaCO3 solution – i.e., the number of H+ released when a 1M solution of CaCO3 is passed through the resin. The figures in the formula above allow you to calculate the number of moles of NaOH required to neutralise the amount of H+ released after exchange, (V x M). This in effect is the number of H+ released. This is then correlated to mg/dm3 (ppm) of CaCO3 (50 x 1000/V1). Mw of CaCO3 is 100g per mole but each Ca2+ releases 2 x H+ on exchange so 100/2 = 50 Revised Calculation for Iron Determination will be ppm of Fe = V x M x 28 x 1000 since the sample contains Fe2+ Vl The results should not be quoted as EMA = ppm CaCO3 but simply as ppm of Fe2+ depending on what you have calculated. Volume 7.8 273.75 224.9375 32.375 9.116667 29.945 Calculation of conc 72.795 5859.875 8587.625 331.955 102.42 256.755 Linearity The graph shows linearity despite the fact that it has high deviation. Conclusion In Atomic Absorption Spectroscopy (AAS), The results are linear and depicts the direct proportionality of the Fe concentration solution into the given range (0 - 10 µg/mL) with absorbance. The results also bear notable accuracy and precision. Similarly, Molecular Spectroscopy – Colorimetric assay, the results also are linear despite the fact that they do not possess high degree of accuracy. On the other hand, both REDOX and cation Exchange chromatography represents results with low degree of linearity. Consequently, the study clearly shows that Atomic Absorption Spectroscopy (AAS) is the best method for determining iron in the company. References Chung C. C.,  Lee, Y. C., Herman L. and  Zhang, X. (2004). Analytical method validation and instrument performance verification. Hoboken, N.J: John Wiley & Sons.  Dulski, T. (1996). A manual for the chemical analysis of metals. West Conshohocken, PA: ASTM.  Iwona W. and  Bernd D. (2008). NMR spectroscopy in pharmaceutical analysis. Amsterdam Boston: Elsevier.  Paul B., and Helmut, G. (2005). Validation in chemical measurement. Berlin New York: Springer. Rubinson, J. (1998). Contemporary chemical analysis. Upper Saddle River, NJ: Prentice Hall.  Rubinson, K. (1987). Chemical analysis. Boston: Little, Brown. Sivasankar, B. (2008). Engineering chemistry. New Delhi: Tata McGraw-Hill.  Zabicky, J. (2009). The chemistry of metal enolates. Chichester, West Sussex, England Hoboken, NJ: John Wiley.  Read More