COMPARATIVE DETERMINATION OF CALCIUM AND MAGNESIUM IN FOOD SUBSTANCES USING EDTA-TITRIMETRY AND FLAME ATOMIC ABSORPTION SPECTROMETRY (FAAS)

A comparative study was carried out for the determination of calcium and magnesium in milk and water melon (food sources of calcium and magnesium). Mixed standard solutions of calcium and magnesium (spike) were added to the samples before digesting with a mixture of concentrated nitric acid and concentrated hydrochloric acid (1:3). The calcium and magnesium content of the digest were determined using flame atomic absorption spectrophotometer (FAAS) and EDTA titration. The percentage recovery for the spikes were as follows: by FAAS determination: the recoveries for the milk samples were within the range (50.0 – 83.3%) for calcium and (48.5 – 83.2%) for magnesium; the recoveries for the watermelon sample were (100%) for calcium and magnesium (49.2 – 83.4%).  By EDTA titration: the recoveries for the milk samples were (110.7 -177.8%) for calcium and (89.0 -148.1%) for magnesium; the recoveries for the watermelon samples were (89.0 -133.0%) for calcium and (110.7 – 177.8%) for magnesium. The mean values are: by FAAS determination: for the milk samples: 69.41 ± 0.25 for calcium and 68.03 ± 0.26 for magnesium, for the water melon samples: 100.00 ± 0.00 for calcium and 66.83 ± 0.26. By EDTA titration: for the milk samples: 140.50 ± 0.24 for calcium and 125.30 ± 0.25 for magnesium, for the water melon samples: 111.00 ± 0.26 for calcium and 140.50 ± 0.24 for magnesium. Similarity of the relative standard deviation shows that both methods have similar degree of precision. However, the recoveries by both methods shows better recovery by EDTA titration indicating that the determination of these metals are better with EDTA titration.

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 TABLE OF CONTENT                                                  VI  Title page               -----------------------------------------------------------------------------------          I  Approval page        ------------------------------------------------------------------------------------        II Dedication                -----------------------------------------------------------------------------------             III Acknowledgement   ------------------------------------------------------------------------------------       IV Abstract                 -----------------------------------------------------------------------------------         V  Table of content        ---------------------------------------------------------------------------------         VI  Chapter One  1.0 Introduction       --------------------------------------------------------------------              1  1.1 Calcium as an essential nutrient    -----------------------------------------------------------               2  1.2 Magnesium as an essential nutrient     -----------------------------------------------------                 4  1.3 Industrial uses of calcium   -----------------------------------------------------------------                 6   1.4 Industrial uses of magnesium     -----------------------------------------------------------                 6  1.5 Aim of the study    --------------------------------------------------------------------------                 7   1.6 Objective of the study   ---------------------------------------------------------------------                 7                                                                                                                                                                           Chapter Two 2.0 Literature review     -----------------------------------------------------------------                  9 2.1 Quantitative analysis   ----------------------------------------------------------------------                  9 2.2 Classical analysis     ------------------------------------------------------------------------                  10 2.2.1 Gravimetric analysis    -------------------------------------------------------------------                 10 2.2.1.1Gravimetric analysis of calcium and magnesium ------------------------------------                  11  2.2.2 Volumetric analysis   ---------------------------------------------------------------------                11 2.2.2.1Complexometric titrimetry   -------------------------------------------------------------                12 2.2.3 Limitations of classical analysis   --------------------------------------------------------                14 2.3 Instrumental analysis     ---------------------------------------------------------------------               14  2.4 Spectroscopy    -------------------------------------------------------------------------------                  15 2.4.1 Atomic Absorption spectrophotometry (AAS)    ---------------------------------------                 15 2.4.2Calibration curve   --------------------------------------------------------------------------                17 2.4.3Internal standardization     -----------------------------------------------------------------                18 2.4.4 Standard addition    ------------------------------------------------------------------------                19 2.4.5 Interferences encountered in flame atomic absorption spectroscopic analysis (FAAS) -          20 2.4.6 Interferences in the FAAS determination of calcium and magnesium   -----------------             22                                                                                                                                                              2.4.7 Sample preparation   ---------------------------------------------------------------------                23    Chapter Three  3.0 Experimental   ----------------------------------------------------------------------------                   25  3.1 Apparatus and reagent   ----------------------------------------------------------------                      25  3.2 Preparation of samples   ----------------------------------------------------------------                     25 3.2.1 Preparation of watermelon samples   ------------------------------------------------                     25 3.2.2 Preparation of milk samples   --------------------------------------------------------                     26 3.3 Preparation of solutions    --------------------------------------------------------------                     27 3.3.1 Preparation of EDTA solution   ------------------------------------------------------                    27 3.3.2 Preparation of zinc solution   --------------------------------------------------------                     27 3.3.3Preparation of buffer solution    -----------------------------------------------------                      28 3.3.4 Preparation of Eriochrome black-T indicator   -----------------------------------                        28       3.3.5 Preparation of KOH solution   ------------------------------------------------------                       28 3.4 Standardization of EDTA solution   --------------------------------------------------                       28       3.5 Determination of calcium and magnesium in samples using EDTA titration   -----------              29 3.5.1 Determination of calcium in samples using EDTA   -------------------------------           30 3.5.2 Determination of magnesium in samples using EDTA   ----------------------------------            30 3.6 Determination of calcium and magnesium in samples using AAS   -----------------------            31 
Chapter Four  4.1 Result      ----------------------------------------------------------------------------------------            33 4.2 Discussion   -------------------------------------------------------------------------------------             41 4.3 Conclusion   -----------------------------------------------------------------------------------              42 REFERENCES    --------------------------------------------------------------------------------                43