Sample Gravimetric Spectrophotometric 1 54.7 55 2 58.5 55.7 3 66.8 62.9 4 46.1 45.5 5 52.3 51.1 6 74.3 75.4 7 92.5 89.6 8 40.2 38.4 9 87.3 86.8 10 74.8 72.5 11 63.2 62.3 12 68.5 66