Question

I dont know how to do question 1 part (iv)

1. (a) [15 marks] Total ascorbic acid can be analysed by spectrophotometric method based on the oxidation of ascorbic acid to dehydroascorbic acid by bromine water in the presence of acetic acid. After coupling with 2,4-dinitrophenylhydrazine (DNPH) a red complex that absorbs at 521 nm is produced. The following data were obtained for a series of ascorbic acid standards: 25 UNU [ascorbic acid] No. of replicate Average Standard ppm analyses (N) absorbance at deviation 521 nm 0.0 0.0071 0.0009 10.0 5 0.1005 0.0094 20.0 5 0.2002 0.0084 30.0 0.3001 0.0084 40.0 0.4003 0.0085 50.0 0.5004 0.0110 Calculate the calibration sensitivity of the method. Calculate the analytical sensitivity at 10.0 ppm. (iii) Calculate the coefficient of variation for the absorbance at 10.0 ppm. (iv) Calculate the limit of detection (LOD) for the method. Calculate the limit of quantitation (LOQ) for the method. A sample of fresh guava weighing 20.5 grams was blended until homogenised, filtered and diluted to 250.00 mL in a volumetric flask. Three 25.00-ml portions were treated and analysed the same way as the above standards. The average absorbance obtained for three trials was 0.2501. Calculate the ascorbic acid content in terms of mg per 100 g fresh weight. (vi)

Answer 1

Dear student kindly find the complete solution of Part (1V) OF question 1(a) and give your positive feedback if you properly understood the solution..

if any problem let me know...

Warm Regards

Dr. Rakhee

PART (iv) LOD ☺ LOB (Limit of Blank) = mean blank + 1.645 (SD blank) = 0.0071 +1-645 (0.0009) ☺ = 0.0071 +0.0014805 = 0.00858 LOD = LOB + 1.645 ( SDLOW concentration Sample) LOD = k0B + 1.645 (0.0094) LOD = 0.00858+ 0.01546 CS Scanned with Op CamScanner = 0.02 4043