Calculate the concentration (mol/L) of 24-dichlorophenoxyacetic acid in the working standard solution used for quantitative analysis of the analyte

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uestionGas chromatography and the quantitative method of standard addition to constant volume were used to investigate the concentration of 24dichlorophenoxyacetic acid (a chlorinated phenoxy herbicide) in a water sample from Lake Eildon.
Liquid-liquid extraction using dichloromethane was used to extract 1.00 L of water sample and the combined extracts were made up to 25 mL in a volumetric flask. A 5.00 mL aliquot of the combined extract was added to each of two 10 mL volumetric flasks. To one flask was added 50.00 L of a 1.150 x 10-4 M standard solution of 24dichlorophenoxyacetic acid. Both flasks were then made up to the final volume. The GC analysis of 10.00 L of injected sample from each flask resulted in peak areas of 245 mV.s and 290 mV.s for the signal in the chromatograms due to 24dichlorophenoxyacetic acid.
(Relative molar mass of 24-dichlorophenoxyacetic acid = 221.04 g.mol-1)
(i). Calculate the concentration (mol/L) of 24-dichlorophenoxyacetic acid in the working standard solution used for quantitative analysis of the analyte
(ii). Write the standard addition equation and identify the terms to be applied
(iii). Apply the standard addition equation and determine the concentration in mg/L of 24dichlorophenoxyacetic acid in the original water sample from Lake Eildon
(iv). Identify the likely sources of experimental error in the laboratory method and calculate the percentage error in the value for the concentration of 24dichlorophenoxyacetic acid determined in (iii) (2 + 4 = 6 marks). Briefly discuss how you would confirm the validity of the value determined in (iii)
(v). Discuss the likely health risks associated with a concentration of 30 g/L of 24dichlorophenoxyacetic acid as compared to typical values found in Australian drinking waters
(vi) Discuss the effectiveness of dissolved oxygen to other common water treatment processes to effectively remove 24dichlorophenoxyacetic acid from Australian drinking waters

 

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