10. A reversed-phase HPLC method can be used to determine the concentration of a
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Question
10. A reversed-phase HPLC method can be used to determine the concentration of acetylsalicylic acid (ASA) and caffeine (CAF) in analgesic tablets using salicylic acid (SA) as an internal standard. A series of standards was prepared by adding known amounts of acetylsalicylic acid and caffeine to 250-mL Erlenmeyer flasks and adding 100 mL of methanol. A 10.00-mL aliquot of a standard solution of salicylic acid was then added to each. The following results were obtained for a typical set of standard solutions.A sample of an analgesic tablet was placed in a 250-mL Erlenmeyer flask and dissolved in 100 mL of methanol. After adding a 10.00-mL portion of the internal standard, the solution was filtered. Analysis of the sample gave a peak height ratio of 23.2 for ASA and of 17.9 for CAF. (a) Determine the amount (in milligrams) of ASA and CAF in the tablet. (b) Why is it necessary to filter the sample? (c) The directions indicate that approximately 100 mL of methanol is used to dissolve the standards and samples. Why is it not necessary to measure this volume more precisely? (d) In the presence of moisture, ASA decomposes to SA and acetic acid. What complication might this present for this analysis? How might you evaluate whether this is a problem? A sample of an analgesic tablet was placed in a 250-mL Erlenmeyer flask and dissolved in 100 mL of methanol. After adding a 10.00-mL portion of the internal standard, the solution was filtered. Analysis of the sample gave a peak height ratio of 23.2 for ASA and of 17.9 for CAF. (a) Determine the amount (in milligrams) of ASA and CAF in the tablet. (b) Why is it necessary to filter the sample? (c) The directions indicate that approximately 100 mL of methanol is used to dissolve the standards and samples. Why is it not necessary to measure this volume more precisely? (d) In the presence of moisture, ASA decomposes to SA and acetic acid. What complication might this present for this analysis? How might you evaluate whether this is a problem? 10. A reversed-phase HPLC method can be used to determine the concentration of acetylsalicylic acid (ASA) and caffeine (CAF) in analgesic tablets using salicylic acid (SA)as an internal standard. A series of standards was prepared by adding known amounts of acetylsalicylic acid and caffeine to 250-mL Erlenmeyer flasks and adding 100 mL of methanol A 10.00-mL aliquot of a standard solution of salicylic acid was then added to each. The following results were obtained for a typical set of standard solutions. milligrams of peak height ratios for standard CAF ASA/SA CAF/SA ASA 200.0 20.0 20.5 10.6 40.0 25.1 250.0 23.0 36.8 300.0 60.0 30.9 A sample of an analgesic tablet was placed in a 250-mL Erlenmeyer flask and dissolved in 100 ml. of methanol. After adding a 10.00-mL portion of the internal standard, the solution was filtered. Analysis of the sample gave a peak height ratio of23.2 for ASA, and of 17.9 for CAF. (a) Determine the amount (in milligrams) ofASA and CAF in the tablet. it necessary to filter the sample? (c) The directions indicate that approximately 100 mL of methanol is used to dissolve the standards and samples Why is it not necessary to measure this volume more precisely? (d) In the presence of moisture, ASA decomposes to SA and acctic acid. What complication might this present for this analysis? How might you evaluate whether this is a problem?
Explanation / Answer
Solution:
The computation are expressed below,
(a) ASA and CSF
Amount of analyte = Peak area / Response factor
Amount of ASA = 23.2/50 = 0.064 microgram per ml
Amount of CSF = 17.9 / 50 = 0.358 microgram per ml
(b) The filtration of sample is must as it helps in removal of impure particulates gets dissolved by methanol solvent, if used without filtering will result in abnormal peak ratios yielding error result hence it is always suggested to filter the sample at first hand.
(c) The solvent methanol is used for dissolution of tablets which helps in removal of excipients and other impure substance hence there is no need of measuring volume at precise.
(d) As methanol solvent is used there will be of no consequence from mositure presence as methanol removes moisture contents hence no complication arises until unless on reducing the volume of methanol.
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