You are a chemist working for a pharmaceutical company that produces a wide range of vitamin products. Today, your work list includes testing a batch of “2Bs Vitamins"; a vitamin supplement that contains a mixture of Vitamin Bl and B6. Your task is to determine that each tablet in the batch contains the specified quantity of cach vitamin. Sample preparation includes collecting ten (10) tablets at random from the batch, crushing them, and homogenizing the crushed tablets. 350 mg of the homogenized powder was accurately weighed and placed in a 50 mL volumetric flask and dissolved in 0.1M HCI and diluted to volume. 0.5 mL of this solution was then placed in a 100 mL volumetric flask and diluted to volume. Normally, you would analyse this vitamin mixture using an HPLC, because it is easier to first separate the 2B's into their individual components and then quantitate. Unfortunately for you, however, the HPLC is down, and you must use UV-VIS spectrophotometry to do the job. 2.0 As a first step, you place some of the prepared sample in a lcm cuvette and – Sample do a scan from 200 to 320 nm in order - Vitamin B1 to determine àmax for each vitamin. 1.5 – Vitamin B6 The result is the spectrum labelled "Sample" in Figure 1.' Your second step is to prepare 1.0 individual solutions of cach vitamin and run similar scans for each vitamin. The result are the two spectra labelled "Vitamin BI" and "Vitamin B6" in 0.5 Figure I. (a) What is àmax and why did you 0.0 200 220 240 260 280 300 320 measure it? Wavelength, nm (b) Why can you not use direct calibration and the original scan of Figure 1. Absorption spectra of vitamins B1 and B6 (individual) and the mixture in the tablet sample. the mixture to determine the concentration of cach vitamin in the prepared sample? PLEASE TURN TO THE NEXT PAGE Absorbance
You are a chemist working for a pharmaceutical company that produces a wide range of vitamin products. Today, your work list includes testing a batch of “2Bs Vitamins"; a vitamin supplement that contains a mixture of Vitamin Bl and B6. Your task is to determine that each tablet in the batch contains the specified quantity of cach vitamin. Sample preparation includes collecting ten (10) tablets at random from the batch, crushing them, and homogenizing the crushed tablets. 350 mg of the homogenized powder was accurately weighed and placed in a 50 mL volumetric flask and dissolved in 0.1M HCI and diluted to volume. 0.5 mL of this solution was then placed in a 100 mL volumetric flask and diluted to volume. Normally, you would analyse this vitamin mixture using an HPLC, because it is easier to first separate the 2B's into their individual components and then quantitate. Unfortunately for you, however, the HPLC is down, and you must use UV-VIS spectrophotometry to do the job. 2.0 As a first step, you place some of the prepared sample in a lcm cuvette and – Sample do a scan from 200 to 320 nm in order - Vitamin B1 to determine àmax for each vitamin. 1.5 – Vitamin B6 The result is the spectrum labelled "Sample" in Figure 1.' Your second step is to prepare 1.0 individual solutions of cach vitamin and run similar scans for each vitamin. The result are the two spectra labelled "Vitamin BI" and "Vitamin B6" in 0.5 Figure I. (a) What is àmax and why did you 0.0 200 220 240 260 280 300 320 measure it? Wavelength, nm (b) Why can you not use direct calibration and the original scan of Figure 1. Absorption spectra of vitamins B1 and B6 (individual) and the mixture in the tablet sample. the mixture to determine the concentration of cach vitamin in the prepared sample? PLEASE TURN TO THE NEXT PAGE Absorbance
Chemistry for Engineering Students
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ISBN:9781337398909
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Chapter11: Chemical Kinetics
Section: Chapter Questions
Problem 11.42PAE: Amoxicillin is an antibiotic packaged as a powder. When it is used to treat babies and small...
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Question
Transcribed Image Text:You are a chemist working for a pharmacecutical company that produces a wide range of vitamin products. Today,
your work list includes testing a batch of “2Bs Vitamins"; a vitamin supplement that contains a mixture of Vitamin
B1 and B6. Your task is to determine that each tablet in the batch contains the specified quantity of cach vitamin.
Sample preparation includes collecting ten (10) tablets at random from the batch, crushing them, and
homogenizing the crushed tablets. 350 mg of the homogenized powder was accurately weighed and placed in a
50 mL volumetric flask and dissolved in 0.1M HCl and diluted to volume. 0.5 mL of this solution was then placed
in a 100 mL volumetric flask and diluted to volume.
Normally, you would analyse this vitamin mixture using an HPLC, because it is easier to first separate the 2B's
into their individual components and then quantitate. Unfortunately for you, however, the HPLC is down, and
you must use UV-VIS spectrophotometry to do the job.
As a first step, you place some of the
prepared sample in a lem cuvette and
do a scan from 200 to 320 nm in order
2.0
- Sample
- Vitamin B1
to determine Amax for cach vitamin.
1.5
The result is the spectrum labelled
- Vitamin B6
"Sample" in Figure 1.'
Your second step is to prepare
individual solutions of each vitamin and
1.0
run similar scans for each vitamin. The
result are the two spectra labelled
0.5
"Vitamin B1" and “Vitamin B6" in
Figure 1.
(a) What is Amax and why did you
0.0
200
220
240
260
280
300
320
measure it?
Wavelength, nm
(b) Why can you not use direct
calibration and the original scan of
the mixture to determine the
Figure 1. Absorption spectra of vitamins B1 and B6 (individual)
and the mixture in the tablet sample.
concentration of each vitamin in
the prepared sample?
PLEASE TURN TO THE NEXT PAGE
Absorbance
Transcribed Image Text:You are stumped for a while, because you really don't want to spend all day running columns, and then having to
measure the column fractions with UV-VIS. Your colleague however tells you that it is possible to use the
spectrum of the mixture to determine the concentration of cach vitamin in the mixture.
(c) Briefly explain why it is possible to use the spectrum of the mixture to determine the concentration of each
vitamin in the mixture.
Now that you realise that it is possible, you get some information about the molar absorptivities of cach vitamin
at cach Amax, and list it in Table 1.
Table 1. The molar absorptivities of Vitamins B1 and B6 measured in pure samples of each.
E (M' cm')
a (nm)
Vitamin B1
Vitamin B6
423
5075
240
11280
285
1504
(d)(1) Use the information in Table 1 and the absorbance of the sample mixture at the relevant wavelengths
(Figure 1) to determine the concentration of Vitamin B1 in the diluted, prepared sample.
(d)(i) Determine the mass of Vitamin B1 in one of the vitamin tablets. (MW Vitamin B1: 300.81)
(e) Sketch a diagram of the double-beam scanning spectrophotometer that you would have used to generate
the spectra in Figure 1.
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