Techniques for preparation of gaseous samples with a desired concentration of analyte

Сентябрь 6, 2022

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Techniques for preparation of gaseous samples with a desired concentration of analyte

Содержание

2. Aim Learn to prepare gaseous samples with desired concentration of a solute
3. Importance Preparation of calibration samples (standards) Conducting chemical reactions in gas phase Production of commercial gases
4. Advantages of having the skill More accurate calibration and analytical measurements Lower consumption of expensive materials
5. Example - quantification
6. Concentrations of calibration standards are 20% greater than they should be
7. Concentration general measurement unit stating the amount of solute present in a known amount of solution
8. Units of concentrations of gases Liquid samples: volume %; mol/L; g/L; ppm (w/v); ppb (w/v); ppt
9. Types of concentrations Volume/volume – does not change with T and P Mass / volume –
10. Main formula for conversions p – pressure (ambient or partial), kPa V – volume, L m
11. Exercise Convert 50 ppm (v/v) of hydrogen sulfide in air to mg/m3 Now we need to
12. Solution (continued) V = 50 mL; R=8.31 L· kPa / (moL K); M (H2S) = 34
13. Solution (continued) Q: will the C increase if temperature is increased to 30 ⁰C?
14. Question What is the partial pressure of H2S at this concentr.? m = 0.0655 g; V
15. Quiz 1/2 1 – 37 2 – 55 3 – 25 4 - 43 5 –
16. Quiz 2/2 1 – 49 µg/m3 2 – 56 µg/m3 3 – 64 µg/m3 4 -
17. Question What equipment and glassware is used for preparing liquid solutions?
18. Calibrated gas sampling bulb To prepare gas standard, inject small amount (
19. Exercise How many nanograms of naphthalene should be injected into a 500-mL bulb filled with “zero”
20. Exercise (continued) What concentration should the injected solution have if the injected volume is 5.0 µL?
21. Exercise Solution of benzene (5.00 µL) in methanol with concentration 10 mg/mL was injected to calibrated
22. Task Convert this concentration to ppmV Convert this concentration to Pa
23. Question How many microliters of water can be introduced to a 250-mL flask containing dry air
24. Task 2 How many microliters of methanol can be introduced to a 250-mL flask containing air
25. Gas tight syringes PTFE plunger
26. Serial gas dilution (10000x) 1000 mL 1000 mL 1000 mL Pure gas 100 µL/L (100 ppm)
27. Method 2 C = 0 C > 0 Tuduri et al., 2001
28. New Era NE-1002X
29. Example “Zero” air is supplied at 100 mL/min rate Benzene solution in methanol (C = 50
30. Calculation
32. Скачать презентацию

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Aim
Learn to prepare gaseous samples with desired concentration of a solute

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Importance
Preparation of calibration samples (standards)
Conducting chemical reactions in gas phase
Production of

commercial gases (LPG, etc.)

Conducting research experiments

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Advantages of having the skill
More accurate calibration and analytical measurements
Lower consumption

of expensive materials

More accurate and reliable experimental research

Higher quality of manufactured products

Greater satisfaction of the employer / salary

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Example - quantification

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Concentrations of calibration standards
are 20% greater than they should be

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Concentration
general measurement unit stating the amount of solute present in a

known amount of solution

Amount – mass, volume or amount of substance

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Units of concentrations of gases
Liquid samples:
volume %;
mol/L;
g/L;
ppm (w/v); ppb

(w/v); ppt (w/v)

Solid samples:
weight %;
g/kg;
ppm (mg/kg or μg/g); ppb (μg/kg); ppt (ng/kg)

Gaseous samples:
volume %;
ppm (v/v) – milliliters of gaseous compound in 1 m3 of gas mixture;
ppm (w/v) – milligrams of gaseous compound in 1 m3 of gas mixture
mg/m3, µg/m3, ng/m3

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Types of concentrations
Volume/volume – does not change with T and P
Mass

/ volume – depends on T and P

atm (or bar) – (partial) pressure units

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Main formula for conversions
p – pressure (ambient or partial), kPa
V –

volume, L

m – mass, g; M – molar mass, g/mol

R – gas constant, 8.31 L ∙ kPa / (mol ∙ K)

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Exercise
Convert 50 ppm (v/v) of hydrogen sulfide in air to mg/m3

Now

we need to find the weight of 50 mL of hydrogen sulfide. For that purpose, we can use ideal gas law:

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Solution (continued)

V = 50 mL; R=8.31 L· kPa / (moL K);

M (H2S) = 34 g/moL

Pressure and temperature are not given. But let’s imagine that we are in Almaty now. The pressure is 680 mmHg, temperature 10°C

We need to convert temperature to K: T = 273 + 10 = 283 K
The pressure must be converted to kPa. We know that 760 mmHg = 101.325 kPa. P = 101.325 kPa x 680 mmHg / 760 mmHg = 90.66 kPa

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Solution (continued)

Q: will the C increase if temperature is increased to

30 ⁰C?

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Question
What is the partial pressure of H2S at this concentr.?
m =

0.0655 g; V = 1000 L

p = 0.00453 kPa = 4.53 Pa

Q: will the partial pressure increase if temperature is increased to 30 ⁰C?

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Quiz 1/2
1 – 37
2 – 55
3 – 25
4 - 43
5 –

Sulfur dioxide concentration in Almaty air now is 37 µg/m3. Convert this concentration to ppbV. Atmospheric pressure is 740 mmHg, temperature 25⁰C.

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Quiz 2/2
1 – 49 µg/m3
2 – 56 µg/m3
3 – 64 µg/m3
4

- 51 µg/m3

5 – 61 µg/m3

Sample bag (V = 1.00 L) was filled with 0.70 L of air having benzene concentration 56 µg/m3. Sampling was done at a temperature -10⁰C. Then, the bag was transported to the laboratory where the temperature was 25⁰C. What is the benzene concentration in the air inside a sampling bag stored in the lab?

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Question
What equipment and glassware is used for preparing liquid solutions?

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Calibrated gas sampling bulb
To prepare gas standard, inject small amount (<10

uL) of analyte to bulb

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Exercise
How many nanograms of naphthalene should be injected into a 500-mL

bulb filled with “zero” air to prepare air with naphthalene concentration 50 ng/L

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Exercise (continued)
What concentration should the injected solution have if the injected

volume is 5.0 µL?

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Exercise
Solution of benzene (5.00 µL) in methanol with concentration 10 mg/mL

was injected to calibrated bulb having volume 250 mL and filled with air. All injected solution were evaporated. What is the concentration of benzene in the air inside bulb (in µg/L)

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