Waters Sep-Pak DNPH-Silica Cartridges - Manual (Page 10)

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Waters Sep-Pak DNPH-Silica Cartridge
10
5. Analyze all three cartridges by HPLC.
6. Subtract the value from the blank cartridge from the values
determined from the other two cartridges.
7. Calculate and sum of the total captured DNPH-derivative from
both cartridges 1 and 2.
8. Divide the amount of DNPH-derivative determined from the first
cartridge by the total amount determined form cartridges 1 and
2. Multiply by 100. This is the percentage of DNPH-derivatives
captured on the first cartridge. This value should exceed 95%
otherwise, some of the sample broke through to the second
cartridge.
Example: Measuring Sample Breakthrough
To measure breakthrough:
Expected concentration of formaldehyde is 500 ppbv. Flow rate is
2.0 L/min. A sample volume if 100 liters yields:
Analyte ppmv Carbonyl Collected
concentration x molecular x air volume = µg Carbonyl
weight
Analyte molar volume at 1 atm/25 °C
This calculates to:
0.66 µL x 30.03 g/mole x 100 L = 81 µg formaldehyde
24.46 L/mole
The actual results are shown in Table 7. To calculate the percent
captured on the first sampler, divide the quantity captured on sampler
1 by the total quantity captured, then multiply by 100. Since this
value is less than 95%, and the total carbonyl amount exceeded
2.3 µmoles, breakthrough occurred.
Table 7: Breakthrough Example HPLC Results
In the above example, only a single carbonyl source was present.
Under many test conditions more than one carbonyl source may be
present in significant concentrations. These other compounds will
consume DNPH, effectively reducing the capacity of the sampler for
the compound of interest. To assure that the capacity of the sampler
has not been exceeded, compare the DNPH peak areas of the sample to
a similarly eluted blank. The DNPH peak area in all samples must be
no less than 50% of the DNPH peak area of the blank. This ensures
the sampler capacity has not been exceeded.
Sampler Amount (µg) Quantity Captured
Sampler – blank (µg)
Percent Captured on
Sampler
Sampler 1 75.06 75.00 91.8
Sampler 2 6.72 6.66 8.2
Blank 0.06 - -