polyethylene components with triaxially-compressed packed
beds and Luer fittings equipped with end caps and plugs.
• T hegold-coloredaluminumcompressionringontheSep-Pak
DNPH-Silica cartridge allows for easy identification.
II. usInG seP-PAK dnPH-sILICA CArtrIdGes
a. Theory of Operation
Waters Sep-Pak DNPH-Silica cartridges trap aldehydes and ketones in
gasses by reacting them with the DNPH in the cartridge to form stable
1,2 ,3
hydrazone derivatives
place during sample collection. The derivatives are later eluted and
analyzed. Analysis should take place within two weeks.
Figure 2: Derivitization Reaction
. The derivitization reaction (Figure 2) takes
Figure 1: Cutaway View
Table 1: Physical/Chemical Properties
Hold-Up Volume0.7 mL
Particle Size55 to 105 µm
Collection Efficiency>95% for sampling rates up to 2 L/min
CapacityApproximately 75 µg formaldehyde
Quantity of DNPH-Silica0.35 g/cartridge (1.0 mg DNPH)
Operating Temperature*10 °C to 100 °C
Dimensions4.3 cm total length
2.0 cm o.d. at widest point
1.0 cm i.d.
0.9 cm bed length
* Evaluate cartridge performance for individual high-temperature
methods.
b. Preventing Contamination
Contamination is most likely to occur during sample preparation.
Before eluting the derivatives, clean all glassware by rinsing with
acetonitrile and heating to 60 °C in a vacuum oven for at least
30 minutes. Eluting the samples in a nitrogen-purged glove box
further reduces the risk of contamination.
The acetonitrile used to elute the DNPH derivatives can also be a
source of contamination. Even HPLC-grade acetonitrile may have
unacceptable levels of carbonyl contaminants. A concentration of
10 µg/L of any aldehyde or ketone contaminant will add 0.1 µg to
the blank values determined for the DNPH derivatives per cartridge.
Follow the procedure in Appendix A to test your acetonitrile.
c. Collecting the Sample
Caution: Beware of unintentional exposure of the cartridges and
eluted samples to aldehyde and ketone sources. Laboratory air often
holds high concentrations of acetone. Labeling inks and adhesives as
well as packaging containers (including vials with plastic caps) are all
possible sources of contamination.
Waters Sep-Pak DNPH-Silica Cartridge
2
[ Care and Use ManUal ]
Caution: Ozone (usually present in urban air) degrades the hydrazone
4
derivatives
. Place an Ozone Scrubber Cartridge (Waters Part
number: WAT054420) on the inlet of the Sep-Pak DNPH-Silica
cartridge.
Notice: Do not use Sep-Pak DNPH-Silica cartridges to process liquid
samples.
To collect the sample:
1. Take the cartridge from its pouch. Remove and save the end cap
and plug.
2. Connect the cartridge to a pump with flexible plastic tubing.
The cartridge is bidirectional (flow can be in either direction).
Figure 3 shows the flow rate through a cartridge versus applied
vacuum.
3. Draw the sample through the cartridge. Record the flow rate and
collection time.
4. Reseal the cartridge with its end cap and plug.
5. Store the cartridge in the provided pouch with appropriate
identification. If possible, seal the pouch using a heat sealer,
®
or store the cartridge in a glass container with a Teflon
-lined
cap. Keep the samples cool (<4 °C). Elute the cartridge within
two weeks.
The volume of air passed through the cartridge must be large
enough for the quantity of DNPH derivative formed to be several
times greater than the background level (Table 2). The United
States Environmental Protection Agency (US EPA) recommends
3
that this level be at least 10 times of that of the background
.
Figure 4 shows the ranges of sample volumes to use as a function
of expected concentration. If you can not predict the concentration
of total carbonyl compounds in a sample, follow the procedure in
Appendix C, Measuring Sample Breakthrough.
Table 2: Background Levels of DNPH Derivatives
Compoundµg DNPH Derivative per Cartridgeµg as Carbonyl Compound per