Analysis of Carbonyls Using a Dual-Layer LpDNPH Sampling Tube and HPLC

By: Kristen Schultz, and Jamie Desorcie, Reporter US Volume 30.1

The dual-layer LpDNPH sorbent tube is an air sampling device designed for sampling carbonyls (e.g. formaldehyde) in ambient, indoor, and industrial atmospheres. Carbonyls are trapped on our high-purity silica gel adsorbent coated with 2,4-dinitrophenylhydrazine (2,4-DNPH) where they are converted to stable hydrazone derivatives. The derivatives are eluted from the tube in acetonitrile (Figure 1) and analyzed by HPLC.

Figure 1. Reaction of 2,4-DNPH with acetonitrile

The ORBO™-555 is a 6 mm O.D. x 110 mm length dual-layer DNPH glass sampling tube containing 300 mg of LpDNPH in the front section and 150 mg in the back section (Figure 2). The back section functions as a back-up bed for incidences of breakthrough sometimes associated with single bed DNPH cartridges in higher concentration environments or when you are not certain of the concentration.

Figure 2. ORBO™-555 Sampling Tube

ORBO-555 Features and Benefits

  1. Low pressure drop enables use at high sampling rates of 1.5 – 2.0 L/min, even with personal sampling pumps
  2. High purity LpDNPH adsorbent for greater accuracy in trace analysis
  3. Manufactured in a controlled, low carbonyl environment
  4. Low background

An airborne mixture of carbonyl compounds was generated by vaporizing a mixture of formaldehyde, acetaldehyde, acetone and hexanal. The air mixture was sampled using a dual-layer LpDNPH tube (Cat. No. 54020-U) at a flow rate of 1 L/min for 120 minutes. The sampling tube was oriented such that air passed first through the 300 mg (primary) bed, followed by the 150 mg (secondary) bed. At the end of the sampling period, the packing beds were removed and placed in 15 mL vials. Acetonitrile (5 mL) was added to each vial. The mixtures were allowed to set for 1 hour with occasional agitation. The packing beds were also removed from an unused sampling tube (blank) and these were extracted in an identical manner. Aliquots of the solutions above the settled silica were removed and analyzed using HPLC. Calibration was achieved using a mixture of single-component carbonyl-DNPH calibration standards.


Table 1. Blank Tube
  Primary Bed Secondary Bed
DNPH 1.1 mg 0.5 mg
Formaldehyde 0.03 µg 0.01 µg
Acetaldehyde 0.01 µg 0.01 µg
Acetone 0.04 µg 0.02 µg
Hexanal N.D. N.D.
N.D.=Not Detected.


Table 2. Sample Tube (Blank Values Subtracted)
  Primary Bed (µg) Secondary Bed Total (µg)
Formaldehyde 3.74 0.00 3.74
Acetaldehyde 1.12 0.00 1.12
Acetone 3.93 0.00 3.93
Hexanal 0.96 0.00 0.96


Table 3. Measured Airborne Concentrations (µg/m3)
Formaldehyde Acetaldehyde Acetone Hexanal
31.2 9.3 32.8 8.0


Figure 3. Acetonitrile Extract of Sample Tube (Primary Bed)

column: Ascentis Express C18, 15cm x 4.6mm I.D., 2.7µm particles (53829-U)
mobile phase A: Water
mobile phase B: Acetonitrile
flow rate: 0.5 mL/min.
temp.: ambient
det.: UV, 360 nm
injection: 10 µL
Gradient Program: Min
  1. 2,4-Dinitrophenylhydrazine (DNPH)
2. Formaldehyde-DNPH
3. Acetaldehyde-DNPH
4. Acetone-DNPH
5. Hexanal-DNPH


Figure 4. Acetonitrile Extract of Blank Tube (Primary Bed)
Conditions and Peak IDs are the same as Figure 3.

The dual-layer LpDNPH ORBO-555 tube is an effective sampler for measuring airborne carbonyl concentrations (Table 3). The low background levels as shown in the blank tube (Figure 2/ Table 1) in the sampler allow for accurate measurements of low concentration samples or samples collected in situations where short sampling times are needed. The results (Figure 3/Table 2) indicate that under the sampling conditions employed, there was no breakthrough of formaldehyde, acetaldehyde, acetone or hexanal.


Featured Products
Description Qty. Cat. No.
ORBO-555 Dual-Layer LpDNPH Sampling Tube 20 54020-U
Ascentis Express C18 HPLC Column
15 cm x 4.6 mm, 2.7 µm 1 53829-U
Single Component Carbonyl-DNPH Solutions
Formaldehyde-2,4-DNPH, Certified Reference Material
1 mL CRM47177
Acetaldehyde-2,4-DNPH, Certified Reference Material 1 mL CRM47340
Acetone-2,4-DNPH, Certified Reference Material 1 mL CRM47341
Hexaldehyde-2,4-DNPH, Certified Reference Material 1 mL CRM47178


Method Applications

Our LpDNPH products are suitable for use in the following methods:

US EPA TO-11A – Method for the Determination of
Formaldehyde in Ambient Air Using Adsorbent Cartridge
Followed by High Performance Liquid Chromatography

ASTM Method D5197 – Standard Test Method for
Determination of Formaldehyde and Other Carbonyl
Compounds in Air

NIOSH 2016, Appendix B – Formaldehyde
US EPA IP-6A – Determination of Formaldehyde and Other
Aldehydes in Indoor Air Using a Solid Adsorbent Cartridge

US EPA 100 – Sampling for Formaldehyde and Other
Carbonyl Compounds in Indoor Air

TRADEMARKS: Ascentis, ORBO - Sigma-Aldrich Co. LLC

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