2.3. Experimental procedure
2.3.1. GD-FI procedure
The ground solid sample (0.2070.02 g, fraction 60–80 mm) was
placed in a capped 1 mL glass vial, acting as the suspension
reservoir, which was located in an ultrasonic thermostating bath.
Then 0.3 mL of 2 M NaOH and 0.1 mL of water or ammonium
standard solution (in case of calibration or recovery experiments)
were injected manually through the cap septum using two hypodermic
syringes (Fig. 1A) resulting in the generation of molecular
ammonia. This was followed by 5 min of purging the suspension/
solution with nitrogen, delivered through a syringe needle piercing
the cap septum and connected to Tygon tubing linked to the
scrubber (Fig. 1A). During purging, the acceptor solution in the
acceptor chamber of the GD cell remained static to allow the
accumulation of ammonia diffusing across the hydrophobic porous
membrane from the nitrogen stream passing through the donor
chamber. These processes led to a change in the color of the mixed
acid–base indicator acceptor solution located in the acceptor
chamber of the GD cell. After 5 min stop-flow time the acceptor
stream was re-started and a transient absorbance peak was
recorded at 580 nm whose maximum was related to the concentration
of ammonium in the corresponding sample or standard
solution. Nitrogen was passed through the donor line of the GD-FI
system for 1 min after each measurement to avoid sample crosscontamination.
Fig. 1. Schematic diagrams of the proposed GD-FI system (A) and its GD cell (B).
I.I. Timofeeva et al. / Talanta 142 (2015) 140–144 141
2.3.2. GC–MS measurements of volatile amines in concrete samples
Each building material sample (471 g) was shaken with 10 mL
of 1 M HCl for 1 min. After sedimentation of the suspension the
aqueous supernatant was aspirated into a 5 mL syringe. Then
0.5 mL of this solution was filtered through a syringe filter and
analyzed by the GC–MS system. The GC was fitted with an RTX-5
MS capillary column (5% diphenyl and 94% dimethyl polysiloxane,
30 m 0.25 mm i.d., 0.25 μm coating). The injector temperature
was kept at 220 °C while the interface temperature and the ion
source were at 200 °C. Helium was used as the carrier gas at a flow
rate of 2 mL min1
. A sample volume of 1 μL was injected in
splitless mode with 1 min of purge time. The electron ionization
source was run at 70 eV. For identification of volatile amines,
library search was carried out using NIST, NBS and Wiley GC–MS