Henry's law constants of carbonyl-pentafluorobenzyl hydroxylamine (PFBHA) derivatives in aqueous solution

Article abstract of DOI:10.1021/je025545i

In situ derivatization of airborne carbonyls can increase the efficiency of sampling methods aimed at the quantification of these trace components in urban and rural and rural atmospheres. The design of efficient samplers based on aqueous solutions of the

Full text of DOI:10.1021/je025545i

J . Chem. Eng. Data 2002, 47, 1481-1487
1481
Hen r y’s La w Con sta n ts of Ca r bon yl-P en ta flu or oben zyl
Hyd r oxyla m in e (P F BHA) Der iva tives in Aqu eou s Solu tion
Hu go Desta illa ts* a n d M. J u d ith Ch a r les
Department of Environmental Toxicology, University of California, Davis, California 95616
In situ derivatization of airborne carbonyls can increase the efficiency of sampling methods aimed at the
quantification of these trace components in urban and rural atmospheres. The design of efficient samplers
based on aqueous solutions of the derivatization reagent O-(2,3,4,5,6-pentafluorobenzyl) hydroxylamine
(PFBHA) requires knowledge of how the carbonyl-PFBHA derivatives partition between water and air.
We have determined the Henry’s law constant at 25 °C for 16 PFBHA derivatives of carbonyls that
represent typical analytes present in the ambient environment. The inert gas stripping method was
employed, followed by measurement of the aqueous concentration of the derivatives by GC-ion trap mass
spectrometry (GC/ITMS). The values of the Henry’s law constants ranged from (37 to 268) Pa‚m3‚mol-1
.
We evaluated several molecular descriptors to investigate quantitative structure-property relationships
(QSPRs) for the partition behavior of these compounds. The molecular volume, the molecular surface
area, and the polarizability correlate better with kH, while the dipole moment proved to be an extremely
insensitive descriptor. The temperature dependence of kH in the range (5 to 25) °C was evaluated. These
data led to the estimation of ∆H∞ and ∆S∞, which ranged from ∆H∞ ) (17 to 60) kJ ‚mol-1 and ∆S∞ ) (36
to 170) J ‚K-1‚mol-1
.
In tr od u ction
O-(2,3,4,5,6-Pentafluorobenzyl) hydroxylamine (PFBHA)
is a popular derivatization reagent for trace organic
analysis of carbonyls.1-7 The product of the reaction is an
oxime which is thermally stable and insensitive to light.4,8
Applications of PFBHA derivatization include the analysis
of airborne carbonyls emitted into the atmosphere by
anthropogenic and biogenic sources,4-7,9,10 the analysis of
polar organic byproducts of drinking water disinfection
with ozone,11-14 and the study of carbonyls generated by
lipid peroxidation and other biological processes.15,16
The employment of PFBHA derivatization improves the
sensitivity and resolution of gas chromatography methods
toward carbonyls.6 The advantages of this method com-
pared with the classical 2,4-dinitrophenylhydrazine (DNPH)
derivatization are (1) higher stability of the R,â-unsatu-
rated carbonyl (e.g., acrolein, crotonaldehyde) and dicar-
bonyl (e.g., glyoxal, methylglyoxal) derivatives;17,18 (2) the
ability to distinguish R-dicarbonyls from hydroxycarbonyls;
and (3) the ability to obtain unambiguous molecular weight
determinations by interpretation of the electron ionization
(EI), methane chemical ionization (CH4-CI), and penta-
fluorobenzyl alcohol chemical ionization (PFBOH-CI) ion
trap mass spectra.1,3,6
F igu r e 1. Chemical reactions taking place in solution and
partition of the solutes to the gas phase during sampling with in
situ derivatization.
tion.17,18 In previous work, we observed a relationship
between the kH values of free carbonyls and the collection
efficiency in sampling devices that rely on partitioning of
the carbonyls to aqueous solutions (e.g., impingers and mist
chambers).1 While the partitioning of the solutes from the
gas to the aqueous phase is an important process that
affects the collection efficiency, several other processes also
should be considered, such as the hydration and formation
of gem-diols, the possible decomposition of labile analytes
and their hydrates in water, PFBHA derivatization rates,
and evaporative loss of free and derivatized carbonyls. In
Figure 1, we illustrate these processes at the liquid-air
interface. The extent of evaporation of free carbonyls can
be estimated from Henry’s law constants for these com-
pounds that are readily available in the literature.27-34
However, no information exists regarding the Henry’s law
constants of the PFBHA derivatives. The objective of this
In situ PFBHA derivatization has been implemented in
the collection of airborne carbonyls by sampling with water-
based techniques such as impingers and mist chambers,1,19
and also in methods that utilize solid sorbents.20-23 An
important reason for developing sampling procedures with
in situ PFBHA derivatization is to stabilize labile or
reactive carbonyls, which in some cases cannot be pre-
served in stainless steel canisters24,25 or dissolved in water,
both in its underivatized form26 and by DNPH derivatiza-
* E-mail: mjcharles@ucdavis.edu; hdestaillats@ucdavis.edu. Phone:
530-754-8757. Fax: 530-752-3394.
10.1021/je025545i CCC: $22.00 © 2002 American Chemical Society
Published on Web 09/19/2002

1482 J ournal of Chemical and Engineering Data, Vol. 47, No. 6, 2002
work is to provide experimental information on the kH of
carbonyl-PFBHA derivatives that can be used to gain
insight into processes affecting the collection efficiency of
sampling devices that rely on dissolution of gas-phase
analytes.
The Henry’s law constant (kH) is a thermodynamic
parameter that plays a fundamental role in the description
of many industrial, toxicological, and environmental proc-
esses that transport chemicals between gaseous and aque-
ous phases. It is defined as
tanal, decanal, acrolein, crotonaldehyde, p-tolualdehyde,
fluorenone, glyoxal, hydroxyacetone, and 3-hydroxy-3-
methyl-2-butanone, were purchased from Aldrich Chemical
Co. (Milwaukee, WI); benzaldehyde was purchased from
Acros Organics (New J ersey). These standards were uti-
lized without further purification. O-(2,3,4,5,6-Pentafluoro-
benzyl) hydroxylamine was purchased from Aldrich (Mil-
waukee, WI) and further purified by recrystallizing two
times in distilled isopropyl alcohol (Fisher Scientific,
Pittsburgh, PA). High-purity HPLC quality dichloromethane
was purchased from Burdick and J ackson (Muskegon, MI)
and distilled. The HPLC grade water (Fisher Scientific,
Pittsburgh, PA) employed in the sampling was distilled
over KMnO4 to oxidize the organics in the water. The
glassware was silanized by immersion in a 15 vol %
solution of dichlorodimethylsilane in toluene to minimize
analyte adsorption to the container walls.
Deter m in a tion of Hen r y’s La w Con sta n t. We deter-
mined the kH by the inert gas stripping (IGS) method,
developed by Mackay et al.37-39 A flow of N2(g) was
introduced in the bottom of a column containing an aqueous
solution of the analytes and was dispersed in small bubbles
at a known and constant flow rate. The gas flowed through
the well-mixed aqueous solution column, ensuring that the
gas exiting the column was in equilibrium with the liquid.
By measuring the decrease of the solute concentration in
water, kH can be calculated from a simple mass balance
for the solute. During the stripping process, the mass
balance for the solute can be expressed in terms of transfer
rates from the liquid to the gaseous phase as
f2
kH ) lim
(1)
x f0
x2
2
where f2 is the solute fugacity and x2 is the solute mole
fraction in the liquid solution.35 For dilute (x2 < 10-3) and
low-volatility organic solutes, the Henry’s law constant is
often expressed as the ratio of the equilibrium partial
pressure of the solute (pg, expressed in Pa) divided by its
aqueous concentration (Cw, expressed in mol‚m-3).
pg
kH
)
(2)
Cw
The dimensionless Henry’s law constant (air-water parti-
tion coefficient, kaw) is related to the kH through the ideal
gas law, as follows:
kH
Cg
kaw
)
)
(3)
RT Cw
∂Cw pgG
The kH can be estimated in some cases as the ratio of the
solute’s standard vapor pressure and its aqueous solubility
at 25 °C.36 This approach is limited to solutes that present
very low solubility in water and for which precise measure-
ments of both quantities are available. The latter is not
the case in the present work.
-V
)
(5)
∂t
RT
where V is the volume of the liquid, G is the gas flow rate,
R is the gas constant, and T is the temperature of the
system. Combining eqs 1 and 2 and integrating from the
The temperature dependence of kaw (or kH) is expressed
by the Gibbs-Helmholz equation:
initial conditions t ) 0 and Cw ) C° (the initial concen-
w
tration), the expression
-RT ln kaw ) ∆H∞ - T∆S∞
(4)
Cw
kHG
ln
) -
t
(6)
(C°)
(
)
VRT
w
where ∆H∞ and ∆S∞ are the molar enthalpy change and
the entropy variation corresponding to the dissolution of a
gaseous solute at infinite dilution, respectively. An estima-
tion of these parameters can be obtained by determining
kH at various temperatures, assuming that ∆H∞ and ∆S∞
are independent of temperature (a reasonable assumption
over small temperature ranges).
In the present study, we report the experimental deter-
mination of Henry’s law constants (in the range 37 to 268
Pa‚m3‚mol-1) corresponding to 16 carbonyl-PFBHA de-
rivatives, and the temperature dependence study for 8 of
those, for temperature ranging from (5 to 25) °C. The
carbonyls investigated represent typical analytes observed
in urban atmospheric sample extracts, such as aliphatic
saturated C1-C10 carbonyls (formaldehyde, acetaldehyde,
acetone, 2-butanone, 2-pentanone, hexanal, octanal, and
decanal), aliphatic unsaturated carbonyls (acrolein and
crotonaldehyde), monoaromatic carbonyls (benzaldehyde
and p-tolualdehyde), oxygenated polyaromatic hydro-
carbons (9-fluorenone), dicarbonyls (glyoxal), and hydroxy-
carbonyls (hydroxyacetone and 3-hydroxy-3-methyl-2-
butanone).
can be used to obtain the experimental kH value from the
slope of the linear regression of ln(Cw/ C°) versus time,
when all other parameters are fixed.
w
P r epa r a tion of Aqu eou s Solu tion s of P FBHA-Ca r -
bon yl Der iva tives. The derivatization reaction was carried
out in an aqueous solution containing a mixture of the
studied carbonyls (in the range 50 to 7500 µg mL-1, total
molar concentration 0.6 mM) and excess PFBHA (5 mM).
Each individual carbonyl concentration was lower than the
corresponding solubility in water, when that value existed.
The solution was kept in the dark at room temperature
for 24 h to ensure reaction completion. A 2 L sample was
prepared by 1:500 dilution of the original solution with
water (HPLC grade, Fisher). The diluted solution (concen-
tration of carbonyls ranging from 0.1 to 15 µg mL-1) was
employed to determine the kH (1 L was used in each column
experiment). Initial concentrations corresponding to each
carbonyl PFBHA derivative are reported in Table 1. In each
case, concentrations were lower than the corresponding
solubility in water. The experimental uncertainty associ-
ated with the initial concentrations was between 3% and
6%.
Exp er im en ta l Section
Exper im en ta l Deter m in a tion s of kH. The apparatus
employed consisted of two glass columns (60 cm height, 51
mm i.d.), which allowed for simultaneous determination
Rea gen ts. Authentic standards for formaldehyde, acet-
aldehyde, acetone, 2-butanone, 2-pentanone, hexanal, oc-

J ournal of Chemical and Engineering Data, Vol. 47, No. 6, 2002 1483
Ta ble 1. kH Deter m in ed a t 298 K for 16
Ta ble 2. Ver ifica tion of th e Exp er im en ta l Meth od ’s
Ca r bon yl-P F BHA Der iva tives, Com p a r ed w ith Th ose
Rep or ted for th e F r ee Ca r bon yls in Aqu eou s Solu tion
P er for m a n ce, Ba sed on Kn ow n kH Va lu es of Ar om a tic
Solu tes
C0
kH(this work)
kH(free)a
C0
µM
kH(this work)
kH(lit.)
%
carbonyl
µg‚mL-1 Pa‚m3‚ mol-1 Pa‚m3‚mol-1 ref
Pa‚m3‚mol-1 Pa‚m3‚mol-1 rel diff ref
Saturated Aliphatic Carbonyls
toluene
1227
495.0
476.2
526.3
588.2
666.7
41.7
47.6
27.8
40.0
3.8 45
-6.3 46
-18.8 47
-34.7 48
1.2 49
formaldehyde
acetaldehyde
7.07
61.3 ( 6.2
0.030
0.033
5.88
7.69
9.09
2.86
3.13
5.00
5.56
29
27
29
30
27
29
28
29
30
34
29
29
29
14.1
53.0 ( 4.9
naphthalene
biphenyl
132
42.2
29.6
-12.8 37
acetone
12.3
0.62
90.3 ( 5.9
215 ( 12
10.1
6.1 49
-35.1 37
2-butanone
251 M-1‚cm-1; naphthalene, λmax ) 276 nm, ꢀ ) 2500
M-1‚cm-1; biphenyl, λmax ) 250 nm, ꢀ ) 15850 M-1‚cm-1).
The experimentally determined kH values, reported in
Table 2 are in good agreement with literature data, which
indicates that, under the present experimental conditions,
equilibrium between the liquid and gas phases is attained
satisfactorily.
2-pentanone
hexanal
octanal
0.65
0.49
0.19
0.21
268 ( 41
173 ( 17
126 ( 21
41 ( 26
8.33
20.83
50.0
decanal
163.93
Unsaturated Aliphatic Carbonyls
acrolein
crotonaldehyde
1.62
1.18
105.2 ( 4.2
147 ( 15
11.1
1.96
31
34
Extr a ction , Isola tion , a n d Ga s Ch r om a togr a ph y/
Ma ss Spectr om etr y. The PFBHA-carbonyl derivatives in
the samples were extracted in CCl2H2 after acidification
with H2SO4(aq). Residual water in the extract was elimi-
nated by passing the extracts through anhydrous Na2SO4(s)
columns (8 cm length, 5 mm i.d.). The eluate was collected
and reduced to 200 µL by evaporation of the solvent under
a mild N2(g) stream. The extract was split into two (100
µL) aliquots. The PFBHA derivatives in one extract were
analyzed by using GC/ion trap mass spectrometry (GC/
ITMS). The PFBHA derivatives of carbonyls containing
hydroxyl or carboxyl moieties in the second aliquot were
silylated by using a 10:1 mixture of BSTFA and trimethyl-
chlorosilane (TMCS, catalyst) and were further analyzed
by GC/ITMS.
Monoaromatic Carbonyls
benzaldehyde
3.99
199 ( 21
2.38
2.70
29
27
28
p-tolualdehyde
0.84
151 ( 28
[0.91]b
Polyaromatic Carbonyls
9-fluorenone
glyoxal
1.42
91 ( 22
[<7.9]c
32
Dicarbonyls
0.55
62 ( 24
<3.3 × 10-4 27
Hydroxycarbonyls
hydroxyacetone
3-hydroxy-3-methyl-
2-butanone
0.31
0.095
37 ( 13
81 ( 23
0.0128
n.a.d
33
a
b
kH for free carbonyl, literature values. Value for the isomer
methyl phenyl ketone. c Value for 9-H-fluorene. n.a.: no data
d
available.
A Varian Star 3400 CX gas chromatograph interfaced
to a Saturn 2000 ion trap mass spectrometer was utilized.
The injector was programmed to maintain a temperature
of 280 °C during the first minute, and then it was increased
to 310 °C at 50 °C/min (splitless injection mode). High-
resolution gas chromatographic (HRGC) separation was
performed on a 30 m × 0.25 mm (i.d) DB-17 HRGC column
with a 0.25 µm film thickness (Agilent Technologies,
Folsom, CA). The oven temperature was programmed to
maintain a temperature of 70 °C for 1 min. The oven
temperature was increased to 100 °C at a rate of 5 °C/min,
and then it was increased to 280 °C at a rate of 10 °C/min
and to 310 °C at a rate of 30 °C/min. The temperature was
maintained at 310 °C/min for 10 min. Methane chemical
ionization (CH4-CI) ion trap mass spectra were obtained
with a filament current of 10 µA and an ion trap temper-
ature of 150 °C. Automatic reaction control using a
maximum ionization time of 500 µs, a maximum reaction
time of 80 ms, and an ion target of 5000 was employed.
Methane was introduced into the ion trap until the ratio
between the m/z 17 and m/z 29 ions was about 1:1. The
masses were scanned from 50 to 650 amu.
Id en tifica tion a n d Qu a n tifica tion . The approach to
identify the carbonyls was described in previous work.6,19
Briefly, the molecular weight of the carbonyls is determined
by the presence of the (M + H)+ ion in the methane CI
mass spectra, and identification is based on interpretation
of the mass spectrum and matching the relative retention
time to that of an authentic standard. The retention times
and relative retention times of the PFBHA or PFBHA/
BSTFA derivatives studied in this work were previously
determined.19 The (M + H)+ ions of PFBHA and PFBHA/
of kH in two different solutions. External glass cooling
jackets were used for circulation of a thermostatic fluid.
The columns were silanized internally to minimize analyte
adsorption to the column walls. Silanization of the columns
was performed by filling them with a 15 vol % solution of
dichlorodimethylsilane in toluene. The temperature was
controlled by an external bath with heating and refrigerat-
ing capabilities (VWR-Polysciences), capable of keeping
the system within (0.1 °C of the set value. The tempera-
ture in each column was monitored with digital thermom-
eters calibrated to (0.1 °C. The gas flow rate was regulated
with independent flow controllers in each column, which
were calibrated with a soap film flow meter in the range
(10 to100) mL/min. Nitrogen gas (99.997% Airgas), injected
into the bottom of each column, was previously saturated
with water by bubbling into a preconditioning flask. The
solutions in each column were stirred with magnetic bars.
Samples (1 mL) were withdrawn at a specific time by
means of a glass syringe and were stored in amber glass
vials with PTFE seals prior to extraction and analysis. The
exact mass of each aliquot was determined with an error
of (10 mg ((1%).
To evaluate the experimental approach, we determined
the Henry’s law constants of three organic solutes for which
kH values were determined previously. The solutes were
toluene, naphthalene, and biphenyl. These kH values
expand over an order of magnitude, within the range of kH
values expected for our PFBHA-carbonyl derivatives.
Individual solutions were prepared for each solute, and the
concentration was determined spectrophotometrically at 25
°C (Hewlett-Packard 8452-A; toluene, λmax ) 262 nm, ꢀ )

1484 J ournal of Chemical and Engineering Data, Vol. 47, No. 6, 2002
F igu r e 2. Typical experimental results obtained in the determination of Henry’s law constants of carbonyl-PFBHA derivatives. C and
C0 are the actual and initial concentrations of the analyte in the aqueous phase, respectively. A, acetone; B, acrolein; C, 2-butanone; D,
crotonaldehyde.
BSTFA derivatives were used for quantification, which was
accomplished by internal standardization. A linear calibra-
tion curve was constructed for each analyte by plotting the
[(peak area of the derivative of the analyte)/(peak area of
the derivative of the internal standard)] versus concentra-
tion of the analyte in the range (50 to 1000) pg/µL. 13C3-
acetone (retention time tr ) 9.65 min) was employed as the
internal standard to quantify saturated and unsaturated
aliphatic carbonyls. 4-Fluorobenzaldehyde (tr ) 17.65 and
17.77 min) was utilized as the internal standard to quantify
aromatic carbonyls and dicarbonyls, and 4-hydroxy-13C6-
benzaldehyde (tr ) 21.61 min for the PFBHA derivative
and 21.78 for the PFBHA-BSTFA derivative) was em-
ployed as the internal standard to quantify hydroxy-
carbonyls.
number of C atoms in the carbonyl, reaching a maximum
near C5 (2-pentanone), and further decreases at higher
molecular weights. Such behavior indicates that increasing
the molecular size of the solute may affect differently its
chemical potential in the gaseous and aqueous phases. By
replacing the fugacity f2 in eq 1 with the Raoult’s law
expression for the vapor pressure pg ) x2p° γ∞, the Henry’s
g
law constant can be expressed as the product of the limiting
activity coefficient in water γ∞ and the vapor pressure of
the pure solute p° as follows:35,40
g
kH ) γ∞p°
(7)
g
The magnitude of the limiting activity coefficient γ∞ is an
indication of the deviation of dilute solutes from Raoult’s
law. In the case of nonelectrolyte organic solutes in water,
γ∞ is usually larger than 1, and for large aromatic solutes
of the kind of the studied PFBHA derivatives, it typically
ranges between 104 and 106.40,41 Thus, γ∞ is related to the
solute’s tendency to escape from aqueous solution, and it
likely increases with the molecular size of the derivatives.
Resu lts a n d Discu ssion
Deter m in a tion of kH a t 25 °C. To exemplify the results,
in Figure 2, we present plots of experimental values
obtained in the determination of kH of the PFBHA deriva-
tives of acetone, acrolein, 2-butanone, and crotonaldehyde,
where C is the actual concentration measured at a given
stripping time and C0 is the initial analyte concentration.
The individual data errors were within 3-6% in all cases,
based on the standard deviation of the slope of chromato-
graphic calibration curves. In Table 1, we report the
Henry’s law constant values determined for these and the
other 12 derivatives corresponding to various types of
carbonyls. The kH values were calculated using eq 6, and
they range from (37 to 268) Pa‚m3‚mol-1. The experimental
errors indicated for each kH were estimated from the
standard deviation of the linear regression equations.
The data corresponding to derivatives of saturated
aliphatic carbonyls suggest that kH increases with the
In contrast, the vapor pressure p° decreases at higher
g
molecular weight within a homologous series of com-
pounds.41 Therefore, it is reasonable to assume that a
balance between growing γ∞ and decreasing p° is respon-
g
sible for the overall observed bell-shaped behavior of kH.
Experimental data are not available for γ∞ and p° of the
g
studied solutes, and traditional predictive methods for γ∞
such as UNIFAC and other group contribution techniques
are not precise when applied to large organic solutes in
aqueous solution.40
Given the large number of chemicals of potential concern,
the difficulties of kH experimental determinations, and

J ournal of Chemical and Engineering Data, Vol. 47, No. 6, 2002 1485
F igu r e 3. Quantitative structure-property relationships (QSPRs) between the determined kH values of carbonyl-PFBHA derivatives
and the Le Bas molecular volume, Vm(Le Bas), molecular surface area, Sm, polarizability, R, and dipole moment, µ, estimated for the
following: b, aliphatic saturated carbonyls; O, aliphatic unsaturated carbonyls; 1, monoaromatic carbonyls; 3, oxy-PAH; 9, dicarbonyls;
0, hydroxycarbonyls. The curves represent the data fit with eq 8.
Ta ble 3. Molecu la r Descr ip tor s of Mod el Com p ou n d s
Ta ble 4. F ittin g P a r a m eter s for Eq 8
µ
R
Å3
Sm
Vm
Vm(Le Bas)
cm3‚mol-1
X
a
b
c
d
D
Å2
Å3
Vm
Sm
R
69.1
63.6
43.2
168.5
166.6
191.4
271
453.8
22.5
23.9
38.4
2.99
formaldehyde
acetaldehyde
acetone
2-butanone
2-pentanone
hexanal
octanal
decanal
acrolein
crotonaldehyde
benzaldehyde
p-tolualdehyde
9-fluorenone
glyoxal
2.974 14.58 336 505
3.151 16.42 373 562
3.198 18.25 388 600
3.136 20.09 415 653
3.115 21.92 447 705
3.013 23.76 496 775
3.014 27.43 557 883
3.018 31.10 618 990
3.218 18.06 391 599
3.525 19.90 427 654
3.019 24.24 461 726
3.235 26.08 491 778
3.014 33.13 523 877
1.466 28.39 573 907
2.653 18.89 403 623
185.6
207.8
230.0
252.2
274.4
296.6
341.0
385.4
222.6
244.8
274.2
296.4
329.1
363.8
237.4
281.8
the vacuum was fully optimized without symmetry con-
straints, performing restricted RHF calculations. The mo-
lecular volume was also estimated by the classical Le Bas
method, which is based on the summation of atomic
volumes with adjustments for ring formation and other
contractions due to specific bonds.41 In Figure 3, the
correlation between kH and these descriptors is presented
(only the Le Bas volume is shown, for simplicity). With the
exception of the dipole moment (Figure 3D), all other
properties can be correlated with the experimental kH
values, yielding a simple bell-shaped dependence, which
includes not only saturated aliphatic carbonyl derivatives
but also most of the other categories, except hydroxycar-
bonyls. Data for hydroxycarbonyl-PFBHA derivatives
exhibit kH values that are significantly lower than those
of other derivatives with similar molecular volume, surface
area, or polarizability. This can be explained by the
presence of a hydroxyl group in these molecules, which
provides additional stability in water due to hydrogen
bonding, thus reducing their tendency to escape from
solution (i.e., fugacity). The only important difference
between the correlation based on polarizability and those
corresponding to the solute volume and surface area is
related with the values for the 9-fluorenone derivative
(represented with a white triangle in Figure 3). This is a
more polarizable compound as compared with the rest of
the solutes due to its larger number of π electrons, and it
behaves as an outlier in the polarizability plot.
hydroxyacetone
3-hydroxy-3-methyl- 2.211 22.56 443 717
2-butanone
scientific interest in elucidating the fundamental molecular
determinants of physical-chemical properties, a consider-
able effort has been devoted to generating quantitative
structure-activity (or structure-property) relationships
(QSARs/QSPRs).41,42 In the present study, we correlate the
experimental kH values with several molecular descriptors
for solute-solvent and solute-solute interactions, such as
the solute molecular surface area (Sm), the molecular
volume (Vm), its dipole moment (µ), and polarizability (R).
The values employed for these descriptors are presented
in Table 3. We computed these properties by performing
AM1 semiempirical quantum chemistry calculations of the
16 PFBHA-carbonyl derivatives with the Hyperchem
software package.43,44 The geometry of each derivative in

1486 J ournal of Chemical and Engineering Data, Vol. 47, No. 6, 2002
Ta ble 5. Tem p er a tu r e Effect on th e Hen r y’s La w Con sta n t (kH) a n d th e Air -Wa ter P a r tition Coefficien t (ka w ) for Eigh t
Ca r bon yl-P F BHA Der iva tives in th e Ra n ge (5 to 25) °C
kH/Pa‚m3‚mol-1
103kaw
∆H∞
∆S∞
T ) 298 K
T ) 288 K
T ) 278 K
T ) 298 K
T ) 288 K
T ) 278 K
kJ ‚mol-1
J ‚K-1‚mol-1
acetone
acrolein
90.3 ( 5.9
105.2 ( 4.2
215 ( 12
48.5 ( 3.1
48.5 ( 7.2
90.0 ( 6.7
100.4 ( 4.5
27.7 ( 6.1
20.8 ( 5.2
183 ( 29
33.4 ( 3.6
26.7 ( 7.4
46.7 ( 8.8
60.1 ( 6.0
10.0 ( 3.8
13.4 ( 3.9
147 ( 23
36.9
43.0
88.1
60.3
25.0
21.6
109.7
81.6
20.5
20.5
38.1
42.5
11.7
8.81
77.7
68.5
14.6
11.7
20.4
26.3
4.3
5.8
64.4
49.8
31.7
44.6
50.0
28.5
59.9
44.7
18.2
17.0
78.6
123.5
147.3
72.4
170.9
117.6
42.6
2-butanone
crotonaldehyde
formaldehyde
acetaldehyde
2-pentanone
benzaldehyde
147 ( 15
61.3 ( 6.2
52.9 ( 4.9
268 ( 41
199 ( 21
162 ( 29
113 ( 27
36.5
A simple mathematical description of the dependence of
kH with Vm, Sm, and R can be obtained by Gaussian fitting
of the data sets plotted in Figure 3A-C with the equation
estimated ∆H∞ and ∆S∞ are of the same order of magnitude
as that of values reported for the temperature dependence
of Henry’s law constants for PCBs.39
P er for m a n ce of Wa ter -Ba sed Air Sa m pler s with in
Situ P FBHA Der iva tiza tion . The values reported in the
literature for kH of most of the underivatized (i.e., free)
carbonyls studied in the present work are reported in Table
1 (data for 3-hydroxy-3-methyl-2-butanone were not avail-
able). In almost all cases, with the single exception of
decanal, the reported Henry’s law constants of the free
carbonyls were lower than those determined for their
PFBHA derivatives in the present work. In some extreme
cases, corresponding to low molecular weight solutes and
hydroxylated carbonyls, the kH values of the free carbonyls
are 3 to 5 orders of magnitude lower than those of
derivatized carbonyls. This indicates that PFBHA deriva-
tives can be considerably more volatile than the free
analyte, and therefore the risk of volatilization losses
during sampling is higher when PFBHA is added to the
collection solution. This fact underscores the importance
of evaluating the volatilization rates, on the basis of the
Henry’s constant values of both free and derivatized
carbonyls. In previous research, we report collection ef-
ficiencies of 0.94 for glycolaldehyde, 0.86 for hydroxy-
acetone and glyoxal, and 0.83 for methylglyoxal when
sampling for 10 min using two mist chambers in series.
The Henry’s law constants for the free carbonyls (or
“effective” kH values, which include hydration products)
were lower than 0.03 Pa‚m3‚mol-1 (or higher than 3000
M‚atm-1). We also reported breakthrough of acrolein,
methacrolein, crotoaldehyde, p-tolualdehyde, methyl gly-
oxal, benzaldehyde, hydroxy acetone, and glycolaldehyde
among other analytes when sampling for 4 h when using
four impingers in series.1,19 The high collection efficiencies
when using the mist chambers indicate that, at least for
the considered analytes, the higher volatility of their
PFBHA derivatives does not seem to affect dramatically
the observed collection efficiency. Furthermore, the empiri-
cal collection efficiency in mist chambers correlated well
with a theoretical model that did not take into account the
derivatization of the analytes.1 Considering that the sam-
pling time with the mist chamber is very short (10 min),
these results suggest that the PFBHA derivatization of
carbonyls is a slow reaction and that volatilization of a
carbonyl-PFBHA derivative does not affect the collection
efficiency. In contrast, when using impingers which utilize
longer sampling times (e.g., 4-8 h), the presence of the
analytes in the fourth impinger in the previous work19
suggests that formation of the PFBHA derivatives and
subsequent volatilization can become a problem when long
sampling times are involved. Clearly, obtaining quantita-
tive information about the kinetics of PFBHA derivatiza-
tion is an important step toward understanding processes
affecting the collection efficiency for methods that rely on
in situ PFBHA derivatization of airborne carbonyls.
2
(X - c)
kH ) a + b exp -0.5
(8)
(
)
[
]
d
where X indicates Vm, Sm, or R. The fitting parameters a,
b, c, and d corresponding to eq 8 as applied to the data in
Figure 3A-C are presented in Table 4. Considering the
effect of the activity coefficient (γ∞) and the vapor pressure
(p°) on kH discussed above (see eq 7), the initial growth
g
observed for low molecular weight derivatives can be
attributed to a regime in which the increase in γ∞ predomi-
nates, while the declining kH values for higher molecular
weights arise from the exponential decay of the vapor
pressure (p°). The Gaussian curves exhibit good correla-
g
tion with most saturated aliphatic-, unsaturated ali-
phatic-, and aromatic carbonyl-PFBHA derivatives, as
well as those of dicarbonyls. The polarizability (R) seems
to present a slightly better performance as a molecular
descriptor (R2 ) 0.870) as compared with the molecular
volume (Vm, R2 ) 0.859) and surface area (Sm, R2 ) 0.787).
Data for hydroxycarbonyl-PFBHA derivatives were not
used in the correlation with any molecular descriptor, while
the polyaromatic derivative was excluded only in the case
of R, where it behaved as an outlier.
The three descriptors Vm, Sm, and R have a high
correlation among each other. It is, therefore, not surpris-
ing to see that kH versus each of the three descriptors
exhibits a similar bell-shaped relationship. The dipole
moment instead proved to be an extremely insensitive
descriptor, as can be seen in Figure 3D. Its value is
essentially dominated by the PFBHA common core of the
structure, with negative partial charges located on the N
atom (about -0.2 e) and on the five F atoms (-0.06 to
-0.08 e). The glyoxal derivative contains two PFBHA units,
exhibiting the lowest molecular dipole moment for sym-
metry reasons. Hydroxycarbonyl derivatives also present
a lower molecular dipole, due to the partial negative
charges located on the O atoms (about -0.3 e).
Tem per a tu r e Depen d en ce fr om 5 to 25 °C. The effect
of temperature on kH was evaluated for the PFBHA
derivatives of acetone, acrolein, 2-butanone, crotonalde-
hyde, formaldehyde, acetaldehyde, 2-pentanone, and benz-
aldehyde. From the slope and intercept of the linear
regression of ln kaw versus T-1, we estimate values of ∆H∞
and ∆S∞, according to eq 4. These parameters, together
with the corresponding kH and kaw, are reported in Table
5. Small variations were observed in the temperature
dependence parameters (in the ranges 17 < ∆H∞/kJ ‚mol-1
< 60 and 36 < ∆S∞/J ‚K-1‚mol-1 < 170, respectively). The
more volatile derivatives among the analyzed solutes (those
corresponding to 2-pentanone and benzaldehyde) were less
sensitive to temperature changes (i.e., lower ∆H∞). The

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Received for review May 3, 2002. Accepted August 11, 2002. The
authors thank the Atmospheric Chemistry Program, National
Science Foundation (Grant No. 0003137), and the California Air
Resources Board (Contract No. 318) for supporting this work.
J E025545I