Low HCl Concentration Research Articles

Poly( o-methoxyaniline)–palladium systems: effect of preparation conditions on physico-chemical properties

Physico-chemical properties of poly( o-methoxyaniline) (POMA) –palladium systems prepared in the PdCl 2/HCl aqueous solutions depend on the HCl concentration in the solution. At low HCl concentration ( 0.66×10 −3 M ) a two-phase system composed of the polymer phase and large crystalline metallic palladium particles (revealed by X-ray diffraction and scanning electron microscopic studies) is formed. At higher HCl concentrations (0.1 and 1 M) the presence of metallic Pd particles has not been detected. Based on spectroscopic investigations (IR, UV-Vis and XPS techniques) it has been established that formation of Pd metal proceeds on the account of partial oxidation of the POMA chain. Protonation of POMA with palladium chlorocomplexes as counterions and coordination of palladium(II) ions by the nitrogen and oxygen atoms of POMA are additional reactions taking place in the PdCl 2 solution of low HCl concentration. These are the only reactions in the PdCl 2 solutions of higher HCl concentrations. In the work, POMA–palladium systems are compared with POMA protonated in the appropriate HCl solutions.

Large Cage Face-Centered-Cubic Fm3m Mesoporous Silica: Synthesis and Structure

The synthesis and precise structural characterization of highly ordered three-dimensional close-packed cage-type mesoporous silica is reported. The siliceous mesoporous material is proven to be commensurate with the face-centered-cubic Fm3m symmetry in high purity by a combination of experimental and simulated powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The cage-type calcined samples were additionally characterized by nitrogen physisorption. The aqueous synthesis method to prepare large cage mesoporous silica with cubic Fm3m structure is based on the use of EO106PO70EO106 triblock copolymer (F127) at low HCl concentrations, with no additional salts or organic additives. Here, emphasis is put on the low HCl concentration regime, allowing the facile thermodynamic control of the silica−triblock copolymer mesophase self-assembly. Further, simple application of hydrothermal treatments at various temperatures ranging from 45 to 150 °C enables the tailoring of the mesopore diameters and apertures. The combination of experimental and simulated XRD patterns and TEM images is confirmed to be a very powerful means for the accurate elucidation of the structure of new mesoporous materials.

Optical pH Sensing Characteristics in Dye-Doped Sol–Gel Coating Film Based on the Energy Transfer

Optical pH sensing characteristics based on the energy transfer using the sol–gel coating film doped with coumarin 6 and rhodamine 6G were examined. The dynamic range was a wider pH region from 1.0 to 10.0 and an optimum molar ratio of the two dyes existed from the viewpoint of the highest sensitivity for all pH levels. The response time for pH change from 1.0 to 10.0 was faster than that from pH 10.0 to pH 1.0. At a low HCl concentration as a catalyst, response times were constant under some molar ratio of the two dyes and agreed with that of coumarin 6-doped sol–gel coating film. At a high HCl concentration as a catalyst, response times which depend on the pore size in the silica network were long and constant, irrespective of the molar ratio of the two dyes. These characteristics were not significantly affected by the passage of days.

Leaching of Manganese Nodule in Hydrochloric Acid in Presence of Sphalerite

This paper reports the results of hydrochloric acid leaching of manganese nodule and sphalerite in combination. Combined leaching was observed to be more effective than the individual leaching of either sphalerite or nodule. The dissolution occurs through three major routes: 1) cyclic action of Fe3+/Fe2+ redox couple, 2) galvanic interaction between ZnS and MnO2 and 3) action of Cl2 gas generated from MnO2-HCl reaction on ZnS. All three routes play a role in the dissolution process at relatively lower HCl concentrations, whereas the last route is dominant at a higher hydrochloric acid concentration.

Leaching of Manganese Nodule in Hydrochloric Acid in Presence of Sphalerite

This paper reports the results of hydrochloric acid leaching of manganese nodule and sphalerite in combination. Combined leaching was observed to be more effective than the individual leaching of either sphalerite or nodule. The dissolution occurs through three major routes: 1) cyclic action of Fe3+/Fe2+ redox couple, 2) galvanic interaction between ZnS and MnO2 and 3) action of Cl2 gas generated from MnO2-HCl reaction on ZnS. All three routes play a role in the dissolution process at relatively lower HCl concentrations, whereas the last route is dominant at a higher hydrochloric acid concentration.

Gold solubility, speciation, and partitioning as a function of HCl in the brine-silicate melt-metallic gold system at 800°C and 100 MPa

A vapor-undersaturated synthetic brine was equilibrated with metallic gold and a haplogranitic melt at 800°C and 100 MPa to examine the solubility, speciation and partitioning of gold in the silicate melt-brine-metallic gold system. The starting composition of the NaCl-KCl-HCl-H2O brine was 70 wt.% NaCl (equivalent) with starting KCl/NaCl ranging from 0.5 to 1. KCl/HCl was varied from 3.2 to 104 to evaluate the solubility and partitioning of gold as a function of the concentration of HCl in the brine. Inclusions of brine were trapped in a silicate glass during quench. Inclusion-poor and inclusion-rich portions of glass were analyzed for gold and chloride by using neutron activation analysis. The inclusion-poor glass yielded an estimate of the solubility of gold and chloride in the silicate melt. The solubility of gold in the melt, at gold metal saturation, was estimated as ≈1 ppm. The solubility of gold in the brine was estimated by mass balance, given the concentration of gold and chloride in the inclusion-poor and inclusion-rich glasses. The solubility of gold metal at low-HCl concentrations in the brine, CHClb, (3 × 103 to 1.1 × 104 ppm) is ≈40 ppm (by weight) and is independent of the HCl concentration under those conditions. For CHClb of 1.1 × 104 to 4.0 × 104 ppm, the solubility of gold increased from 40 to 840 ppm, and the solubility is given by: log CAub = [2.2 · log CHClb] − 7.2(1) These data suggest that a significant amount of gold is not chloride complexed in brines at low-HCl concentrations (< 1.1 × 104 ppm), but that gold-chloride complexes, possibly AuCl2H, are important at elevated concentrations of HCl (> 1.1 × 104 ppm). The calculated Nernst partition coefficient (DAub/m) for gold between a brine and melt varied from 40 to 830 over a range of brine HCl concentrations of 3 × 103 to 1.1 × 104 ppm. Our results indicate a significant amount of gold can be transported by a brine in the magmatic-hydrothermal environment independent of the fugacity of sulfur in the system. Thus brines provide an effective mechanism for the scavenging of gold from a crystallizing melt and transport into an associated magmatic-hydrothermal system, regardless of their sulfur contents.

Aluminium corrosion in hydrochloric acid solutions and the effect of some organic inhibitors

Electrochemical behaviour of pure aluminium in HCl solutions of different concentration, in presence and absence of organic inhibitors has been studied by potentiostatic and potentiodynamic methods. The evolution of the electrode surface was examined by optical microscope. The resistance of aluminium against corrosion in solutions with low concentrations of HCl can be attributed to a rapidly formed surface oxide. The presence of the chloride ions creates extensive localized attack. In strong acidic solutions no passive–active transition up to high overvoltages was observed. The increase of HCl concentration led, in all the cases, to the increase of the dissolution rate of aluminium in according to the dissolution proposed mechanism and Pourbaix diagram. The existence of an oxide layer on the metal at an appreciable coverage and thickness leads to anomalously high anodic and cathodic Tafel slopes (at high overpotential), which is not the case for potentials in the range of about 70mV around the stationary corrosion potential. The addition of surfactants leads in all cases to the inhibition of the corrosion process. The results obtained indicate that, Tween 20 and 81 are more effective to inhibit the corrosion of pure aluminium than hexadecylpyridinium bromide (HDPB). Under the critical micelle concentration (CMC), the inhibition of used surfactants is negligible. At a concentration higher than the CMC, the inhibiting action increases rapidly. The inhibition process was attributed to the formation of adsorbed film on the metal surface that protects the metal against corrosive agents. The sigmoidal shape of the adsorption isotherm confirm the applicability of Frumkin’s equation to describe the adsorption process of the three surfactants tested in 0.5M HCl solution on an aluminium electrode.

Extraction studies of platinum group metals with cyanex 925 in toluene—role of tin(II) chloride in their separation

Extraction of platinum group metals Os(VIII), Ru(IV), and Ir(III) was carried out from aqueous chloride media with Cyanex 925 in the absence and in the presence of tin(II) chloride. In the presence of hydrochloric acid (HCl) alone, only Os(VIII) and Ru(IV) get extracted quantitatively, while extraction of Ir(III) was incomplete. Further, Os(VIII) could be extracted at lower concentrations of HCl and Ru(III) at higher concentrations (3.5–5.0 M). In the presence of tin(II) chloride, the extraction of Ir(III) increases and becomes quantitative. However, it decreases to some extent in the case of Os(VIII) and Ru(IV). The extraction conditions for all the metal ions were optimized under influence of variables such as HCl concentration, reagent concentration, tin(II)chloride concentration, equilibration time, stripping agents, and effect of diverse ions. The separation of individual metal ions Os(VIII), Ru(IV), and Ir(III) was carried out by taking advantage of differences in their extraction and stripping conditions towards Cyanex 925. The methods developed were applied to the recovery of these metal ions from some real catalysts samples.

The influence of HCl on SO 2 absorption in the spray dry scrubbing process

To examine the influence of HCl on SO 2 removal in the spray dry scrubbing process, preliminary experiments on the effect of adding CaCl 2 to the lime slurry on SO 2 absorption efficiency were performed in a laboratory scale spray dryer. It was found that the SO 2 removal efficiency is augmented at CaCl 2 concentrations up to 1.2 g/l in the lime slurry. This is ascribed to the influence of the prolonged drying process. However, SO 2 absorption efficiency cannot be improved further at higher CaCl 2 concentrations. A simple estimation shows that this cannot be ascribed solely to the influence of the drying behavior of the droplets and more complex explanations have to be found. Subsequently, experiments on the simultaneous absorption of SO 2 and HCl were performed. It was found that the SO 2 removal efficiency is enhanced at low HCl concentrations in the flue gas. This is ascribed to the formation of CaCl 2 in the droplets, resulting in a prolonged drying process. After reaching a maximum, the SO 2 removal efficiency falls again at higher HCl concentrations. This can be explained with the competing absorption process in which HCl is thermodynamically favored.

Effects of catalytic acid and templating surfactant concentrations on mesostructure of submillimeter-thick mesoporous silica by solvent evaporation synthesis

Submillimeter-thick films of mesoporous silica were synthesized by the solvent evaporation method using tetraethoxysilane (TEOS) and cetyltrimethylammonium chloride (CTAC) as the silica source and the templating agent, respectively. The effects of HCl/TEOS and CTAC/TEOS molar ratios were investigated. It was revealed that a high CTAC concentration and a low gelation rate at a low HCl concentration were favorable for the formation of highly ordered mesostructures, since the mesostructure is governed by the concentration of CTAC at gelation of the solution. The pore diameter increased as the CTAC/TEOS ratio decreased, suggesting the intermediation between a silica wall and a CTAC micelle by a water layer whose thickness increases with the increase in the H 2O/CTAC ratio.

Transport of niobium(V) through a TBP–Alamine 336 supported liquid membrane from chloride solutions

The transport of niobium(V) in chloride medium through a supported liquid membrane (SLM), using Alamine 336 and tributyl phosphate (TBP) as carriers, has been investigated. The work has been undertaken by first determining the liquid–liquid extraction distribution of niobium(V) between aqueous solution and different organic solutions. Optimum conditions for both extraction and stripping were established. The mixture of Alamine 336 and TBP provided the best extraction in high chloride medium, while low HCl concentration stripped the ion from the loaded organic phase. Transport experiments were carried out with a permeation cell having a continuous flow system and constant agitation. The study of the liquid membrane included the chemical conditions, i.e. carrier concentration and hydrochloric acid concentration in the feed solution. Maximum niobium recovery at 10% of Alamine 336 in TBP was obtained at HCl concentration between 6 and 7 mol/dm 3. The mechanism postulated is referred to a synergistic extraction of Nb(V) by means of a co-transport process. Nb(V) can be concentrated in the stripping solution and the SLM showed a good performance for Nb–Ta separation.

High-Temperature Corrosion of Iron at 900°C in Atmospheres Containing HCl and H2O

The corrosion behavior of iron at 900°C in gas mixtures of O2/N2, H2O/O2/N2, HCl/H2O/O2/N2, H2O/N2, and HCl/H2O/N2 was observed. Parabolic oxide-scaling kinetics were observed in all cases, except HCl/H2O/N2 containing 2.5% HCl. This gas produced linear weight-loss kinetics caused by FeCl2 vaporization. Lower HCl concentrations in H2O/N2 led to no chloride formation. In all cases, the reaction products reflected a close approach to local equilibrium between scale and gas. The presence of H2O led to oxide-scale-surface faceting, and in the presence of free oxygen, to acceleration of the sublayer growth of FeO.

Development of surface plasmon resonance-based immunoassay for aflatoxin B(1).

Aflatoxins are a group of highly toxic fungal secondary metabolites that occur in Aspergillus species and may contaminate foodstuffs and feeds. Two different anti-aflatoxin B(1) antibodies were examined to develop a surface plasmon resonance (SPR)-based immunoassay to aflatoxin B(1). A conjugate consisting of aflatoxin B(1)-bovine serum albumin (BSA) was immobilized on the dextran gel surface. Competition between immobilized aflatoxin B(1) conjugate and free aflatoxin B(1) in solution for binding to antibody injected over the surface formed the basis for the assay. Regeneration of the antibody from the immobilized conjugate surface is essential for the development of such an inhibitive immunoassay. Problems were encountered with the regeneration of the sensor surface, due to the high-affinity binding of the antibodies. Conventional regeneration solutions consisting of low concentrations of NaOH and HCl worked to a degree, but regeneration was at the expense of the integrity of the immobilized conjugate. A polyclonal anti-aflatoxin B(1) antibody was produced and was found to be regenerable using an organic solution consisting of 1 M ethanolamine with 20% (v/v) acetonitrile, pH 12.0. This combined high ionic strength and extreme pH, as well as chaotrophic properties and allowed the development of an inhibitive immunoassay. The assay had a linear range of 3.0-98.0 ng mL(-1) with good reproducibility.

Gaseous etching of 6H–SiC at relatively low temperatures

A comparison was made of on- and off-axis 6H–SiC substrate surfaces etched in H 2, atomic hydrogen, C 2H 4/H 2, and HCl/H 2 at the relatively low-temperature range of 1400–1500°C. Well-defined terraces with three-bilayer height steps were obtained on the on-axis 6H–SiC substrates etched as low as 1450°C, with reproducibility dependent on the history or cleanliness of the reactor. The effects of adding HCl depended on its concentration and temperature; i.e. at low temperature and high HCl concentration, the surface had a hillock pattern, while well-defined steps formed at the reverse conditions. The etch rate with atomic hydrogen was high even at a low temperature (1200°C), and it produced a surface pattern with hillock depressions. The surface after etching depended on the original substrate surface condition; polishing damage caused by high applied load always resulted in a worse surface after etching. Off-axis substrates were smoother, while the original off-cut step pattern was not changed after etching in H 2.

ACE-2 HILLCLOUD. An overview of the ACE-2 ground-based cloud experiment

The ACE‐2 HILLCLOUD experiment was carried out on the island of Tenerife in June–July 1997 to investigate the interaction of the boundary layer aerosol with a hill cap cloud forming over a ridge to the north‐east of the island. The cloud was used as a natural flow through reactor to investigate the dependence of the cloud microphysics and chemistry on the characteristics of the aerosols and trace gases entering cloud, and to simultaneously study the influence of the physical and chemical processes occurring within the cloud on the size distribution, chemical and hygroscopic properties of the aerosol exiting cloud. 5 major ground base sites were used, measuring trace gases and aerosols upwind and downwind of the cloud, and cloud microphysics and chemistry and interstitial aerosol and gases within the cloud on the hill. 8 intensive measurement periods or runs were undertaken during cloud events, (nocturnally for seven of the eight runs) and were carried out in a wide range of airmass conditions from clean maritime to polluted continental. Polluted air was characterised by higher than average concentrations of ozone (>50 ppbv), fine and accumulation mode aerosols (>3000 and >1500 cm−3, respectively) and higher aerosol mass loadings. Cloud droplet number concentrations N, increased from 50 cm−3 in background maritime air to >2500 cm−3 in aged polluted continental air, a concentration much higher than had previously been detected. Surprisingly, N was seen to vary almost linearly with aerosol number across this range. The droplet aerosol analyser (DAA) measured higher droplet numbers than the corrected forward scattering spectrometer probe (FSSP) in the most polluted air, but at other times there was good agreement (FSSP=0.95 DAA with an r2=0.89 for N<1200 cm−3). Background ammonia gas concentrations were around 0.3 ppbv even in air originating over the ocean, another unexpected but important result for the region. NO2 was present in background concentrations of typically 15 pptv to 100 pptv and NO˙3 (the nitrate radical) was observed at night throughout. Calculations suggest NO˙3 losses were mainly by reaction with DMS to produce nitric acid. Low concentrations of SO2(∼30 pptv), HNO3 and HCl were always present. HNO3 concentrations were higher in polluted episodes and calculations implied that these exceeded those which could be accounted for by NO2 oxidation. It is presumed that nitric and hydrochloric acids were present as a result of outgassing from aerosol, the HNO3 from nitrate rich aerosol transported into the region from upwind of Tenerife, and HCl from sea salt aerosol newly formed at the sea surface. The oxidants hydrogen peroxide and ozone were abundant (i.e., were well in excess over SO2 throughout the experiment). Occasions of significant aerosol growth following cloud processing were observed, particularly in cleaner cases. Observations and modelling suggested this was due mainly to the take up of nitric acid, hydrochloric acid and ammonia by the smallest activated aerosol particles. On a few occasions a small contribution was made by the in‐cloud oxidation of S(IV). The implications of these results from HILLCLOUD for the climatologically more important stratocumulus Marine Boundary Layer (MBL) clouds are considered.

Autopalmitoylation of tubulin.

Pure rat brain tubulin is readily palmitoylated in vitro using [3H]palmitoyl CoA but no added enzymes. A maximum of approximately six palmitic acids are added per dimer in 2-3 h at 36-37 degrees C under native conditions. Both alpha and beta tubulin are labeled, and 63-73% of the label was hydroxylamine-labile, presumed thioesters. Labeling increases with increasing pH and temperature, and with low concentrations of guanidine HCl or KCl (but not with urea) to a maximum of approximately 13 palmitates/dimer. High SDS and guanidine HCl concentrations are inhibitory. At no time could all 20 cysteine residues of the dimer be palmitoylated. Polymerization to microtubules, or use of tubulin S, markedly decreases the accessibility of the palmitoylation sites. Palmitoylation increases the electrophoretic mobility of a portion of alpha tubulin toward the beta band. Palmitoylated tubulin binds a colchicine analogue normally, but during three warm/cold polymerization/depolymerization cycles there is a progressive loss of palmitoylated tubulin, indicating decreased polymerization competence. We postulate that local electrostatic factors are major regulators of reactivity of tubulin cysteine residues toward palmitoyl CoA, and that the negative charges surrounding a number of the cysteines are sensitive to negative charges on palmitoyl CoA.

Infrared and Raman studies of palladium—nitrogen-containing polymers interactions

In the present research the nature of interactions of poly(4-vinylpyridine) (PVP) and polyaniline (PANI) with various Pd2+ chlorocomplexes existing in PdCl2–HCl–H2O solutions have been studied using IR (MIR, FIR) and Raman spectroscopies. It has been found that these interactions involve the nitrogen atoms of the polymers. In the PdCl2 solutions of high HCl concentration containing [PdCl4]2− and [PdCl3(H2O)]− as the major species acid–base type reaction (protonation) with the formation of the polymer salt as well as the coordination of Pd2+ ions by the nitrogen atoms of the polymer take place. In the PdCl2 solutions of low HCl concentration containing [PdCl2(H2O) 2] as the major species protonation proceeds to a small extent. The main process in this case is most probably hydrolysis of the latter with the precipitation of hydrated palladium hydroxide or oxide on the polymer surface. In the case of PANI the oxidation–reduction between this precipitate and PANI takes place. It results in the oxidation of the polymer chain.

Multiple pH-Induced Morphological Changes in Aggregates of Polystyrene-block-poly(4-vinylpyridine) in DMF/H2O Mixtures

Multiple changes in the aggregate morphologies of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) diblocks have been observed as a function of the apparent pH (pH*) in DMF/H2O mixtures. The pH* changes were induced by adding HCl (in the concentration range 400 nM−20 mM) or NaOH (100 nM−20 mM). On the acid side, as the pH* increases from 7 (20 mM HCl) to 12.3 (the pH* of the original polymer solution without any additional microions), the aggregate morphology changes from large compound micelles (LCMs) to a mixture of spheres, rods, and vesicles (pH* = 8), to spheres (pH* = 8.4), to rods (pH* = 11.8), and then back to spheres (pH* = 12.3). In the presence of NaOH, as the pH* increases from 12.3 to 18 (20 mM NaOH), the morphology changes to rods (pH* = 12.6), then back to spheres again (pH* = 17.5), and finally to a mixture of spheres, rods, lamellae, and vesicles (pH* = 18). This level of morphological complexity as a function of pH* is unprecedented. The reasons for the behavior can be ascribed to the amphiprotic nature of P4VP in DMF. The addition of either an acid or a base introduces ionic groups into the corona chains. Thus electrostatic repulsion is introduced and the aggregate morphology changes generally in the direction of bilayers to spheres. However, due to the existence of multiple equilibria, some of the added microions are free, which decreases the steric−solvation interaction and decreases the electrostatic repulsion by shielding. This decrease in the corona repulsion tends to decrease the coil dimensions in the corona. As a result, the morphology is driven in the direction of spheres to bilayers. Therefore, a competition between unshielded electrostatic repulsion and shielding coupled with a decrease of the steric−solvation interaction is induced. At relatively low concentrations, the decrease of the steric−solvation interaction dominates, while at relatively high concentrations, the shielding dominates. In intermediate regions, the unshielded electrostatic repulsion is dominant. The morphological transitions induced by extremely low concentrations of HCl or NaOH (100 nM−1 μM) are very surprising. The effect of a neutral salt (NaCl) on the neutral copolymer and the effect of pH* on a quaternized copolymer were also explored.

The duodenal motility response to HCl is influenced by NO and prostaglandins

In this study the following questions were addressed: (1) Does HCl affect duodenal motility in rats with postoperative ileus? (2) If so, at what luminal HCl concentration does this occur? (3) If HCl increases duodenal motility, is this effect associated with disturbance of mucosal integrity? (4) Do prostaglandins and NO affect the duodenal motility response to HCl? Proximal duodenum was perfused in situ with saline or HCl (3, 10 and 100 mM) in anesthetized rats. Duodenal motility was assessed by measuring intraluminal pressure and myoelectric activity. Mucosal integrity was determined as blood-to-lumen clearance of 51Cr-EDTA. Rats were divided into four subgroups: (1) Controls; (2) rats treated with the nitric oxide synthase (NOS) inhibitor N ω-nitro- l-arginine-methyl-ester (L-NAME); (3) rats treated with the cyclooxygenase (COX) inhibitor indomethacin; and (4) rats treated with L-NAME and indomethacin. Very few duodenal contractions occurred during saline perfusion or in response to HCl in controls. The stimulatory effect of L-NAME on motility varied among animals. In L-NAME-treated rats motility was increased by 10 and 100 mM HCl, and in the latter case it subsequently decreased. Indomethacin induced motility in all animals. This effect was markedly reduced by perfusion with 10 and 100 mM HCl and transiently inhibited by the NO donor nitroprusside. In L-NAME+indomethacin-treated rats, 10 and 100 mM HCl decreased motility, but to a lesser extent than in rats treated with indomethacin alone. Only 100 mM HCl increased mucosal permeability in all groups. It is concluded that HCl does not affect duodenal motility in rats with postoperative ileus unless they are treated with inhibitors of NOS or of COX. HCl induces transmission of both excitatory and inhibitory signals to duodenal smooth muscle, and the inhibitory signals, mediated by prostaglandins and NO, predominate under control conditions. The threshold luminal [H +] for its effect on duodenal motility appears to lie between 3 and 10 mM HCl. The HCl-induced changes in duodenal motility occur at a lower HCl concentration than that required to increase 51Cr-EDTA permeability, suggesting that the motility response is not triggered by mucosal injury.

Effect of Hydrochloric Acid on Sampling and Analysis of Semivolatile Organic Compounds in Incineration Flue Gas. 1. Chlorophenols

The recoveries of 16 isomers of chlorophenols (CPs) from the adsorbent (XAD-2) of the MM5 train are affected by hydrochloric acid (HCl) present in the incinerator flue gas. At 2.05 and 5.53 mg/L in flue gas, HCl caused desorption of CPs from XAD-2. The desorption is dependent upon the number of chloro substituents in the CPs. The Soxhlet extraction behaviors of CPs from XAD-2 in the presence or the absence of HCl were also studied in the laboratory. The results explain the previously reported low recovery of pentachlorophenol from XAD-2 when the flue gas contained none or very low concentrations of HCl. An extraction procedure for complete CPs recoveries from XAD-2 is proposed that involved two sequential extractions: first with dichloromethane and then with the addition of 1.0 mL of 1.0 M aqueous HCl on XAD-2 and followed by the subsquent extraction with dichloromethane. This procedure does not affect other semivolatile compounds on XAD-2 and leads to [13C6]pentachlorophenol surrogate recovery of 90 ± 6...