A simple solution to the problem of selective detection of phosphate and arsenate by the molybdenum blue method.

We report a simple and fast method for the quantification of both phosphate and arsenate in water using the molybdenum blue method. The method does not require established pre-treatment procedures for physically separating arsenate and phosphate or reducing the arsenate to arsenite. In our method, the heteropolymolybdate ions in the solution are precipitated and collected on a membrane that is transparent in both the visible and infrared regions of the spectrum. The phosphate is determined by recording a visible spectrum in transmission mode through the membrane. This membrane is then air-dried, and then an infrared spectrum is recorded through the membrane in transmission mode. The concentration of arsenate is then determined from the intensity of an As-O band positioned at 879 cm-1 in the infrared spectrum. Using this method, a detection limit of 0.86 µg L-1 phosphate and 13.9 µg L-1 arsenate in water was achieved. Matrix spikes on environmental samples gave a 108% recovery of arsenate and a 105% recovery of phosphate over a dynamic range of 25-250 µg L-1 of arsenate and phosphate in the sample.

A new approach for measuring water concentration in oil using copper sulfate powder and infrared spectroscopy.

An approach for measuring water concentration in oil, based on the use of CuSO4 particles and infrared spectroscopy, is described. The particles interact with both dissolved water and water droplets to form the monohydrate, CuSO4·H2O. These particles are collected on an infrared transparent membrane and then an infrared spectrum in transmission mode is recorded. Strong interaction of the water with the CuSO4 shifts and intensifies the water bending mode to produce a unique band at 1743 cm-1. The method provided values which are equivalent to those measured by Karl Fischer titration over the range of 10 to 3500 mg L-1 with a linearity R2 value of > 0.99 and an average %RSD for all measurements was 6%. No matrix specific calibrations are required.

Measurement of water concentration in oils using CaO powder and infrared spectroscopy.

A simple method for measuring water concentration from 1 to 10000 mg L-1 is described. The approach involves adding CaO powder to an oil sample and measuring the amount of Ca(OH)2 produced by the reaction of CaO with water. Collection of the powder occurs by passing a fixed volume of the oil through an infrared transparent membrane and the amount of water is determined from the intensity of the OH stretching mode of Ca(OH)2 at 3645 cm-1. The approach is demonstrated with transmission, vegetable, and extreme pressure oils. These oils represent classes of oils that are problematic for measurement by transmission infrared spectroscopy, using a fixed pathlength cell, as described in ASTM method E2412. Values for the water levels equivalent to those measured by Karl Fischer titration are obtained with a linearity R2 value of > 0.996 and %RSD of 6.7% over a wide detection range of 1 mg L-1 to 10000 mg L-1. No calibration is required, as the amount of water is determined using the extinction coefficient for the band at 3645 cm-1.

A reagentless and rapid method to measure water content in oils.

A simple method for measuring water levels from 1 mg L-1 to 5000 mg L-1 in oils that uses no chemical reagents or matrix specific calibrations is described. The approach involves capturing the water from the oil on an infrared transparent membrane and then recording an IR spectrum in transmission mode through the membrane. A classic spectrum of liquid water is obtained for all oil types, as both dissolved water and emulsion-based water are extracted to form an adsorbed layer of water on the membrane surface. The method was tested with three types of oils that are identified as difficult in the ASTM method E2412, as these oils, exhibit distortions in the water bands due to interactions of the water with the oil, or have significant levels of scattering due to the presence of water droplets. In comparing water concentrations measured by Karl Fischer titration, a high level of linearity (R2 > 0.995) is obtained over the range of 1 mg L-1 to 5000 mg L-1 with slope values of 0.99 for power steering fluid, 0.98 for vegetable oils, and 0.95 for extreme pressure fluid. This shows that water concentration obtained by the membrane method were comparable to those obtained by Karl Fischer. No matrix calibrations were needed as the concentration of water in oil was determined using literature values for the extinction coefficients of water. The wide detection range is obtained by varying the volume of oil (30 µL-30 mL) passed through the membrane and by choosing the water band for quantification.

A solventless method for detecting trace level phosphate and arsenate in water using a transparent membrane and visible spectroscopy.

The molybdenum blue method is the American Public Health Association (APHA) approved method for the detection and quantification of phosphate in water. The standard molybdenum blue method, APHA 4500 PE has a detection limit of 30 µgL-1 phosphate (10 µgL-1 phosphorus) in freshwater with a 5 cm cuvette. To further lower the detection limit to sub µgL-1 levels, we have developed a simple, fast, and solventless method for conversion of phosphate present in solution to a solid for quantification by Visible spectroscopy. The process converts the anionic heteropolymolybdate ions into a solid colloidal precipitate by charge neutralization with the cationic surfactant cetyltrimethylammonium bromide (CTAB), and the precipitate is then captured on a Visible transparent membrane. A Visible spectrum is then recorded in transmission mode through the membrane and the concentration of the phosphate is determined from the intensity of a band cantered at 700 nm. Using this method, the detection limit for phosphate in water is lowered to 0.64 µgL-1. The approach has also been extended to detect arsenate in water with a detection limit of 4.8 µgL-1 arsenate. . The method is also used to investigate real matrices with accuracy that matches the standard APHA method for detection of phosphate in water.

Controlled growth of layer-by-layer assembled polyelectrolyte multilayer films under high electric fields.

HYPOTHESIS: The application of an external electric Field (E-Field) to control layer-by-layer (LBL) growth of polyelectrolyte multilayers (PEM) typically involves hydrolysis of the water at the electrodes. We hypothesize that by isolating the electrodes from contact with the water, high E-Fields could be used to control the conformation of the polyelectrolytes in the solution phase and thus, enable non-chemical control of the LBL growth. EXPERIMENTAL: Attenuated total reflectance infrared spectroscopy was used to monitor the bound fraction and adsorbed amount as a function of time for the sequential addition of polyacrylic acid and polydiallyldimethylammonium chloride adsorbed on a TiO2 film under the applied E-Field. FINDINGS: The direction of the E-Field relative to the TiO2 film controlled the PEM growth, resulting in non-linear growth or decay. In the case of non-linear LBL decay, there was a decrease in adsorbate mass in successive layers to a point of no growth.

Photodegradation of taste and odor compounds in water in the presence of immobilized TiO2-SiO2 photocatalysts.

Disinfection by ultraviolet (UV) radiation is a growing trend in public water treatment systems because of its effectiveness with respect to inactivation of protozoa and other pathogenic microorganisms. However, removal of different classes of organic compounds, including taste and odor compounds in water is not effective with UV irradiation. In this study, a novel TiO2-based immobilized photocatalyst is developed to enhance the UV photodegradation of two of the major taste and odor compounds, 2-methylisoborneol (MIB) and Geosmin (GSM) in water. Evonik (formerly Degussa) P-25 powder-modified TiO2 was immobilized on glass slides using TiO2-SiO2 sol-gel mixture as the binder and calcined at 500 °C. Several catalyst films with different Si amounts were synthesized and characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and scanning electron microscopy (SEM). Photocatalytic degradation of MIB and GSM was investigated by irradiating aqueous solutions under UV-A light (350 nm). Generation of hydroxyl radicals (OH) was also assessed to evaluate the activity of the photocatalyst films. Catalyst films with surface ratios of Ti:Si ≈6 showed similar degradations rates but better robustness compared to immobilized P25 films.

Supercritical Fluid Atomic Layer Deposition: Base-Catalyzed Deposition of SiO2.

An in situ FTIR thin film technique was used to study the sequential atomic layer deposition (ALD) reactions of SiCl4, tetraethyl orthosilicate (TEOS) precursors, and water on nonporous silica powder using supercritical CO2 (sc-CO2) as the solvent. The IR work on nonporous powders was used to identify the reaction sequence for using a sc-CO2-based ALD to tune the pore size of a mesoporous silica. The IR studies showed that only trace adsorption of SiCl4 occurred on the silica, and this was due to the desiccating power of sc-CO2 to remove the adsorbed water from the surface. This was overcome by employing a three-step reaction scheme involving a first step of adsorption of triethylamine (TEA), followed by SiCl4 and then H2O. For TEOS, a three-step reaction sequence using TEA, TEOS, and then water offered no advantage, as the TEOS simply displaced the TEA from the silica surface. A two-step reaction involving the addition of TEOS followed by H2O in a second step did lead to silica film growth. However, higher growth rates were obtained when using a mixture of TEOS/TEA in the first step. The hydrolysis of the adsorbed TEOS was also much slower than that of the adsorbed SiCl4, and this was overcome by using a mixture of water/TEA during the second step. While the three-step process with SiCl4 showed a higher linear growth rate than obtained with two-step process using TEOS/TEA, its use was not practical, as the HCl generated led to corrosion of our sc-CO2 delivery system. However, when applying the two-step ALD reaction using TEOS on an MCM-41 powder, a 0.21 nm decrease in pore diameter was obtained after the first ALD cycle whereas further ALD cycles did not lead to further pore size reduction. This was attributed to the difficulty in removal of the H2O in the pores after the first cycle.

Dynamics of layer-by-layer growth of a polyelectrolyte multilayer studied in situ using attenuated total reflectance infrared spectroscopy.

Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to study the dynamic layer-by-layer (LBL) growth of a sodium polyacrylate (NaPA)/poly(diallydimethylammonium) chloride (PDADMAC) multilayer on TiO2 particles. Molecular weights (Mw) used were 30 and 60 kDa for NaPA and 8.5 and 150 kDa for PDADMAC. IR spectra were recorded in situ as a function of time and were used to obtain the dynamic mass adsorbed and bound fraction of the polymers during each deposition step. For 30 kDa NaPA layers, the dynamics of adsorption show an initial rapid rise in mass followed by a slow increase toward a plateau value upon LBL with 150 kDa PDADMAC. In contrast, the 60 kDa NaPA layers achieve a plateau quickly and do not show a slow increase toward a plateau. In the case of LBL with 150 kDa PDADMAC, the dynamics of the bound fraction of polymer per layer suggest that polymer diffusion and conformational rearrangement occur for the layers of 30 kDa NaPA but not for the 60 kDa NaPA layers. Furthermore, PDADMAC adsorption profiles show that there is no diffusion of the PDADMAC layers and that PDADMAC flattens onto the underlying layer. A linear growth in the mass adsorbed per layer was observed for 150 kDa PDADMAC with both molecular weights of NaPA. In the case of 8.5 kDa PDADMAC, smaller growth increments and the desorption of underlying layers were observed. This work demonstrates the use of ATR-IR in obtaining the dynamics of LBL multilayer formation. Furthermore, it provides an example in which polymer diffusion during LBL film formation does not lead to exponential growth.

Molecular dynamics of the interaction of anionic surfactants with liposomes.

The time dependent molecular interactions of sodium dodecyl sulfate (SDS) with dipalmitoylphosphatidylcholine (DPPC) liposomes were studied using attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. In particular, the ATR spectra provided information on the dynamic amount of SDS incorporated and DPPC expelled in the DPPC structure along with structural information on the molecular nature of the SDS/DPPC assemblies. It was found that the uptake of SDS was always mirrored by the ejection of DPPC molecules from the liposomes and that the incorporation of SDS followed two routes; SDS intercalated into the DPPC liposomes and SDS was bound electrostatically to the charged surface of the DPPC liposome.

An infrared spectroscopic based method for mercury(II) detection in aqueous solutions.

A new method that uses solid phase extraction (SPE) coupled with FTIR spectroscopy to detect Hg(II) in aqueous samples is described. The technique is envisioned for on-site, field evaluation rather than lab-based techniques. This paper presents the "proof of principle" of this new approach toward measurements of Hg(II) in water and identifies mass transport issues that would need to be overcome in order to migrate from a lab based method to field operation. The SPE material supported on a Si wafer is derivatized with an acylthiosemicarbazide, which undergoes a reaction in the presence of aqueous Hg(II) to form an oxadiazole ring. The progress of the reaction is monitored by IR spectroscopy. Following EPA guidelines, the method of detection limit (MDL) for the SPE/IR was 5 µg of Hg(II)cm(-2). In a 1L sample and a 1cm(2) Si wafer, this translates to a detection limit of 5 ppb. This system shows a high selectivity toward aqueous Hg(II) over other thiophilic heavy metal ions such as Pb(II), Cd(II), Fe(III), and Zn(II) and other metal ions such as Ni(II), Mn(II), Co(II), Cu(II), In(III), Ru(III), Na(I), and Ag(I) in aqueous solutions.

A comparison of the behavior of cholesterol, 7-dehydrocholesterol and ergosterol in phospholipid membranes.

A molecular description of the effect of incorporation of cholesterol (CHOL), 7-dehydrocholesterol (7DHC) and ergosterol (ERGO) on the structure of DPPC or EggPC liposomes is provided. Data obtained from ATR-IR spectroscopy, detergent solubility and zeta potential measurements show that the insertion of the various sterols alters the packing arrangement of the tails and headgroup of the PC lipids and may lead to lipid domain formation. On a molecular basis, the differences in lipid packing architecture are traced to differences between the ring and tail structure of the three sterols and these differences in structure produce different effects in DPPC liposomes in the gel phase and EggPC liposomes in the fluid phase. Specifically, CHOL has a relatively flat and linear structure and among the three sterols, shows the strongest molecular interactions with DPPC and EggPC lipids. An extra double bond in the fused ring of 7DHC hinders a tightly packing arrangement with DPPC lipids and leads to less domain formation than CHOL whereas 7DHC clearly produces more lipid domain formation in EggPC. ERGO produces similar structural changes to 7DHC in the tail and headgroup region of DPPC. Nevertheless, ERGO incorporation into DPPC liposomes produces more domain formation than 7DHC.

Detection of spores using electric field-assisted FTIR-ATR.

An approach that integrates an electric field with an attenuated total reflection Fourier transform infrared spectroscopy (FTIR-ATR) flow through cell was used to detect spores in aqueous environments. A "proof of concept" in terms of the principle features of the method is described. It is shown that under an electric field, the negatively charged spores migrate and are concentrated on the surface of a ZnSe internal reflection element (IRE). No coating on the IRE is required, and a maximum amount adsorbed was obtained within the time needed to record the first spectrum. The amount adsorbed depends on both the pH and the ionic strength. Lowering the pH decreases the charge density and reduces the lateral-lateral repulsion force, leading to a higher packing density on the IRE. Reversal of the field does not overcome the strong attraction between the spores and the IRE. However, repeated measurements can be performed as the spores are completely and rapidly removed from the IRE by simply adding the next sample. The intensity of the infrared bands is due to mass loading of the spores on the IRE and setting a minimum value of 1 x 10(-3) absorbance; this requires a total of approximately 4 x 10(6) spores/cm(2). The theoretical detection limit in terms of spore concentration for our cell cavity height of 1.5 mm is approximately 10 ppm or 2.5 x 10(7) spores/cm(3).

Detection of Bacillus globigii spores using a Fourier transform infrared-attenuated total reflection method.

The use of an alumina-coated ZnSe internal reflection element (IRE) to detect spores by attenuated total reflection infrared spectroscopy (FTIR-ATR) was investigated. Two methods for coating the IRE with alumina are described. It is shown that the adsorption proceeds through an interaction of the carboxylate groups on Bacillus globigii (BG) and positively charged sites on the alumina. The amount adsorbed is highly dependent on solution pH and passes through a maximum value near pH 5, which is dictated by the charge density on the spores and the charge density on the alumina surface. Furthermore, it is shown that lateral-lateral repulsion between the spores limits the maximum adsorbed amount, giving rise to a detection limit of 10(7) spores per cm2 of the IRE.

An infrared spectroscopic based method to measure membrane permeance in liposomes.

A new method for studying membrane permeance in liposomes is described. The method uses liposomes fabricated to contain IR probe molecules with CN moieties in combination with attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The liposomes are adsorbed on a TiO2 coated ATR crystal and remain intact to flowing aqueous solutions. A change in permeance is determined by monitoring the time dependent decrease in the intensity of a band due to CN groups. It is shown that the transport of the probe molecule depends on the size of the probe molecule and the structure of the liposome membrane. A much clearer molecular understanding of membrane permeance is obtained when the information derived from transport of the probe molecules is combined with the membrane packing arrangement determined from the infrared bands due to the lipids.

Live cell adhesion assay with attenuated total reflection infrared spectroscopy.

Living confluent fish fibroblast cells RTG-P1 from rainbow trout adherent on diamond were examined by attenuated total reflection (ATR) infrared (IR) spectroscopy. In particular, IR spectra were recorded dynamically during the adsorption of the cells onto the diamond and during their biochemically induced structural responses to the subsequent addition of trypsin and cytochalasin D. It is shown that changes in the IR spectra result from changes in cell morphology and surface coverage. The results demonstrate the potential and the applicability of ATR IR spectroscopy for live cell adhesion assays.

Dual WO(3) based sensors to selectively detect DMMP in the presence of alcohols.

A size selective approach to improving selectivity in semiconducting metal oxides (SMO) sensors was obtained by tailoring the architecture of WO(3) powders. The key for achieving high selectivity is based on using a dual sensor configuration where the response on a porous WO(3) powder sensor was compared to the response on a nonporous WO(3) powder sensor. Detection selectivity between methanol and dimethyl methylphosphonate (DMMP) is obtained because the access of a gas molecule in the interior pore structure of WO(3) is size dependent leading to a size dependant magnitude change in the conductivity of SMO sensor.

Reaction of silanes in supercritical CO2 with TiO2 and Al2O3.

Infrared spectroscopy was used to investigate the reaction of silanes with TiO2 and Al2O3 using supercritical CO2 (Sc-CO2) as a solvent. It was found that contact of Sc-CO2 with TiO2 leads to partial removal of the water layer and to the formation of carbonate, bicarbonate, and carboxylate species on the surface. Although these carbonate species are weakly bound to the TiO2 surface and can be removed by a N2 purge, they poison the surface, resulting in a lower level of reaction of silanes with TiO2. Specifically, the amount of hexamethyldisilazane adsorbed on TiO2 is about 10% of the value obtained when the reaction is performed from the gas phase. This is not unique to TiO2, as the formation of carbonate species also occurs upon contact of Al2O3 with Sc-CO2 and this leads to a lower level of reaction with hexamethyldisilazane. This is in contrast to reactions of silanes on SiO2 where Sc-CO2 has several advantages over conventional gaseous or nonaqueous methods. As a result, caution needs to be applied when using Sc-CO2 as a solvent for silanization reactions on oxides other than SiO2.

A simple FTIR technique for estimating the surface area of silica powders and films.

A simple technique using FTIR spectroscopy to estimate the surface area of porous and non-porous silica powders is presented. The surface area is estimated by comparing the integrated area of the band due to isolated silanol groups on different silicas. We have found that by using a fumed silica as a calibrant, an accuracy of about 7% in the surface area of several silica materials is obtained when compared to the surface area computed by BET nitrogen adsorption techniques. The FTIR technique for computing surface area is simple and takes very little time to complete the analysis. The principle advantage of this method is that it enables surface area measurements of silica films on porous supports. To the best of our knowledge, there are no other methods that provide this information.

Templated surfactant readsorption on polyelectrolyte-induced depleted surfactant surfaces.

Changes in the structure of a surfactant adsorbed on oxidized silicon arising from interaction with a polyelectrolyte have been studied using polarized infrared attenuated total reflection spectroscopy. Specifically, the cationic surfactant cetyltrimethylammonium bromide (CTAB) was found to form a highly ordered layer on oxidized silicon at a concentration of 5.5 x 10(-5) M and a pH of 9.6. Addition of a solution of the anionic polyelectrolyte poly(styrenesulfonate) to the ordered CTAB layer resulted in a rapid and dramatic decrease in the surface excess of CTAB. Interestingly however, the interfacial order of the residual surfactant was retained for a time period greater than 1 h, before decreasing. Reintroduction of a surfactant solution prior to destabilization of the residual interfacial CTAB resulted in the readsorption of the surfactant, the recovery of the initial equilibrium coverage, and the maintenance of an ordered CTAB conformation. This desorption/readsorption process may be subsequently repeated without destroying the order of the CTAB on the surface. If however sufficient time is allowed for the residual interfacial surfactant to destabilize prior to readdition of CTAB, the degree of surfactant order remains low, despite the rapid reobtainment of a surface excess equal to or greater than that initially measured. These results are interpreted in terms of polymer/surfactant interfacial complexation and the removal of adsorbed surfactant into solution. The ordering behavior of the residual surfactant suggests that CTAB is left on the surface in isolated patches of highly ordered species that maintain their order until two-dimensional diffusion leads to a more homogeneous surfactant surface distribution and hence the loss of conformational order. The degree of orientation order assumed by surfactant readsorbing on a depleted surface appears to be templated by the order of the residual interfacial surfactant, suggestive of a two-dimensional epitaxial growth mechanism for CTAB readsorption.