Path-length Cell Research Articles

Effect of equilibration time on the structural gradient in the vertical direction for bicontinuous microemulsions in Winsor-III and -IV systems.

Bicontinuous microemulsions (BMEs), self-assembly systems consisting of oil and water nanodomains separated by surfactant monolayers, have many applications. However, changes in structure and properties of BMEs in the vertical direction can affect BMEs' utility. This study's objective was to determine the effect of equilibration time (τeq) on structural changes in the vertical direction for bicontinuous phases of Winsor-III (WIII) systems in situ or after being isolated, for D2O + H2O/1-dodecane/sodium dodecyl sulfate (SDS)/1-pentanol/NaCl at 22 °C. Small-angle neutron scattering (SANS) measurements were performed using a vertical stage sample environment that precisely aligned samples in the neutron beam. SANS data were fitted by the Teubner-Strey (TS) model and changes in TS-derived parameter values were observed. For 10 min ≤ τeq ≤ 4 h, the effective activity of the bicontinuous phase's surfactant monolayers increased with time at all vertical positions. At short equilibration (τeq = 10 min), small but significant amounts of water and oil were transiently emulsified near the WIII upper liquid-liquid interface. WIII systems underwent a relaxation process after being transferred to narrow 1 mm pathlength cells, resulting in a decrease of surfactant activity for the top half of the bicontinuous phase. For isolated bicontinuous phases, results suggest that SDS was desorbed from the BMEs by quartz near the bottom, while near the top, the water concentration near was relatively high. The results suggest that WIII systems should equilibrate for at least 4 hours after being prepared and transferred to a container that differs in cross sectional area and surfactant behavior in BMEs can change near interfaces.

A new iodometric microwave-assisted method for peroxide determination in Secondary Organic Aerosols

Peroxides (H2O2, ROOR, ROOH) play an important atmospheric role in both the gas and particle phases. Several techniques are available in the literature for their quantification, although current techniques are very expensive or time-consuming. In the present work, a new fast and sensitive iodometric-spectrophotometric method, based on the traditional one, has been developed for the trace SOA (Secondary Organic Aerosols)-bound peroxides of laboratory-generated samples. The proposed method is based on the acceleration by microwave radiation of the reaction of peroxides with potassium iodide in acid medium. Iodine is liberated and in the presence of excess of iodide forms I3− that could be monitored at three different wavelengths (288, 351 and 420 nm). The linear range of concentrations of the method is at least 1–35 μM. The limit of detection of the method was 1 μM without degasification and decreased to 0.25 μM with degasification, respectively. The optimum conditions and other analytical parameters were evaluated for H2O2, tert-butyl hydroperoxide and cumene hydroperoxide. The main advantages of the new method in comparison with the traditional method are: it is less time consuming, it is applicable even in the presence of oxygen, it has a lower limit of detection (for 1 cm pathlength cell) and there are no sensitivity differences between different peroxides types.The proposed method has been successfully applied and compared with the traditional method for the determination of peroxides in SOA generated in laboratory by the gas phase ozonolysis of α-pinene.

Pilot study CCQM-P172 – spectroscopic methods for HNO3 value assignment

Pilot study CCQM-P172 – spectroscopic methods for HNO3 value assignment

Micro-fabricated caesium vapor cell with 5 mm optical path length

Micro-fabricated vapor cells have applications in a number of emerging quantum technology-based devices including miniaturized atomic magnetometers, atomic clocks, and frequency references for laser systems. Increasing the cell optical path length (OPL) and smallest cell dimension are normally desirable to increase the signal to noise ratio (SNR) and minimize the de-polarization rate due to collisions between atomic or molecular species and the cell walls. This paper presents a fully wafer-level scalable fabrication process to manufacture vapor cells with dimensions approaching those of glass-blown cells. The fabrication process is described, and spectroscopic measurements (optical absorption and magnetic resonance) are reported. A magnetic resonance linewidth of 350 Hz is demonstrated, and this is the smallest linewidth reported to date for a micro-fabricated vapor cell.

Room temperature measurements of the collision-induced absorption by H2+CO2 mixtures near 2.4 µm

Using a 101 m absorption path-length cell, Fourier transform spectra of H2+CO2 mixtures have been recorded at room temperature in the region around 2.4 µm. This enables to quantify the absorption induced, by collisions with CO2, in the central part of the fundamental band of H2. These measurements, which cover 39504400 cm−1 range, validate previous fully independent computations.

Molecular Structural Evolution of Near-Infrared Cationic Aggregation-Induced Emission Luminogens: Preclinical Antimicrobial Pathogens Activities and Tissues Regeneration

Molecular Structural Evolution of Near-Infrared Cationic Aggregation-Induced Emission Luminogens: Preclinical Antimicrobial Pathogens Activities and Tissues Regeneration

A Low-Cost NDIR-Based N2O Gas Detection Device for Agricultural Soils: Assembly, Calibration Model Validation, and Laboratory Testing.

This research presents a low-cost, easy-to-assemble nondispersive infrared (NDIR) device for monitoring N2O gas concentration in agricultural soils during field and laboratory experiments. The study aimed to develop a cost-effective instrument with a simple optic structure suitable for detecting a wide range of soil N2O gas concentrations with a submerged silicone diffusion cell. A commercially available, 59 cm path-length gas cell, microelectromechanical systems (MEMS)-based infrared emitter, pyroelectric detector, two anti-reflective (AR) coated optical windows, and one convex lens were assembled into a simple instrument with secure preciseness and responsivity. Control of the IR emitter and data recording processes was achieved through a microcontroller unit (MCU). Tests on humidity tolerance and the saturation rate of the diffusion cell were carried out to test the instrument function with the soil atmosphere. The developed calibration model was validated by repeatability tests and accuracy tests. The soil N2O gas concentration was monitored at the laboratory level by a specific experimental setup. The coefficient of determination (R2) of the repeatability tests was more than 0.9995 with a 1–2000 ppm measurability range and no impact of air humidity on the device output. The new device achieved continuous measuring of soil N2O gas through a submerged diffusion cell.

Cell size influences inorganic carbon acquisition in artificially selected phytoplankton.

Cell size influences the rate at which phytoplankton assimilate dissolved inorganic carbon (DIC), but it is unclear whether volume-specific carbon uptake should be greater in smaller or larger cells. On the one hand, Fick's Law predicts smaller cells to have a superior diffusive CO2 supply. On the other, larger cells may have greater scope to invest metabolic energy to upregulate active transport per unit area through CO2 -concentrating mechanisms (CCMs). Previous studies have focused on among-species comparisons, which complicates disentangling the role of cell size from other covarying traits. In this study, we investigated the DIC assimilation of the green alga Dunaliella tertiolecta after using artificial selection to evolve a 9.3-fold difference in cell volume. We compared CO2 affinity, external carbonic anhydrase (CAext ), isotopic signatures (δ13 C) and growth among size-selected lineages. Evolving cells to larger sizes led to an upregulation of CCMs that improved the DIC uptake of this species, with higher CO2 affinity, higher CAext and higher δ13 C. Larger cells also achieved faster growth and higher maximum biovolume densities. We showed that evolutionary shifts in cell size can alter the efficiency of DIC uptake systems to influence the fitness of a phytoplankton species.

Development and Validation of Chemometric Assisted FTIR Spectroscopic Method for Simultaneous Estimation of Valsartan and Hydrochlorothiazide in Pure and Pharmaceutical Dosage Forms

Objectives: To develop a new Chemometric assisted Fourier transform infrared (FTIR) spectroscopic method for the simultaneous estimation of valsartan and hydrochlorothiazide in pharmaceutical dosage forms. Methods: The method involves the preparation of solid pellets of valsartan and hydrochlorothiazide using KBr and direct measurement using reduced path length cell. The wave numbers for quantitative estimation were selected with aid of chemometrics software and the spectra were measured in absorbance mode. Results: The infrared spectra showed different peaks with baseline correction, among which intense, clear and proportionate peaks were selected at 1600 cm-1 and 3361 cm-1 corresponding to amide (C=O) and amine (N-H) functional groups for valsartan and hydrochlorothiazide respectively for quantitative estimation were assessed using Chemometrics. Beer Lambert’s law was obeyed over the concentration range of 5-25μg/mg for valsartan and 10-50 μg/mg for hydrochlorothiazide. The method was validated according to ICH guidelines. Conclusion: The developed method was cost effective and fulfilled most validation requirements in a range of concentrations suitable for quality control of both in pure and solid dosage form. This method can be used as an alternative method for HPLC, UV or pharmacopoeial methods as quality control check in pure and marketed formulations. Key words: Chemometrics, FTIR, Hydrochlorothiazide, ICH guidelines, Method validation Valsartan.

Role of Thermolysin in Catalytic-Controlled Self-Assembly of Fmoc-Dipeptides

In recent years, short peptide self-assembled materials, prepared under the control of the thermolysin catalyst, have been investigated extensively and shown to acquire various morphologies and fun...

FT-NIRS Coupled with PLS Regression as a Complement to HPLC Routine Analysis of Caffeine in Tea Samples.

Daily consumption of caffeine in coffee, tea, chocolate, cocoa, and soft drinks has gained wide and plentiful public and scientific attention over the past few decades. The concentration of caffeine in vivo is a crucial indicator of some disorders—for example, kidney malfunction, heart disease, increase of blood pressure and alertness—and can cause some severe diseases including type 2 diabetes mellitus (DM), stroke risk, liver disease, and some cancers. In the present study, near-infrared spectroscopy (NIRS) coupled with partial least-squares regression (PLSR) was proposed as an alternative method for the quantification of caffeine in 25 commercially available tea samples consumed in Oman. This method is a fast, complementary technique to wet chemistry procedures as well as to high-performance liquid chromatography (HPLC) methods for the quantitative analysis of caffeine in tea samples because it is reagent-less and needs little or no pre-treatment of samples. In the current study, the partial least-squares (PLS) algorithm was built by using the near-infrared NIR spectra of caffeine standards prepared in tea samples scanned by a Frontier NIR spectrophotometer (L1280034) by PerkinElmer. Spectra were collected in the absorption mode in the wavenumber range of 10,000–4000 cm−1, using a 0.2 mm path length and CaF2 sealed cells with a resolution of 2 cm−1. The NIR results for the contents of caffeine in tea samples were also compared with results obtained by HPLC analysis. Both techniques provided good results for predicting the caffeine contents in commercially available tea samples. The results of the proposed study show that the suggested FT-NIRS coupled with PLS regression algorithun has a high potential to be routinely used for the quick and reproducible analysis of caffeine contents in tea samples. For the NIR method, the limit of quantification (LOQ) was estimated as 10 times the error of calibration (root mean square error of calibration (RMSECV)) of the model; thus, RMSEC was calculated as 0.03 ppm and the LOQ as 0.3 ppm.

Inlaid microfluidic optics: absorbance cells in clear devices applied to nitrite and phosphate detection

A novel type of microfluidic absorbance cell is presented here that inlays black poly(methyl methacrylate) (PMMA) into a clear PMMA substrate to realize an isolated optical channel with microlitre volumes. Optical measurements are frequently performed on microfluidic devices, offering effective, quick, and robust chemical analysis capabilities on small amounts of sample. Many lab-on-chip systems utilize micrometer-sized channels to analyze liquid samples via light-absorbance measurements, but this requires sophisticated coordination of light through a small cross-section, often requiring collimating and beam-steering optics. Here, we detail the fabrication process to realize long path length absorbance cells based on a simple hybrid-material approach. A z-shape microchannel structure crosses a clear-black interface at both ends of the absorbance cell, thereby creating integral optical windows that permit light coupling into a microchannel completely embedded in black PMMA. Furthermore, we have integrated v-groove prisms on either side of the microfluidic channel. The prisms enabled seamless integration with printed circuit boards and permit the optical elements to be located off-chip without use of epoxies or adhesives. Three path lengths, 10.4, 25.4, and 50.4 mm, were created and used to characterize the novel cell design using typical colorimetric measurements for nitrite and phosphate. We compare the attenuation coefficient measured by our optical cells with the literature, showing excellent agreement across nutrient concentrations from 50 nM–50 μM. The measurements were performed with well-known reagent-based methods, namely the Griess assay for nitrite and the molybdovanadophosphoric acid or the ‘yellow method’ for phosphate. The longest 50.4 mm path length cell had a limit-of-detection of 6 nM for nitrite and 40 nM for phosphate, using less than 12 μl of fluid. The inlaid fabrication method described permits robust and high-performance optical measurements with broad applicability for in situ marine sensors and for numerous lab-on-chip sensors based on colorimetric assays. One such application is shown whereby two inlaid absorbance cells are integrated with four microfluidic check valves to realize a complete lab-on-chip nitrite sensor.

Optimum Cell Pathlength or Volume for Absorbance Detection in Liquid Chromatography: Transforming Longer Cell Results to Virtual Shorter Cells.

The cell volume permissible for a specified degree of loss of efficiency can be computed from response volume considerations. For an open tubular column, the permissible illuminated length can be computed for the unretained peak. Similar estimations can be made for the maximum permissible cell volume with a packed column for a given column efficiency and flow rate. The packed column case does require an assumption on the degree to which the cell behaves as a mixer. An altogether different question is if the data from a long cell, with its considerable advantage in S/N, can be used and the associated dispersion mathematically removed. Experimental data for a variable path length (0-60 mm) HPLC detection cell indicate that an exponential model fits the observed dispersion. Once fit parameters are determined, the same can be applied to a peak, not part of the original training set, obtained in a longer path cell and the effects of dispersion mathematically reversed without major loss of S/N. Results with shorter path cell dispersion characteristics are then obtained with much higher S/N. A comparison is made with Fourier transform-inverse Fourier transform based deconvolution that can be used to achieve the same ends.

Time-Resolved Temperature-Jump Infrared Spectroscopy at a High Repetition Rate.

Time-resolved temperature-jump infrared absorption spectroscopy at a 0.5 to 1 kHz repetition rate is presented. A 1 kHz neodymium-doped yttrium aluminum garnet (Nd:YAG) laser pumping an optical parametric oscillator provided >70 µJ, 3.75 µm pump pulses, which delivered a temperature jump via excitation of the O-D stretch of a D2O solution. A 10 kHz train of mid-infrared probe pulses was used to monitor spectral changes following the temperature jump. Calibration with trifluoroacetic acid solution showed that a temperature jump of 10 K lasting for tens of microseconds was achieved, sufficient to observe fast processes in functionally relevant biomolecular mechanisms. Modeling of heating profiles across ≤10 µm path length cells and subsequent cooling dynamics are used to describe the initial <100 ns cooling at the window surface and subsequent, >10 µs cooling dynamics of the bulk solution.

Steps Toward Full Wavelength Range Calibration for Circular Dichroism Spectroscopy

Circular dichroism (CD) measurements are important for the characterization of higher-order molecular structure in the biopharmaceutical industry. Comparing CD measurements between laboratories has been difficult. To reduce CD measurement uncertainty, good laboratory practice requires the measurement of cell path length. NIST has recently launched Standard Reference Material (SRM) 2082 for path length using absorbance intensity at 280 nm. Most CD instruments simultaneously measure both CD and absorbance spectra. Far ultraviolet measurements of CD spectra are usually made in cells with path lengths appropriate to the intended use of SRM 2082. One of the components of this standard, L-tryptophan, is chiral and could also be used as a reference material for CD intensity at 223 nm. However, the shape of the CD spectrum over many wavelengths is often used to describe the higher-order structure of biopharmaceuticals suggesting we need a more encompassing method. We will describe our efforts to develop a method to calibrate a CD instrument across the full wavelength range of the measured spectrum using SRM 2082.

Fully automatic system for lead monitoring in water

A fully automatic multisyringe flow injection analysis - lab on valve system (MSFIA-LOV) with assisted automatic stirring for Pb (II) determination exploiting a long path-length liquid waveguide capillary cell (LWCC) for spectrophotometric detection was developed. On-line extraction of lead was performed inside of a microcolumn using a selective solid phase extraction (PB-resin), followed by the Pb-PAR complex formation with 4-(2-pyridylazo) resorcinol (PAR) as chromogenic reagent, to obtain a spectrophotometric detection at 520 nm. The assistance of automatic mechanical agitation to increase the analytical signal was made by using a rotary motor whose movement through a stainless steel rod, allowed to form a submersible agitator device. The limit of detection (LOD) of the developed method is 0.79 μg L−1, allowing the analysis well below the guideline values for lead in drinking water. The analytical parameters achieved, such as the good precision (RSD 4.2%), the analysis frequency and its fully automation make of this method a portable tool for low-cost Pb (II) detection system for water samples. The method has been successfully validated by means of a groundwater certified reference material (BCR®-610). It was also applied to different water matrices (groundwater, commercial bottled water and tap water) with recoveries close to 100%.

Spectroscopic gas detection using a Bragg grating - stabilized external cavity laser, custom written in planar integrated silica-on-silicon.

We present the development of an external cavity Bragg grating stabilized laser for tunable diode laser spectroscopy (TDLS). Our design uses a planar integrated silica-on-silicon platform incorporating a custom written Bragg grating as the wavelength-selective element of the laser cavity. We have developed a prototype singlemode laser at 1651 nm and performed a detailed characterization of its performance for the purpose of spectroscopic measurement of methane at this wavelength using a 25 cm path-length single-pass cell. Mode hop-free tuning of 0.13 nm has been demonstrated at frequencies of up to 10 kHz. A single-point limit of detection for TDLS of ΔI/I0 = 8.3 × 10-5 AU was achieved, which is consistent with the performance of standard distributed feedback lasers. The new device exhibits a side-mode suppression ratio of -40 dB and a low RIN of <-150 dB/Hz, and thus avoids the high levels of noise or instability normally associated with larger, mechanically driven external cavity lasers. The silica-on-silicon platform has the potential for low-volume manufacturing of special lasers at the custom wavelengths required for gas detection, without the need for investment in foundry solutions.

Multi-Component and Multi-Point Trace Gas Sensing in Wavelength Modulation Spectroscopy Based on Wavelength Stabilization

Multi-component and multi-point trace gas sensing in the wavelength modulation spectroscopy is demonstrated based on the frequency-division multiplexing and time-division multiplexing technology. A reference photodetector is connected in series with a reference gas cell with the constant concentration to measure the second-harmonics peak of the components for wavelength stabilization in real time. The central wavelengths of the distributed feedback lasers are locked to the target gas absorption centers by the reference second-harmonics signal using a digital proportional-integral-derivative controller. The distributed feedback lasers with different wavelengths and modulation frequencies are injected into the gas cell to achieve multi-components gas measurement by the frequency-division multiplexing technology. In addition, multi-point trace gas sensing is achieved by the time-division multiplexing technology using a photoswitch and a relay unit. We use this scheme to detect methane (CH4) at 1650.9 nm and water vapor (H2O) at 1368.597 nm as a proof of principle with the gas cell path length of 10 cm. The minimum detection limits achieved for H2O and CH4 are 1.13 ppm and 11.85 ppm respectively, with three-point gas cell measurement; thus 10.5-fold and 10.1-fold improvements are achieved in comparison with the traditional wavelength modulation spectroscopy. Meanwhile, their excellent R-square values reach 0.9983 and 0.99564 for the concentration ranges of 500 ppm to 2000 ppm and 800 ppm to 2700 ppm, respectively.

Sample Volume Reduction Using the Schwarzschild Objective for a Circular Dichroism Spectrophotometer and an Application to the Structural Analysis of Lysine-36 Trimethylated Histone H3 Protein.

With the increasing interest in scarce proteins, reducing the sample volume for circular dichroism (CD) spectroscopy has become desirable. Demagnification of the incident beam size is required to reduce the sample volume for CD spectroscopy detecting transmitted light passed through the sample. In this study, the beam size was demagnified using a focal mirror, and small-capacity sample cells were developed in an attempt to reduce the sample volume. The original beam size was 6 × 6 mm2; we successfully converged it to a size of 25 × 25 μm2 using the Schwarzschild objective (SO). The new sample cell and SO allowed the required sample volume to be reduced to 1/10 (15 → 1.5 μL), when using a 15 μm path length cell. By adopting a smaller sample cell, further sample reduction could be achieved. By using the SO system, the secondary structural contents of the lysine-36 trimethylated histone H3 protein were analyzed. The trimethylation induced the increment of helix structures and decrement of unordered structures. These structural alterations may play a role in regulating cellular function(s), such as DNA damage repair processes.

New and improved infrared absorption cross sections for trichlorofluoromethane (CFC-11)

Abstract. Trichlorofluoromethane (CFC-11), a widely used refrigerant throughout much of the twentieth century and a very potent (stratospheric) ozone-depleting substance (ODS), is now banned under the Montreal Protocol. With a long atmospheric lifetime, it will only slowly degrade in the atmosphere, so monitoring its vertical concentration profile using infrared-sounding instruments, and thereby validating stratospheric loss rates in atmospheric models, is of great importance; this in turn requires high-quality laboratory spectroscopic data. This work describes new high-resolution infrared absorption cross sections of trichlorofluoromethane/dry synthetic air over the spectral range 710–1290 cm−1, determined from spectra recorded using a high-resolution Fourier transform spectrometer (Bruker IFS 125HR) and a 26 cm pathlength cell. Spectra were recorded at resolutions between 0.01 and 0.03 cm−1 (calculated as 0.9/MOPD; MOPD: maximum optical path difference) over a range of temperatures and pressures (7.5–760 Torr and 192–293 K) appropriate for atmospheric conditions. This new cross-section dataset improves upon the one currently available in the HITRAN (HIgh-resolution TRANsmission) and GEISA (Gestion et Étude des Informations Spectroscopiques Atmosphériques) databases through an extension to the range of pressures and temperatures, improved signal-to-noise and wavenumber calibrations, the lack of channel fringing, the better consistency in integrated band intensities, and additionally the coverage of the weak combination band ν2+ν5.