A low-cost method for determination of calcium carbonate in cement by membraneless vaporization with capacitively coupled contactless conductivity detection

This work presents a flow analysis method for direct quantitation of calcium carbonate in cement without pretreatment of the sample. The method is based on online vaporization of CO₂ gas following acidification of the sample inside a small chamber that has a flow of acceptor solution passing around it. Solubilization of the CO₂ gas into the acceptor stream changes the conductivity of the acceptor solution causing an increase of signal at the capacitively coupled contactless conductivity detection (C⁴D) placed at the outlet of the vaporization chamber. This chamber is an adaption from previous work reported on ‘membraneless vaporization’ (MBL-VP).The method can be used in the quality control of production of mixed cement. These cement materials usually have calcium carbonate contents at high concentration range (e.g., 33-99% (w/w) CaCO₃). Analysis of samples by this method is direct and convenient as it requires no sample pretreatment. The method is low-cost with satisfactory accuracy and acceptable precision.     

Formaldehyde encapsulated in lithium-decorated metal-organic frameworks: a density functional theory study

The stability of monomeric formaldehyde encapsulated in the lithium-decorated metal-organic framework Li-MOF-5 was investigated by means of density functional calculations with the M06-L functional and the 6-31G(d,p) basis set. To assess the efficiency of Li-MOF-5 for formaldehyde preservation, we consider the reaction kinetics and the thermodynamic equilibrium between formaldehyde and its trimerized product, 1,3,5-trioxane. We propose that trimerization of encapsulated formaldehyde takes place in a single reaction step with an activation energy of 34.5 kcal mol(-1). This is 17.2 kcal mol(-1) higher than the corresponding activation energy in the bare system. In addition, the reaction energy of the system studied herein is endothermic by 6.1 kcal mol(-1) and the Gibbs free energy (ΔG) of the reaction becomes positive (11.0 kcal mol(-1)). Consequently, the predicted reverse rate for the trimerization reaction in the Li-MOF-5 is significantly faster than the forward rate. The calculations show that the oligomerization of formaldehyde in Li-MOF-5 is a reversible reaction, suggesting that such a zeolite might be a good candidate material for preserving formaldehyde in its monomeric form.     

Comparison of Cu‐ZSM‐5 Zeolites and Cu‐MOF‐505 Metal‐Organic Frameworks as Heterogeneous Catalysts for the Mukaiyama Aldol Reaction: A DFT Mechanistic Study

The density functional theory (DFT) model ONIOM(M06L/6‐311++G(2df,2p):UFF was employed to reveal the catalytic activity of Cu^II in the paddle‐wheel unit of the metal‐organic framework (MOF)‐505 material in the Mukaiyama aldol reaction compared with the activity of Cu‐ZSM‐5 zeolites. The aldol reaction between a silyl enol ether and formaldehyde catalyzed by the Lewis acidic site of both materials takes place through a concerted pathway, in which the formation of the C? C bond and the transfer of the silyl group occurs in a single step. MOF‐505 and Cu‐ZSM‐5 are predicted to be efficient catalysts for this reaction as they strongly activate the formaldehyde carbonyl carbon electrophile, which leads to a considerably lower reaction barrier compared with the gas‐phase system. Both MOF‐505 and Cu‐ZSM‐5 catalysts stabilize the reacting species along the reaction coordinate, thereby lowering the activation energy, compared to the gas‐phase system. The activation barriers for the MOF‐505, Cu‐ZSM‐5, and gas‐phase system are 48, 21, and 61 kJ mol^?1, respectively. Our results show the importance of the enveloping framework by stabilizing the reacting species and promoting the reaction.     

Zone fluidics for measurement of octanol–water partition coefficient of drugs

A novel zone fluidics (ZF) system for the determination of the octanol–water partition coefficient (P_ow) of drugs was developed. The ZF system consisted of a syringe pump with a selection valve, a holding column, a silica capillary flow-cell and an in-line spectrophotometer. Exact microliter volumes of solvents (octanol and phosphate buffer saline) and a solution of the drug, sandwiched between air segments, were sequentially loaded into the vertically aligned holding column. Distribution of the drug between the aqueous and octanol phases occurred by the oscillation movement of the syringe pump piston. Phase separation occurred due to the difference in densities. The liquid zones were then pushed into the detection flow cell. In this method, absorbance measurements in only one of the phase (octanol or aqueous) were employed, which together with the volumes of the solvents and pure drug sample, allowed the calculation of the P_ow. The developed system was applied to the determination of the P_ow of some common drugs. The log (P_ow) values agreed well with a batch method (R² = 0.999) and literature (R² = 0.997). Standard deviations for intra- and inter-day analyses were both less than 0.1log unit. This ZF system provides a robust and automated method for screening of P_ow values in the drug discovery process.     

Quantitative analysis of aglycone quercetin in mulberry leaves (Morus alba L.) by capillary zone electrophoresis.

A capillary zone electrophoresis method was established for analysis of aglycone quercetin in mulberry leaves (Morus alba L.). The influence of, e.g., background electrolyte concentrations and pH, surfactant concentrations, organic solvents, temperature, and voltage on the separation of aglycone quercetin, rutin, quercitrin, kaempferol, catechin, and gallic acid was systematically investigated. The optimum condition providing baseline separation of all compounds within 16.5 min was obtained in 150 mM boric acid (pH 10.0) using a fused-silica capillary with an effective length of 42.5 cm (50 microm inner diameter), temperature of 32 degrees C, and voltage of 15 kV. Method assessment was performed by standard addition method using rutin as an internal standard. Linearity of the method was excellent (r(2) > 0.999) over the concentration tested (40-160 microg/mL). The relative standard deviations (%RSDs) from injection, intraday, and interday precision were less than 2.5%. Recoveries were good (asymptotically equal to 100.0%,%RSD = 0.8%) with a limit of detection (LOD) and limit of quantitation (LOQ) of 0.86 and 3.16 microg/mL (%RSD = 1.8%), respectively. The aglycone quercetin found in the mulberry leaves was 0.452 g/100 g (%RSD = 0.6%) on dry weight.     

Ethylene Epoxidation with Nitrous Oxide over Fe–BTC Metal–Organic Frameworks: A DFT Study

The epoxidation of ethylene with N₂O over the metal‐organic framework Fe–BTC (BTC=1,3,5‐benzentricarboxylate) is investigated by means of density functional calculations. Two reaction paths for the production of ethylene oxide or acetaldehyde are systematically considered in order to assess the efficiency of Fe–BTC for the selective formation of ethylene oxide. The reaction starts with the decomposition of N₂O to form an active surface oxygen atom on the Fe site of Fe–BTC, which subsequently reacts with an ethylene molecule to form an ethyleneoxy intermediate. This intermediate can then be selectively transformed either by 1,2‐hydride shift into the undesired product acetaldehyde or into the desired product ethylene oxide by way of ring closure of the intermediate. The production of ethylene oxide requires an activation energy of 5.1 kcal mol^?1, which is only about one‐third of the activation energy of acetaldehyde formation (14.3 kcal mol^?1). The predicted reaction rate constants for the formation of ethylene oxide in the relevant temperature range are approximately 2–4 orders of magnitude higher than those for acetaldehyde. Altogether, the results suggest that Fe–BTC is a good candidate catalyst for the epoxidation of ethylene by molecular N₂O.     

Identification of carbohydrates by matrix-free material-enhanced laser desorption/ionisation mass spectrometry

Matrix-assisted laser desorption/ionisation time-of-flight mass spectrometry (MALDI-TOF-MS) is a sensitive mass spectrometric technique which utilises acidic materials as matrices for laser energy absorption, desorption and ionisation of analytes. These matrix materials produce background signals particularly in the low-mass range and make the detection and identification of small molecules difficult and nearly impossible. To overcome this problem this paper introduces matrix-free material-enhanced laser desorption/ionisation mass spectrometry (mf-MELDI-MS) for the screening and analysis of small molecules such as carbohydrates. For this purpose, 4,4'-azo-dianiline was immobilised on silica gel enabling the absorption of laser energy sufficient for successful desorption and ionisation of low molecular weight compounds. The particle and pore sizes, the solvent system for suspension and the sample preparation procedures have been optimised. The newly synthesised MELDI material delivered excellent spectra with regard to signal-to-noise ratio and detection sensitivity. Finally, wheat straw degradation products and Salix alba L. plant extracts were analysed proving the high performance and excellent behaviour of the introduced material.