“Bubble Bunch” phenomenon in operation of a bubble column

While studying the operation of a rectangular bubble column in laboratory scale, it was observed that under certain circumstances tiny bubbles attach to larger bubbles without causing them to coalesce. In other words, bubbles with large diameters (d > 5 mm) swept tiny bubbles (d < 1 mm) in their way to the top of the column resulting in grapelike clusters of bubbles. This phenomenon was named “bubble bunch” by us and its effect on total gas holdup and interfacial area was discussed. Although it was found to have almost no affect on gas holdup, bubble bunch can increase the interfacial area up to 10% more than what is anticipated in the literature. The process of film thinning was modeled for this phenomenon and coalescence efficiency was calculated as a function of interfacial tension.      

Capillary electrochromatography of three β2-agonists in human urine using a lauryl methacrylate-based monolithic column

A new method of online concentration capillary electrochromatography using a lauryl methacrylate-based monolithic column was developed for determination of three β(2)-agonists including salbutamol, procaterol, and formoterol. The separation parameters including acetonitrile concentration, running buffer pH, and concentration were evaluated. To improve the sensitivity, an online concentration method with combination of the chromatographic zone-sharpening effect and field-enhanced sample-stacking effect has been developed in which the concentration parameters including injection voltage, injection time, as well as sample matrix were systematically studied. Under the optimized conditions, baseline separation of three β(2)-agonists was achieved within 4 min. When compared to the conventional sample injection, this online concentration technique increased their corresponding sensitivities up to 45-, 36-, and 320-fold, respectively. Furthermore, good repeatability was obtained with relative standard deviations (RSDs) for migration times within 0.84% and those for peak areas less than 6.35% (n = 5) in the experiment. The proposed method was successfully applied to the determination of above-mentioned β(2)-agonists in urine sample. The recoveries of spiked urine samples were between 82.4% and 109.1% with RSDs less than 9.97%.     

How does column packing microstructure affect column efficiency in liquid chromatography?

Full three-dimensional computer simulations of the fluid flow and dispersion characteristics of model nonporous chromatographic packings are reported. Interstitial porosity and packing defects are varied in an attempt to understand the chromatographic consequences of the packing microstructure. The tracer zone dispersion is calculated in the form of plate height as a function of fluid velocity for seven model particle packs where particles are selectively removed from the packs in clusters of varying size and topology. In an attempt to examine the consequences of loose but random packs, the velocities and zone dispersion of seven defect-free packs are simulated over the range 0.36< or =epsilon< or =0.50, where epsilon is the interstitial porosity. The results indicate that defect-free loose packings can give good chromatographic efficiency but the efficiency can vary depending on subtle details of the pack. When the defect population increases, the zone dispersion increases accordingly. For a particle pack where 6% of the particles are removed from an epsilon=0.36 pack, approximately 33% of the column efficiency is lost. These results show that it is far more important in column packing to prevent defect sites leading to inhomogeneous packing rather than obtaining the highest density pack with the smallest interstitial void volume.     

Synthesis of affinity column of phosphatidylinositol-3,4-diphosphate

Phosphatidylinositol polyphosphates (PIPx) are related with tyrosine kinase activation, cell proliferation and carcinogenesis. In order to investigate the action mechanism of PIPx, it is desirable to synthesize affinity column of PI-3,4-P2, which is expected to be able to isolate the binding proteins of PI-3,4-P2. Thyramine reacted with CH-Sepharose 4B giving column 13. The p-amino group of 3'-(1',2'-distearoyl-glyceryl)-1-(2-p-aminobenzyl)-3,4-di-O-phosphoryl-myo-inosityl phosphate (12) was diazotized, then diazo-coupled with column 13 to give PI-3,4-P2 affinity column 14. This PI-3,4-P2 affinity column is an effective tool to pick up binding proteins of PI-3,4-P2.     

Application of dispersive liquid–liquid microextraction for the determination of donepezil in urine by HPLC using a core–shell column

A rapid and novel method combining dispersive liquid–liquid microextraction and high-performance liquid chromatography coupled with fluorescence detection was developed for the determination of donepezil in human urine. Parameters affecting extraction efficiency and chromatographic determination, such as the type and volume of the extraction and disperser solvent, pH of sample for dispersive liquid–liquid microextraction, mobile-phase composition, pH, column oven temperature, and flow rate for chromatographic determination, were evaluated and optimized. Using a C₁₈ core–shell column (7.5 × 4.6?mm, 2.7?μm), the determination of donepezil was accomplished within 5?min. Under optimum conditions, developed method was linear in the range of 0.5–25?ng?mL^?1 with the correlation coefficient >0.99. Limit of detection was 0.15?ng?mL^?1. The relative standard deviation at three concentration levels (2, 12.5, and 20?ng?mL^?1) was less than 11% with accuracy in the range of 96.9–102.8%. The results of this study demonstrate that the use of dispersive liquid–liquid microextraction and core–shell column can be considered as a powerful tool for the analysis of donepezil in human urine.     

Optimized use of a 50 μm ID secondary column in comprehensive two-dimensional gas chromatography–mass spectrometry

The objective of the present research is directed towards the optimized use of a 50 μm ID secondary column, in a comprehensive two-dimensional gas chromatography–quadrupole mass spectrometry (GC × GC–qMS) system. The analytical aim was achieved by exploiting a split-flow GC × GC approach, and a rapid-scanning qMS instrument. The stationary phase combination consisted of an apolar (silphenylene polymer) 30 m × 0.25 mm ID column, linked by means of a Y-union, to an MS-connected 1 m × 0.05 mm ID polar one [poly(ethyleneglycol)], and to a 0.20 m × 0.05 mm ID uncoated capillary segment; the latter was connected to a manually operated split-valve. It will be herein demonstrated that the split-flow GC × GC approach, successfully employed in previous H₂-based, flame ionization detection experiments, provides equally satisfactory results using mass spectrometric detection and helium as carrier gas. An optimized split-flow GC × GC–qMS method was developed and exploited for the analysis of a perfume sample. The results attained were compared with those observed using the same analytical column combination, but with no flow-splitting. It was found that it is not convenient to employ a 50 μm ID secondary column in a conventional GC × GC–MS instrument. On the contrary, the use a 50 μm ID secondary column, in a split-flow, twin-oven system, provided a good performance. A recently developed comprehensive chromatography software was used for data processing.     

Determination of isoflavones in rat serum using liquid chromatography–tandem mass spectrometry with a highly efficient core–shell column

Consumption and nutritional supplementation of soy and soy-based products have been linked to health benefits such as lower cholesterol and triglyceride levels, and decreased incidence of cardiovascular disease and diabetes. In this study, we have developed a sensitive, specific, and robust method using high-performance liquid chromatography–tandem mass spectrometry (HPLC-MS/MS) for determination of serum isoflavones. A new highly efficient pentafluorophenyl phase core–shell column was first used to separate all isoflavones within 3 min, a separation time which is comparable to ultra-pressure liquid chromatography (UPLC) and micro-HPLC. A two-enzyme hydrolysis system with sulfatase and β-glucuronidase has also been developed to improve the efficiency of deconjugation of conjugated isoflavones in serum. The corresponding conjugated isoflavones were used to evaluate recoveries. In addition to duplicates, the method of standard addition was also applied in sample analysis for quality control. The developed method was applied to the analysis of 32 serum samples and was shown to be specific, sensitive and reproducible.     

Separation of cesium-137 from uranium fission products via a Neoflon® column supporting tetraphenylboron

Cesium is a member of the Group I alkali metals, very reactive earth metals that react vigorously with both air and water. The chemistry of cesium is much like the chemistry of neighboring elements on the periodic table, potassium and rubidium. This close relation creates many problems in plant-life exposed to cesium because it is so easily confused for potassium, an essential nutrient to plants. Radioactive ¹³⁴Cs and ¹³⁷Cs are also chemically akin to potassium and stable cesium. Uptake of these radioactive isotopes from groundwater by plant-life destroys the plant-life and can potentially expose humans to the radioactive affects of ¹³⁴Cs and ¹³⁷Cs. Much experimental work has been focused on the separation of ¹³⁷Cs from uranium fission products. In previous experimental work performed a column consisting of Kel-F supporting tetraphenylboron (TPB) was utilized to separate ¹³⁷Cs from uranium fission products. It is of interest at this time to attempt the separation of ¹³⁴Cs from 0.01M EDTA using the same method and Neoflon in the place of Kel-F as the inert support. The results of this experiment give a separation efficiency of 88% and show a linear relationship between the column bed length and the separation efficiency obtained.     

Optimization separation of five phosphoamidothioate enantiomers using a series of silica and chiral column by high-performance liquid chromatography

A computer-assisted method is described for optimization of multi-component,mobile phase selection for separation of five phosphoamidothioate enantiomers with a series of silica and chiral columns in normal phase HPLC.The method is based on the triangular solvent selection concept using a statistical scanning method.The optimization of the separation over the experimental region is based on a special polynomial estimation from seven experimental runs,and resolution (Rs) is used as the selection criterion.Excellent agreement was obtained between predicted and experimental data.     

Fabrication of column chip made of PMMA for μFIA

We proposed a low cost fabrication procedure of a poly(methylmethacrylate) (PMMA) column chip. 3D microchannel structure consisting of four columns in a chip for a mother die was fabricated using dry film photoresist and photolithography technique. Electroforming was applied to the mother die in order to obtain a Ni mold, then, the pattern was transferred to PMMA by hot press. The column had a dam structure to keep enzyme-immobilized microbeads with volume of 640 nL. The column chip was applied for a micro flow injection analysis (μFIA) system. For a demonstration, we measured lactose using two columns in series. One column was set on upper stream and filled with chitosan microbeads immobilized with β-galactosidase, the other was on downstream and filled with the beads immobilized with glucose oxidase. The lactose detection was accomplished less than 90s after the sample injection. The biosensing system also showed a high performance for lactose detection in wide range of 1 μM to 1mM. These results show that the column chip and our microfluidic biosensing system have the potential to assist minuaturization with small sample volume and short determination time for a sequential analysis.     

The application of ‘Z’-shaped UV cells in open-tubular capillary column liquid chromatography

Summary Z-shaped UV cells for packed capillary columns cannot be used in open-tubular capillary column liquid chromatography (OT-LC) because of their relatively large volume. With post-column solvent make-up, a commercial Z-shaped cell (volume 100 nl) was used in our OT-LC system, resulting in 9-fold sensitivity increase against on-column UV detection and with little efficiency loss. A small volume (5 nl) Z-shaped cell allows the direct coupling of the cell to high efficiency columns. For dilute samples, 9-19-fold sensitivity enhancement could be obtained. However, column efficiency decreases with increasing signal level as a result of peak deformation.     

Is phospholipid-saturated alkyl column a convenient replacement for immobilized-artificial-membrane?

Three phosphatidylcholine (PC)-saturated C(8)/C(18) stationary phases prepared using biologically representative membrane lipids (purchasable L-alpha-PC and pure 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine) have been developed to compare with IAM (immobilized-artificial-membrane) and C(8)/C(18) columns. These PC-coated stationary phases were found to be stable and reproducible for retention experiments. The retention characteristics of nucleobases on these coated phases deviate significantly from those on the IAM counterpart, but surprisingly similar to those of the underlying C(8)/C(18) columns. An inter-phase model has been proposed and explored for interpretation of the results.     

Fast and universal HPLC method for determination of permethrin in formulations using 1.8-μm particle-packed column and performance comparison with other column types

An HPLC method has been developed for the fast separation and quantification of permethrin using C18 column packed with 1.8 μm particles. The method is specific with good resolution to degradation products and to other present components. It has acceptable validation results. The run time is 4.5 min (or may be within 1.6 min is rapid resolution mode) with an organic solvent consumption of 3.6 mL per run. The method has been applied to samples of formulations for various uses: mattress cleaner, shampoo, and veterinary powder. The performance of the applied column is compared with other common column types. The relationships between linear velocity of the mobile phase (u) and resolution factor (Rs), back-pressure (ΔP), and efficiency (H) are presented. The experimental data shows the advantages of 1.8-μm particle columns to be a significant reduction in solvent consumption (by factor of 4.4 and 1.5) and a reduction in run-time (by factor 4.7 and 1.5), and the weaknesses are a high back-pressure and lower efficiency. Finally, it has been shown that use of 1.8-μm particle packed columns with conventional HPLC systems is possible, but with limitations in mobile phase flow-rate.     

Characterization of a 2.6 μm Kinetex porous shell hydrophilic interaction liquid chromatography column in supercritical fluid chromatography with a comparison to 3 μm totally porous silica

The first systematic study of the performance of a porous shell, hydrophylic interaction liquid chromatography (HILIC) column in supercritical fluid chromatography (SFC) is presented. Observed efficiency on 2.6-μm porous shell particles exceeded all reports using UHPLC on 100-mm long columns packed with <2-μm totally porous particles. A Kinetex 4.6 × 150 mm, 2.6 μm HILIC column significantly outperformed a 3 μm Luna totally porous silica of the same length and diameter. A 17 component, low molecular weight test mix, consisting of a range of small drug-like molecules was separated isocratically on each column, with similar selectivity, but the porous shell column required ½ the time (≈2 min vs. 4 min), with almost 50% higher efficiency. Even little retained compounds (k < 0.5) exhibited more than 30,000 plates under some conditions. Reduced plate heights were higher than previously reported on porous shell particles in both HILIC and rHPLC, with the lowest value of 1.62. Significant fronting was sometimes observed. The cause of the fronting was not determined. The least symmetrical peaks showed the highest apparent efficiency. Pressure drop at optimum velocity (2.5 ml/min) and low modifier concentrations was <60 bar, and only exceeded 250 bar at near double optimum flow and 65% modifier. Peak widths were mostly just over 0.01 min (20 Hz) wide. There was a loss of efficiency when the injection volume was increased. The chromatograph was shown to have extremely low extra-column dispersion, on the order of 5–10 μL², which is also the lowest reported in an SFC, in spite of using standard components. This is likely due to turbulent flow in the tubing and fittings.     

Direct chiral separation of abscisic acid by high-performance liquid chromatography with a phenyl column and a mobile phase containing γ-cyclodextrin

Abscisic acid (2-cis,4-trans-abscisic acid) is a plant hormone that has an asymmetric carbon atom. We tried to separate the enantiomers of native abscisic acid by HPLC using a phenyl column and a chiral mobile phase containing γ-cyclodextrin. The optimum mobile phase conditions were found to be 0.8% (w/v) γ-cyclodextrin, 4% (v/v) acetonitrile, and 20 mM phosphate buffer (pH 6.0). It was found that (R)-abscisic acid was earlier detected than (S)-abscisic acid. Since γ-cyclodextrin is hardly retained on a phenyl column, it was suggested that (R)-abscisic acid formed a more stable complex with γ-cyclodextrin than the (S)-abscisic acid. Abscisic acid in an acacia honey sample was successfully enantioseparated with the proposed method and only (S)-abscisic acid was detected. A biologically inactive 2-trans,4-trans-abscisic acid, which was prepared by irradiation of abscisic acid with a light-emitting diode lamp at 365 nm, was partially enantioseparated by the proposed method. Since the irradiation of (S)-abscisic acid-induced cis-to-trans isomerization to produce one 2-trans,4-trans-abscisic acid enantiomer, it is reasonable that racemization did not proceed during the cis-to-trans isomerization. (S)-Abscisic acid and probably (S)-2-trans,4-trans-abscisic acid were detected in a honey sample, where the peak area of (S)-abscisic acid was 7 times larger than that of (S)-2-trans,4-trans-abscisic acid.     

Production of β-carotene from beet molasses by Blakeslea trispora in stirred-tank and bubble column reactors

The effect of aeration rate and agitation speed on β-carotene production from molasses by Blakeslea trispora in a stirred-tank fermentor and optimization of the production of the pigment in a bubble column reactor were investigated. In addition, a central composite design was employed to determine the maximum β-carotene concentration at optimum values for the process variables (aeration rate, sugar concentration, linoleic acid, kerosene). By image analysis of the morphology of the fungus, a quantitative characterization of the hyphae and zygospores formed was obtained. The hyphae were differentiated to intacthyphae, vacuolated hyphae, evacuated cells and degenerated hyphae. An increased proportion of zygospores was correlated to high β-carotene production. In the stirred-tank fermentor, the highest concentration of the carotenoid pigment (92.0 mg/L) was obtained at an aeration rate of 1.5 vvm and agitation speed of 60 rpm. In the bubble column reactor, the aeration rate and concentration of sugars, linoleic acid, kerosene, and antioxidant significantly affected the production of β-carotene. In all cases, the fit of the model was found to be good. Aeration rate, sugar concentration, linoleic acid, and kerosene had a strong positive linear effect on β-carotene concentration. Moreover, the concentration of the pigment was significantly influenced by the negative quadratic effects of the given variables and by their positive or negative interactions. Maximum β-carotene concentration (360.2 mg/L) was obtained in culture grown in molasses solution containing 5% (w/v) sugar supplemented with linoleic acid (37.59 g/L), kerosene (39.11 g/L), and antioxidant (1.0 g/L).     

Application of multi-capillary column – ion mobility spectrometry (MCC-IMS) in rubber chemistry and technology

In this paper the possibility for authentication and differentiation of various styrene butadiene rubbers (SBRs) was investigated. Seven types of SBR were analyzed by multi-capillary column (MCC) ion mobility spectrometer (IMS) and their spectra compared. The analysis of volatile organic compounds (VOCs) releasing from the rubbers revealed the presence of characteristics signals, which can be assigned only to a specific material. Such “markers”, when defined for other polymer materials, can be used for their authentication. In the second part of the paper, the blend of epoxidized natural rubber and poly-3-hydroxybutyrate-co-4-hydroxybutyrate (ENR/P(3,4)HB) was subjected to different types of aging. MCC-IMS spectra of not aged, thermal, climatic and UV aged samples were collected and differences between the signals discussed. The study showed possibility of authentication of polymeric materials and processes. The paper is a some kind of introduction to the use of analytical properties and advantages of MCC-IMS technique in chemistry, technology and exploitation of polymer materials.     

Chromatographic properties of a capillary column with the Aerosil modified with nematic 4-methoxy-4′-ethoxyazoxybenzene

The chromatographic properties of a SCOT capillary column with the Aerosil modified with a nematic liquid crystal of 4-methoxy-4′-ethoxyazoxybenzene were studied. The Rohrschneider constants and retention factors were determined for substances from various classes. The microheterogeneous adsorbent SCOT(SiO₂ + MEAB) belongs to medium-polarity stationary phases by its selectivity. It was shown that, in the temperature range 95–110°C, the studied column possessed high values of para-meta selectivity, efficiency, and capacity with respect to arenes and polar substances. Examples of rapid separations of mixtures containing isomers of different types are presented.     

Implementation of a quality system in a clinical laboratory – Evaluation of quality indicators

 The aim of this study was to evaluate the primary experience of implementing a quality system in a clinical laboratory. The second interrelated aim was to evaluate the quality and financial indicators needed for continuous measurement of quality, decision making in the laboratory management and everyday process control in analytical work. The quality process itself should be evaluated because the building up of a quality system requires a considerable amount of resources. The most effective and practical ways of using a quality system as a management tool should be found and the need for financial appraisal when the quality system is implemented is stressed. According to our study, when the effects of the quality system were evaluated, the managers of the laboratory had not considered the appropriate financial indicators. The quality indicators considered to be the best were internal quality control, external quality assessment and customer satisfaction surveys. The first benefits of the quality system evaluated by the personnel were other than the purely financial benefits, they include a more systematic and empowering approach to laboratory management, better working instructions, better knowledge of the methods and equipment, and fewer errors. The financial evaluation of a quality process in a public-owned clinical laboratory is complicated due to the fact that financial indicators are not as far developed and diverse as in industrial organisations. When starting to implement a quality system, it is important to pay attention to all measures that motivate the staff and help them benefit from the practical effects of the system. Received: 10 November 1999 / Accepted: 12 January 2000     

Unusual Formation of a β-linked Disaccharide in a Nis Glycosylation

Abstract

The N-halosuccinimide glycosylation is a highly selective reaction that leads to trans-configured 1-alkoxy-2-halo-glycosides (halo = bromo, iodo).²³ As an exception to the generally observed exclusive formation of α-linked glycosides in such reactions,² we obtained a 3 / 1 mixture of α- and β-disaccharide 6 and 7, when we treated the silylated glycal 4 with NIS (N-iodosuccinimide) and the glycoside 5.⁴ The similarly protected arabino glycal 9, on the other hand, gave exclusively the expected α-linked saccharide 11, when treated with NIS and the alcohol component 10.⁵ Silylated glycals 4 and 9 were obtained from L-digitoxal 1 ⁶ and L-rhamnal 8 ⁷ by treatment with tert-butyldiphenylchlorosilane⁸ and tert-butyldimethylchlorosilane,⁹ respectively. In both cases the 3-O-silylated derivatives formed in high yields. Only in case of the ribo-configuration minor amounts of a 4-O-silylated product 3 were identified.