Retention Of Polar Compounds Research Articles

Biosilica as a New Stationary Phase in HILIC Mode

The aim of this work was to use the biosilica obtained from diatoms (microalgae) cultivated under laboratory conditions as a new stationary phase to fill the chromatographic column and test it in high-performance liquid chromatography. Biosilica is an inorganic polymer consisting of orthosilicate units formed by organisms such as diatoms or siliceous sponges. The results showed that the prepared columns were characterized by relatively high efficiency, comparable to a commercially available material HALO HILIC of dp = 2.7 μm. The retention of polar compounds under a high acetonitrile content was worse than that on HALO HILIC, but it was proportionally lower when the surface area of both materials was compared. As model test solutes, nucleosides and nucleobases have undergone testing. They were examined separately for retention, and attempts to separate test mixtures were successful.

A New Definition of the Stationary Phase Volume in Mixed-Mode Chromatographic Columns in Hydrophilic Liquid Chromatography.

Polar columns used in the HILIC (Hydrophilic Interaction Liquid Chromatography) systems take up water from the mixed aqueous–organic mobile phases in excess of the water concentration in the bulk mobile phase. The adsorbed water forms a diffuse layer, which becomes a part of the HILIC stationary phase and plays dominant role in the retention of polar compounds. It is difficult to fix the exact boundary between the diffuse stationary and the bulk mobile phase, hence determining the column hold-up volume is subject to errors. Adopting a convention that presumes that the volume of the adsorbed water can be understood as the column stationary phase volume enables unambiguous determination of the volumes of the stationary and of the mobile phases in the column, which is necessary for obtaining thermodynamically correct chromatographic data in HILIC systems. The volume of the aqueous stationary phase, Vex, can be determined experimentally by frontal analysis combined with Karl Fischer titration method, yielding isotherms of water adsorbed on polar columns, which allow direct prediction of the effects of the composition of aqueous–organic mobile phase on the retention in HILIC systems, and more accurate determination of phase volumes in columns and consistent retention data for any mobile phase composition. The n phase volume ratios of 18 columns calculated according to the new phase convention strongly depend on the type of the polar column. Zwitterionic and TSK gel amide and amine columns show especially strong water adsorption.

Ultra-fast forensic toxicological screening and quantitation under 3 minutes with a QTOF HPLC-MS/MS system

Objectives HPLC-MS/MS technology combines separation (HPLC) and detection (MS, and MS/MS) and is widely used for screening applications. Mostly, the duration of HPLC runtime in these studies vary from 5 to 20 min. For high-throughput laboratories, a fast screening method is desired. There are mainly two approaches to acquire fragmentation information for screening purpose of compounds by HPLC-MS/MS: Information-Dependent-Acquisition (IDA) or Data-Dependent-Acquisition (DDA) and MS/MS All . For IDA-MS/MS, a survey scan is performed to collect the information on the precursor ions, followed by multiple dependent MS/MS scans for a number of most abundant precursor/candidate ions. MS/MS All with SWATH ® acquisition is a novel MS/MS All technique. In every data cycle, the instrument acquires TOF-MS information first, and then it sequentially acquires MSMS information of all precursor ions across a specified mass range in pre-divided mass windows. Both of these two data acquisition approaches are compatible with retrospective data interrogation. In this study, we aimed to develop an ultra-fast screening method in a forensic toxicological setting using the SCIEX X500R QTOF system with SCIEX OS software 1.0. We also aim to compare IDA-MS/MS and MS/MS All with SWATH ® acquisition for this fast screening method. Methods Blank human urine samples were spiked with multiple drugs commonly found in forensics setting at different concentration levels. Typically, samples were diluted 10-fold in 10% methanol and centrifuged. The clear supernatants were transferred to auto-sampler vials and 10 μL samples were injected. HPLC separation was on a 20 × 2 mm cartridge-type column with cartridge holder. Mobile phase A was 10 mm ammonium formatted in water and mobile phase B was 0.1% formic acid in methanol. HPLC runtime was 2.5 min Data was acquired, processed and reported in SCIEX OS software 1.0. Results Good separation for all the analytes tested and good retention for polar compounds. Sample set 1 was blank urine samples spiked with more than 85 compounds at different levels (CO1 means cutoff number for Sample set 1). Despite a very short HPLC runtime (less than 3 min), the method showed excellent sensitivity. The calibration curve for one of the analytes (JWH 210 5-OH metabolite) is showed. Sample set 2 were also urine samples with both calibrators (spiked with a different group of 84 compounds, CO 2 means cutoff number for sample set 2) and unknown samples. It showed true positive rate in the calibrators for set 2. No false positive was identified. It showed the true positive rate with different HPLC methods and MS/MS acquisition methods. Conclusion In this study, we have developed a super-fast screening/quantitation method in forensic setting under 3 minutes using the SCIEX X500R QTOF system. Two non-targeted data acquisition methods: IDA-MS/MS and MS/MS All with SWATH ® acquisition were both tested and compared. Depending on the specific requirement of the screening method, both IDA-MS/MS and SWATH® acquisition have their advantage and disadvantage in certain areas and the user should be flexible to adopt either approach with appropriate method settings. For Research Use Only. Not for use in diagnostic procedures.

Sol-Gel Hybrid Cyanopropyltriethoxysilane-methyltrimethoxysilane as Adsorbent for Dispersive-Micro Solid Phase Extraction of Selected Organophosphorus Pesticides in Water Samples

Commercial solid phase extraction (SPE) sorbents normally used for organophosphorus pesticides (OPPS) analysis is C18. However, it show low retention for polar compounds and is rather expensive. The limitations are overcome through the development of a new sol-gel hybrid material, cyanopropyltriethoxysilane-methyltrimethoxysilane (CNPrTEOS-MTMOS). Sol-gel hybrid CNPrTEOS-MTMOS was successfully synthesized and applied as an adsorbent for dispersive-micro-SPE (D-µ-SPE) of three selected OPPs from several water samples. Extracted analytes were analyzed using gas chromatography-mass spectrometry. Under the optimum conditions (100 mg CNPrTEOS-MTMOS as adsorbent, 10 mL water samples, 7 min extraction time, 300 µL methanol as desorption solvent and 3 min desorption time), the method showed excellent detection limits (0.01-0.004 µg L-1 at S/N = 3) and linear range achieved were 0.01-10 µg L-1. The CNPrTEOS-MTMOS sorbent offers an alternative sorbent material for the extraction of OPPs of various polarity. The developed D-µ-SPE method was successfully applied for the simultaneous analysis of OPPs in several water samples and results were compared with published results. Sol-gel hybrid CNPrTEOS-MTMOS showed high potential as an alternative adsorbent for D-µ-SPE technique for OPPs.

Multi-target screening of biological samples using LC-MS/MS: focus on chromatographic innovations.

Multi-target screening of biological fluids is a key tool in clinical and forensic toxicology. A complete toxicological analysis encompasses the sample preparation, the chromatographic separation and the detection. The present review briefly covers the new trends in sample preparation and detection and mainly focuses on the chromatographic stage, since a lot of technical improvements have been proposed over the last years. Among them, columns packed with sub-2μm fully porous particles and sub-3μm core-shell particles allow for significant improvements of resolution and higher throughput. Even if reversed-phase LC remains the most widely used chromatographic mode for toxicological screening, hydrophilic interaction chromatography and supercritical fluid chromatography appear as promising alternatives for attaining orthogonal selectivity, retention of polar compounds, and enhanced MS sensitivity.

Underivatized amylose and cellulose as new stationary phases for hydrophilic interaction chromatography

Two polysaccharide stationary phases have been newly suggested for application in hydrophilic interaction chromatography (HILIC). Both columns (amylose-silica, 250 × 4.6 mm, 5 μm and cellulose-silica, 250 × 4.6 mm, 5 μm) demonstrated a satisfactory retention of polar compounds. The influence of the mobile-phase composition (acetonitrile content, pH, salt concentration) on the retention was in agreement with the HILIC concept. The phases showed a very similar behavior, typical efficiency of about 50,000 plates/m, cellulose retained test compounds somewhat more strongly. Under the experimental conditions, electrostatic (non-HILIC-type) interactions due to the dissociation of silanol groups on the silica surface did not influence the retention, noticeably. The applicability of polysaccharide stationary phases for the chromatography of polar compounds was proven by the separation of mixtures of sugars (fructose, glucose, saccharose, maltose, trehalose) or vitamins (nicotinamide, pyridoxine, riboflavin, thiamine, nicotinic acid, ascorbic acid).

Residual silanols at reversed‐phase silica in HPLC – a contribution for a better understanding

As porous silica gel is the most common adsorbent and support for bonded stationary phase synthesis, residual silanol groups are a recurring problem in the field of liquid chromatography and other separation techniques. Residual silanols most often have a negative effect on the separation process by causing peak tailing. Therefore, there was an attempt to remove residual silanols during stationary-bonded phase synthesis. The type and surface concentration of residual silanols were measured using different instrumental techniques such as NMR and infrared spectroscopy, calorimetry, and various chromatographic methods. Residual silanols exhibit acidic characteristic and they can ionize depending on the environment. Thus, they posses cation-exchange properties and cause the zeta potential of silica particle in liquid environment. Presented review discusses the influence of the residual silanol groups on the solvation process and retention of polar compounds. The novel methodology of residual silanols determination is presented as well as the influence of the silanols on the zeta potential of the stationary-bonded phases in chromatographic conditions.

Preparation and evaluation of carbon coated alumina as a high surface area packing material for high performance liquid chromatography

The retention of polar compounds, the separation of structural isomers and thermal stability make carbonaceous materials very attractive stationary phases for liquid chromatography (LC). Carbon clad zirconia (C/ZrO 2), one of the most interesting, exhibits unparalleled chemical and thermal stability, but its characteristically low surface area (20–30 m 2/g) limits broader application as a second dimension separation in two-dimensional liquid chromatography (2DLC) where high retentivity and therefore high stationary phase surface area are required. In this work, we used a high surface area commercial HPLC alumina (153 m 2/g) as a support material to develop a carbon phase by chemical vapor deposition (CVD) at elevated temperature using hexane vapor as the carbon source. The loading of carbon was varied by changing the CVD time and temperature, and the carbon coated alumina (C/Al 2O 3) was characterized both physically and chromatographically. The resulting carbon phases behaved as a reversed phase similar to C/ZrO 2. At all carbon loadings, C/Al 2O 3 closely matched the unique chromatographic selectivity of carbon phases, and as expected the retentivity was increased over C/ZrO 2. Excess carbon – the amount equivalent to 5 monolayers – was required to fully cover the oxide support in C/Al 2O 3, but this was less excess than needed with C/ZrO 2. Plate counts were 60,000–76,000/m for 5 μm particles. Spectroscopic studies (XPS and FT-IR) were also conducted; they showed that the two materials were chemically very similar.

TYPE C AMINO COLUMNS FOR AFFINITY AND AQUEOUS NORMAL PHASE CHROMATOGRAPHY: SYNTHESIS AND HPLC EVALUATION

The synthesis of novel stationary phases for the retention of polar compounds and for affinity chromatography was presented. Two amino compounds, 4-diethylamino-2-butyn-1-ol and 3-amino-3-methyl-1-butyne, were bonded to a silica hydride surface using Silica-C and a hydrosilation procedure. The bonding was confirmed using CP – MAS NMR and FTIR techniques. High Performance Liquid Chromatography (HPLC) evaluation of the synthesized HPLC stationary phases was performed using the Neue Test. Aqueous Normal Phase (ANP) properties of synthesized amino phases were confirmed using a broad range of polar compounds. Type III-O trypsin inhibitor from chicken egg white was used to test the affinity aspect of the amino bonded trypsin column.

An unconventional Neoproterozoic – Early Cambrian source rock interval in southern Oman: Implications for oil and gas generation

ABSTRACT The Neoproterozoic – Early Cambrian Ara intra-salt petroleum system in Oman has been the subject of several studies since the early 1990s, not least because of the exploration success that has accompanied the emergence of the play. As one of the oldest known commercial hydrocarbon systems, the properties of the source organic matter have been of particular interest. The Ara intra-salt hydrocarbon system consists of the Al Shomou Silicilyte, a rock which is composed of pure microcristalline silica, and carbonate colloquially known as “stringers”. Both occur as slabs encased in the Ara salt. In the case of the Silicilyte, the slabs can be shown to act both as source rock and reservoir. However, in the case of the carbonate stringers, the association is more ambiguous. A set of rock and oil samples have been selected from different wells penetrating the silicilyte and carbonate stringer plays to better characterize and understand these systems. As far as the sedimentary organic matter is concerned, the Al Shomou Silicilyte domain has an average Total Organic Carbon (TOC) of approximately 4 wt.%. The carbonate-prone domains exhibit rare organic-rich lithofacies (TOC of approximately 2 wt.%) and additional intra-salt shales (TOC of approximately 4 wt.%). The organic matter present in both the Silicilyte and carbonate plays is associated with a hypersaline and anoxic depositional environment, rich in sulfur, and showing very similar chemical signatures (bulk composition, elemental analysis, biomarker content, δ13C). The organic matter associated with these sequences is characterized by an unusual “asphaltenic” nature. Compared to classical fossil organic matter taken at an equivalent maturity level, the organic matter found in the intra-salt silicilyte, shales or carbonates releases a large amount of solvent soluble material, which is very rich in Nitrogen-Sulfur-Oxygen (NSO) compounds, implying a standard Type II-S kerogen. However, the organic matter differs from this classic characterization of kerogen (solvent insoluble) in that a large proportion appears to be a sulfur-rich “soluble” kerogen, which has not been previously described. Independent geochemical parameters (Rock-Eval analysis, kinetic parameters) seem to be consistent with this hypothesis. The thermal maturity of the whole set of samples examined places them in the oil window. Moreover, Thermochemical Sulfate Reduction (TSR) did not occur in these samples. As far as the soluble part is concerned, differences in the molecular (significant molecular variations for norhopanes, secobenzohopanes, carotane, X compounds, thianes, thiolanes) and sulfur isotopic composition were demonstrated, and are assumed to reflect subtle variations in depositional settings between Silicilyte and carbonate stringers. The specific properties of this unconventional organic matter has to be accounted for in the thermal modeling of oil and gas generation. Although the kinetic distribution for kerogen cracking is close to that of a Type II-S kerogen, it is slightly more mono-energetic. A compositional 2-D basin modeling (Temis 2D) was performed on a cross-section through the South Oman Salt Basin, using specific kinetic parameters measured on this unconventional Neoproterozoic – Early Cambrian kerogen (based on a linear grouping of insoluble kerogen and NSO like “soluble kerogen” kinetic parameters). The gas-to-oil ratio GOR prediction was improved within the silicilyte, when compared to the use of classical parameters assigned to Type II-S kerogen. Finally, the microcrystalline silica mineral matrix of the silicilyte plays is proposed to play a major role in the composition of the fluid, which is expelled and produced by imposing a strong geochromatographic effect on fluids and the retention of polar compounds. The preferential release of aliphatics would lead to the production of oils exhibiting a strong condensate character. This effect has to be considered when modeling the actual composition of the movable fluid in the silicilyte. The significance of the geochromatographic effect is yet to be quantified, but according to available observations, we suggest that this geochromatographic effect could explain the observed API gravity difference between oils produced from silicilyte and carbonate plays.

Multivariate analysis of retention and distribution of aroma compounds in barrier dispersion coatings

AbstractThe influence of drying conditions, latex type, talc content and amount of added aroma compounds on the retention and distribution of aroma compounds in barrier dispersion coatings was explored using static headspace gas chromatography combined with multivariate data analysis. The model aroma system consisted of an alcohol, an ester, an aldehyde, a ketone and two terpenes. Four latex grades based on styrene‐acrylate and styrene‐butadiene were studied. It was found that non‐polar aroma compounds were retained best in styrene‐butadiene latex, while polar ones were retained more in the styrene‐acrylate latex. Talc increased the retention of all the aroma compounds. The retention of polar compounds was higher with shorter drying times, which is probably due to greater losses during the later steps of the film formation process when internal water was evaporated. Polarity and talc also affected the partition of the aroma compounds between air and film. Copyright © 2007 John Wiley & Sons, Ltd.

On-line multi-bed sorption trap for VOC analysis of large-volume vapor samples: injection plug width, effects of water vapor and sample decomposition

A multibed on-line sorption trap is used to preconcentrate organic vapors from air samples and inject the analytes into a GC separation column. Injection plug widths depend on the boiling point for the lipophilic compounds and on the polarity and boiling point for the polar compounds. Injection plug widths are sufficiently small (0.7-0.8 s) as to allow the direct injection of the most volatile compounds into the GC column without the need for a second focusing device. The presence of water in the samples has an effect on the retention of polar compounds by the trap. However, this effect is reproducible for a fixed water content and so can be overcome by using calibration standards under the same conditions of humidity as the samples. The thermal decomposition of many volatile organic compounds in an on-line sorption trap during the GC analysis of air samples is examined. The results show that degradation of unstable compounds is governed by the amount of heat transferred to the compounds during desorption (i.e., applied temperature and pulse duration). The use of an on-line trap results in the immediate transfer of desorbed compounds to the analytical column, which can reduce the formation of artifacts.

Influence of chemical modification of polymeric resin on retention of polar compounds in solid-phase extraction

Three polymeric adsorbents, two of which had been chemically modified with different hydrophilic functional moieties and the third, which was the corresponding unmodified polystyrene-divinylbenzene (PSDVB) resin, were compared for solid-phase extraction (SPE) of several polar pesticides and phenolic compounds from water samples. The SPE system was online coupled to a liquid chromatograph with UV detector.

Retention of organic compounds in capillary gas chromatography using humid carrier gases

The influence of humid carrier gases (nitrogen and carbon dioxide) on the retention of polar compounds in a capillary column with polypropylcyanophenylsiloxane stationary liquid phase OV-225 was studied. It is noted that when humid carbon dioxide is used as the carrier gas, the retention of primary amines sharply increases.