Polysiloxane Stationary Phases Research Articles

Comparison of System Constants of Thermostable Polysiloxane Stationary Liquid Phases of Different Origins

Comparison of System Constants of Thermostable Polysiloxane Stationary Liquid Phases of Different Origins

Comparison of System Constants of Thermostable Polysiloxane Stationary Liquid Phases of Different Origins

The expansion of possible areas of use of modern gas chromatography is largely determined by the thermal stability of stationary liquid phases (SLP), which allows the separation of complex mixtures of high-boiling compounds. A way to increase the thermal stability of nonpolar and weakly polar polysiloxane SLPs is to introduce rigid fragments into the polysiloxane chain. Currently, there is an extensive set of columns with thermostable SLPs, which, in some cases, have the index “ms”. However, in most cases, the nature of these phases and the methods for preparing the columns are not disclosed. In this work, using the linear free energy relationship (LFER) model, we compared the selectivity of a number of proprietary columns with in-house columns in which the siloxane–silarylene phase and the column preparation methods themselves are known. Various types of intermolecular interactions are considered within the framework of the LFER model.

A Novel Validated HS-GC-MS method for the trace level determination of Acetyl chloride as Isopropyl acetate in various anti-cancer drug substances

A novel, simple and precise headspace gas chromatography-mass spectrometry (HS-GC-MS) method was developed and validated for the determination of acetyl chloride (AC) in various anti-cancer drug substances like bendamustine HCl, Ibrutinib, trifluridine and abemaciclib drug substances. In this methodology, AC reacts with isopropyl alcohol and is converted into isopropyl acetate. Hence AC is quantified as Isopropyl acetate. The lower level of detection was achieved on the capillary GC column (DB-624, Fused silica capillary column; 30 m length; 0.32 mm internal diameter, coated with 6% Cyanopropylphenyl and 94% dimethyl polysiloxane stationary phase of 1.8 μm film thickness) with electron impact ionization (EI) technique by GC-MS in selective ion monitoring (SIM) mode. The mass ions were selected for the quantifier is 63 and the qualifier is 87 for isopropyl acetate. The performance of the method was assessed by evaluating the specificity, linearity, sensitivity, precision, accuracy and robustness experiments. The established limit of detection and limit of quantification values for the AC were 0.1 and 0.3 μg/g, respectively. This developed method was found to be linear with a correlation coefficient is greater than 0.999 for all four drug substances. The average recoveries of AC in bendamustine HCl, ibrutinib, trifluridine and abemaciclib were obtained 106.1, 109.0, 97.4 and 101.6%, respectively. The proposed method was validated successfully as per ICH guidelines. Hence, the proposed method can be routinely used for the quantification of AC in various anti-cancer drug substances.

GC-MS analysis of oxysterols and their formation in cultivated liver cells (HepG2).

Oxysterols play a key role in many (patho)physiological processes and they are potential biomarkers for oxidative stress in several diseases. Here we developed a rapid gas chromatographic-mass spectrometry-based method for the separation and quantification of 11 biologically relevant oxysterols bearing hydroxy, epoxy, and dihydroxy groups. Efficient chromatographic separation (resolution≥ 1.9) was achieved using a medium polarity 35%-diphenyl/65%-dimethyl polysiloxane stationary phase material (30 m × 0.25 mm inner diameter and 0.25 μm film thickness). Based on thorough analysis of the fragmentation during electron ionization we developed a strategy to deduce structural information of the oxysterols. Optimized sample preparation includes (i) extraction with a mixture of n-hexane/iso-propanol, (ii) removal of cholesterol by solid phase extraction with unmodified silica, and (iii) trimethylsilylation. The method was successfully applied on the analysis of brain samples, showing consistent results with previous studies and a good intra- and interday precision of ≤20%. Finally, we used the method for the investigation of oxysterol formation during oxidative stress in HepG2 cells. Incubation with tert-butyl hydroperoxide led to a massive increase in free radical formed oxysterols (7-keto-chol> 7β-OH-chol>> 7α-OH-chol), while 24 h incubation with the glutathione peroxidase 4 inhibitor RSL3 showed no increase in oxidative stress based on the oxysterol pattern. Overall, the new method described here enables the robust analysis of a biologically meaningful pattern of oxysterols with high sensitivity and precision allowing us to gain new insights in the biological formation and role of oxysterols.

A New Stationary Phase for Capillary Gas Chromatography: Calix[4]resorcinarene Functionalized with Imidazolium Cationic Units

In this work, a novel calix[4]resorcinarene-based ionic liquid (C4RA-2IL) was synthesized, structurally characterized, and statically coated on capillary column as stationary phase for capillary gas chromatography (GC). The column efficiency of the C4RA-2IL column is 3345 plates m−1, which are determined by n-dodecane at 120 °C. Based on its McReynolds constants, the C4RA-2IL column showed moderate polarity. Particularly, the C4RA-2IL column show high separation performance for a wide range of analytes and some difficult separation of meta/para-isomers. Moreover, it exhibited excellent selectivity for critical aromatic isomers of chloroaniline, bromaniline, iodoaniline, toluidine and xylidine isomers and shows advantageous separation capability over the commercial polysiloxane stationary phase. This work presents a promising future of calixarene-based ionic liquid as a new type of stationary phase in GC separations.

Investigation and Comparison of 5 % Diphenyl – 95 % Dimethyl Polysiloxane Capillary Columns

In gas chromatography, for the analysis, the most important thing is the well-chosen column. After having decided about which stationary phase is the best for our measurement and we know the length, the inner diameter and film thickness, we can buy the column from a lot of manufacturers. The products of these manufacturers’ look similar to each other, but they are different, because of the different manufacturing technologies. These differences could have significant influence on the separation. It is so important to compare the „same” columns, despite the manufacturers’ efforts to produce the best quality columns.5 % diphenyl – 95 % dimethyl polysiloxane stationary phase is widely used. Its slight polarity makes it able to determine very different compounds from the alkanes, through volatiles, drugs, fatty acid methyl esters, amines or phenols.In our work, we tested 5 % diphenyl – 95 % dimethyl polysiloxane stationary phase columns with an 8-component mixture. These columns were from different manufacturers. During isothermal conditions, we determined the height equivalent of theoretical plates on 8 linear velocity level. We represented these parameters as the function of linear velocity. With a constant linear velocity, we measured the excess sorption enthalpy and entropy. From the chromatograms we spotted differences in the retention and in resolution, which is important if we use the column for volatiles or for complex samples. With these parameters we can show many differences between the columns. These parameters have significant influence when we want to use our column for a given task.

Amphiphilic calix[4]arenes as a highly selective gas chromatographic stationary phase for aromatic amine isomers

Efficient separation of aromatic amine isomers is a challenging issue in chemical industry and environmental analysis. Here we report the use of p-amino-tetradecyloxy-calix[4]arene (C4A-NH2) as a novel stationary phase for gas chromatographic (GC) separations. The statically coated C4A-NH2 capillary column showed a high column efficiency of 4332 plates/m for a 0.25 mm ID column and medium polarity. The C4A-NH2 stationary phase exhibited an excellent separation performance both for aromatic amine isomers and a complex mixture of aliphatic analytes with a wide ranging polarity, showing distinct advantages over the commercial polysiloxane stationary phases via diversified molecular interactions covering H-bonding, π-π, van der Waals interactions and shape-fitting selectivity. The retention mechanisms of aromatic amine isomers on C4A-NH2 column were further investigated by quantum chemistry calculations. In addition, the C4A-NH2 column showed good column repeatability with relative standard deviation (RSD) values of 0.03%-0.07% for run-to-run, 0.10%-0.27% for day-to-day and 2.6%–5.7% for column-to-column, respectively, and thermal stability up to 240℃.

Performance and selectivity of lower-rim substituted calix[4]arene as a stationary phase for capillary gas chromatography.

This work presents the investigation of p-tert-butyl(tetradecyloxy)calix[4]arene (C4A-C10) as stationary phase for capillary gas chromatographic (GC) separations. The statically-coated C4A-C10 capillary column showed weak polarity and column efficiency of 2566 plates per m determined by n-dodecane at 120 °C. Impressively, the C4A-C10 column exhibited extremely high resolving capability for a wide range of analytes from nonpolar to polar, including n-alkanes, esters, ketones, aldehydes, alcohols and bromoalkanes. Most importantly, the C4A-C10 column exhibited an excellent separation performance for positional, structural and cis-/trans-isomers. Among them, the column displayed advantageous resolving capability over the commercial polysiloxane stationary phase for aromatic amine isomers. Moreover, the C4A-C10 column showed good column repeatability with RSD values below 0.06% for run-to-run, 0.12–0.27% for day-to-day and 2.8–5.3% for column-to-column.

A flexible and convenient strategy for synthesis of ionic liquid bonded polysiloxane stationary phases

Ionic liquid bonded polysiloxanes (PILs) are a class of polysiloxanes whose side chains contain ionic liquid (IL) moieties. Considering their excellent selectivity and thermo-stability, PILs have great potentials in the development of polar stationary phases for gas chromatography. In this paper, a novel synthesis strategy for PILs is proposed to diversify PIL stationary phases and also facilitate the study on relationships between stationary phase structure and separation performances. The polysiloxane with imidazole groups at the side chains was synthesized firstly, and then these imidazole groups further reacted with halogenated compounds to produce various IL groups. Upon this, fifteen PIL stationary phases differing in IL content, IL group or combination of different IL groups have been synthesized and used to prepare capillary columns through static coating method. These columns have quite different general polarity indexes (the average value of all Rohrschneider-McReynolds constants in this paper) falling in a broad range from 218 to 717, and most columns have column efficiency values over 3000 plates/m. In addition, IL content, structure of the IL and combination of different IL groups have noticeable influences on interaction features of the stationary phases. After that, the separation performances of these PIL stationary phases were demonstrated by separating various mixed samples of aliphatic esters, dichloro-anilines, alcohols, aromatic amines, substituted alkanes, and so on. In order to reveal the relationship of interaction characteristics and separation performances, a set of indexes of contribution rates (CRs) is proposed. Based on CRs, the separation selectivity of the PIL stationary phases has been discussed in detail. The results indicate that there are significant differences in the separation selectivity not only between PILs and conventional polar stationary phases, but also among different PILs. All of these imply a family of practical PILs with special selectivity could be constructed upon this synthesis strategy.

Phytochemical screening of Leucaena leucocephala leaf essential oil and its antibacterial potentials

Objective: The study aimed to identify the phytochemical composition of Leucaena leococephala leaf and evaluate the antimicrobial potential of the essential oil from the leaf. Material and Methods: The sample was subjected to Clevenger apparatus to extract the oil. The essential oil was characterized by chromatography method (GC-MS). The GC-MS was performed on Perkin Elmer gas chromatography model Clarus 680 equipped with HP-5 fused capillary column (5%) phenylmethyl polysiloxane stationary phase with 30m length, 0.25µm of film thickness and 0.25oc and 280oc respectively. Antibacterial activity using Agar Disc Method. Result: The result obtained from the GC-MS presented thirty phytochemicals of which Neophytadiene (9.48%), Octadecane (3.15%), 1-Octadecyne (3.85%), Phytol (52.51%) and Hexacosane (7.26%) are major. The antibacterial potential activities were observed in various ways with zone of inhibition diameters ranging from 0.70±0.00mm to1.27±0.06mm for staphylococcus aureus and Klebsielia pneumonia respectively among the six-concentration selected (25, 50, 100, 250, 500, and 1000ppm). Conclusion: It is investigated in this present studies that Leucaena leococephala essential oil can be utilized against the management of antibacterial diseases particularly Klebsielia pneumonia and Staphylococcus aureusas well as used in the Pharmaceutical and Cosmetics industry.

GC-MS and GC-IR analysis of regioisomeric cannabinoids related to 1-(5-fluoropentyl)-3-(1-naphthoyl)-indole

The compounds in this study are the regioisomeric 2-, 3-, 4-, 5-, 6- and 7-(1-naphthoyl) substituted 1-(5-fluoropentyl)-indoles and the 3-(1-naphthoyl) substituted isomer in this series is also known as AM-2201. These compounds are structurally similar to JWH-018 except for the additional fluorine at the terminal end of the n-pentyl side-chain. These six regioisomeric compounds have the identical elemental composition (C24H22FNO) and differ in the position of attachment of the 1-napthoyl group on the indole ring. The electron ionization mass spectra showed similar major fragment ions with a molecular radical cation of significant abundance at m/z 359. The six compounds have similar fragment ions at m/z 127 and 155 for the naphthyl and naphthoyl cations. There is a prominent fragment ion at m/z 342 [M−17]+ in the EI-MS of 1-(5-fluoropentyl)-3-, 4-, 5- and 6-(1-naphthoyl)-indoles due to the loss of the hydroxyl group and this ion is most prominent in the 3-(1-naphthoyl) substituted isomer (AM-2201).The six compounds were separated using gas chromatography on a capillary column containing a trifluoropropylmethyl polysiloxane (Rtx-200) stationary phase. The elution order appears to be related to the steric crowding of the indole ring substituents. The 7- and 2-(1-naphthoyl) substituted isomers eluted first due to the possibility for maximum interactions between the naphthyol and alkyl side-chains.The vapor phase infrared spectra differentiate among these six compounds based on the position of the 1-naphthoyl group on the indole ring. The vapor phase spectra for these compounds are compared to the non-fluorinated analogues, JWH-018 and its regioisomeric equivalents.

Poly(3-hexylthiophene) stationary phase for gas chromatographic separations of aliphatic and aromatic isomers

This work describes the investigation of utilizing a chain-typed thiophene-based π-conjugated polymer, i.e., poly(3-hexylthiophene) (P3HT), as the stationary phase for gas chromatography (GC). The P3HT column was statically prepared and investigated for its column efficiency, polarity, separation performance, repeatability and thermal stability. As a result, it showed moderate polarity and column efficiencies of 3260, 3310 and 3790 plates/m for 1-octanol, naphthalene and n-dodecane, respectively. As evidenced, it exhibited high-resolution performance for aliphatic and aromatic isomers, including those critical pairs such as phenanthrene/anthracene and p-/m-benzenediol isomers. Moreover, it displayed stronger retention for alkanes, alcohols and phenols in comparison to the polysiloxane stationary phase with close polarity. Also, the P3HT column had good repeatability and reproducibility with the RSD values less than 0.05% for run-to-run, 0.17–0.54% for day-to-day and 2.7–5.2% for column-to-column, and good thermal stability up to 260 °C. This work demonstrates the promising future of the thiophene-based polymer and its derivatives in separation science.

Hexagonal boron nitride stationary phase for gas chromatography

This work describes the separation performance of utilizing hexagonal boron nitride (h-BN) as the stationary phase for capillary gas chromatography (GC). The statically coated h-BN column showed moderate polarity and achieved column efficiencies of 3455 plates/m and 3800 plates/m for naphthalene and n-dodecane, respectively. With temperature-dependent structure properties, the h-BN stationary phase exhibited stronger retention for polycyclic aromatic hydrocarbons (PAHs) over phthalic acid esters (PAEs) and showed advantageous separation performance over the g-C3N4 and commercial polysiloxane stationary phases. Moreover, it displayed preferential retention for halogenated analytes and high resolution performance for structural and positional isomers. In addition, the h-BN column showed good column repeatability with relative standard deviation (RSD) values of 0.03%–0.07% for run-to-run, 0.31%–0.71% for day-to-day and 2.6%–5.3% for column-to-column, respectively, and thermal stability up to 260 °C.

Synthesis and Applications of a Novel 3,4-Bis(2-Fluoro-5-Trifluoromethyl Phenyl)-2,5-Diphenyl Phenyl Grafted Polysiloxane Stationary Phase

A novel polyphenyl-grafted polysiloxane stationary phase named 3,4-bis(2-fluoro-5-(trifluoromethyl)phenyl)-2,5-diphenyl phenyl grafted polysiloxane stationary phase (FFMP) was synthesized through a Diels–Alder reaction with a high column efficiency (average number of plates: 3700 plates/m; achieved by naphthalene at 120 °C) and simultaneously coated on fused silica capillary tubes to prepare a gas chromatographic column with excellent performance. The column performance test results indicated that the FFMP columns could work properly up to 360 °C, as evidenced by the chromatogram of the polyethylene pyrolysis mixture. The thermogravimetric analysis curve showed that the decomposition temperature of the FFMP was up to 380 °C. The FFMP columns were also applied in the separation and analysis of multimixtures, such as Grob test mixtures, benzene mixtures and fatty acid esters, and as well as a medium polar stationary phase (according to the results of McReynolds constants, the sum of ∆I was 779.) The FFMF columns exhibited excellent separation selectivity for these substances because of the conjugated system formed by the polyphenyl side chain connected by single bonds. This conjugated system can promote the delocalization of π-electrons as well as enhance the forces of π–π interaction, and the dipole-induced dipole action between the FFMP stationary phase and the analytes.

Differentiation of homologous and regioisomeric methoxy-cathinone derivatives by GC–MS, MS/MS and GC–IR

A combination of GC–MS, MS/MS and GC–IR techniques can be used to differentiate the nine methoxy cathinone derivatives related to the designer drug MDPV. Nine homologous and regioisomeric methoxyphenyl-aminoketone cathinone derivatives were prepared from the three commercially available 2-, 3- and 4-methoxybenzaldehydes. The gas chromatographic separation of the nine precursor methoxyphenones was achieved on a 100% dimethyl polysiloxane (Rtx®-1) stationary phase and the regioisomeric aminoketones were resolved on a 5% diphenyl, 95% dimethyl polysiloxane (Rtx®-5) stationary phase. The chemical ionization mass spectra (CI–MS) show only one major peak occurring at the mass of the protonated molecular ion (M+1)+ while the EI–MS spectra display primarily the iminium cation fragment. The MS/MS product ion spectra for the three homologous iminium cations yield a homologous series of ions representing the loss of 42Da from the parent species. MS/MS experiments confirmed the loss of 42Da occurring via pyrrolidine ring fragmentation for iminium cations having the methyl and ethyl side-chains and via side-chain fragmentation for the n-propyl side-chain. The vapor phase infrared spectra in the range of 1300–1150cm−1 show unique and characteristic absorption pattern for each of the three regioisomeric methoxy-group substitution patterns.

Polarizable polysiloxane stationary phase containing a cyano unit attached to an aromatic side group for highly selective separation of H-bonding and aromatic analytes

A new polarizable polysiloxane stationary phase containing a cyano unit attached to an aromatic side group, called CPPP [14.6% 3,4-bis(4-cyanophenyl)-2,5-diphenyl phenyl polysiloxane], was synthesized and used as a stationary phase for capillary gas chromatography (GC).

Exploitation of a microporous organic polymer as a stationary phase for capillary gas chromatography

Microporous organic polymers (MOPs) have emerged as a new class of functional porous materials with unique characteristics and potential uses in diverse areas. However, the field of MOPs for gas chromatographic (GC) separations has not been well explored. Herein, a MOP namely KAPs-1 was dynamic coated onto a capillary column for the first time. The fabricated column exhibited a nonpolar nature and the column efficiency for n-dodecane was up to 7769 plates m−1. The KAPs-1 coated column showed high GC separation performance for a series of volatile organic compounds (VOCs) including the challenging ethylbenzene and xylene isomers, which could not be resolved at baseline on the commercial 5% phenyl polysiloxane stationary phase. Moreover, the relative standard deviations for five replicate determinations of the studied analytes were 0.0–0.6%, 0.9–3.2%, 1.1–5.9%, 0.8–3.7% for retention time, peak area, peak height and peak width, respectively. To investigate the interaction between some analytes and the stationary phase, thermodynamic and kinetic parameters were also evaluated. The results of this study show it is very promising to utilize MOPs as stationary phases for capillary GC.

Trace Level Determination of Mesityl Oxide and Diacetone Alcohol in Atazanavir Sulfate Drug Substance by a Gas Chromatography Method.

A capillary gas chromatography method with a short run time, using a flame ionization detector, has been developed for the quantitative determination of trace level analysis of mesityl oxide and diacetone alcohol in the atazanavir sulfate drug substance. The chromatographic method was achieved on a fused silica capillary column coated with 5% diphenyl and 95% dimethyl polysiloxane stationary phase (Rtx-5, 30 m x 0.53 mm x 5.0 µm). The run time was 20 min employing programmed temperature with a split mode (1:5) and was validated for specificity, sensitivity, precision, linearity, and accuracy. The detection and quantitation limits obtained for mesityl oxide and diacetone alcohol were 5 µg/g and 10 µg/g, respectively, for both of the analytes. The method was found to be linear in the range between 10 µg/g and 150 µg/g with a correlation coefficient greater than 0.999, and the average recoveries obtained in atazanavir sulfate were between 102.0% and 103.7%, respectively, for mesityl oxide and diacetone alcohol. The developed method was found to be robust and rugged. The detailed experimental results are discussed in this research paper.

Cyclotriveratrylene as a new-type stationary phase for gas chromatographic separations of halogenated compounds and isomers

Cyclotriveratrylene (CTV) is reported here for the first time as stationary phase for capillary gas chromatographic (GC) separations. CTV stationary phase showed weak polarity comparable to the conventional 5% phenyl polysiloxane stationary phase but exhibited different retention behaviours and higher resolution for some of the indicated analytes. Most importantly, CTV stationary phase exhibited preferential selectivity for halogenated compounds, positional and geometrical isomers. Effect of column temperature on retention and thermal stability of CTV column were also investigated. Moreover, CTV capillary column showed good repeatability in terms of run-to-run, day-to-day and column-to-column. The unique physicochemical features and efficient separation ability for analytes of close properties show the potential of CTV as a new-type stationary phase in GC as well as separation science.

GC–MS studies on the six naphthoyl-substituted 1-n-pentyl-indoles: JWH-018 and five regioisomeric equivalents

The GC–MS properties of the synthetic cannabinoid drug of abuse 3-(1-naphthoyl)-1-pentylindole (JWH-018) and all 5 of its’ regioisomeric 1-naphthoyl substituted 1-n-pentylindoles are compared in this report. These compounds have the 1-naphthoyl-group attached at each of the possible substituent positions of the indole ring. The six compounds have the same elemental composition C24H23NO and the same substituents attached to the indole ring. The electron ionization mass spectra showed equivalent regioisomeric major fragment ions resulting from cleavage of the groups attached to the central indole nucleus. The characteristic (M−17)+ fragment ion at m/z 324 resulting from the loss of an OH group was significant in the EI-MS of 3-, 4-, 5- and 6-(1-naphthoyl)-1-pentylindole. Fragment ions occurred at m/z 127 and 155 for the naphthyl and naphthoyl cations common to all six regioisomeric substances. Indole containing fragments produced the cations at m/z 284, 270, 214 and 186. The unique fragment at m/z 141 observed in the 1,2- and 1,7-isomers resulted from a rearrangement involving the two indole substituents to yield the C10H7CH2+ cation. The major points of EI-MS differentiation of the synthetic cannabinoid JWH-018 from the other five isomers are the high relative abundance of both the m/z 144 ion and the m/z 324 ion in the JWH-018 spectrum.GC separations on a capillary column containing a trifluoropropyl methyl polysiloxane (Rtx-200) stationary phase provided excellent resolution of these six compounds. The elution order appears related to the relative distance between the two indole substituents with the lowest retention associated with minimum distance between the groups attached to the indole nucleus.