Relative Standard Deviations Of Peak Areas Research Articles

Statistical reliability of a relative standard deviation of chromatographic peak area estimated by a chemometric tool based on the FUMI theory

In pharmaceutical analysis using a high-performance liquid chromatography (HPLC) system, repeatability assessment is significant to obtain reliable and precise quantitative results. The purpose of the present study is to experimentally show the statistical reliability of a relative standard deviation (RSD) of peak area estimated by a chemometric tool based on probability theory, called the function of mutual information (FUMI) theory, which stochastically provided an RSD of peak area and SD of baseline areas with width k (s(k)) from noises and a signal on a single chromatogram. An ultra-high-performance liquid chromatography with ultraviolet detection (UHPLC-UV) for determining ergosterol was applied as an example of the repeatability assessment. In addition, the statistical reliability of an RSD of peak area in the UHPLC-UV system was certified according to a chi-square (χ2) distribution. The 712 values of s(k) were experimentally obtained from a data series of 1001 points in the noise regions of 712 chromatograms. The histogram of χ2 of s(k) was well-fitted to the χ2 distribution curve (freedom degree, ν = 50), indicating that the statistical reliability of an RSD of the peak area in the UHPLC-UV estimated by the FUMI theory (n = 1) was equivalent to that estimated by 50 runs of chromatographic measurements.

Rapid Determination of Lignans in Schisandra chinensis by Supramolecular Solvent (SUPRAS)-Based Extraction and High-Performance Liquid Chromatography–Tandem Mass Spectrometry (HPLC-MS)

A supramolecular solvent (SUPRAS)-based sample preparation method was proposed for the determination of lignans in Schisandra chinensis (S. chinensis) fruit. The optimal conditions were: proportion of hexafluoroisopropanol in SUPRAS: 35% (v/v), solid-to-liquid ratio: 20:1 mg/mL, and vortex time: 30 s. Additionally, simple, rapid, and sensitive high-performance liquid chromatography coupled with triple quadrupole mass spectrometry and multiple reaction monitoring was employed to simultaneously quantify seven lignans in S. chinensis. The validation showed that the linearity from 0.01 to 20.83 µg/mL was excellent (all R 2 ≥ 0.99). The lowest limits of quantification were from 0.14 to 17.79 ng/mL. The relative standard deviation (RSD) of the intra-day retention time and peak area were from 0.12% to 0.21% and 2.35% to 6.41%. The RSD of retention time and peak area for the inter-day precision ranged from 0.17% to 0.32% and 3.83% to 7.39%. The average recoveries (80.21%–114.53%) demonstrated good accuracy for all analytes. The developed procedure was employed to determine lignans in processed and raw S. chinensis fruit. The lignans were concentrated in the seeds and the wine-processed material had the highest content. This study provides a reference for the analysis of S. chinensis fruit for lignans.

Liquid-phase microextraction of aromatic amines: hollow fiber–liquid-phase microextraction and parallel artificial liquid membrane extraction comparison

Aromatic amines (AA) are carcinogenic compounds that can enter the human body through many sources, one of the most important being tobacco smoke. They are excreted with the urine, from which they can be extracted and measured. To that end, hollow fiber-liquid-phase microextraction (HF-LPME) and parallel artificial liquid membrane extraction (PALME) were optimized for the analysis of representative aromatic amines, as alternatives to liquid–liquid extraction (LLE). Relevant extraction parameters, namely organic solvent, extraction time, agitation speed, and acceptor solution pH, were studied, and the two optimized techniques—HF-LPME: dihexyl ether, 45 min, 250 rpm, and pH 1; PALME: undecane, 20 min, 250 rpm and pH 1—were compared. Comparison of the optimized methods showed that significantly higher recoveries could be obtained with PALME than with HF-LPME. Therefore, PALME was further validated. The results were successful for nine different AA, with regression coefficients (R2) of at least 0.991, limits of detection (LOD) of 45–75 ng/L, and repeatability and peak area relative standard deviations (RSD) below 20%. Furthermore, two urine samples from smokers were measured as proof of concept, and 2-methylaniline was successfully quantified in one of them. These results show that PALME is a great green alternative to LLE. Not only does it use much smaller volumes of toxic organic solvents, and sample—enabling the study of samples with limited available volumes—but it is also less time consuming and labor intensive, and it can be automated.Graphical

Sevoflurane Exposure of Clinical Doses in Pregnant Rats Induces Vcan Changes without Significant Neural Apoptosis in the Offspring

Background and Objectives: Sevoflurane is a commonly used inhalational anaesthetic in clinics. Prolonged exposure to sevoflurane can induce significant changes in lipid metabolism and neuronal damage in the developing brain. However, the effect of exposure of pregnant rats to clinical doses of sevoflurane remains unclear. Materials and Methods: Twenty-eight pregnant rats were randomly and equally divided into sevoflurane exposure (S) group, control (C) and a blank group at gestational day (G) 18; Rats in S group received 2% sevoflurane with 98% oxygen for 6 h in an anesthetizing chamber, while C group received 100% oxygen at an identical flow rate for 6 h in an identical chamber. Partial least squares discriminant analysis (PLS-DA), ultra performance liquid chromatography/time-of-flight mass spectrometry(UPLC/TOF-MS) and MetaboAnalyst were used to analysis acquire metabolomics profiles, and immunohistochemical changes of neuronalapoptosis in hippocampus and cortex of neonatal rats were also analyzed. Results: This study aimed to explore lipidomics and transcriptomics changes related to 2% sevoflurane exposure for 6 h in the developing brains of newborn offspring rats. Ultra-performance liquid chromatography/time-of-flight mass spectrometry (UPLC/TOF-MS) and RNA sequencing (RNA-seq) analyses were used to acquire metabolomics and transcriptomics profiles. We used RNA-seq to analyse the expression of the coding and non-coding transcripts in neural cells of the cerebral cortex. No significant differences in arterial oxygen tension (PaO2), arterial carbon dioxide tension (PaCO2), or arterial blood gas were found between the groups. The relative standard deviation (RSD) of retention times was <1.53%, and the RSDs of peak areas ranged from 2.13% to 8.51%. Base peak chromatogram (BPC) profiles showed no differences between the groups. We evaluated the partial least square-discriminant analysis (PLS-DA) model. In negative ion mode, R2X was over 70%, R2Y was over 93%, and Q2 (cum) was over 80%. Cell apoptosis was not remarkably enhanced by TUNEL and haematoxylin and eosin (HE) staining in the sevoflurane-exposed group compared to the control group (p > 0.05). Glycerophospholipid (GP) and sphingolipid metabolism disturbances might adversely influence neurodevelopment in offspring. The expression of mRNAs (Vcan gene, related to neuronal development, function and repair) of the sevoflurane group was significantly increased in the differential genes by qRT-PCR verification. Conclusions: GP and sphingolipid metabolism homeostasis may be potential therapeutic approaches against inhalational anaesthetic-induced neurodegenerative disorders. Meanwhile, sevoflurane-induced Vcan changes indicated some lipidomic and transcriptomic changes, even if neural cell apoptosis was not significantly changed in the usual clinical dose of sevoflurane exposure.

Qualitative and quantitative analysis of β-sitosterol marker in virgin camellia oil and virgin olive oil

Abstract Camellia oil and olive oil with superior economic value are easily adulterated with other, cheaper oils. It is difficult to identify both oils by traditional methods because of their similar fatty acid profiles. In the present study, a novel method for qualitative and quantitative analysis of β-sitosterol using GC/MS and GC/FID was developed to identify camellia oil and olive oil. The method validation of β-sitosterol analysis showed good linearity and satisfactory values for recovery, accuracy, precision, and repeatability. The linear regression coefficient (R2) of the calibration curve was 0.9985. An acceptable limit of detection (0.36 mg/100 g) and limit of quantification (1.20 mg/100 g) were achieved. The spiked recoveries were 95.0% to 100.3%. The relative standard deviation (RSD) of within-day precision was less than 3.26%, and the RSD of retention times and peak areas for repeatability were within 0.03% and 1.08%, respectively. The contents of β-sitosterol in virgin camellia oil and virgin olive oil were in the range of 14.1–30.2 mg/100 g and 94.3–173.2 mg/100 g, respectively, indicating that the β-sitosterol content in the former is seven times that in the latter, and β-sitosterol could be a potential marker for the authentication and adulteration detection of both oils.

Chemometric evaluations of repeatability and detection limit in high-performance liquid chromatography with electrochemical detection

The function of mutual information (FUMI) theory proposes that it is possible to obtain a relative standard deviation (RSD) of the peak area of an analyte from baseline noises and a signal on a single chromatogram when the analyte concentrations are proportional to their peak areas. In this study, we demonstrate that the FUMI theory using noise parametrization by the difference method is applicable for the evaluations of repeatability and detection limit (DL) in high-performance liquid chromatography with electrochemical detection (HPLC-ECD). HPLC-ECD for determining vincristine (VCR) was taken as an example, and VCR was detected on a glassy carbon surface at +0.8 V vs. Ag/AgCl. In the comparisons of precision profiles (plots of RSD of peak area against concentrations of an analyte), the stochastically estimated RSD (N = 1) by the FUMI theory fell within the 95% confidence intervals of statistically estimated RSD (N = 6) by repetitive measurements. Furthermore, the DL obtained by the FUMI theory (3.3×SD) was almost the same value as that by the signal-to-noise ratio (S/N) = 3. Moreover, we introduced a manual method for signal-noise resolution to obtain noise parameters from a chromatogram with low-pass Bessel filter processing. In conclusion, our results show that the FUMI theory using noise parametrization by the difference method can be applied to the evaluations of repeatability and DL in HPLC-ECD without and with a low-pass Bessel filter.

Optimizing test approaches for the detection of exposed metal surfaces within a chromatographic flow path

It is critical to the success of any chromatography-based assay that the performance of the LC instrument be checked for its readiness and ability to perform the intended analysis. This includes gaging the suitability of a system to fulfill the purpose of different types of methods. One type of analysis that requires special consideration is the analysis of compounds which are prone to a particular form of non-specific binding, namely metal adsorption, where analytes interact and potentially adsorb to metal contained within the chromatographic flow path. For an analysis of compounds which are susceptible to metal adsorption, ideally a system suitability test would be performed to ensure there will not be any sample loss or detrimental peak shape effects resulting from potential analyte-to-metal interactions. To help chromatographers assess system inertness concerns like this, we have developed a method of testing LC systems for metal interactions using adenosine 5′-(α,β-methylene)diphosphate (AMPcP). This nucleotide analog has been confirmed to have a propensity to adsorb to titanium and stainless-steel frits and is resistant to hydrolysis and stable to long-term storage and repeat use (as is befitting of any reagent proposed for system suitability testing). AMPcP has been used in a flow injection test (no column in-line) to monitor for losses in recovery and peak shape perturbations that can potentially be present in any chromatography system manufactured with one or more metal based components. In this approach, sequential injections of AMPcP were made without a column and various peak attributes were monitored and ultimately correlated to the amount of metal surface area in the flow path. The ability of this method to discriminate between inert chromatographic surfaces versus exposed metal surfaces was verified by comparing peak areas, peak shapes, and injection repeatability for AMPcP using a UHPLC equipped with MP35N metal alloy components versus an equivalent UHPLC equipped with an ethylene bridged hybrid organic-inorganic surface (or so-called hybrid surface technology). Injections of caffeine were also explored to establish a negative control for this system suitability measurement. Caffeine does not interact with metal surfaces and can therefore give an instrument specific representation of peak shape and dispersion as well as an indication of overall mechanical system performance. Additionally, replicate injections of AMPcP and caffeine onto a UHPLC partially configured with hybrid surface technology (HST) readily identified exposed metal surfaces through an increased peak area relative standard deviation as well as a reduction in absolute recovery. Finally, a novel visualization tool was developed to provide an alternative method of determining system inertness without having to perform chromatographic calculations but instead a graphical peak shape comparison between a negative control, caffeine, and the metal sensitive AMPcP test probe.

Synthesis of a covalent organic framework with hydrazine linkages and its application in open-tubular capillary electrochromatography

Recently, covalent organic frameworks (COFs), owning to their excellent and unique properties, are attracting the attention of numerous researchers in some areas, especially the domain of chromatographic separation. However, the application of hydrazine linkages COFs in open-tubular capillary electrochromatography (OT-CEC) lies in the early stage at present. Herein, a well-crystallized hydrazine-linked COF (Tf-DHzOH) was synthesized successfully from 2,5-dihydroxyterephtalohydrazide and 1,3,5-triformyl-benzene. Tf-DHzOH was firstly regarded as a stationary phase material to prepare the Tf-DHzOH coated capillaries with different coating thickness by covalent bonding in this work. The characterization results showed that Tf-DHzOH was successfully synthesized. The separation performance and stability of the Tf-DHzOH coated capillary were evaluated by considering amino acids, sulfonamides, tetracyclines and benzene compounds as analytes. The relative standard deviations (RSDs) of separation time in the intra-day (n = 9), inter-day (n = 6), column-to-column (n = 3) and batch-to-batch (n = 3) were 0.76–4.97%, 1.59–5.94%1.78–8.72% and 1.66%–8.23%, respectively, the RSDs of peak areas were 1.90–5.16%, 1.73–5.24%, 1.26–7.33% and 3.77%–11.24%, respectively. It was confirmed that there was no visible change of separation efficiency after the Tf-DHzOH-coated capillary was used more than 200 runs. The results make clear that 2D hydrazine-linked COF (Tf-DHzOH) has superior potential as the stationary phase in OT-CEC for chromatographic separation.

Establishment of substance P modified affinity chromatography for specific detection and enrichment of Mas-related G protein–coupled receptor X2

Mas-related G protein-coupled receptor X2 (MrgX2) has been identified to be critical in drug-induced pseudo-allergic reactions and allergic diseases. Herein, an affinity high-performance liquid chromatography was established for the specific detection and enrichment of MrgX2. Substance P was used as an affinity ligand and immobilized on a glutaraldehyde-modified amino silica gel. The successful grafting of substance P was characterized by infrared spectroscopy, elemental analysis, X-ray photoelectron spectroscopy, thermogravimetric analysis, and nitrogen adsorption and desorption analyzes. The prepared materials were then used as the stationary phase to investigate the retention behavior of MrgX2 recombinant protein on the affinity column. The results obtained with the analytical techniques show the specificity and selectivity of the MrgX2 recombinant protein on the affinity column. The repeatability and reproducibility for the analysis of MrgX2 on the NH2-Silico@GD@SP column show relative standard deviation (RSD) values lower than the acceptance criteria of 2 and 5% of retention time, and RSD of peak areas < 7%. The RSD value of the results obtained for the control of the activity of the prepared columns respond to the acceptance criteria of 5% and proves that the NH2-Silico@GD@SP column are stable until 48 h. The suitability of the NH2-Silico@GD@SP column offline SEC system has been tested by using MrgX2 as positive control. The results of this experiment indicate that the offline system may be used to analyze the retention fraction. MrgX2 extracted from human mast cells LAD2 was also verified. An obvious retention can be observed and the natural MrgX2 was concentrated 114.6 times compared with the original complex components by using the affinity column. These results may provide a new approach for the specific detection and enrichment of G-protein-coupled receptors.

Capillary coated with three-dimensional covalent organic frameworks for separation of fluoroquinolones by open-tubular capillary electrochromatography

The Schiff-base reaction of 1,3,5-triformylphloroglucinol (Tp) and tetra(4-aminophenyl)methane (TAM) was performed for the synthesis of a three-dimensional covalent organic framework named 3D TpTAM, which was obtained by an ultrasound-assisted method for the first time. The morphology and structure of the synthesized TpTAM were characterized through various methods. Then, TpTAM-coated capillary columns were subsequently prepared by a covalent bonding method within a short time and applied for the separation of fluoroquinolones by capillary electrochromatography (CEC) with good resolution and reproducibility. The intraday relative standard deviations (RSDs) of the retention time and peak areas were 0.88%–0.95% and 2.27%–3.81%, respectively. The interday RSDs of retention time and peak areas were 0.71%–0.89% and 0.88%–3.60%, respectively. The column-to-column RSDs of retention time and peak areas were less than 1.90% and 13.56%, respectively. The interbatch RSDs of retention time and peak areas were less than 3.48% and 3.89%, respectively. The TpTAM-coated capillary columns could be used for no less than 100 runs with no observable changes in the separation efficiency. The separation mechanism was also studied, which indicated that π-π stacking effects, hydrophobic interactions and hydrogen bonding were the main factors. The results revealed that 3D TpTAM should have superior potential as the stationary phase in CEC for chromatographic separation.

Improving data quality in liquid chromatography-mass spectrometry metabolomics of human urine

Signal variation is a common drawback in untargeted metabolomics using liquid chromatography-mass spectrometry (LC-MS), mainly due to the complexity of biological matrices and reduced sample preparation, which results in the accumulation of sample components in the column and the ion source. Here we propose a simple, easy to implement approach to improve data quality in untargeted metabolomics by LC-MS. This approach involves the use of a divert valve to direct the column effluent to waste at the beginning of the chromatographic run and during column cleanup and equilibration, in combination with longer column cleanups in between injections. Our approach was tested using urine samples collected from patients after renal transplantation. Analytical responses were contrasted before and after introducing these modifications by analyzing a batch of untargeted metabolomics data. A significant improvement in peak area repeatability was observed for the quality controls, with relative standard deviations (RSDs) for several metabolites decreasing from ∼60% to ∼10% when our approach was introduced. Similarly, RSDs of peak areas for internal standards improved from ∼40% to ∼10%. Furthermore, calibrant solutions were more consistent after introducing these modifications when comparing peak areas of solutions injected at the beginning and the end of each analytical sequence. Therefore, we recommend the use of a divert valve and extended column cleanup as a powerful strategy to improve data quality in untargeted metabolomics, especially for very complex types of samples where minimum sample preparation is required, such as in this untargeted metabolomics study with urine from renal transplanted patients.

In situ fabrication of 3D COF-300 in a capillary for separation of aromatic compounds by open-tubular capillary electrochromatography

Two-dimensional (2D) COFs have been successfully applied for various applications, such as capillary electrochromatography (CEC). Compared with 2D COFs, three-dimensional (3D) COFs have higher surface area and lower density, which should have superior potential as the separation medium in CEC. However, the 3D COFs on the inner wall of capillary is hard to fabricate in situ. Up to date, the application of 3D COFs in open-tubular capillary electrochromatography (OT-CEC) is still considered a challenge. For the first timethe COF-300-coated capillary was prepared by in situ growth (COF-300 was made from terephthalaldehyde and tetra-(4-anilyl)-methane) on OT-CEC. Benzene, methylbenzene, styrene, ethylbenzene, naphthalene, 1-methylnaphthalene, and propylbenzene were used to evaluate the performance of the COF-300-coated capillary by OT-CEC. For three consecutive runs, the intraday relative standard deviations (RSDs) of migration time and peak areas were 0.1-0.4% and 2.5-8.3%, respectively. The interday RSDs of migration time and peak areas were 0.2-0.5% and 1.0-10.8%, respectively. Five groups of aromatic co mpounds were used to further study the separation mechanism, which indicated that hydrophobic interaction and size selection interaction are the main factors. It should be noted that the COF-300-coated capillary can be used for more than 140 runs with no observable changes ofthe separation efficiency. Graphical abstract The 3D COF-300-coated capillary was prepared by in situ growth for OT-CEC. Six groups of aromatic compounds were separated by 3D COF-300-coated capillary. Size selection and hydrophobic interaction affect the migration time of analytes.

Assessing accuracy, precision and selectivity using quality controls for non-targeted analysis

The benchmarks to assess reproducibility are not well defined for non-target analysis. Parameters to evaluate analytical performance, such as accuracy, precision and selectivity, are well defined for target analysis, but remain elusive for non-target screening analysis. In this study, quality control (QC) guidelines are proposed to assure reliable data in non-target screening methodologies using a simple set of standards. Workflow reproducibility was assessed using an in-house QC mixture containing selected compounds with a wide range of polarity that can be detected either by electrospray ionization (ESI) in positive or negative mode. The analysis was performed by online solid phase extraction (SPE) liquid chromatography coupled to high resolution mass spectrometry (LC-HRMS). Data processing was done by a commercially available software, Compound Discoverer v. 3.0 using an environmental working template, which searched a multitude of databases, including Chemspider, EPA Toxcast, MzCloud among others. We have specifically evaluated method specificity, precision, accuracy and reproducibility in terms of peak area and retention time variability, true positive identification rate, intraday (within days) and interday (consecutive days) variations and the use of QC samples to reduce false positives. The method showed a satisfactory accuracy with an identification rate of ≥70% for most of the QC compounds. Precision estimated based on peak area relative standard deviation (RSD) ranged between 30 and 50% for most of the compounds. Data normalization to a single internal standard did not improve peak area variability. Retention time precision showed great repeatability and reproducibility (RSD ≤ 5%). In addition, a simple model of RT vs log Kow was designed based on our QC mixtures to efficiently reduced false positives by an average of 49.1%.

Miniature and fully portable gradient capillary liquid chromatograph

A robust, portable and miniature battery powered gradient capillary liquid chromatograph (total weight ∼2.7 kg, without battery ∼2.0 kg), with integrated microfluidic injection, column heating and high sensitivity low-UV absorbance detection is presented. The portable capillary chromatograph, was applied with a packed reversed-phase capillary column (100 mm × 300 μm I.D., 5 μm ODS), housed within an integrated capillary column heater controlled by a proportional-integral-derivative (PID) chip module. The system delivered retention time and peak area relative standard deviation in isocratic mode of <0.7% (n = 10) and <3.3% (n = 10), respectively, and <0.1% (n = 10) and <2.3% (n = 10) respectively, for gradient elution mode. Detection was based upon a 255 nm light-emitting diode (LED) using one of two commercial capillary flow-cell options, namely a high sensitivity 12 nL Agilent capillary z-cell (HSDC) and a 45 nL Thermo Fisher Scientific UZ-View™ flow cell (UZFC). The HSDC, housed within a 3D printed detector arrangement, gave an effective pathlength of 1.01 mm (84% of nominal pathlength) and stray light of only 0.2%. Limits of detection for four test small molecule pharmaceuticals ranged from 65 to 101 μg L−1 based upon a 316 nL injection volume, with separation efficiencies of between 18,000 and 29,700 N m−1, with sub-4 min run times. The portable capillary LC system was successfully coupled to a small footprint portable mass spectrometer (Microsaic 4500 MiD) to demonstrate compatibility and ‘point-of-need’ miniaturised LC-MS capability.

Nuclear Magnetic Resonance Spectroscopy to Identify Metabolite Biomarkers of Nonresponsiveness to Targeted Therapy in Glioblastoma Tumor Stem Cells.

Glioblastoma is the most common and malignant brain tumor, and current therapies confer only modest survival benefits. A major obstacle is our ability to monitor treatment effect on tumors. Current imaging modalities are ambiguous, and repeated biopsies are not encouraged. To scout for markers of treatment response, we used NMR spectroscopy to study the effects of a survivin inhibitor on the metabolome of primary glioblastoma cancer stem cells. Applying high resolution NMR spectroscopy (1H resonance frequency: 800.03 MHz) to just 3 million cells per sample, we achieved sensitive and high resolving determinations of, e.g., amino acids, nucleosides, and constituents of the citric acid cycle. For control samples that were cultured, prepared, and measured at varying dates, peak area relative standard deviations were 15-20%. Analyses of unfractionated lysates were performed for straightforward compound identification with COLMAR and HMDB databases. Principal component analysis revealed that citrate levels were clearly upregulated in nonresponsive cells, while lactate levels substantially decreased following treatment for both responsive and nonresponsive cells. Hence, lactate and citrate may be potential markers of successful drug uptake and poor response to survivin inhibitors, respectively. Our metabolomics approach provided alternative biomarker candidates compared to spectrometry-based proteomics, underlining benefits of complementary methodologies. These initial findings make a foundation for exploring in vivo MR spectroscopy (MRS) of brain tumors, as citrate and lactate are MRS-visible. In sum, NMR metabolomics is a tool for addressing glioblastoma.

Assessment of Repeatability in Supercritical Fluid Chromatography with Electrochemical Detection Based on the ISO 11843 Part 7.

The present study proposes a method for the assessment of repeatability in supercritical fluid chromatography with electrochemical detection (SFC-ECD), based on the ISO 11843 part 7 (ISO 11843-7:2018) which can theoretically provide detection limits and standard deviation (S.D.) through the stochastic properties of baseline noise without repetitive measurements of real samples. On the baseline noise of SFC-ECD, large-amplitude and periodic noises with less than 0.05 Hz were observed, and the power spectrum of the baseline noise showed 1/f fluctuation (f = frequency). It was found that the present power spectrum analysis, according to the law of error propagation, can provide suitable noise parameters to calculate S.D. of baseline noise and a relative S.D. (RSD) of peak area by ISO 11843-7. The chromatographic determinations of α-, β-, γ- and δ-tocopherol have been taken as examples. In the present SFC-ECD, the RSDs of peak areas for α-, β-, γ- and δ-tocopherol obtained by ISO 11843-7 were within 95% confidence intervals of the RSD of them obtained by repetitive measurements (n = 6). Thus, we found that ISO 11843-7 is applicable to the assessment of repeatability in SFC-ECD for determining tocopherols without repetitive measurements.

Separation of inorganic anions by capillary ion chromatography with UV detection using poly(vinylimidazole-co-ethylene dimethacrylate) monolithic column

Poly(1-vinylimidazole-co-ethylene dimethacrylate) (VIM-EDMA) monolithic stationary phase was applied for separation of inorganic anions by capillary ion chromatography (IC). The retention of inorganic anions on the VIM-EDMA column was investigated using various salt solutions as the eluent. Good separation of inorganic anions was obtained on VIM-EDMA monolithic column using NH4Cl as the eluent. Good mechanical stability and low swelling propensity values (0.12 and −0.02 for ACN and MeOH, respectively) were obtained. The column repeatability was also examined by determining the relative standard deviations (RSDs) of retention time and peak area of target anions. Relatively low RSDs (n = 7) of retention time (<2.3%) and peak area (<8.8%) were obtained on the VIM-EDMA column. The utilization of VIM-EDMA column for potential environmental application was also demonstrated by determining the occurrence of inorganic anions in various environmental water samples without sample preparation process.

Open-tubular capillary electrochromatographic determination of ten sulfonamides in tap water and milk by a metal-organic framework-coated capillary column.

In this study, a metal-organic framework (MOF), [Mn(cam)(bpy)], was synthesized and characterized by thermogravimetric analysis, scanning electron microscopy, and Fourier transform infrared spectrometry. An open-tubular capillary column was fabricated from [Mn(cam)(bpy)] via the amide coupling method. Ten types of sulfonamides were separated through the fabricated capillary column, which showed a good limits of detection (<0.07μg/mL) and linear ranges (1-100 or 5-100μg/mL) with a high correlation coefficients (R2 > 0.9987). The intra-day, inter-day and column-to-column relative standard deviations (RSDs) in the migration times ranged from 0.44 to 4.87%, and the peak area RSDs ranged from 0.80 to 7.28%. The developed capillary electrochromatography method can be successfully utilized for the determination of sulfonamides in tap water and milk samples.

Tantala-based sol-gel coating for capillary microextraction on-line coupled to high-performance liquid chromatography

A sol-gel organic-inorganic hybrid sorbent, consisting of chemically integrated tantalum (V) ethoxide (TaEO) and polypropylene glycol methacrylate (PPGM), was developed for capillary microextraction (CME). The sol-gel sorbent was synthesized within a fused silica capillary through hydrolytic polycondensation of TaEO and chemical incorporation of PPGM into the evolving sol-gel tantala network. A part of the organic-inorganic hybrid sol-gel network evolving in the vicinity of the capillary walls had favorable conditions to get chemically bonded to the silanol groups on the capillary surface forming a surface-bonded coating. The newly developed sol-gel sorbent was employed to isolate and enrich a variety of analytes from aqueous samples for on-line analysis by high-performance liquid chromatography (HPLC) equipped with a UV detector. CME was performed on aqueous samples containing trace concentrations of analytes representing polycyclic aromatic hydrocarbons, ketones, alcohols, amines, nucleosides, and nucleotides. This sol-gel hybrid coating provided efficient extraction with CME-HPLC detection limits ranging from 4.41pM to 28.19 pM. Due to direct chemical bonding between the sol-gel sorbent coating and the fused silica capillary inner surface, this sol-gel sorbent exhibited enhanced solvent stability. The sol-gel tantala-based sorbent also exhibited excellent pH stability over a wide pH range (pH 0–pH 14). Furthermore, it displayed great performance reproducibility in CME-HPLC providing run-to-run HPLC peak area relative standard deviation (RSD) values between 0.23% and 3.83%. The capillary-to-capillary RSD (n=3), characterizing capillary preparation method reproducibility, ranged from 0.24% to 4.11%. The results show great performance consistency and application potential for the sol-gel tantala-PPGM sorbent in various fields including biomedical, pharmaceutical, and environmental areas.

Quantitation of underivatized branched-chain amino acids in sport nutritional supplements by capillary electrophoresis with direct or indirect UV absorbance detection.

The branched-chain amino acids (BCAAs) including leucine (Leu), isoleucine (Ile) and valine (Val) play a pivotal role in the human body. Herein, we developed capillary electrophoresis (CE) coupled with conventional UV detector to quantify underivatized BCAAs in two kinds of sport nutritional supplements. For direct UV detection at 195 nm, the BCAAs (Leu, two enantiomers of Ile and Val) were separated in a background electrolyte (BGE) consisting of 40.0 mmol/L sodium tetraborate, and 40.0 mmol/L β-cyclodextrin (β-CD) at pH 10.2. In addition, the indirect UV detection at 264 nm was achieved in a BGE of 2.0 mmol/L Na2HPO4, 10.0 mmol/L p-aminosalicylic acid (PAS) as UV absorbing probe, and 40.0 mmol/L β-CD at pH 12.2. The β-CD significantly benefited the isomeric separation of Leu, L- and D-Ile. The optimal conditions allowed the LODs (limit of detections) of direct and indirect UV absorption detection to be tens μmol/L level, which was comparable to the reported CE inline derivatization method. The RSDs (relative standard deviations) of migration time and peak area were less than 0.91% and 3.66% (n = 6). Finally, CE with indirect UV detection method was applied for the quantitation of BCAAs in two commercial sport nutritional supplements, and good recovery and precision were obtained. Such simple CE method without tedious derivatization process is feasible of quality control and efficacy evaluation of the supplemental proteins.