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PubMed2006

Adenoviral urokinase-type plasminogen activator (uPA) gene transfer enhances venous thrombus resolution.

INTRODUCTION: There is an increase in the natural level of urokinase-type plasminogen activator (uPA) activity within the thrombus during venous thrombus resolution. The use of uPA as a thrombolytic agent in the treatment of acute iliofemoral deep vein thrombosis is not suitable for all patients. This study aimed to determine whether thrombus resolution could be enhanced by upregulating uPA expression using adenoviral gene transfer as an alternative method of delivery. METHODS: The production of functional uPA by an adenoviral gene construct (ad.uPA) was confirmed by a colorimetric substrate assay and fibrin plate lysis. Thrombus was formed in the inferior vena cava of wild-type mice and injected, 48-hours after induction, with either a control virus at 10(8) plaque-forming units (pfu) or ad.uPA at 10(7) or 10(8) pfu. Thrombi were removed and weighed 7 days after treatment. Activity of metalloproteinase (MMP) 2 and 9 was measured by zymography and the release of vascular endothelial growth factor (VEGF) and D-dimer levels by enzyme-linked immunoabsorbent assay. The results were expressed as a mean +/- SEM. Values were standardized for wet weight or for soluble protein content (mg/sol protein). RESULTS: Treatment with ad.uPA reduced thrombus weight by twofold compared with thrombi treated by control virus (15.1 +/- 1.1 mg vs 7.4 +/- 1.3 mg, P = .004). Urokinase activity (17 +/- 3 pg/mg wet weight) was detected in all treated thrombi, but there was no dose-dependent effect. D-dimer activity was increased twofold after treatment with ad.uPA (1.7 +/- 0.15 ng/mg of sol protein vs 0.8 +/- 0.1 ng/mg of sol protein, P = .0015) and was associated with a reduction in thrombus size (P = .03). Urokinase overexpression did not affect the activity of MMP2, MMP9, or VEGF in the thrombus. CONCLUSION: Increasing urokinase activity within the thrombus significantly enhanced natural thrombus resolution by a fibrinolytic action. Therapeutic delivery of ad.uPA in patients may provide a novel method of treating deep vein thrombosis. CLINICAL RELEVANCE: The use of urokinase as a thrombolytic agent in the treatment of acute iliofemoral deep vein thrombosis is not suitable for all patients. This study aimed to determine whether thrombus resolution could be enhanced by upregulating urokinase expression using adenoviral gene transfer as an alternative method of therapeutic delivery. The study shows that by increasing urokinase activity within the thrombus, natural thrombus resolution can be significantly enhanced. The delivery of ad.uPA in patients may provide a novel method of treating deep vein thrombosis.

Adenoviridae↗

PubMed2005

Atomic resolution STEM analysis of defects and interfaces in ceramic materials.

Atomic resolution scanning transmission electron microscopy (STEM) analysis, in particular the combination of Z-contrast imaging and electron energy-loss spectroscopy (EELS) has been successfully used to measure the atomic and electronic structure of materials with sub-nanometer spatial resolution. Furthermore, the combination of this incoherent imaging technique with EELS allows us to correlate certain structural features, such as defects or interfaces directly with the measured changes in the local electronic fine-structure. In this review, we will discuss the experimental procedures for achieving high-resolution Z-contrast imaging and EELS. We will describe the alignment and experimental setup for high-resolution STEM analysis and also describe some of our recent results where the combined use of atomic-resolution Z-contrast imaging and column-by-column EELS has helped solve important materials science problems.

Journal Article↗

PubMed2005

Localization bias and spatial resolution of adaptive and non-adaptive spatial filters for MEG source reconstruction.

This paper discusses the location bias and the spatial resolution in the reconstruction of a single dipole source by various spatial filtering techniques used for neuromagnetic imaging. We first analyze the location bias for several representative adaptive and non-adaptive spatial filters using their resolution kernels. This analysis theoretically validates previously reported empirical findings that standardized low-resolution electromagnetic tomography (sLORETA) has no location bias. We also find that the minimum-variance spatial filter does exhibit bias in the reconstructed location of a single source, but that this bias is eliminated by using the normalized lead field. We then focus on the comparison of sLORETA and the lead-field normalized minimum-variance spatial filter, and analyze the effect of noise on source location bias. We find that the signal-to-noise ratio (SNR) in the measurements determines whether the sLORETA reconstruction has source location bias, while the lead-field normalized minimum-variance spatial filter has no location bias even in the presence of noise. Finally, we compare the spatial resolution for sLORETA and the minimum-variance filter, and show that the minimum-variance filter attains much higher resolution than sLORETA does. The results of these analyses are validated by numerical experiments as well as by reconstructions based on two sets of evoked magnetic responses.

Algorithms↗

PubMed2006

Spatial resolution dependence of DTI tractography in human occipito-callosal region.

Diffusion tensor imaging (DTI) and fiber tracking have been used to measure the fiber structural connectivity in humans in a non-invasive manner. However, low sensitivity is a principal limitation of these methods, causing a large number of possibly missing fiber tracts (FTs). Here we studied how the spatial resolution affects the sensitivity of the fiber tracing by rescaling data to different resolutions. Our data suggest that the spatial resolution can change the degree of the asymmetric cross-callosal connections in the lower visual field (loVF) compared to the upper visual field (upVF). Among connections from loVF, a larger voxel size resulted in a smaller number of FTs that was not commensurate to the number of seed points, while the number of connections from upVF was not significantly affected by variation in seeding point numbers. We conclude from our study that the spatial resolution of the acquired data will have to be taken into consideration in interpreting DTI fiber tracking data. Our results further suggest that the acquisition resolution of around 2 mm iso-voxel in the conventional DTI scheme can reconstruct the asymmetric upper and lower white matter structure in occipito-callosal region.

Adult↗

PubMed2005

Idiopathic juxtafoveal retinal telangiectasis: new findings by ultrahigh-resolution optical coherence tomography.

OBJECTIVE: To investigate the capabilities of ultrahigh-resolution optical coherence tomography (UHR OCT); to compare with the commercially available OCT standard-resolution system, StratusOCT, for imaging of idiopathic juxtafoveal retinal telangiectasis (IJT); and to demonstrate that UHR OCT provides additional information on disease morphology, pathogenesis, and management. DESIGN: Retrospective, observational, interventional case series. PARTICIPANTS: Nineteen eyes of 10 patients diagnosed with IJT in at least one eye. METHOD: All patients were imaged with UHR OCT and StratusOCT at the same visit. A subset of patients was also imaged before and after treatment of IJT. MAIN OUTCOME MEASURES: Ultrahigh- and standard-resolution cross-sectional tomograms of IJT pathology. RESULTS: Using both standard- and ultrahigh-resolution OCT, we identified the following features of IJT: (1) a lack of correlation between retinal thickening on OCT and leakage on fluorescein angiography, (2) loss and disruption of the photoreceptor layer, (3) cystlike structures in the foveola and within internal retinal layers such as the inner nuclear or ganglion cell layers, (4) a unique internal limiting membrane draping across the foveola related to an underlying loss of tissue, (5) intraretinal neovascularization near the fovea, and (6) central intraretinal deposits and plaques. In 63% of cases, the presence of abnormal vessels and a discontinuity of the photoreceptor layer correlated with visual acuity. CONCLUSIONS: Ultrahigh-resolution OCT improves visualization of the retinal pathology associated with IJT and allows identification of new features associated with it. Some of these features, such as discontinuity of the photoreceptor layer, are revealed only by UHR OCT.

Adult↗

PubMed2006

Redefining lamellar holes and the vitreomacular interface: an ultrahigh-resolution optical coherence tomography study.

OBJECTIVES: To define optical coherence tomographic (OCT) criteria for the diagnosis of a lamellar macular hole, and to increase understanding of lamellar hole pathogenesis by examining fine anatomic features using ultrahigh-resolution optical coherence tomography (UHR OCT). DESIGN: Retrospective observational case series. PARTICIPANTS: Nineteen eyes of 18 patients with lamellar holes were imaged with UHR OCT between 2002 and 2004. METHODS: A UHR OCT system was developed for use in the ophthalmology clinic. All 6 UHR OCT images for each eye imaged were examined. Lamellar holes were diagnosed based on a characteristic OCT appearance. Criteria for the OCT diagnosis of a lamellar hole were as follows: (1) irregular foveal contour; (2) break in the inner fovea; (3) intraretinal split; and (4) intact foveal photoreceptors. From 1205 eyes of 664 patients imaged with UHR OCT, and retrospectively reviewed, 19 eyes of 18 patients were diagnosed with a lamellar hole based on these criteria. All 19 eyes were also imaged with standard resolution OCT. Their charts were retrospectively reviewed. MAIN OUTCOME MEASURES: Standard and ultrahigh-resolution OCT images. RESULTS: On chart review, clinical diagnosis of a lamellar hole was made in only 7 of 19 eyes (37%). Twelve of 19 eyes (63%) had an epiretinal membrane (ERM) on clinical examination. Ten of 19 eyes (53%) had a posterior vitreous detachment. On UHR OCT, 17 of 19 eyes (89%) had ERMs. Eleven ERMs had an unusual thick appearance on UHR OCT. Due to poor visual acuity, 4 eyes underwent vitrectomy. Only 1 of 4 surgeries (25%) was visually and anatomically successful. Another eye improved visually, but a lamellar hole persisted. One eye progressed to a full-thickness macular hole preoperatively, which reopened after surgery. One eye developed a full-thickness hole postoperatively. CONCLUSIONS: The diagnosis of a lamellar hole can be made based on OCT criteria, which could be applied to both standard and ultrahigh-resolution OCT. The increased resolution of UHR OCT sheds light on the pathogenesis of the lamellar hole. Epiretinal membranes were visualized on UHR OCT in the majority of eyes. Many ERMs had an unusual thick appearance on UHR OCT, which may represent either trapped vitreous or posterior hyaloid, and may help stabilize retinal anatomy. Conversely, ERM contraction may play a role in lamellar hole formation. Vitrectomy surgery was anatomically and visually successful in only 1 of 4 patients, suggesting caution when performing vitrectomy on lamellar holes.

Aged↗

PubMed2005

Use of ultra-high-resolution data for temporal bone dissection simulation.

OBJECTIVES: For the past 5 years, our group has been developing a virtual temporal bone dissection environment for training otologic surgeons. Throughout the course of our development, a recurring challenge is the acquisition of high-resolution, multimodal, and multi-scale data sets that are used for the visual as well as haptic (sense of touch) display. This study presents several new techniques in temporal bone imaging and their use as data for surgical simulation. METHODS: At our institution (OSU), we are fortunate to have a high-field (8 Tesla) magnetic resonance imaging (MRI) research magnet that provides an order of magnitude higher resolution compared to clinical 1.5T MRI scanners. Magnetic resonance imaging has traditionally been superb at delineating soft tissue structure, and certainly, the 8T unit does indeed do this at a resolution of 100-200 microm(3). To delineate the bony structure of the mastoid and middle ear, computed tomography (CT) has traditionally been used because of the high signal-to-noise ratio delineating bone signal from air and soft tissue. We have partnered with researchers at other institutions (CCF) to make use of a "microCT" that provides a resolution of 214 x 214 x 390 micrometers of bony structure. RESULTS: This report provides a description of the 2 methodologies and presentation of the striking image data capable of being generated. See images presented. CONCLUSIONS: Using these 2 new and innovative imaging modalities, we provide an order of magnitude greater resolution to the visual and haptic display in our temporal bone dissection simulation environment.

Cadaver↗

PubMed2005

Novel omega -- 3-derived local mediators in anti-inflammation and resolution.

The integrated inflammatory response of the host is essential in health and disease. Hence, it is important to achieve a more complete understanding of the local cellular and molecular events that govern the formation and actions of local mediators that can serve as endogenous local mediators of resolution. Because these compounds in experimental animal models of inflammation can control the duration and magnitude of inflammation, knowledge of their formation and actions may provide new avenues for appreciating the molecular basis of many inflammatory diseases. The first of these endogenous local counterregulators recognized were the lipoxins, which are trihydroxytetraene-containing mediators generated from arachidonic acid during cell-cell interactions via transcellular biosynthesis. Because this circuit of lipoxin formation appears to be of physiological relevance in resolution, therapeutic modalities targeting this and related systems should allow for the development of novel therapeutic agents (i.e., agonists of the important cellular and physiological responses required for timely resolution). This review offers a general overview of recent advances from studies by the author and colleagues on the biosynthesis and bioactions of the novel anti-inflammatory lipid mediators, resolvins, docosatrienes, and neuroprotectins as well as their endogenous aspirin-triggered epimeric counterparts. These previously unappreciated families of lipid-derived mediators were originally isolated from experimental murine models of acute inflammation captured during the natural spontaneous resolution phase. They possess anti-inflammatory, pro-resolving, and protective properties. Inappropriate resolution mechanism(s) may underlie our current appreciation of the inflammatory phenotype(s) that characterizes many prevalent human diseases where inflammation is now acknowledged to play an important role in the disease process. Moreover, these new pathways give opportunities to appreciate the complex roles of neutrophils in the generation of potent host protective lipid mediators that may be harnessed for the design of novel treatments for a wide range of diseases where inflammation contributes to the pathophysiology of the disorder.

Animals↗

PubMed2003

Sub-Angstrom resolution enzyme X-ray structures: is seeing believing?

Recent technical advances in crystallographic analysis, particularly highly focused and high brilliance synchrotron beam lines, have significantly improved the resolutions that are attainable for many macromolecular crystal structures. The Protein Data Bank (http://www.rcsb.org/pdb/) contains an increasing number of atomic resolution structures, which are providing a wealth of structural information that was not previously visible in lower resolution electron density maps. Here, we review the importance of visualizing hydrogen atoms and multiple sidechain conformations or anisotropy, as well as substrate strain, at sub-Angstrom resolution. The additional structural features that are visible in the electron density maps as a result of atomic resolution data provide a better understanding of the catalytic mechanisms of cholesterol oxidase, ribonuclease A, beta-lactamase, serine proteases, triosephosphate isomerase and endoglucanase.

Binding Sites↗

PubMed2006

Enhancement of resolution in core-loss and low-loss spectroscopy in a monochromated microscope.

The significant enhancement of the energy resolution in the new generation of commercially available monochromated transmission electron microscopes presents new challenges in term of selecting the correct experimental conditions and understanding the various effects that can potentially influence the quality of the EELS data. In this respect we investigated the effect of point spread function of the detector and spectrum-diffraction mixing on the energy resolution and the intensity of the zero loss peak tails. Alternative approaches to improve the energy resolution by mathematical methods have been tested. By using a simple and commonly available test case (Si L(2,3) edges) we assessed the efficiency of the deconvolution algorithms to improve the resolution. The results show that the deconvolution is not always successful in improving the resolution of the core loss EELS data and the results may not always be reliable. Contrary to this, the application of the Richardson-Lucy deconvolution algorithm on some bandgap measurements data appears to be very effective. The procedure proved successful in removing the contribution of the zero-loss peak tails and allows an easier access to spectroscopic information starting at energy losses as low as of 0.5 eV with monochromated spectra and 1 eV with the non-monochromated spectra.

Journal Article↗

PubMed2002

Effect of preinfarction angina pectoris on ST-segment resolution after primary coronary angioplasty for acute myocardial infarction.

The presence of preinfarction angina has been shown to exert a favorable effect on left ventricular function after acute myocardial infarction (AMI). Whether or not preinfarction angina is beneficial for myocardial tissue reperfusion, however, remains to be determined. We sought to evaluate the influence of preinfarction angina on resolution of ST-segment elevation, which could be affected by microcirculatory damage after recanalization therapy. We studied 96 patients with a first AMI in whom Thrombolysis In Myocardial Infarction (TIMI)-3 flow in the infarct-related artery was established by primary angioplasty. Percent reduction in the sum of ST elevation from baseline to 1 hour after angioplasty (percent delta summation operator ST) was examined. Poor ST resolution, defined as percent delta summation operator ST <50%, was observed in 25 patients, who had a worse clinical outcome, larger infarct size, and poorer left ventricular function. On multivariate analysis, the absence of preinfarction angina, as well as anterior wall infarction, were major independent predictors of poor ST resolution, whereas age, sex, coronary risk factors, ischemic time, Killip class on admission, multivessel disease, initial TIMI flow grade, and extent of collaterals were not significant. Patients with preinfarction angina had a greater degree of ST-segment resolution than those without angina (71 +/- 21% vs 49 +/- 43%, p = 0.02). Additional ST elevation after reperfusion was noted exclusively in patients without preinfarction angina (p = 0.02). Preinfarction angina is associated with a greater degree of ST-segment resolution in patients with TIMI-3 flow after primary angioplasty, suggesting a protective effect of preinfarction angina against microcirculatory damage after reperfusion.

Adult↗

PubMed1997

Prognostic value of slow resolution of ST-segment elevation following successful direct percutaneous transluminal coronary angioplasty for recovery of left ventricular function.

Our objective was to investigate the significance of the slow resolution of ST-segment elevation following a successful direct percutaneous transluminal coronary angioplasty (PTCA). ST-segment elevations were calculated from electrocardiograms recorded before PTCA and 1 hour after reperfusion. Forty-nine patients experiencing their first anterior acute myocardial infarction and who had undergone direct PTCA were classified into 3 groups: 17 patients with rapid ST resolution (group I), 23 patients with persistent ST elevation (group II), and 9 patients with ST reelevation (group III). Left ventricular function was evaluated by using single-plane cineventriculography performed in the acute stage, at discharge, and 4 months later. Peak creatine kinase activity was significantly increased: group III (4,046 +/- 634 IU), group II (3,336 +/- 772 IU), and group I (2,410 +/- 994 IU); p <0.05. Ejection fraction and regional wall motion in the acute stage were identical in each group. However, they were significantly higher in group I (67 +/- 6%, -1.01 +/- 0.30), followed by group II (56 +/- 6%, -1.90 +/- 0.41) and group III (38 +/- 7%, -2.79 +/- 0.46); p <0.01 4 months later. Multiple regression analysis revealed that the ST resolution was the only significant variable that indicated the recovery of regional wall motion. A good linear correlation was documented between the ST resolution and the recovery of regional wall motion. We concluded that a slow ST resolution after successful direct PTCA is a negative predictor of recovery of left ventricular function, especially when ST reelevation is evident.

Aged↗

PubMed1992

High-pass resolution perimetry in eyes with ocular hypertension and primary open-angle glaucoma.

We analyzed the results of high-pass resolution perimetry on normal eyes, eyes with ocular hypertension, and eyes with primary open-angle glaucoma. The subjects were matched for age and lens density. We controlled for refraction, visual acuity, pupil size, miotic medications, and learning effects. Under these conditions the glaucomatous eyes showed a significant reduction in overall resolution threshold compared to both normal (P less than or equal to .01) and hypertensive eyes (P less than .01). The hypertensive eyes were not significantly different from normal. Standard increment threshold fields and high-pass resolution visual fields had an agreement of abnormality of 67%. Resolution perimetry showed a 92% agreement with standard perimetry in the location of the defect, when the defect was apparent on both tests. These results indicated that resolution perimetry may be useful for diagnosis and management of primary open-angle glaucoma.

Aged↗

PubMed1995

Comparison of high-pass resolution perimetry and standard automated perimetry in glaucoma.

PURPOSE: We sought to ascertain whether high-pass resolution perimetry would provide results comparable to those of standard perimetry. METHODS: Thirty-four eyes with primary open-angle glaucoma, 37 eyes suspected of having glaucoma, and 36 normal control eyes were matched for age and lens density. We controlled for refraction, pupil size, and learning effects. Standard and ring visual fields were obtained with the Humphrey perimeter and the Frisén ring perimeter, respectively. Each test was judged according to the Glaucoma Hemifield Test (a statistical visual field analysis method) to be outside normal limits (abnormal) or not outside normal limits (normal or borderline). RESULTS: Under these conditions, both tests identified 19 of 34 (56%) glaucoma eyes as outside normal limits. High-pass resolution perimetry determined that 34 of 36 (94%) normal eyes were not outside normal limits; standard perimetry determined that all 36 normal eyes were not outside normal limits. High-pass resolution perimetry determined 12 of 37 (32%) eyes that were glaucoma suspects were outside normal limits; standard perimetry determined three of the 37 (8%) glaucoma suspect eyes were outside normal limits. Overall agreement between the two tests was 65%. CONCLUSION: With the Glaucoma Hemifield Test, high-pass resolution perimetry was comparable to standard perimetry in sensitivity and specificity, and identified a slightly higher percentage of patients at risk for glaucoma as abnormal. These results suggest that high-pass resolution perimetry should continue to be explored as an alternative to standard perimetry for the diagnosis and treatment of glaucoma.

Female↗

PubMed1988

Changes in the sarcoplasmic reticulum membrane profile induced by enzyme phosphorylation to E1 approximately P at 16 A resolution via time-resolved x-ray diffraction.

Time-resolved x-ray diffraction studies of the isolated sarcoplasmic reticulum (SR) membrane have provided the difference electron density profile for the SR membrane for which the Ca2+ ATPase is transiently trapped exclusively in the first phosphorylated intermediate state, E1 approximately P, in absence of detectable enzyme turnover vs. that before ATP-initiated phosphorylation of the enzyme. These diffraction studies, which utilized the flash-photolysis of caged ATP, were performed at temperatures between 0 and -2 degrees C and with a time-resolution of 2-5 s. Analogous time-resolved x-ray diffraction studies of the SR membrane at 7-8 degrees C with a time resolution of 0.2-0.5 s have previously provided the difference electron density profile for the SR membrane for which the Ca2+ ATPase is only predominately in the first phosphorylated intermediate state under conditions of enzyme turnover vs. that before enzyme phosphorylation. The two difference profiles, compared at the same low resolution (approximately 40 A), are qualitatively similar but nevertheless contain some distinctly different features and have therefore been analyzed via a step-function model analysis. This analysis was based on the refined step-function models for the two different electron density profiles obtained independently from x-ray diffraction studies at higher resolution (16-17 A) of the SR membrane before enzyme phosphorylation at 7.5 and -2 degrees C. The step-function model analysis indicated that the low resolution difference profiles derived from both time-resolved x-ray diffraction experiments arise from a net movement of Ca2+ ATPase protein mass from the outer monolayer to the inner monolayer of the SR membrane lipid bilayer. The conserved redistribution of this protein mass is however somewhat different for the two cases, especially at the extravesicular membrane surface containing the Ca2+ATPase "headpiece." However, the conserved redistribution of protein mass within the SR membrane lipid bilayer common to both cases is clearly due to E1~P formation.

Animals↗

PubMed2006

[Intraoperative intact parathyroid hormone determination as a predictive factor of hyperparathyroidism resolution].

INTRODUCTION: The objectives of this study were: a) to evaluate the effectiveness of intraoperative intact parathyroid hormone (PTHi) determination as a marker of hyperparathyroidism resolution; b) to establish the minimum number of blood samples required; and c) to determine whether cervical manipulation increases baseline PTHi levels. PATIENTS AND METHOD: We performed a prospective study in 45 patients. Three intraoperative blood PTHi determinations were performed: at baseline and at 10 and 25 minutes after excising the lesion. To analyze the effects of cervical manipulation, in 19 patients, 2 further determinations were made after 2 minutes of massage on both sides of the neck. A decrease of > 50% in PTHi values between postexeresis samples and the baseline sample (gradient > 50%) was used as diagnostic and therapeutic criteria and normalization of calcemia was used as a criteria for complete resolution. RESULTS: Whenever the lesion causing hyperparathyroidism was extirpated, PTHi levels decreased at 10 and 25 minutes after exeresis. This decrease was predictive of complete resolution when the gradient was > 50. Cervical manipulation (massage) did not increase PTHi values. In patients with complete resolution, blood calcium levels also returned to normal. CONCLUSIONS: 1. Intraoperative PTHi determination with a gradient > 50 is an excellent prognostic marker of resolution. 2. Only 2 PTHi samples are required: one at baseline and another at 10 minutes after exeresis. 3. Preoperative cervical manipulation does not increase PTHi values.

Adult↗

PubMed2000

High-performance liquid chromatographic resolution of reverse isomers of 1,2-diacyl-rac-glycerols as 3,5-dinitrophenylurethanes.

The resolution of reverse isomers remains a major unsolved problem in glycerolipid chromatography. We have investigated the separation of the reverse isomers of 1,2-diacyl-rac-glycerols under a variety of high-performance liquid chromatography (HPLC) conditions. The reverse isomers of diacylglycerols having various pairs of acyl groups including short and highly unsaturated chains, which were prepared by partial Grignard degradation of the corresponding triacylglycerols, were chromatographed as 3,5-dinitrophenylurethanes. Excellent resolution was achieved for the reverse isomers of very different pairs of acyl groups, such as acetate-palmitate and docosahexaenoate-palmitate, by chiral-phase HPLC on columns containing (R)- and (S)-1-(1-naphthyl)ethylamine polymeric phases, reversed-phase HPLC on a highly efficient C18 column (4 microm particle size) and silver ion HPLC on a silver loaded cation-exchange column. The chiral-phase HPLC also permitted complete enantiomer resolution for all the reverse isomers examined. No satisfactory resolution by any of the HPLC methods, however, was obtained for the reverse isomers possessing minor differences in chain lengths and degree of unsaturation, such as laurate-palmitate and oleate-linoleate. The limitations of resolution and characteristics of elution are described.

Chromatography, High Pressure Liquid↗

PubMed2003

Net analyte signal as a deconvolution-oriented resolution criterion in the optimisation of chromatographic techniques.

The performance of two multivariate calibration measurements, multivariate selectivity (SEL(s)) and scalar net analyte signal (scalar NAS), as chromatographic objective functions (COFs), was investigated. Since both assessments are straightforwardly related to the quantification of analytes in the presence of interferents, they were expected to confer new features in the optimisation of compound resolution, not present in conventional assessments. These capabilities are especially interesting in situations of low resolution, where peak deconvolution becomes an attractive alternative. For comparison purposes, chromatographic resolution (R(s)) and peak purity (p(s)) were used as reference COFs. In order to correlate COFs with the probability of deconvolution error, an artificial peak crossing was used to generate 73 different peak arrangements, which were deconvolved using three different methods. SEL(s) exhibited the best correlation, which allowed predicting properly the risk of obtaining inaccurate deconvolutions. The optimisation of a poorly resolved mixture of 16 aromatic compounds by reversed-phase liquid chromatography with methanol-water and acetonitrile-water mobile phases was examined to investigate the differences in performance among the resolution criteria. In situations like these, SEL(s) tends to consider acceptable mobile phase compositions with partial coelution, which permits however the deconvolution with low errors. In contrast, p(s) selects compositions where the resolution of some compounds is sacrificed to enhance the separation of others. Scalar NAS was not so favourable as expected, since it depends on sampling frequency and peak widening. SEL(s) was not affected by these factors.

Acetonitriles↗