Column Dimensions Research Articles

Online polar two phase countercurrent chromatography×high performance liquid chromatography for preparative isolation of polar polyphenols from tea extract in a single step.

Herein, we report an on-line two-dimensional system constructed by counter-current chromatography (CCC) coupling with preparative high-performance liquid chromatography (prep-HPLC) for the separation and purification of polar natural products. The CCC was used as the first dimensional isolation column, where an environmental friendly polar two-phase solvent system of isopropanol and 16% sodium chloride aqueous solution (1:1.2, v/v) was introduced for low toxicity and favorable resolution. In addition, by applying the stop-and-go flow technique, effluents pre-fractionated by CCC was further purified by a preparative column packed with octadecyl silane (ODS) as the second dimension. The interface between the two dimensions was comprised of a 6-port switching valve and an electronically controlled 2-position 10-port switching valve connected with two equivalent holding columns. To be highlighted here, this rationally designed interface for the purpose of smooth desalination, absorption and desorption, successfully solved the solvent compatibility problem between the two dimensional separation systems. The present integrated system was successfully applied in a one-step preparative separation and identification of 10 pure compounds from the water extracts of Tieguanyin tea (Chinese oolong tea). In short, all the results demonstrated that the on-line 2D CCC×LC method is an efficient and green approach for harvesting polar targets in a single step, which showed great promise in drug discovery.

일반강도 슬래브로 간섭받은 모서리 기둥의 유효압축강도

In this study, a prediction model for the effective compressive strength of corner columns with intervening normal strength concrete slabs was developed. A structural analogy between high-strength concrete column-normal strength concrete slab joint and brick masonry was used to develop the prediction model. In addition, the aspect ratio of slab thickness to column dimension was considered in the models. The reliability of the new prediction model was evaluated by comparison with experimental results and its superiority was demonstrated by comparison with previous models proposed by design codes and other researchers. As a result, with average test-to-predicted ratios of 1.09, a standard deviation of 0.15, the newly developed equation provided superior predictions in terms of accuracy and consistency over all of the existing effective strength prediction approaches including KCI structural concrete design code (2012).

Experimental behavior of hybrid FRP–concrete–steel double-skin tubular columns under combined axial compression and cyclic lateral loading

Hybrid FRP–concrete–steel double-skin tubular columns (DSTCs) are a new form of hybrid columns, consisting of an outer tube made of fiber reinforced polymer (FRP) and an inner tube made of steel, with the space between filled with concrete. In hybrid DSTCs, the three constituent materials are optimally combined to achieve several advantages not available with existing columns, including their excellent corrosion resistance and seismic performance. Although two existing studies have examined the seismic performance of circular hybrid DSTCs, they have been limited to normal strength concrete, small column dimensions, and small void ratios (ratios between the inner diameter and the outer diameter of the annular concrete section). Against this background, this paper presents the first experimental study on hybrid DSTCs filled with HSC subjected to axial compression in combination with cyclic lateral loading. A relatively large column section (with a diameter of 300mm) was chosen to allow reliable experimental modeling of real columns. The test results indicate that hybrid DSTCs possess excellent ductility and seismic resistance even when high strength concrete with a cylinder compressive strength of around 120MPa is used; column damage is concentrated in a small plastic hinge region near the column bottom end; and the performance of hybrid DSTCs can be enhanced by filling the inner void in the plastic hinge region. The test results provide valuable data needed for the formulation and verification of a theoretical model for the hysteric behavior of hybrid DSTCs, particularly when they are filled with HSC.

SIMULATION MODEL PROPOSED FOR ESTIMATION OF MODAL DISPLACEMENT OF RC BUILDING LOCATED IN SEISMIC ZONE-V (IS-1893-2002) FROM KNOWN PARAMETERS

The seismic analysis and design of reinforced concrete (RC) frames is still an unresolved issue due to its complex behavior as the performance of RC building is linked to the features of the structural system, which have many influencing parameters. In this study, an attempt has been made to investigate the displacement scenario of RC residential building seismically located in Zone-V due to the influence of some basic parameters (column dimension, beam dimension, grade of concrete, floor height and seismic weight) in order to obtain a relation which could be used to estimate the expected lateral displacement owing to those selected parameters. In this study, a total of 297 RC buildings designed as per the Indian codal provisions [IS-1893-2002] were analyzed by linear static method using SAP2000 by varying selected and feasible input parameters chosen. The resulting displacements for the change of each parameter were obtained and finally a generalized equation relating the expected displacement as a function of those selected parameters was established using the regression method. The results of the comparison between the displacements obtained from analysis with that of the equation so formed shows that the proposed relation can be used directly to determine the expected displacement with high reliability.

Dimensions and aspect ratios of natural ice crystals

Abstract. During the 2006 Tropical Warm Pool International Cloud Experiment (TWP-ICE) in the tropics, the 2008 Indirect and Semi-Direct Aerosol Campaign (ISDAC) in the Arctic, and the 2010 Small PARTicles In CirrUS (SPARTICUS) campaign at mid-latitudes, high-resolution images of ice crystals were recorded by a Cloud Particle Imager at temperatures (T) between −87 and 0 °C. The projected maximum dimension (D'), length (L'), and width (W') of pristine columns, plates, and component bullets of bullet rosettes were measured using newly developed software, the Ice Crystal Ruler. The number of bullets in each bullet rosette was also measured. Column crystals were further distinguished as either horizontally oriented columns or columns with other orientations to eliminate any orientation effect on the measured dimensions. The dimensions and aspect ratios (AR, the dimension of the major axis divided by the dimension of the minor axis) of crystals were determined as functions of temperature, geophysical location, and type of cirrus. Dimensions of crystals generally increased with temperature. Columns and bullets had larger dimensions (i.e., W') of the minor axis (i.e., a axis) for a given dimension (i.e., D' orL') of the major axis (i.e., c axis), and thus smaller AR, as T increased, whereas this trend did not occur for plate crystals. The average number of branches in bullet rosettes was 5.50 ± 1.35 during three campaigns and 6.32 ± 1.34 (5.46 ± 1.34; 4.95 ± 1.01) during TWP-ICE (SPARTICUS; ISDAC). The AR of bullets increased with the number of branches in bullet rosettes. Most dimensions of crystals and ARs of columnar crystals measured during SPARTICUS were larger than those measured during TWP-ICE and ISDAC at −67 < T < -35 °C and at −40 < T < −15 °C, respectively. The relative occurrence of varying pristine habits depended strongly on cirrus type (i.e., anvil or non-anvil clouds), with plates especially occurring more frequently in anvils. The L–W relationships of columns derived using current data exhibited a strong dependence on temperature; similar relationships determined in previous studies were within the range of the current data.

An approach to enhance pnetCDF performance in environmental modeling applications

Abstract. Data intensive simulations are often limited by their I/O (input/output) performance, and "novel" techniques need to be developed in order to overcome this limitation. The software package pnetCDF (parallel network Common Data Form), which works with parallel file systems, was developed to address this issue by providing parallel I/O capability. This study examines the performance of an application-level data aggregation approach which performs data aggregation along either row or column dimension of MPI (Message Passing Interface) processes on a spatially decomposed domain, and then applies the pnetCDF parallel I/O paradigm. The test was done with three different domain sizes which represent small, moderately large, and large data domains, using a small-scale Community Multiscale Air Quality model (CMAQ) mock-up code. The examination includes comparing I/O performance with traditional serial I/O technique, straight application of pnetCDF, and the data aggregation along row and column dimension before applying pnetCDF. After the comparison, "optimal" I/O configurations of this application-level data aggregation approach were quantified. Data aggregation along the row dimension (pnetCDFcr) works better than along the column dimension (pnetCDFcc) although it may perform slightly worse than the straight pnetCDF method with a small number of processors. When the number of processors becomes larger, pnetCDFcr outperforms pnetCDF significantly. If the number of processors keeps increasing, pnetCDF reaches a point where the performance is even worse than the serial I/O technique. This new technique has also been tested for a real application where it performs two times better than the straight pnetCDF paradigm.

Failure Analysis and Damage Assessment of RC Columns under Close-In Explosions

AbstractBlast loads acting on structural components under close-in explosions are nonuniform; therefore, the damage to structural members under such blast loads is local and the failure mechanism is more complex as compared with that of distance explosions. Because of the lack of an accurate blast load model, a precise damage analysis method, an efficient damage assessment method, and practical protective measures, the blast-resistant design of structural members under close-in explosions faces great challenges. In this paper, a fluid-solid coupling numerical method is proposed and then used to investigate the failure mechanism of reinforced concrete (RC) columns under close-in explosions. The results show that local failure, such as crushing, cratering, and spall of concrete, is more likely to happen when the RC column is subjected to close-in blast loads. Parametric studies are carried out to investigate the influences of column dimensions and the reinforcement ratio on the damage degree of RC columns. ...

DEVELOPMENT OF HYDROCARBON GAS CAPTURE UNIT FROM THE RESERVOIRS

Petroleum products storage systems, consisting mainly of reservoir parks, play an important role in the petroleum refining and petrochemical industries. There is continuous shipment of finished products from crude oil distillation plants in reservoir parks. Part of primary processing products is used as the raw material for secondary processes, such as catalytic cracking, catalytic reforming, visbreaking and other smooth functioning, as well as the entire enterprise, is ensured by the presence of reservoir park. The main equipment of reservoir parks is vertical steel cylindrical reservoirs using for receiving, keeping and loading of gasoline, kerosene, diesel fuel, vacuum gas oil, fuel oil and other petroleum products. In the operation of reservoir park losses occur from evaporation of petroleum products. As a result, emissions of hydrocarbon gases through the respiratory valves cause significant harm to the environment. Problem solving is provided with the variant of hydrocarbon gas capture unit from the reservoirs constituting a system for the collection, storage and shipment. The work analyzes petroleum products losses which occur when stored in reservoirs. On the basis of the computer simulation method there was created a technological model in the program Petro SIM Express, which identified the main dimensions of the absorption column. The dependencies of the degree of recovering hydrocarbon gases (HCG) from the diesel fuel consumption, its temperature, as well as the concentration of hydrocarbon gases in the mixture of air and gasoline vapors are obtained. The volume of capacitance E-1 for diesel fuel is determined. Equipping the unit will not require significant capital expenditures as the equipment can be used from the reserve of the enterprise or made at the machinery and repair plant. The application of the hydrocarbon gas capture unit allows to a considerable extent to solve the problem of irrecoverable losses of petroleum products stored in the tank farm, as well as to improve the environmental situation of both the enterprise and surrounding areas.

Numerical Simulation for Predicting Fire Behavior of Axially Loaded Circular Concrete Filled Steel Tubular Columns

The present study investigates the behavior of axial loaded circular concrete filled hollow steel section (CFHSS) columns. A nonlinear finite element model using ABAQUS program was developed to investigate the fire behavior of the inspected columns from previous fire tests. The study variables include column dimensions, steel section wall thickness, concrete strength, concrete types (plain or reinforced), and fire protection thickness. The comparison indicated that the results obtained from the model were within acceptable limit of accuracy of 15%. A sensitivity study was carried out to investigate the influence of the output of the numerical model including the Poisson’s ratio of concrete, thermal conductance at the steel-concrete interface, frictional contact at steel-concrete interface, and imperfection buckling of columns. Based on the sensitivity analysis, several modelling suggestions were given in this paper which will be beneficial for further study.

Comment on "Observation and modelling of HO<sub>x</sub> radicals in a boreal forest" by Hens et al. (2014)

Though as a researcher one is always happy when peers find one’s work useful and accordingly cite it, it is unfortunate when the respective paper is cited incorrectly. Hens et al. (2014) write “Studies on oxidation processes in monoterpene–dominated environments are rare. Direct OH reactivity measurements in a boreal forest, conducted by Sinha et al. (2008), and a box model study investigating the OH reactivity budget (Mogensen et al., 2011) revealed a significant fraction of ‘unknown OH reactivity’.” Firstly, the reference of Sinha et al. (2008) must be an error, since that refers to a publication about the method development of the comparative reactivity method (CRM) together with first field tests conducted in the tropical rainforest of Suriname and the urban atmosphere of Mainz – but not in a boreal forest. We assume that Hens et al. (2014) instead are thinking of the paper by Sinha et al. (2010). Further, it is correct that Mogensen et al. (2011) found a large fraction of unaccounted OH reactivity; however, they did not reach that conclusion using a box model. Instead they presented the first model study of the total OH reactivity in a boreal forest using a one-dimensional column model with near-explicit chemistry (Boy et al., 2011; Mogensen et al., 2011). There exist earlier publications where the OH reactivity has been addressed using a 1-D model; for example, the OH loss has been simulated with respect to certain primary emitted organic compounds (e.g. Stroud et al., 2005). By including the dimension of the entire column of the boundary layer, we are capable of providing valuable information. For example, as shown in Mogensen et al. (2011), the reactivity of OH has a distinct vertical profile, which is obviously not captured by a box model. Due to practical limitations, one can only measure the reactivity of OH (and other parameters of any other compound) at one or a few points in space. To our knowledge, at the time of publication of Mogensen et al. (2011), there existed no publications describing that the OH reactivity had been measured at more than one height simultaneously at one site. Mao et al. (2012) had conducted such experiments in 2009; however, the article appeared later than Mogensen et al. (2011). Another exception is the aircraft measurements conducted by Mao et al. (2009); however those measurements did not capture the lowest part of the boundary layer. Mogensen et al. (2011) therefore gave the first hints about how the space-dependent canopy emission and boundary layer meteorology could affect the reactivity in a boreal forest. Hereby we got the first glimpse of how the reactivity of OH could look outside of that one measured height. After publication of Mogensen et al. (2011), several measurement and modelling papers have followed investigating the vertical dimension of the OH reactivity (e.g. Mao et al., 2012; Pratt et al., 2012; Hansen et al., 2014).

Reliability Analysis of RC Columns and Frame with FRP Strengthening Subjected to Explosive Loads

Some structures, both military and civilian, might experience explosive loads during their service life. Owing to high uncertainties in blast load predictions and structural parameters, accurate assessment of the performances of structures under explosion loads is a challenging task. For example, a number of experimental studies using fiber-reinforced plastic (FRP) strengthening of RC structures have been reported in the literature. Most of these studies demonstrate that FRP strengthening is effective in increasing the blast load–carrying capacities of RC structures. However, significant variations in the effectiveness of FRP strengthening have also been observed owing to the large uncertainties in blast loading, RC and FRP material properties, and workmanship in preparing the test specimens and conducting experimental tests. Very few studies that take into consideration these uncertainties in analyzing the effectiveness of FRP strengthening of RC structures on blast loading resistance can be found in the literature. This study performs a reliability analysis to assess the performance of RC columns with or without FRP strengthening in resisting blast loads. Statistical variations of blast loading predictions derived in a previous study are adopted in this study. To define structural performance, pressure-impulse (P-I) curves with a damage criterion on the basis of axial load-carrying capacity that were developed in previous studies for RC columns without strengthening or with FRP strip, FRP wrap, or both FRP strip and wrap strengthening are used. Considering the uncertainties in blast loading predictions and RC column and FRP material properties and dimensions, limit-state functions corresponding to different damage levels of RC columns with or without FRP strengthening are formulated. The statistical variations of blast loading, RC column dimension, longitudinal and transverse reinforcement ratio, and concrete, steel, and FRP material strength and FRP thickness are considered. The failure probabilities of RC columns corresponding to different damage levels with or without FRP strengthening are calculated. The effectiveness of FRP strengthening on the RC column’s blast loading resistance capacities is discussed. The importance of considering the random fluctuations on blast loading and RC column parameters in assessing the blast loading effect on RC columns is demonstrated. A structural system reliability analysis is also carried out to examine the probability of structural collapse as a result of blast loading applied to the front of an example two-span multistory RC frame. The results obtained in this study demonstrate the effectiveness of FRP strengthening on structure protection and can also be used to assess RC structure performance under blast loadings.

High Energy Pipe Break analysis for the pipelines of a nuclear power plant: No standard case

The aim of this study is to show the application of the High Energy Pipe Break (HEPB) a level 3 methodology analysis, applied to the study of the pipelines of a standard pressurized water reactor. In particular, in this paper, a numerical approach for simulating the pipe impact against a reinforced concrete column is provided in order to evaluate a correct design of the column in terms of steel rebar and column dimension. Moreover, to finalize the problem, the coupled analysis (thermofluidynamic and mechanical) to calculate a real thrust force on the pipe is provided and the results of the new numerical analysis is shown.

A combination of computational fluid dynamics (CFD) and adaptive neuro-fuzzy system (ANFIS) for prediction of the bubble column hydrodynamics

This paper shows a combination of computational fluid dynamics (CFD) and adaptive neuro-fuzzy inference system (ANFIS) to propose a new viewpoint for multiphase flow modeling, including the accuracy of soft computing techniques in the prediction of a three dimensional (3D) bubble column reactor. Since there are some difficulties (i.e., high computational time in numerical methods and expensive equipment in experimental techniques) in predicting bubble column reactors, particularly at different column locations and various operation conditions, soft computing methods can be developed as a favorable replacement for conventional measurement and prediction techniques. This study employs CFD beside the ANFIS method to simulate the bubble column hydrodynamics for homogeneous regime. Existing experimental, numerical and correlation results in the previous studies have been used to validate the implementation of the current CFD investigation. The liquid velocity, turbulent kinetic energy and gas hold-up (air volume fraction) have been used as input training data in the ANFIS model. The ANFIS results have been also compared with the CFD results, using root-mean-square error (RMSE), coefficient of determination (R2) and Pearson's coefficient (r). Both CFD and ANFIS prediction methods illustrate that, towards the bubble column center, the gas hold-up is higher than wall regions. The results show that ANFIS is a robust method to predict bubble column hydrodynamics properties.

Advancement in stationary phase for peptide separation helps in protein identification: Application to atheroma plaque proteomics using nano-chip liquid chromatography and mass spectrometry

In the last decades, proteomics has largely progressed. Mass spectrometry and liquid chromatography (LC) are generally used in proteomics. These techniques enable proper separation of peptides and good identification and/or quantification of them. Later, nano-scaled liquid chromatography, improvements of mass spectrometry resolution and sensitivity brought huge advancements. Enhancements in chemistry of chromatographic columns also brought interesting results.In the present work, the potency of identification of proteins by different nano-chip columns was studied and compared with classical LC column. The present study was applied to cardiovascular field where proteomics has shown to be highly helpful in research of new biomarkers. Protein extracts from atheroma plaques were used and proteomics data were compared. Results show that fewer spectra were acquired by the mass spectrometer when nano-chip columns were used instead of the classical ones. However, approximately 40% more unique peptides were identified by the recently optimized chip named Polaris-HR-chip-3C18 column, and 20% more proteins were identified. This fact leads to the identification of more low-abundance proteins. Many of them are involved in atheroma plaque development such as apolipoproteins, ceruloplasmin, etc.In conclusion, present data shows that recent developments of nanoLC column chemistry and dimensions enabled the improved detection and identification of low-abundance proteins in atheroma plaques. Several of them are of major interest in the field of cardiovascular disease.

Simultaneous determination of bromate, chlorite and haloacetic acids by two-dimensional matrix elimination ion chromatography with coupled conventional and capillary columns

A new, highly sensitive and reliable two-dimensional matrix elimination ion chromatography (IC) method was developed for simultaneous detection of bromate, chlorite and five haloacetic acids. This method combined the conventional IC in first dimension with capillary IC in the second dimension coupled with suppressed conductivity detection. The first dimension utilizes a high capacity column to partially resolve matrix from target analytes. By optimizing the cut window, the target analytes were selectively cut and trapped in a trap column through the use of a six-port valve, while the separated matrix were diverted to waste. The trapped target analytes were delivered on to the capillary column for further separation and detection. Temperature programming was used to improve selectivity in second dimension column to obtain complete resolution of the target analytes. Compared to the performance of one-dimensional IC, the two-dimensional approach resulted in a significant increase in sensitivity for all target analytes with limit of detection ranging from 0.30 to 0.64μg/L and provided more reliable analysis due to second column confirmation. Good linearity was obtained for all the target analytes with correlation coefficients >0.998. The proposed method was successfully applied to the determination of oxyhalides and haloacetic acids in various matrices with recoveries ranging from 90 to 116% and RSD less than 6.1%. The method allows direct injection of samples and the use of columns with different selectivity, thus significantly reduces the level of false positive results. The method is fully automated and simple, making it practical for routine monitoring of water quality. The satisfactory results also demonstrated that the two-dimensional matrix elimination method coupled with capillary IC is a promising approach for detection of trace substances in complex matrices.

Simultaneous determination of vitamins A, D3 and E in infant formula and adult nutritions by online two-dimensional liquid chromatography

A rapid method for the simultaneous determination of vitamins A, D3 and E in infant formula and adult nutritions has been developed using online two-dimensional liquid chromatography (2D-LC). First of all, C8 and polar embedded C18 columns were chosen as the first and second dimensional column respectively according to hydrophobic-subtraction model, which constituted excellent orthogonal separation system. The detection wavelengths were set at 263 nm for vitamin D3, 296 nm for vitamin E and 325 nm for vitamin A. The purification of vitamin D3 and quantifications of vitamins A and E were completed simultaneously in the first dimensional separation using the left pump of Dual Gradient LC (DGLC) with methanol, acetonitrile and water as mobile phases. The heart-cutting time window of vitamin D3 was confirmed according to the retention time of vitamin D3 in the first dimensional separation. The elute from the first dimensional column (1-D column) which contained vitamin D3 was collected by a 500 µL sample loop and then taken into the second dimensional column (2-D column) by the right pump of DGLC with methanol, acetonitrile and water as mobile phases. The quantification of vitamin D3 was performed in the second dimensional separation with vitamin D2 as internal standard. At last, this method was applied for the analysis of the three vitamins in milk powder, cheese and yogurt. The injected sample solution with no further purification was pre-treated by hot-saponification using 1. 25 kg/L KOH solution and extracted by petroleum ether solvent. The recoveries of vitamin D3 spiked in all samples were 75.50%-85.00%. There was no statistically significant difference for the results between this method and standard method through t-test. The results indicate that vitamins A, D3 and E in infant formula and adult fortified dairy can be determined rapidly and accurately with this method.

Investigation of the Effect of Structural System on the Behaviour of the Behavior of the Buildings with Sheer-Wall Frame System

This research aims to study and to compare structural members load carrying capacity for frame structure and shear wall- frame structure. Comparisons are made for different column dimensions and different locations of shear walls. Commercial software package, ideCAD Static 7, is employed for dynamic modal analysis of structures.

Effect of column size on punching shear behaviour of multi panel RC flat plate

In flat plate floor system, due to variation of slab panel and loading pattern, various sizes of column within same thickness of slab are designed. Variation of column size is also used in high rise building in different floors within same type flat plate. In both cases punching shear capacity of flat plate is calculated by the same type of code equation. Code equations for punching strength of concrete do not consider column size or dimension as a parameter. In the present study, the effect of column size in punching shear behaviour of flat plate is identified by numerical finite element study of multi-panel flat plate. The load carrying capacity of multi panel flat plate having various column sizes is also compared with various codes of prediction. Normalised punching shear strength decreases with increase of column size is obtained in this study.

Evolution and Composition of the Traditional Timber Structure Column Bases in the Southern Region of China - A Case Study of Shaoxing City

As a very unique structural component of traditional timber architecture, column base is a natural combination of stone carving technology and timber structure system, from which we can understand the broad and profound traditional architectural culture. In This paper, the emergence and evolution of the column bases art history was firstly described to analyze the factors that promote the development and changes of column bases. Moreover, Finally, the dimension of column bases was introduced. The results of this paper can be taken as the reference for the development of the antique buildings and the new Chinese architecture.

Effect of pressure pulses at the interface valve on the stability of second dimension columns in online comprehensive two-dimensional liquid chromatography

Users of online comprehensive two-dimensional liquid chromatography (LCxLC) frequently acknowledge that the mechanical instability of HPLC columns installed in these systems, particularly in the second dimension, is a significant impediment to its use. Such instability is not surprising given the strenuous operating environment to which these columns are subjected, including the large number (thousands per day) of fast and large pressure pulses resulting from interface valve switches (on the timescale of tens of milliseconds) associated with very fast second dimension separations. There appear to be no published reports of systematic studies of the relationship between second dimension column lifetime and any of these variables. In this study we focused on the relationship between the lifetimes of commercially available columns and the pressure pulses observed at the inlet of the second dimension column that occur during the switching of the valve that interfaces the two dimensions of a LCxLC system. We find that the magnitude of the pressure drop at the inlet of the second dimension column during the valve switch, which may vary between 10 and 95% of the column inlet pressure, is dependent on valve switching speed and design, and has a dramatic impact on column lifetime. In the worst case, columns fail within the first few hours of use in an LCxLC system. In the best case, using a valve that exhibits much smaller pressure pulses, the same columns exhibit much improved lifetimes and have been used continuously under LCxLC conditions for several days with no degradation in performance. This result represents a first step in understanding the factors that affect second dimension column lifetime, and will significantly improve the usability of the LCxLC technique in general.