Peak Capacity Production Research Articles

Comprehensive two-dimensional gas chromatography under low-pressure conditions

The analysis of thermally labile and high-boiling point compounds by gas chromatography (GC) can be a challenge. One technique to overcome these challenges is low-pressure GC, which uses the vacuum produced from the mass spectrometer and wide-bore columns to elute compounds at significantly lower temperatures. While GC-MS is a powerful technique, comprehensive two-dimensional gas chromatography (GC × GC), allows for resolution of compounds that would typically coelute using GC. In this study, a pesticide standard mixture (8270 MegaMix Standard) was analyzed using a conventional GC × GC-TOFMS configuration (0.25 mm inner diameter (i.d.) to a 0.18 mm i.d. column) and low-pressure GC × GC-TOFMS configuration (0.53 mm i.d. to a 0.53 mm i.d. column). Elution temperatures, sensitivity, and peak capacity were investigated for both configurations. Compounds eluted an average of 30 °C less on the low-pressure GC × GC-TOFMS configuration compared to the conventional GC × GC-TOFMS configuration. Moreover, the compounds were separated in ∼13 min on the low-pressure GC × GC-TOFMS as opposed to 33 min for conventional GC × GC-TOFMS. However, due to the wide-bore columns and faster runtimes the low-pressure GC × GC-TOFMS had a lower, β corrected 2D peak capacity, nc,β,2D, of 1260 while the conventional GC × GC-TOFMS was 3588. Interestingly, both configurations yielded a similar peak capacity production of 93 peaks/min and 107 peaks/min for low-pressure and conventional GC × GC-TOFMS, respectively. A “real world” sample of diesel fuel was tested on the low-pressure and conventional GC × GC-TOFMS configurations and similar results were obtained compared to the pesticide standard mix except the peak capacity production of the low-pressure GC × GC-TOFMS configuration was higher than that of the conventional GC × GC-TOFMS method.

Green comprehensive two-dimensional liquid chromatography (LC × LC) for the analysis of phenolic compounds in grape juices and wine.

Grape juices and wines are rich in numerous groups of polyphenolic compounds which require a dedicated separation technique for such complex samples. LC × LC is considered the best technique for the analysis of such samples as it can achieve better resolution and higher peak capacity compared to 1D LC. The ever-growing demand for protecting the environment necessitates reducing or eliminating hazardous solvents to improve the environmental friendliness of analytical procedures. In this study, propylene carbonate was used as an eco-friendly mobile phase component in comprehensive two-dimensional liquid chromatography to analyze phenolic compounds in grape juices and a dealcoholized wine sample. Novel green RPLC × RPLC-DAD and RPLC × RPLC-MS methods were developed for the first time to identify phenolic compounds in five samples (two red grape juice samples, two white grape juice samples, and one dealcoholized wine sample). Four different RPLC × RPLC systems were developed; three systems were connected to a diode array detector (RPLC × RPLC-DAD), while the fourth system was connected to DAD and MS detectors (RPLC × RPLC-DAD-ESI-MS). Solvent X (propylene carbonate:ethanol, 60:40) was adopted as a green organic modifier in the first dimension (1D) and methanol in the second dimension (2D). The practical peak capacity and the surface coverage were calculated as metrics to measure the separation performance of all proposed systems. The orthogonality values for the setups ranged from 0.64 to 0.92 when calculated by the convex hull method, and from 0.54 to 0.80 when calculated by the asterisk equations method. The practical peak capacity production rate ranged from 14.58 to 22.52 peaks/min. The results revealed that the phenolic compounds were separated efficiently with good coverage of the 2D separation space and high peak capacity. A total of 70 phenolic compounds were detected based on MS data and information from the literature.

Segmented Microfluidics-Based Packing Technology for Chromatographic Columns

Nanoflow liquid chromatography-mass spectrometry (NanoLC-MS) has become the method of choice for the analysis of complex biological systems, especially when the available sample amount is limited. The preparation of high-performance capillary columns for nanoLC use is still a technical challenge. Here, we report a segmented microfluidic method for the preparation of packed capillary columns, where liquid segments were used as soft, dynamic, and well-dispersed slurry reservoirs for carrying and delivering micrometer packing particles. Based on this microfluidic packing technology, the column bed was assembled layer-by-layer at a 50 μm resolution, and ultralong capillary columns of 3, 5, and 10 m were fabricated in such a manner. The microfluidically packed columns demonstrated excellent separation efficiencies of 116 000 plates/m. The higher efficiencies obtained at higher slurry concentrations also indicate that a high-quality packed bed can be obtained without sacrificing the packing speed. Kinetic performance limit analysis shows that the microfluidic packed columns have higher peak capacity production efficiency in the high-resolution region, presenting an improved separation impedance of 2800, which is significantly better than columns packed with the conventional slurry packing method. In comparison with a commercial nanoLC column, a 5 m long microfluidic packed column was evaluated for proteomic analysis using a standard HeLa protein digest and presented 261% improvement in peptide identification capability, resulting in significantly enhanced protein identification confidence.

Column selection approach to achieve a high peak capacity in comprehensive three-dimensional gas chromatography

The separation power of comprehensive three-dimensional gas chromatography (GC3) is substantially enhanced through proper selection of the phase volume ratio, β, of each column relative to each other on successive dimensions. Consideration and application of the ratio of phase volume ratios, βr, or β ratio, between successive dimensions has been a relatively un-studied approach to maximize separating power in comprehensive multidimensional GC instrument design. Herein, proper selection of βr in multidimensional GC is shown to control the elution temperature, Te, of analytes throughout a 40 min primary (1D) column separation, and thus better control width-at-base, W, on all three dimensions. Specifically, between the 1D and secondary (2D) columns, a βr of 0.45 was applied, and between the 2D and tertiary (3D) columns a βr of 1.0 was applied. A total ideal peak capacity of 30,600, or a peak capacity production of ~770 peaks/min, was accomplished with the GC3 instrument with the reconfigured parameters. Additionally, due to the complex nature of this three-dimensional data, a novel approach to “slicing” the chromatographic run into user-defined time intervals is shown. This novel way to view the data still elicits a traditional GC×GC chromatograms, but with the focus on 2D × 3D separations. Moreover, due to proper βr selection, every 2 s window (i.e. every 1D modulation period) is shown to have a peak capacity of ~50–100 for each 2D × 3D separation. This high overall peak capacity (30,600) and peak capacity per 1D modulation (~50–100), courtesy of proper column selection, is demonstrated to hold great promise to physically separate truly complex mixtures.

Ultrafast separations via pulse flow valve modulation to enable high peak capacity multidimensional gas chromatography

Ultrafast modulation with a modulation period PM ≥ 50ms via a pulse flow valve is demonstrated for comprehensive two-dimensional gas chromatography (GC×GC) and comprehensive three-dimensional (3D) gas chromatography (GC3). Significant increases in peak capacity and peak capacity production are achieved for GC×GC and GC3 relative to previous studies due to using pulse flow valve modulation. Due to the nature of the “partial” modulation process, the separation dimension following pulse flow valve modulation is not a traditional chromatogram, rather requires data processing to convert the data to expose the encoded chromatographic information, producing “apparent” chromatographic peaks. In the GC×GC mode, a 115-component test mixture was evaluated using a PM of 500ms, creating an apparent 2D peak width-at-base 2W with an average of 25ms, producing a 2nc of 20. Based on the average 1W of 1.0s for the 6min first dimension 1D separation, an ideal peak capacity nc,2D of 7200 is achieved (1,200/min peak production). For a high-speed GC×GC separation (30s run), a PM of 75ms produced apparent 2W of 8ms, ideal for the third dimension of a GC3 instrument. Using the knowledge gained from this high-speed GC×GC experiment, the pulse flow valve was implemented as the second modulator in GC3. Three samples were evaluated in the GC3 mode: a simple mixture containing 18 compounds (to illustrate basic concepts), the 115-component test mixture (to determine peak capacity figures-of-merit), and a diesel spiked with 8 polar compounds (to illustrate chemical selectivity benefits of GC3). For the 115-component test mixture with a 1PM of 1.2s and a 2PM of 60ms, average 1W of 3.2s, 2W of 130ms, and apparent 3W of 13ms were produced, resulting in a 1nc of 210, 2nc of 9.2, and 3nc of 5, respectively. Hence, an ideal peak capacity, nc,3D of ∼10,000 for GC3 was achieved for the 11min 1D separation window of the 115-component test mixture.

Comprehensive two-dimensional gas chromatography using partial modulation via a pulsed flow valve with a short modulation period

Partial modulation via a pulsed flow valve for comprehensive two-dimensional (2D) gas chromatography (GC × GC) is demonstrated, producing narrow peak widths, 2Wb, on the secondary separation dimension, 2D, coupled with short modulation periods, PM, thus producing a high peak capacity on the 2D dimension, 2nc. The GC × GC modulator is a pulse flow valve that injects a pulse of carrier gas at the specified PM, at the connection between the primary, 1D, column and the 2D column. Using a commercially available pulse flow valve, this injection technique performs a combination of vacancy chromatography and frontal analysis, whereby each pulse disturbance in the analyte concentration profile as it exits the 1D column results in data that is readily converted into a 2D separation. A three-step process converts the raw data into a format analogous to a GC × GC separation, incorporating signal differentiation, baseline correction and conversion to a GC × GC chromatogram representation. A 115-component test mixture with a wide range of boiling points (36–372°C) of nine compound classes is demonstrated using modulation periods of PM = 50, 100, 250, and 500ms, respectively. For the test mixture with a PM of 250ms, peak shapes on 2D are symmetric with apparent 2Wb ranging from 12 to 45ms producing a 2nc of ~ 10. Based on the average peak width of 0.93s on the 1D separation for a time window of 400s, the 1D peak capacity is 1nc ∼ 430. Thus, the ideal 2D peak capacity nc,2D is 4300 or a peak capacity production of 650 peaks/min using the PM of 250ms. Additionally, for a PM of 50, 100 and 500ms, the 2nc are 4, 7, and 12, respectively. Retention times on 2D, 2tR, are reproducible having standard deviations less than 1ms. Finally, the processed data is shown to be quantitative, with an average RSD of 4.7% for test analytes.

Fully Automated Portable Comprehensive 2-Dimensional Gas Chromatography Device.

We developed a fully automated portable 2-dimensional (2-D) gas chromatography (GC x GC) device, which had a dimension of 60 cm × 50 cm × 10 cm and weight less than 5 kg. The device incorporated a micropreconcentrator/injector, commercial columns, micro-Deans switches, microthermal injectors, microphotoionization detectors, data acquisition cards, and power supplies, as well as computer control and user interface. It employed multiple channels (4 channels) in the second dimension (2D) to increase the 2D separation time (up to 32 s) and hence 2D peak capacity. In addition, a nondestructive flow-through vapor detector was installed at the end of the 1D column to monitor the eluent from 1D and assist in reconstructing 1D elution peaks. With the information obtained jointly from the 1D and 2D detectors, 1D elution peaks could be reconstructed with significantly improved 1D resolution. In this Article, we first discuss the details of the system operating principle and the algorithm to reconstruct 1D elution peaks, followed by the description and characterization of each component. Finally, 2-D separation of 50 analytes, including alkane (C6-C12), alkene, alcohol, aldehyde, ketone, cycloalkane, and aromatic hydrocarbon, in 14 min is demonstrated, showing the peak capacity of 430-530 and the peak capacity production of 40-80/min.

Comprehensive multidimensional separations of peptides using nano-liquid chromatography coupled with micro free flow electrophoresis.

The throughput of existing liquid phase two-dimensional separations is generally limited by the peak capacity lost due to under sampling by the second dimension separation as peaks elute off the first dimension separation. In the current manuscript, a first dimension nanoliquid chromatography (nLC) separation is coupled directly with a second dimension micro free flow electrophoresis (μFFE) separation. Since μFFE performs continuous separations, no complicated injection or modulation is necessary to couple the two techniques. Analyte peaks are further separated in μFFE as they elute off the nLC column. A side-on interface was designed to minimize dead volume in the nLC × μFFE interface, eliminating this as a source of band broadening. A Chromeo P503 labeled tryptic digest of BSA was used as a complex mixture to assess peak capacity. 2D nLC × μFFE peak capacities as high as 2,352 could be obtained in a 10 min separation window when determined according to the product of the first and second dimension peak capacities. After considering the orthogonality of the two separation modes and the fraction of separation space occupied by peaks, the usable peak capacity generated was determined to be 776. The 105 peaks/min generated using 2D nLC × μFFE was nearly double the previously reported maximum peak capacity production rate achieved using online LC × LC.

Peak sweeping and gating using thermal gradient gas chromatography

When axial temperature gradients are applied in gas chromatography (GC), i.e., “thermal gradient GC” (TGGC), the temperature changes both in time and position, T(t,L), along the column, allowing unique control of the movement and elution of sample components. One method of performing TGGC involves introducing a sample into a column with a preset decreasing temperature gradient along its length, waiting for a short time until the sample separates along the gradient, and then raising the temperature to sweep all of the compounds out of the column and into the detector (i.e., “peak sweeping”). This method of operation is demonstrated here using a simple laboratory apparatus based on simultaneous resistive heating and convective cooling. An experimental comparison between isothermal GC (ITGC), temperature programmed GC (TPGC) and TGGC shows that TGGC is essentially equivalent in performance to TPGC operation when using the same column length (peak capacity production rate of 106, 381 and 469min−1, respectively); however, narrower peaks and higher signal-to-noise are achieved in TGGC. Furthermore, TGGC helps to minimize band broadening and peak tailing that arise from column adsorption and less than perfect sample injection. The low thermal mass of the TGGC system allows rapid column heating (4000°C/min) and cooling (3500°C/min) for selective separation (i.e., “peak gating”) of compounds in a mixture without sacrificing the resolution of earlier or later eluting compounds.

Fast, High Peak Capacity Separations in Gas Chromatography–Time-of-Flight Mass Spectrometry

Peak capacity production (i.e., peak capacity per separation run time) is substantially improved for gas chromatography-time-of-flight mass spectrometry (GC-TOFMS) and applied to the fast separation of complex samples. The increase in peak capacity production is achieved by selecting appropriate experimental conditions based on theoretical modeling of on-column band broadening, and by reducing the injection pulse width. Modeling to estimate the on-column band broadening from experimental parameters provided insight for the potential of achieving GC separations in the absence of off-column band broadening, i.e., the additional band broadening not due to the on-column separation process. To optimize GC-TOFMS separations collected with a commercial instrumental platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a commercially available thermal modulator is adapted and applied (referred to herein as thermal injection) to provide a narrow injection pulse, while the TOFMS provided a data collection rate of 500 Hz, initially averaged to 100 Hz for data storage. The use of long, relatively narrow open tubular capillary columns and a 30 °C/min programming rate were explored for GC-TOFMS, specifically a 20 m, 100 μm inner diameter (i.d.) capillary column with a 0.4 μm film thickness to benefit column capacity, operated slightly below the optimal average linear gas velocity (at ~2 mL/min, due to the flow rate constraint of the TOFMS). Standard autoinjection with a 1:100 split resulted in an average peak width of ~1.2 s, hence a peak capacity production of 50 peaks/min. Metabolites in the headspace of urine were sampled by solid-phase microextraction (SPME), followed by thermal injection and a ~7 min GC separation (with a ~6 min separation time window), producing ~660 ms peak widths on average, resulting in a total peak capacity of ~550 peaks (at unit resolution) and a peak capacity production of ~90 peaks/min (~2-fold improvement relative to standard autoinjection with the 1:100 split). This total peak capacity production achieved is equivalent to, or greater than, that currently utilized in metabolomics studies using GC/MS, but with much slower separations, on the order of 40 to 60 min, corresponding to a 5-fold or greater GC/MS analysis throughput rate.

Experimental Study of the Quantitative Precision for Valve-Based Comprehensive Two-Dimensional Gas Chromatography

For complex sample analysis, there is a need for multidimensional chromatographic instrumentation to be able to separate more compounds, often in shorter time frames. This has led to the development of comprehensive two-dimensional chromatographic instrumentation, such as comprehensive two-dimensional gas chromatography (GC × GC). Lately, much of the focus in this field has been on decreasing peak widths and, therefore, increasing peak capacity and peak capacity production. All of these advancements make it possible to analyze more compounds in a shorter amount of time, but the data still need to remain quantitative to address the needs of most applications. In this report, the relationship among the modulation ratio (M(R)), peak sampling phase (φ), retention time variation (Δt(R)), and how these parameters relate to quantitative analysis precision via the relative standard deviation (RSD) was studied experimentally using a valve-based GC × GC instrument. A wide range of the number of modulations across the first dimension peak width, that is, a M(R) range from ~1 to 10, was examined through maintaining an average first dimension peak width at the base, (1)w(b) of ~3 s and varying the second dimension separation run time from 300 to 2900 ms. An average RSD of 2.1% was experimentally observed at an average M(R) of 2, with a corresponding peak capacity production of ~1200 peaks/min possible. Below this M(R) the RSD quickly increased. In a long-term study of the quantitative precision at a M(R) of 2.5, using 126 replicate injections of a test mixture spanning ~35 h, the RSD averaged 3.0%. The findings have significant implications for optimizing peak capacity production by allowing the use of the longest second dimension run time, while maintaining quantitative precision.

Achieving high peak capacity production for gas chromatography and comprehensive two-dimensional gas chromatography by minimizing off-column peak broadening

By taking into consideration band broadening theory and using those results to select experimental conditions, and also by reducing the injection pulse width, peak capacity production (i.e., peak capacity per separation time) is substantially improved for one dimensional (1D-GC) and comprehensive two dimensional (GC × GC) gas chromatography. A theoretical framework for determining the optimal linear gas velocity (the linear gas velocity producing the minimum H), from experimental parameters provides an in-depth understanding of the potential for GC separations in the absence of extra-column band broadening. The extra-column band broadening is referred to herein as off-column band broadening since it is additional band broadening not due to the on-column separation processes. The theory provides the basis to experimentally evaluate and improve temperature programmed 1D-GC separations, but in order to do so with a commercial 1D-GC instrument platform, off-column band broadening from injection and detection needed to be significantly reduced. Specifically for injection, a resistively heated transfer line is coupled to a high-speed diaphragm valve to provide a suitable injection pulse width (referred to herein as modified injection). Additionally, flame ionization detection (FID) was modified to provide a data collection rate of 5 kHz. The use of long, relatively narrow open tubular capillary columns and a 40 °C/min programming rate were explored for 1D-GC, specifically a 40 m, 180 μm i.d. capillary column operated at or above the optimal average linear gas velocity. Injection using standard auto-injection with a 1:400 split resulted in an average peak width of ∼1.5 s, hence a peak capacity production of 40 peaks/min. In contrast, use of modified injection produced ∼500 ms peak widths for 1D-GC, i.e., a peak capacity production of 120 peaks/min (a 3-fold improvement over standard auto-injection). Implementation of modified injection resulted in retention time, peak width, peak height, and peak area average RSD%’s of 0.006, 0.8, 3.4, and 4.0%, respectively. Modified injection onto the first column of a GC × GC coupled with another high-speed valve injection onto the second column produced an instrument with high peak capacity production (500–800 peaks/min), ∼5-fold to 8-fold higher than typically reported for GC × GC.

The impact of sampling time on peak capacity and analysis speed in on-line comprehensive two-dimensional liquid chromatography

Comprehensive two-dimensional liquid chromatography (2DLC) offers a number of practical advantages over optimized one-dimensional LC in peak capacity and thus in resolving power. The traditional “product rule” for overall peak capacity for a 2DLC system significantly overestimates peak capacity because it neglects under-sampling of the first dimension separation. Here we expand on previous work by more closely examining the effects of the first dimension peak capacity and gradient time, and the second dimension cycle times on the overall peak capacity of the 2DLC system. We also examine the effects of re-equilibration time on under-sampling as measured by the under-sampling factor and the influence of molecular type (peptide vs. small molecule) on peak capacity. We show that in fast 2D separations (less than 1 h), the second dimension is more important than the first dimension in determining overall peak capacity and conclude that extreme measures to enhance the first dimension peak capacity are usually unwarranted. We also examine the influence of sample types (small molecules vs. peptides) on second dimension peak capacity and peak capacity production rates, and how the sample type influences optimum second dimension gradient and re-equilibration times.

Increasing selectivity in comprehensive three-dimensional gas chromatography via an ionic liquid stationary phase column in one dimension

Recent advances in improving the selectivity and performance for a comprehensive, three-dimensional (3D) gas chromatograph (GC(3)) instrument are described. With GC(3), two six-port diaphragm valves are utilized as the interfaces between three, in-series capillary columns housed in a standard GC instrument fitted with a high data acquisition rate flame ionization detector (FID). Modulation periods for sampling from one column to the next are set so that sufficient slices (i.e., modulations) are acquired by the subsequent dimension resulting in comprehensive data. We present GC(3) instrumentation with significantly higher 3D peak capacity than previously reported. An average peak capacity production (i.e., per time) of 180 resolved peaks per minute was experimentally achieved for three representative analytes in a 3D diesel sample separation. This peak capacity production is about 4 times higher than our previous report. We also demonstrate the significant benefit of the added chemical selectivity of the three column GC(3) instrument relative to a two column GC x GC instrument, in which one of the three columns is a triflate ionic liquid stationary phase column with a high selectivity for phosphonated compounds (i.e., di-methyl-methyl phosphonate, di-ethyl-methyl phosphonate and di-isopropyl-methyl phosphonate). Using all three separation dimensions, the 2D separation fingerprint of a diesel sample is simultaneously obtained along with selective information regarding the phosphonated compounds in the diesel samples in the additional dimension.

A graphical method for understanding the kinetics of peak capacity production in gradient elution liquid chromatography

A novel graphical method for assessing the compromise between conditional peak capacity and separation speed for packed bed columns under gradient conditions has been developed and applied to the separation of peptides. This approach is analogous to and complements the conventional “Poppe plot” used to study plate count in isocratic separations. The use of the new plot can assist the design of appropriate column formats (e.g. particle size and column length) for both dimensions in gradient elution two-dimensional liquid chromatography (2DLC). Particularly for the second dimension of 2DLC, we find that smaller particles provide faster separations even though fast separations based on particles smaller than 2 μm are practically limited by the required miniscule column length. We also find that high temperatures strongly enhance the kinetics of peak capacity production whereas higher pressures help achieve larger absolute peak capacities albeit at the cost of longer analysis time.

Accessible proteomics space and its implications for peak capacity for zero‐, one‐ and two‐dimensional separations coupled with FT‐ICR and TOF mass spectrometry

The number and wide dynamic range of components found in biological matrixes present several challenges for global proteomics. In this perspective, we will examine the potential of zero-dimensional (0D), one-dimensional (1D), and two-dimensional (2D) separations coupled with Fourier-transform ion cyclotron resonance (FT-ICR) and time-of-flight (TOF) mass spectrometry (MS) for the analysis of complex mixtures. We describe and further develop previous reports on the space occupied by peptides, to calculate the theoretical peak capacity available to each separations-mass spectrometry method examined. Briefly, the peak capacity attainable by each of the mass analyzers was determined from the mass resolving power (RP) and the m/z space occupied by peptides considered from the mass distribution of tryptic peptides from National Center for Biotechnology Information's (NCBI's) nonredundant database. Our results indicate that reverse-phase-nanoHPLC (RP-nHPLC) separation coupled with FT-ICR MS offers an order of magnitude improvement in peak capacity over RP-nHPLC separation coupled with TOF MS. The addition of an orthogonal separation method, strong cation exchange (SCX), for 2D LC-MS demonstrates an additional 10-fold improvement in peak capacity over 1D LC-MS methods. Peak capacity calculations for 0D LC, two different 1D RP-HPLC methods, and 2D LC (with various numbers of SCX fractions) for both RP-HPLC methods coupled to FT-ICR and TOF MS are examined in detail. Peak capacity production rates, which take into account the total analysis time, are also considered for each of the methods. Furthermore, the significance of the space occupied by peptides is discussed.

Peak capacity, peak-capacity production rate, and boiling point resolution for temperature-programmed GC with very high programming rates

Recent advances in column heating technology have made possible very fast linear temperature programming for high-speed gas chromatography. A fused-silica capillary column is contained in a tubular metal jacket, which is resistively heated by a precision power supply. With very rapid column heating, the rate of peak-capacity production is significantly enhanced, but the total peak capacity and the boiling-point resolution (minimum boiling-point difference required for the separation of two nonpolar compounds on a nonpolar column) are reduced relative to more conventional heating rates used with convection-oven instruments. As temperature-programming rates increase, elution temperatures also increase with the result that retention may become insignificant prior to elution. This results in inefficient utilization of the down-stream end of the column and causes a loss in the rate of peak-capacity production. The rate of peak-capacity production is increased by the use of shorter columns and higher carrier gas velocities. With high programming rates (100-600 degrees C/min), column lengths of 6-12 m and average linear carrier gas velocities in the 100-150 cm/s range are satisfactory. In this study, the rate of peak-capacity production, the total peak capacity, and the boiling point resolution are determined for C10-C28 n-alkanes using 6-18 m long columns, 50-200 cm/s average carrier gas velocities, and 60-600 degrees C/min programming rates. It was found that with a 6-meter-long, 0.25-mm i.d. column programmed at a rate of 600 degrees C/min, a maximum peak-capacity production rate of 6.1 peaks/s was obtained. A total peak capacity of about 75 peaks was produced in a 37-s long separation spanning a boiling-point range from n-C10 (174 degrees C) to n-C28 (432 degrees C).

Effect of high speed on peak capacity in liquid chromatography

In order to decrease the analysis time of a given chromatographic system, many parameters may need to be changed. These changes can adversely affect the chromatographic performance: in particular, the peak capacity may decrease. The peak capacity is a measure of the number of components that can be resolved in a given time. Using this definition of the peak capacity, various options to obtain shorter analysis times were investigated. It was found that such parameters as particle size, column diameter, mobile phase velocity and column length can be changed so that the analysis time decreases without loss of peak capacity. Optimum procedures for that purpose are given. In the course of the analysis, a new efficiency criterion—the rate of peak capacity production—is defined and examined.