Most institutions of higher learning use standardized tests, such as the SAT or ACT, as admissions criteria; however, the use of such tests as a neutral predictor of future college success is debated. The academic portion of the WCS, known as the College Entrance Examination Rank (CEER) score, is determined by an algorithm that accounts for SAT and ACT scores (whichever is higher) and high school class rank normalized by size and competitiveness of the school. In addition to graduation from West Point and future Army performance, the CEER score may be useful in predicting success for other achievements, such as performance on the Fundamentals of Engineering Examination (FEE) and success in the chemical engineering program. The chapter examines longitudinal CEER score and FEE data from West Point chemical engineering majors (2006 to 2018) to determine if there was a statistically significant correlation between CEER scores and success on the chemical engineering FEE.

Per- and polyfluoroalkyl substances (PFAS) are a class of chemicals used in various commercial industries to include food packaging, non-stick repellent, and waterproof products. International environmental protection agencies are currently looking for ways to detect and safely remediate both solid and aqueous PFAS waste due to their harmful effects. Incineration is a technique that disposes of chemicals by breaking down the chemicals at high temperatures, upwards of 1400 °C. Incineration has been used on other related compounds, but PFAS presents a challenge during thermal degradation due to the molecular stability and reactivity of fluorine. Research on the efficacy of this method is currently limited, as the degradation byproducts of PFAS are not fully characterized. Current research is mostly focused on the development of benchtop methods for the safe remediation of solid PFAS waste. Aqueous fire fighting foams (AFFFs) have garnered significant attention due to extensive use since development in the 1960s. Numerous communities that are closely located near airports have been shown to have higher than average PFAS contamination from the repeated use. Detection and remediation of surface, subsurface, and wastewater have become a primary concern for environmental agencies. Use of electrochemical techniques to remove the PFAS contaminants has shown recent promise to help address this issue. Critical to the remediation efforts is development of standardized detection techniques and the implementation of local and international regulations to control the production and use of fluorinated products. No single solution has yet been developed, but much progress has been made in recent years in governmental regulation, detection, and remediation techniques.

One of the greatest advancements in the field of gas chromatography (GC) has been the development of comprehensive two-dimensional gas chromatography (GC x GC). As the field of GC evolved from one-dimensional gas chromatography (1D-GC) to heart cutting (GC-GC), followed by the advent of GC x GC, the critical component at the center of this evolution has been the interface between the separation columns. The interface, referred to as the modulator for GC x GC, links the primary and secondary columns. This review covers the evolution of modulator systems from the founding of GC x GC in 1991 by Liu and Phillips, while focusing on the last six years. Since its inception, modulators have evolved into two distinct categories: thermal, and valve-based. The advantages and shortcomings of each category will be covered. Recent developments in the research, development, and commercialization of these various modulators is provided, with a glimpse into future modulator designs. (C) 2018 Elsevier B.V. All rights reserved.

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.

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.

An ultrafast flow modulation period, P-M of 50 ms, for comprehensive two-dimensional (2D) gas chromatography (GC x GC) with time-of-flight mass spectrometry (TOFMS) detection is demonstrated, producing narrow peak widths, W-2(4 sigma width-at-base on the D-2 dimension), demonstrating the potential for ultrafast (2D) separations with high peak capacity. The modulator is a pulse flow valve that injects a narrow pulse of carrier gas at a user defined P-M, at the union between the D-1 and D-2 columns. The raw data produced combines the properties of vacancy chromatography and frontal analysis. Deconvolution of the raw data using unconstrained multivariate curve resolution alternating least squares (MCR-ALS) analysis facilitates identification and quantification for overlapped analyte peaks. The peak profile loadings obtained from MCR-ALS are converted into traditional appearing GC x GC data through a process commonly used with frontal analysis. An 18-component test mixture at seven different injected mass levels was studied. The D-2 peaks generated ranged from an W-2 of 16 to 36 ms with an average of 26 ms. At an on-column injected mass of 14 ng per analyte, an average mass spectral match value, MV, of 822 was achieved using in-house collected spectra for comparison, with an average match value RSD of 7.1%. Calibration of overlapped test analytes was evaluated using the areas of the MCR-ALS loadings, with excellent quantification demonstrated. The advancement demonstrated in modulation performance for GC x GC represents a significant decrease in P-M as most commercial modulators have a minimum P-M of 1 s, while maintaining the benefits of a duty cycle of essentially 1.0, which promises to enable new chemical analyzer designs, compatible with the vacuum requirements of the TOFMS detector. (C) 2018 Elsevier B.V. All rights reserved.

Scope of Review. Analysis of volatile and semi-volatile analytes by gas chromatography (GC) methods is an indispensable tool in the analytical chemist’s tool box. A myriad of fields of study rely upon the application of GC methods to address an ever growing demand to provide useful chemical information from GC data. As the realm of GC application has expanded, there has been an evolution to develop more powerful instrumental and data analysis approaches to keep pace with the wealth of complex samples that require analysis. To address this challenge, advances in GC instrumentation having evolved from one-dimensional gas chromatography (1D-GC) and heart cutting approaches such as (GC-GC), to instrumentation referred to broadly as multidimensional gas chromatography (MDGC), which can take on many forms. The principle form of MDGC that has gained wide implementation is comprehensive two-dimensional (2D) gas chromatography (GC × GC) as shown in Figure 1A, pioneered nearly 26 years ago by Liu and Phillips.1 Whe...

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.

Development of comprehensive, three-dimensional (3D) gas chromatography with time-of-flight mass spectrometric detection (GC3/TOFMS) is described. This instrument provides four dimensions (4D) of chemical selectivity and includes significant improvements to total selectivity (mass spectrometric and chromatographic), peak identification, and operational temperature range relative to previous models of the GC3 reported. The new instrumental design and data output are evaluated and illustrated via two samples, a 115-component test mixture and a diesel fuel spiked with several compounds, for the purpose of illustrating the chemical selectivity benefits of this instrumental platform. Useful approaches to visualize the 4D data are presented. The GC3/TOFMS instrument experimentally achieved total peak capacity, nc,3D, ranging from 5000 to 9600 (x̅ = 7000, s = 1700) for 10 representative analytes for 50 min separations with component dimensional peak capacities averaging 406, 3.6, and 4.9 for 1D, 2D, and 3D, respectively. Particularly, GC3/TOFMS achieved a combined 2D × 3D peak capacity ranging from 10 to 26 (x̅ = 17.6, s = 5.0), which is similar to what is achieved by 2D alone in a GC × GC operating at equivalent modulation period conditions. The analytical benefits of employing three varied chemical selectivities in the 3D separation coupled with TOFMS are illustrated through the separation and detection of 1,6-dichlorohexane and cyclohexyl isothiocyanate as part of the diesel fuel analysis.