Chromatographic speed classification for liquid chromatography using average theoretical peak time (ATPT).

BACKGROUND: The development of analytical techniques in the field of liquid chromatography has brought new frontiers in performance and analytical speed for the technique. The proper evaluation of the analytical boundaries achieved with those developments was not addressed in the literature, since different liquid chromatography (LC) techniques have not yet received any classification regarding their chromatographic speed. Defining chromatographic analysis speed based simply on analysis time is an outdated concept since it is sample and analyte-dependent. In this context, the application of the Average Theoretical Peak Time concept (ATPT) is proposed as a unified metric for chromatographic speed classification. RESULTS: This metric was evaluated using PCA analysis in a group of more than 50 publications, which generated the classification of LC methods in normal, high, hyper, and ultra-high-speed separations using ATPT. Normal speed (ATPT values greater than 18000 ms/peak) was found in HPLC, nano-LC, SFC, and CEC methods. Therefore, high-speed methods (ATPT values between 4000 and 18000 ms/peak) were found in UHPLC techniques, while LC × LC methods presented higher ATPT values between 1000 and 4000 ms/peak being classified as hyper-speed separations. ATPT can also be used as an optimization parameter, since older methods show higher ATPT values, while recent published papers show lower values of this metric. This behavior is justified due to the improvement of the LC methods over the years. SIGNIFICANCE: This work fulfills the gap in chromatographic definitions and metrics, regarding analytical speed in one-dimensional and multidimensional liquid chromatographic techniques and shows that ATPT metrics is a robust parameter that can be used to classify the separation speed as well as a metric to evaluate the LC Method optimization. It also corrects the historical application of separation time as a metric for chromatographic speed.

Hyperspeed method for analyzing organochloride pesticides in sediments using two-dimensional gas chromatography-time-of-flight mass spectrometry.

Pesticides are traditionally analyzed using conventional gas chromatography. When fast chromatography is associated with comprehensive two-dimensional gas chromatography (GC × GC), the resulting method presents high-resolution separation associated with a higher chromatographic speed. In the present work, a method for pesticide analysis in sediment samples was developed using quick, easy, cheap, effective, rugged, and safe extraction (QuEChERS) and a hyperspeed GC × GC separation. The QuEChERS procedure reported in the literature was extended to incorporate the analytes tetrachloro-m-xylene, decachlorobiphenyl, trans-chlordane, chlordane, endosulfan lactone, and endosulfan ether. To understand the chromatographic method improvement achieved, the recent concept of average theoretical peak time (ATPT) was used. The ATPT improved from that of the traditional GC × GC separation to the proposed method, and the separation speed can be classified as a hyperspeed separation. The limit of detection and quantitation of the compounds in the standard mix ranged from 0.39 to 17.96 µg L-1 and 1.18 to 54.43 µg L-1, respectively. The method showed acceptable RSD% (relative standard deviation) values and little interference of the sediment matrix in the extraction procedure. The developed method was applied to the determination of a mixture of 19 compounds in 16 sediment samples from the Pirapetinga River and Paraíba do Sul River in Brazil.

Average theoretical peak time as a metric to analytical speed in one dimensional and multidimensional gas chromatographic separations.

The definition of a chromatographic analysis speed based simply on analysis time is an outdated concept to define conventional chromatography, fast chromatography, and emerging high-resolution techniques such as comprehensive two-dimensional and comprehensive three-dimensional gas chromatography. Here, the metric average theoretical peak time (ATPT) is proposed for separation speed, considering conventional and multidimensional separations. ATPT can be defined as the time (in ms per peak) needed to elute a theoretical peak in a chromatographic system. Using this metric, it is possible to define ranges, proposed for a normal speed (ATPT higher than 4000 ms/peak), high speed (ATPT range from 600 to 4000 ms/peak), very high speed (ATPT range from 200 to 600 ms/peak), hyper speed (ATPT range from 3.3 to 200 ms/peak) and ultra high speed chromatography (ATPT lower than 3.3 ms/peak), that combines time and efficiency metrics. This metric was applied in several contexts to demonstrate its robustness to evaluate chromatographic separations for different techniques and analytical conditions. Applications also demonstrate the advantages of the use of ATPT as a method development metric tool.

Influence of acquisition rate on performance of fast comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry for coconut fiber bio-oil characterization.

Comprehensive two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC/TOFMS) is used to characterize complex bio-oil samples because of the high peak capacity associated with the high acquisition rate and mass spectra deconvolution capability of TOFMS. A recent application of fast GC × GC for this type of analysis improved sample throughput while achieving the same peak capacity without the use of cryogenic liquids. This work evaluates the effect of the TOFMS data acquisition rate on the quality of the analytical information obtained by GC × GC/TOFMS. In the analysis of coconut fiber bio-oil under fast GC × GC/TOFMS conditions, use of high data acquisition rates (200-300 Hz) increases the number of identifiable peaks by more than 50% compared with that achieved at the conventional rate of 100 Hz. The acquisition rate can affect the peak capacity by a factor of 3 or more. This is the first study to demonstrate the importance of optimizing the data acquisition rate, a parameter that has previously been neglected in the literature, in GC × GC/TOFMS development.

Determining organic pollutants in automotive industry sludge.

In Brazil, the policy for disposing industrial sludge is changing from an emphasis on using controlled landfills to other treatment or co-processing methods; however, the monitoring of organic pollutants is not mandatory. The present study evaluated two general screening methods for organic pollutants in sludge generated in an automotive industrial complex in southern Brazil. The screening was performed using Soxhlet and sonication extractions and Gas Chromatograph coupled with Quadrupole Mass Spectrometry (GC/qMS). It was concluded that both techniques were effective and that most of the compounds identified were alkanes, phenols and esters. Important pollutants were detected in the sludge, which confirms the necessity of monitoring this type of residue.

Retention indices in comprehensive two-dimensional gas chromatography.

The identification of compounds by using gas chromatography (GC) in samples with significant complexity comprising a range of isomeric species, where characterization is based on peak retention times and mass spectra, generates uncertainty for the analyst. This leads to identification errors. The most reliable way to confirm the identification of each compound is based on authentic standard co-injection, which in several cases is economically prohibitive, and often unachievable in the time available for analysis. Retention index procedures are important tools to minimize misidentification of compounds in conventional chromatography. The introduction of comprehensive two-dimensional GC (GC × GC) for analysis of complex samples was a decisive step to increase the analytical capacity of chromatographic techniques. For many samples, the chromatographic resolution increase leads to quantitative expansion in the number of peaks identified, compared with conventional GC analysis. Notwithstanding this improved resolution, limitations still persist in correct peak identification, which suggests the use of retention indices may assist in supporting component identification in this important technique. In this work, approaches to use of the retention index in GC × GC are discussed, based on an evaluation of the literature in this area. Interpretation of effective chain length data for fatty acid methyl esters in the first and second dimensions is presented.

Analysis of organic compounds of water-in-crude oil emulsions separated by microwave heating using comprehensive two-dimensional gas chromatography and time-of-flight mass spectrometry.

In this work the higher peak capacity and resolution of comprehensive two-dimensional gas chromatography (GCxGC) has been successfully applied, for the first time, to tentatively identify several polar organic compounds of organic extracts of aqueous phases resulting from microwave demulsification process of water-in-crude oil emulsions. Results have shown that higher temperatures and longer exposure time to microwave irradiation produced water phases with a wider variety of polar organic compounds. The microwave process showed to be suitable for the extraction of several polar compounds classes of petroleum. The proposed microwave extraction method and GCxGC identification of polar compounds of petroleum samples are of practical interest for the petrochemical industry due to corrosion and related problems associated with these polar compounds in refinery equipments. The GCxGC/time-of-flight MS technique shows to be very important in the total separation of different classes of compounds and allows the identification of many compounds in these classes.

Comparative study of Eucalyptus dunnii volatile oil composition using retention indices and comprehensive two-dimensional gas chromatography coupled to time-of-flight and quadrupole mass spectrometry.

In the present work, the composition of volatile oil from leaves of Eucalyptus dunnii was studied using comprehensive two-dimensional gas chromatography (GCxGC) techniques. Structurally related compounds were found to elute mainly in specific regions of the two-dimensional space, showing orderly distribution with chemical class. Mass spectra of essential oil components were obtained from two different mass spectrometry detection methods: quadrupole (qMS) and time-of-flight (TOFMS), using the same GCxGC system under the same chromatographic conditions. Higher values of Similarity (average S of 914 with TOFMS compared to 880 with qMS) and Reverse (average R of 944 with TOFMS compared to 881 with qMS) were obtained with GCxGC/TOFMS showing its superior performance, which was most likely due to better sensitivity and resolution arising from the TOFMS system, and lack of spectral bias. Also, the number of compounds found in E. dunnii essential oil was 15% higher when TOFMS was used. Most of these are lower abundance components or exhibit low quality mass spectra; this supports the improved sensitivity obtained with TOFMS. A linear relationship (r2=0.998) between experimental retention indices (LTPRI) of 30 standard compounds obtained with GCxGC/TOFMS and GC with flame ionization detection literature retention indices is reported as an aid for compound identification.

Qualitative and quantitative study of nitrogen-containing compounds in heavy gas oil using comprehensive two-dimensional gas chromatography with nitrogen phosphorus detection.

In this work, a GCxGC-nitrogen-phosphorus detection (NPD) methodology was developed to separate and quantitate nitrogen-containing compounds in Brazilian heavy gas oil. First, the NPD performance was improved in order to achieve best GCxGC performance. The geometry of this detector was also evaluated. The use of an extended jet improved significantly the peak shape. The GCxGC separation was studied using both first and second dimension columns with different internal diameters. The use of a thicker film in both dimensions provided better performance. LODs of 0.16-8.49 pg of individual compounds were achieved. Two different extraction techniques of the neutral and basic nitrogen-containing compounds were also evaluated. The method using ion-exchange resins to separate neutral and basic nitrogen-containing compounds was more efficient than the method using modified silica. As an example, the amounts (microg/g) of each class reported were: indole (2.77), alkyl carbazoles ranging from C(0) to C(6+) (1.467), alkyl benzocarbazoles from C(0) to C(4+) (793), alkyl quinolines (31.2) and alkyl benzoquinolines (21.6) were quantitated.

Detector technologies for comprehensive two-dimensional gas chromatography.

The detector is an integral and important part of any chromatographic system. The chromatographic peak profiles (i.e. peak separation) should, ideally, be unaffected by the detector--it should only provide the sensing capacity required at the end of a column separation process. The relatively new technique of comprehensive 2-D GC (GC x GC) extends the performance of GC manyfold, but comes at a price--existing GC systems may not be adequately designed with the requirements of GC x GC in mind. This is primarily the need for precise measurement of very fast peaks entering the detector (e.g. as fast as 50 ms basewidth in some instances). The capacity of the detector to closely track a rapidly changing chromatographic peak profile depends on a number of factors, such as design of flow paths and make-up gas introduction, type of detector response mechanism, and the chemistry of the response. These factors are discussed here as a means to appreciate the technical demands of detection in GC x GC. The MS detector will not be included in this review.

Applications of comprehensive two-dimensional gas chromatography to the characterization of petrochemical and related samples.

This article discusses the application of comprehensive two-dimensional gas chromatography (GC x GC) to samples derived from petrochemicals. The use of GC x GC for characterization of petroleum and petroleum derivatives, through group type analysis, such as benzene, toluene, ethylbenzene, xylenes (BTEX), total aromatic hydrocarbons, polyaromatic hydrocarbons, and heteroatomic sulfur-, oxygen-, and nitrogen-containing compounds is presented. The capability of GC x GC to provide additional chemical-specific information regarding petroleum-processing steps, such as linear alkanes dehydrogenation, Fischer-Tropsch process, hydrogenation and oligomerization, is also described. In addition, GC x GC analyses of petrochemical biomarkers and environmental petrochemical-derived pollutants are reported. The role of comparison of samples through use of simple fingerprint approaches is highlighted.

Identification of some plasticizers compounds in landfill leachate.

In this work it was described a simple method for extraction of plasticizer compounds (mainly phthalate esters and bisphenol A (BPA)) from landfill leachate samples. The samples were submitted to an extraction procedures based on precipitation, solid phase extraction (SPE) and ionic exchange chromatography (IEC). Firstly the landfill leachate sample was acidified by addition of HCl concentrated, in order to precipitate the organic compounds that are less soluble in water. The precipitate was washed with several solvents. The aqueous phase was then submitted to SPE with XAD-4 resin and IEC with Amberlyst A-27 resin. The instrumental analysis was performed by gas chromatography with mass spectrometer detector (GC/MSD) and the compounds were identified by the GC/MSD library (Wiley) and by using some standard substances. These methodologies allow the isolation and identification of the following compounds: dioctylphthalate, diisobutilphthalate, BPA, benzoic acid, palmitic acid and diisopentylphthalate. The methods are very simple, rapid and selective, for plasticizers extraction from landfill leachate matrices.