Heart-cutting technique

Another application of SFC-GC was for the isolation of chrysene, a poly aromatic hydrocarbon, from a complex liquid hydrocarbon industrial sample (24). A 5 p.m octadecyl column (200 cm X 4.6 mm i.d.) was used for the preseparation, followed by GC analysis on an SE-54 column (25 m X 0.2 mm i.d., 0.33 p.m film thickness). The direct analysis of whole samples transferred from the supercritical fluid chromatograph and selective and multi-heart-cutting of a particular region as it elutes from the SFC system was demonstrated. The heart-cutting technique allows the possibility of separating a trace component from a complex mixture (Figure 12.21). 

A commonly used system in environmental analysis is the heart-cutting technique which uses the separation power of the first column to obtain a higher selectivity than with the previously described precolumn enrichment. The two columns are coupled via a switching valve, as shown in Figure 13.5. 

Capillary gas chromatography (GC) using modified cyclodextrins as chiral stationary phases is the preferred method for the separation of volatile enantiomers. Fused-silica capillary columns coated with several alkyl or aryl a-cyclo-dextrin, -cyclodextrin and y-cyclodextrin derivatives are suitable to separate most of the volatile chiral compounds. Multidimensional GC (MDGC)-mass spectrometry (MS) allows the separation of essential oil components on an achiral normal phase column and through heart-cutting techniques, the separated components are led to a chiral column for enantiomeric separation. The mass detector ensures the correct identification of the separated components [73]. Preparative chiral GC is suitable for the isolation of enantiomers [5, 73]. 

The design has been well proved in quality assurance and origin control of flavours and fragrances. A double-oven system is shown in the Fig. 17.3, with two independent temperature controls and two detectors (DM 1, DM 2). A live switching coupling piece is used to switch the effluent flow to either the first detector or the chiral column. With optimum pneumatic adjustment of the MDGC system, certain fractions are selectively transferred onto the chiral main column as they are eluted from the precolumn (heart-cutting technique) [15]. 

On-column injection is preferred, because it occurs at room temperature. Hot injector ports can lead to decomposition of the sample, and to racemization of chiral components. If a single oven system is used, then split injection offers some advantages because it is important not to expose the chiral column to large amounts of solvents. With an MDGC system, the heart-cutting technique removes the solvent from the chiral column, so on-column injection is preferred. 

When column switching is used for sample cleanup, the technique is known as zone cutting. If the fraction of effluent to be transferred from the precolumn to the analytical column is at the front of the precolumn chromatogram, the technique is known as front cutting. Heart-cut technique... 

Swerev M, Ballschmiter K (1986), Chemosphere 15 1123-1126. HPLC and heart cutting techniques of polychlorinated dibenzofurans and dibenzodioxins"... 

Furthermore, enantio-MDGC, employing heart-cutting techniques from DB-1701 as the preseparation column on to heptakis (3-0-acetyl-2,6-di-0-pentyl)-P-cyclodextrin as the chiral main column, was described by Mosandl et al. /2S7 as a powerful tool in the direct enantiomer separation of chiral y-lactones from complex matrices without any further clean-up or derivatization procedures. 

The serial implementation of multiple origins of selectivity is the most practical approach at present. It has been adapted for columnar LC using a "heart cutting" technique (18) introduced in gas chroma tography. 

High-speed chromatography combines column selectivity and special selectivity adjustment techniques with conventional 2DGC to improve the speed of analysis in what is essentially a rapid, heart-cutting technique. " Rapid chromatography requires cryofocusing of analytes in... 

Issaq, Fox, and Muschik used a low-polarity column (DB-1) in the first dimension and a smectic liquid-crystal column in the second dimension for the separation of coeluting congeners of Aroclor 1242,1254, and 1260, using the heart-cutting technique. This procedure requires the use of a gas chromatograph equipped with two independent ovens for optimizing the temperature conditions of each... 

Automated matrix elimination can also be performed using heart-cut techniques. ... 

After preseparation of the oil on a nonchiral stationary phase, the peaks of interest have to be transferred to a second capillary column coated with a chiral phase, a technique usually referred to as heart cutting. In the simplest case, two GC capillaries with different selectivities are serially connected, and the portion of unresolved components from the ef uent of the rst column is directed into a second column, for example, a capillary with a chiral coating. The basic arrangement used in 2D GC (GC-GC) is shown in Figure 2.3. By means of a valve, the individual fractions of interest eluting from the rst column are directed to the second, chiral column, while the rest of the sample may be discarded. With this heart-cutting technique, many separations of chiral oil... 

A sample is usually preseparated on a short precolumn and then directed onto an analytical column (with the same or different selectivity) where actual separation occurs. The heart-cut technique is most often used when the solute coelutes with another sample or when it is situated on the flank of another peak. In this case the interesting part of the chromatogram is cut out and parked on the analytical column, while the rest of the sample is eluted from the precolumn into the waste. Thereafter, the valve is switched back to the analytical column position, and the parked sample... 

All the above-mentioned IC methods for the analysis of bromate and other oxyhalides at trace levels are based on suppressed conductivity detection. No matter whether a carbonate- or hydroxide-selective stationary phase with the respective eluent is used, the minimum detection limit for bromate based on a large-loop injection is between 1 and 2 pg/L. Lower detection limits for bromate can be achieved only with either derivatization techniques, heart-cutting techniques (ICxIC), or hyphenated techniques such as IC-ICP/MS or IC-MS. At present, a nimiber of derivatization methods for the trace analysis of bromate are being discussed that enable the simultaneous analysis of oxyhalides and standard inorganic anions. Wagner et al. [52] introduced an extension of... 

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