Dual columns

Figure 12.17 Schematic diagrams of solvent-flush systems, (a) Dual-column MCS unit, which is positioned prior to the first column (C 1) flushing is earned out with both NV 1 and MFC 2 open, (b) Dual-column DCS unit solvent flushing is carried out via the splitline, with MFC 3 open (NV, needle valve MFC, mass flow control). Reprinted with permission from Ref. (20).

Recently, multidimensional GC has been employed in enantioselective analysis by placing a chiral stationary phase such as a cyclodextrin in the second column. Typically, switching valves are used to heart-cut the appropriate portion of the separation from a non-chiral column into a chiral column. Heil et al. used a dual column system consisting of a non-chiral pre-column (30 m X 0.25 mm X 0.38 p.m, PS-268) and a chiral (30 m X 0.32 mm X 0.64 p.m, heptakis(2,3-di-(9-methyl-6-(9-tert-butyldimethylsilyl)-(3-cyclodextrin) (TBDM-CD) analytical column to separate derivatized urinary organic acids that are indicative of metabolic diseases such as short bowel syndrome, phenylketonuria, tyrosinaemia, and others. They used a FID following the pre-column and an ion trap mass-selective detector following the... 

The sample drawn from the reactor consisted of an acid, several amines, and a neutral species. Two of the components were not resolved to baseline by reversed phase LC, so a dual column reversed phase ion-suppression/ ion-exchange technique was used. A chromatogram of the separation is shown in Figure 5. 

Many IC techniques are now available using single column or dual-column systems with various detection modes. Detection methods in IC are subdivided as follows [838] (i) electrochemical (conductometry, amper-ometry or potentiometry) (ii) spectroscopic (tJV/VIS, RI, AAS, AES, ICP) (iii) mass spectrometric and (iv) postcolumn reaction detection (AFS, CL). The mainstay of routine IC is still the nonspecific conductometric detector. A significant disadvantage of suppressed conductivity detection is the fact that weak to very weak acid anions (e.g. silicate, cyanide) yield poor sensitivity. IC combined with potentiometric detection techniques using ISEs allows quantification of selected analytes even in complex matrices. The main drawback... 

Davis, J.M. (2004). Assessment by Monte Carlo simulation of thermodynamic correlation of retention times in dual-column temperature programmed comprehensive two-dimensional gas chromatography. J. Sep. Sci. 27, 417. 

In general, a comprehensive separation strategy implies the desire to resolve/analyze all components within a sample. In the specific context of a multidimensional chromatographic method, the term is more narrowly applied to indicate that all analytes introduced to the first-dimension separation are also subjected to a second-dimension separation. There are two basic configurations used by our laboratory to carry out comprehensive multidimensional (IEX/RP) protein separations—IEX— Dual Column RP system and IEX—Dual Trap RP system (Figs. 13.1 and 13.2), respectively. 

The IEX—Dual Column RP system configuration shown (Fig. 13.1) utilizes independent pumping systems for each separation dimension. One pumping system... 

Fang et al. [661] have described a flow injection system with online ion exchange preconcentration on dual columns for the determination of trace amounts of heavy metal at pg/1 and sub-pg/1 levels by flame atomic absorption spectrometry (Fig. 5.17). The degree of preconcentration ranges from a factor of 50 to 105 for different elements, at a sampling frequency of 60 samples per hour. The detection limits for copper, zinc, lead, and cadmium are 0.07, 0.03, 0.5, and 0.05 pg/1, respectively. Relative standard deviations are 1.2-3.2% at pg/1 levels. The behaviour of the various chelating exchangers used was studied with respect to their preconcentration characteristics, with special emphasis on interferences encountered in the analysis of seawater. 

Figure 5.17. Dual-column ion exchange preconcentration valve. Sa, Sb samples A and B Ca, Cb ion exchange columns A and B Ea, Eb eluant (2 M nitric acid) for columns A and B Wa, Wb waste lines for samples and eluants A and B W waste lines AAS atomic absorption spectrometer. The dimensions of the base plate of the valve are 70 x 45 x 10 mm. See text for details of operation. Source [661]...

Storr-Hansen, E. and T. Cederberg. 1992. Determination of coplanar polychlorinated biphenyl (CB) congeners in seal tissues by chromatography on active carbon, dual-column high resolution GC/ECD and high resolution GC/high resolution MS. Chemosphere 24 1181-1196. 

Grant et al. (2002) designed a parallel system employing two HTLC columns (Cyclone, 50 x 1 mm, Cohesive Technologies) connected to one analytical column (Zorbax SB-C18, 50 x 2 mm, Hewlett Packard) on a 2300 HTLC. A polyarylethyl ketone (PAEK) six-port Valeo (Valeo Instruments, Texas) was used to increase switching speed and reduce carry-over. Peak focusing was used when the analyte was flushed from the TFC column into the analytical column by aqueous dilution. Compared to the dual column method, the overall time reduction was 1.5 to 4 min per sample with comparable data quality at the linear range of 0.1 to 100 ng/mL. 

Occupational air (breathing zone) Collection on charcoal tubes DMF desorption dual column cap. GC/FID 0.5 g/sample (for 1-4 L sample) Not reported Hakkola and Saarinen 1996... 

Conventionally, it is necessary to use a dual column flow line in packed-column gas chromatography to provide sample and reference gas flows. The recently developed electronic base-line drift compensation system allows a simple column flow line to be used reliably. 

Milk al. Solvent extraction GPC Dual column 0.5 ng/g 100 Rahman et... 

Capillary GC/ECD, dual column capillary GC/ECD, and capillary GC/MS have been used for quantitation of mirex in milk with sensitivity in the low to sub-ppb range (Bush et al. 1983b Mes et al. 1986 Mussalo-Rauhamaa et al. 1993 Rahman et al. 1993 Rehman et al. 1993). Recovery data for milk are generally very good (>70%) (Mes et al. 1993 Mussalo-Rauhamaa et al. 1993 Rahman et al. 1993), but precision data were not reported. 

Durrell GS, Sauer TC. 1990. Simultaneous dual-column, dual-detector gas chromatographic determination of chlorinated pesticides and polychlorinated biphenyls in environmental samples. Anal Chem 62(17) 1867-1871. 

Daft JL. 1983. Gas chromatographic determination of fumigant residues in stored grains, using isooctane partitioning and dual column packings. J Assoc Off Anal Chem 66 228-233. 

Online-dual-column extraction coupled to enantioselective LC-MS was used for the determination of terbutaline enantiomers in human plasma on a commercially available TE CSP [120]. 

Xia, Y.-Q., Bakhtiar, R., and Erankhn, R.B., Automated online dual-column extraction coupled with teicoplanin stationary phase for simultaneous determination of (R)- and (5)-propranolol in rat plasma using liquid chromatography-tandem mass spectrometry, J. Chromatogr. B, 788, 317, 2003. 

Xia, Y.-Q., Liu, D.Q., and Bakhtiar, R., Use of online-dual-column extraction in conjunction with chiral liquid chromatography tandem mass spectrometry for determination of terbutaline enantiomers in human plasma. Chirality, 14, 742, 2002. 

Ojanpera I, Rasanen, I, Vuori E. 1991. Automated quantitative screening for acidic and neutral drugs in whole blood by dual-column capillary gas chromatography. J Anal Toxicol... 

For separation, high resolution capillary columns are used, and in most circumstances each extract is examined by a dual column technique. This is to add a degree of confirmation into the method. 

Table V. Comparison of Single Column and Dual Column ...

Lambertus, G.R., Crank, J.A., McGuigan, M.E., Kendler, S., Armstrong, D.W., and Sacks, R.D., Rapid determination of complex mixtures by dual-column gas chromatography with a novel stationary phase combination and spectrometric detection, /. Chromatogr. A, 1135, 230-240, 2006. 

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