Elution direction

A gas chromatograph (GC) can be used for the chromatographic separation of volatile analytes in complex mixtures prior to mass spectrometric analysis. This becomes especially advantageous if the GC elutes directly ( online ) into the ion source of a mass spectrometer, so-called GC-MS coupling. [63-65] Packed GC columns with a high flow can be connected via a jet-separator, but these are almost out of use at present. [66] Capillary columns provide flow rates in the order of a few milliliters per minute, therefore their back end can be connected directly at the entrance of the ion volume. 

Analytichem International has taken trace enrichment a step further with the development of the Analytichem Automated Sample Preparation LC Module, A ASP LCM. This unit uses derivatized silica in specially configured cassettes on which the sample is off-line enriched by using an inexpensive vacuum manifold. After enrichment, the cassette is placed in the unit, which holds up to 10 cassettes containing 10 samples each, and the enriched samples are eluted directly on the analytical column. Provisions allow for early- and late-eluting bands to be switched to waste. The unit also provides for external control of... 

Tor reference. Positive identification can be made only by collecting the compound or transierring it as it elutes directly into another apparatus for analysis by other means, such as infrared or ultraviolet spectroscopy, mass spectrometry, or nuclear magnetic resonance. Commercially available apparatus is available which combines in a single unit both a gas chromatograph and an infrared, ultraviolet, or mass spectrometer for routine separation and identilicalion. The ancillary system may also be microprocessor-based, with an extensive memory for storing libraries of known infrared spectra or fragmentation patterns (in the case of mass spectrometers). Such systems allow microprocessor-controlled comparison and identilicalion of detected compounds. 

Online coupling SPE to either LC or GC is easily performed. In the simplest method, a precolumn is placed in the sample loop position of a six-port switching valve. After conditioning, sample application, and cleaning via a low-cost pump, the precolumn is coupled to an analytical column by switching the valve into the inject position. The solutes of interest are eluted directly from the piecolumn to the analytical column by an appropriate mobile phase. The sequence can be fully automated (Fig. 28). It is also a simple matter to enhance the gap between two solutes in elution from a precolumn (70). 

An on-line MCAC-HPLC method was developed for OTC, TC, CTC, DMC residues in both liver and kidney samples. The drugs were extracted with succinate buffer, and the extract was diluted with EDTA-pentanesulphonic acid buffer. Diluted extract was then purified on C8 or XAD-2 SPE cartridges previously activated with MeOH, water, and PSA-containing phosphate buffer. The TCs were eluted with MeOH, and the eluate was then injected onto an Anagel-TSK-Chelate-SPW column that had been preloaded with copper(II) sulphate. The TCs were eluted directly onto the analytical column in a column-switching system after washing with both water and MeOH (29). 

It is recommended that the control zone and the collection zone of a XAD-2 tube be analyzed separately if the breakthrough volume of the most volatile chemicals of interest in the sampling conditions is not known. The control zone is removed from the tube to a small glass vial and sonicated with 2 ml of ethyl acetate for 3 min. The resin is filtered rapidly and the supernatant is analyzed. The trapped chemicals are desorbed from the collection zone by eluting 2 ml of ethyl acetate to the back end of the zone. (It is important to note that the elution direction should be opposite to the collection direction.) The eluate is collected in a glass vial under gravity. 

Holtzapple et al. developed an immunoassay method for determination of four fluoroquinolone compounds (including ciprofloxacin) in liver extracts [64]. In this method, an immunoaffinity capture SPE column was used, that contained anti-sarafloxacin antibodies covalently cross-linked to protein G. After interfering liver matrix compounds had been washed away, the bound ciprofloxacin was eluted directly onto the HPLC column. The HPLC system used a 5 pm Inertsil phenyl column (15 cm x 4.6 mm i.d.), with 0.1 M-glycine hydrochloride/acetonitrile (17 3) as the mobile phase (eluted at a rate of 0.7 mL/min). Fluorimetric detection at 444 nm was used after excitation at 280 nm. The recovery of ciprofloxacin ranged from 85.7 to 93.5%, and the detection limit was... 

In terms of antibody-coated stents, the following is a list of potential antibody-containing species that could, in theory, be eluted directly from the surface of the implanted biologic/device combination product, in vivo (Figure 34.2) ... 

Using one of the above procedures, a recovery of 50 to 80% is relatively easy, although devices are available which elute directly from the plate and which claim better than 99% efficiency. These devices frt directly over the spot, after scraping away a ring of stationary phase, and solvent is pumped in from one side of the device and collected at the other side. 

Light-scattering detection Light-scattering detector Known dn/dc as a function of elution Direct MMD measurement, No calibration. Architecture independence No CCD information. No TgS 5, 8... 

Fig. 5.8. (A) General scheme of a dynamic focused microwave-assisted extractor. (B) Experimental set-up used to integrate microwave-assisted extraction with the subsequent steps of the analytical process. (1) Leaching step CT controller, MO microwave oven, S sample, R condenser, WR water reservoir, TCPP two-channel piston pump, ER extract reservoir, SV switching valve. (2) Clean-up/preconcentration step M methanol, A air, B buffer, PP peristaltic pump, F filter, EL elution loop, MC mini-column, R retention direction, E elution direction, 1V1-1V3 injection valves, W waste. (3) Individual separation-detection step HPIV high-pressure injection valve, AC analytical column, DAD diode array detector, SR solvent reservoirs.

Immobilized antibodies have also been used extensively in multidimensional liquid chromatography (MDLC) analyses. As shown in Fig. 2, an affinity column with immobilized anti-HSA is used to capture all of the human serum albumin in a sample, allowing all of the other components to flow through to waste. Then, the affinity chromatography column is eluted directly into a size-exclusion column where albumin... 

Cf, Cm, Am europium is eluted directly after Am. d) nitric stripping of the column contains 1 Ce, ruthenium and cesium. The elution curve is given in figure . The actinides are thus rid of most of lanthanides and other fission products in a single cycle. 

Fats, oils, and lipids are common components of meats, nuts, and dairy products and manufactured goods, such as potato chips, cookies, and chocolate. They are soluble in nonpolar solvents, such as hexane and methylene chloride. The analyte, of course, should also be soluble in the extraction solvent. Typically normal-phase SPE would be used to retain a compound from this extraction solvent. A solid fat may be homogenized in a blender with hexane, filtered or centrifuged, then the solvent would be passed through a normal-phase column for retention of the solute. Another approach is the use of matrix solid-phase dispersion, where the solid would be ground into the silica and C-18 directly, then the analyte eluted directly from the ground mixture with either hexane or methylene chloride. The hexane or methylene chloride extract could then be applied directly to a normal-phase sorbent for separation. Liquid oils may be directly diluted with hexane or methylene chloride and applied to the normal-phase sorbent. Other lipid substances may be handled either as solids or liquids depending on their form. 

In an effort to identify as many components in the wax fraction as possible, short (15 m) HTGC columns interfaced to the mass spectrometer are used. This procedure satisfactorily separates many of the major series of compounds and permits compounds up to about C50 to elute directly into the mass spectrometer. Many of the compounds described below have been identified on the basis of mass spectral interpretation or comparison with other samples where their identities have been confirmed (Hsieh Philp 2001). Confirmation of the components tentatively identified ultimately requires co-injection with authentic standards. 

The real beauty of this system is that the self-cleavage reaction can be performed on an affinity column directly after purification on cellulose beads, so that the protein of interest can be eluted directly without any attached protein affinity tags. Naturally, fusion proteins may be engineered with an intein protein affinity tag fused at either the N- or C-terminus of the protein of interest, as appropriate. 

On the flow path two pneumatic 3-way ball valves used to bypass the filter. Pneumatic 4-way (or an arrangement of 3-way) ball valves are used to bypass the chromatographic column and to revert the elution direction into the chromatographic column. 

The chief drawback of this method is the uncertainty associated with parameter estimation. To overcome this problem, the reaction can be carried out in a chromatographic reactor packed with beads of the immobilized enzyme and the amounts of the enantiomers eluted directly measured. An unsteady-state analysis of such a reaction leads to the following simple expression (Wu, 1998) ... 

Diastereomers may have different responses on the chromatographic systems Pure enantiomers are eluted directly from the column ... 

Figure 4 Experimental setup used to integrate MAE with the subsequent steps of the analytical process. (1) Leaching step. CT, controller MO, microwave oven S, sample R, refrigerant WR, water reservoir TCPP, two-channel piston pump ER, extract reservoir (2) Clean-up/preconcentration step. SV, selecting valve M, methanol A, air B, buffer PP1 and PP2, peristaltic pumps F, filter EL, elution loop MC, minicolumn R, retention direction E, elution direction IV1-IV3, injection valves W, waste. (3) Individual separation-detection step. HPIV, high-pressure injection valve AC, analytical column DAD, diode array detector SR, solvent reservoirs. (Reproduced with permission from Luque de Castro MD and Luque-Garcfa JL (2002) Acceleration and Automation of Solid Sample Treatment Elsevier.)...

Sample preparation Soil was extracted with methanol— 0.01 M calcium chloride dihydrate (4 1), and the extract was filtered and cleaned up on a C-18 cartridge water samples were eluted directly through the cartridge. 

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