Columns direct

Figure 16. Simplified schematic of the architecture of a single CCD pixel. The channel stops permanently define the pixel boundaries in the column direction. The pixel rows are defined by the electric fields applied to the three pixel phases. For a 15 /urn pixel CCD, channel stops are 2-3 /um wide and the phases are each 5 /um wide.

There are two major incompatibilities between HPLC and MS. The first is that the HPLC mobile phase is a liquid, often containing a significant proportion of water, which is pumped through the stationary phase (column) at a flow rate of typically 1 mlmin while the mass spectrometer operates at a pressure of around 10 torr (1.333 22 x 10 " Pa). It is therefore not possible simply to pump the eluate from an HPLC column directly into the source of a mass... 

As in the case in the analysis of food samples, the introduction of relatively inexpensive MS detectors for GC has had a substantial impact on the determination of methylxanthines by GC. For example, in 1990, Benchekroun published a paper in which a GC-MS method for the quantitation of tri-, di-, and monmethylxanthines and uric acid from hepatocyte incubation media was described.55 The method described allows for the measurement of the concentration of 14 methylxanthines and methyluric acid metabolites of methylxanthines. In other studies, GC-MS has also been used. Two examples from the recent literature are studies by Simek and Lartigue-Mattei, respectively.58 57 In the first case, GC-MS using an ion trap detector was used to provide confirmatory data to support a microbore HPLC technique. TMS derivatives of the compounds of interest were formed and separated on a 25 m DB-% column directly coupled to the ion trap detector. In the second example, allopurinol, oxypurinol, hypoxanthine, and xanthine were assayed simultaneously using GC-MS. 

The problem of distillation sequencing was discussed in Chapter 11, where the distillation columns in the sequence were operated on a stand-alone basis using utilities for the reboilers and condensers. Following the approach in Chapter 11, the best few nonintegrated distillation sequences would be found. These sequences would then be heat integrated as discussed above. Figure 21.8 shows how heat integration can be applied within a two-column direct... 

Fig. 11.1. In addition, one area that has yet to be characterized is the use of sequential RP columns with large dead volumes. It seems unlikely that peptides eluting from the RP trap would reconcentrate on the RP column directly in front of the mass spectrometer diminishing the value of the second RP column. This needs further analytical investigation.

For capillary GC, the split/splitless inlet is by far the most common and provides an excellent injection device for most routine applications. For specialized applications, there are several additional inlets available. These include programmed temperature vaporization (PTV) cool on-column and, for packed columns, direct injection. PTV is essentially a split/splitless inlet that has low thermal mass and a heater allowing rapid heating and cooling. Cool injection, which can be performed in both split and splitless mode with the PTV inlet, reduces the possibility of sample degradation in the inlet. Capabilities of the commonly available inlets are summarized in Table 14.3. 

The instrumental design is similar to that of other mass spectrometers described above, with the end of the GC column directly inserted into the ion... 

The injector, columns and valves reside in a low temperature chamber to minimize the loss of deuterium by back exchange (Fig. 12.2). The quenched protein solution is pumped in series through a column containing an immobilized protease and a trap column to capture the peptide fragments. The gradient pump is activated following digestion and the peptides captured on the trap column are eluted and separated over an analytical reverse-phase HPLC column directly into the mass spectrometer. 

If using a GSTrap FF, connect the column directly to a Hi-trap benzamidine FF column. 

Paliadium(il) acetate (98%, Strem Chemicais Inc.), triphenyiphosphine (99%. Fisher Scientific Co.), and sodium acetate (99%, Ruka Chemika) were used without further purification. N,N-Dimethyiacetamide (DMA) was distilled from calcium hydride through a 25-cm Vigreux column directly before use. 

In some cases, the eluate from a MSPD column is adequately clean. However, additional steps are often required to remove coeluted matrix components either by using other solid-phase materials packed at the bottom of the MSPD column or by eluting analytes from the MSPD column directly onto a second SPE... 

Current multiresidue methods for alkaloids typically involve extraction with a polar solvent such as ethanol, evaporation to remove the solvent, and a series of acid/base liquid-liquid partition steps for cleanup. An alternative method is extraction with aqueous acid followed by alkaliniza-tion and extraction into organic solvent or by the use of SPE columns. Direct solvent extraction... 

This compound, thiomescaline, is a byway that takes advantage of one of those vertical columns. Directly below the element oxygen, there is found sulfur, which has much the same binding complexity, but is twice as massive. The... 

Conventional high pressure NICI spectra were obtained using a Hewlett-Packard 5985B quadrupole GC/MS, as described previously (1). Methane was used as the Cl reagent gas and was maintained in the source at 0.2-0.4 torr as measured through the direct inlet with a thermocouple gauge. A 200 eV electron beam was used to ionize the Cl gas, and the entire source was maintained at a temperature of 200° C. Samples were introduced into the spectrometer via the gas chromatograph which was equipped with a 25 meter fused silica capillary column directly interfaced with the ion source. For all experiments, a column coated with bonded 5% methyl phenyl silicon stationary phase, (Quadrex, Inc.) was used and helium was employed as the carrier gas at a head pressure of 20 lbs. Molecular sieve/silica gel traps were used to remove water and impurities from the carrier gas. 

The isotopic analysis requires a proce gre of sufficient specificity and sensitivity to analyze the O-enriched TMPO as a 1% solution in a 90 10 mixture of methanol/water. We have utilized two different instrumental procedures. One employs a gas chromatographic column directly coupled to the mass spectrometer the other, probe microdistillation in the ion source in conjunction with high-resolution mass measurement. The two procedures have consistently yi Jded nearly identical analyses. 

Direct injection simply transfers the entire sample to the analytical column. Direct injection techniques include direct flash vaporization (hot direct injection) and cold on-column. Direct flash vaporization has become popular used with wide-bore capillary columns (> 530 /xm ID) having phase ratios less than 80 and high sample volume capacity and can easily accommodate injections of up to 10 /xl of sample. 

Laboratory lysimeters were constructed of plexiglass tubing (6.2 cm i.d. 0.6 cm wall thickness 90 cm length), supported in a vertical position. A 164 micron pore size corundum disc (6.10 cm diameter 0.6 cm thickness) was placed in each column directly over the drain hole in order to support the fly ash sorbent and to prevent clogging of the outlet. 

All resolution methods mathematically decompose a global instrumental response of mixtures into the contributions linked to each of the pure components in the system [1-10]. This global response is organized into a matrix D containing raw measurements about all of the components present in the data set. Resolution methods allow for the decomposition of the initial mixture data matrix D into the product of two data matrices C and ST, each of them containing the pure response profiles of the n mixture or process components associated with the row and the column directions of the initial data matrix, respectively (see Figure 11.2). In matrix notation, the expression for all resolution methods is ... 

The correct performance of any curve-resolution (CR) method depends strongly on the complexity of the multicomponent system. In particular, the ability to correctly recover dyads of pure profiles and spectra for each of the components in the system depends on the degree of overlap among the pure profiles of the different components and the specific way in which the regions of existence of these profiles (the so-called concentration or spectral windows) are distributed along the row and column directions of the data set. Manne stated the necessary conditions for correct resolution of the concentration profile and spectrum of a component in the 2 following theorems [22] ... 

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