Solvent peak

The effluent from a GC column is already in the gas phase and needs only to be mixed with argon makeup gas before passage into the flame. Precautions need to be taken to divert temporarily the GC flow when the first solvent peak emerges because it contains far too much material for the plasma to withstand. 

The coupled resonance overlaps with the solvent peaks. For additional information see Refs. 116 and 117. 

These columns make the elution of low molecular weight components slower and can he used to separate a solvent peak or other troublesome peaks to realize accurate measurements of the molecular weight distribution. The use of this column with 805L, 806L, 806M, and 807L columns is recommended. 

Figures 6.6 and 6.7 show the effect of a solvent separation column. In the case of Fig. 6.7, the upper part of the figure shows the chromatogram of polyvinyl chrolide, which contains dioctyl phthalate (DOP), using KF-806L. In this case, DOP is not separated from a solvent peak. However, DOP can be separated from the solvent peak using KF-800D in conjunetion with KF-806L (Table 6.6).

Fig. 20. Schematic representation of the unrolled major groove of the MPD 7 helix showing the first hydration shell, consisting of all solvent molecules that are directly associated with base edge N and O atoms. Base atoms are labeled N4,04, N6,06 and N7 solvent peaks are numbered. Interatomic distances are given in Aup to 3,5 A represented by unbroken lines, between 3,5-4,1 A by dotted lines. The eight circles connected by double-lines represent the image of a spermine molecule bound to phosphate groups P2 and P22. There are 20 solvent molecules in a first hydration layer associated with N- and O-atoms l58)...

We normally avoid protonated solvents, because the very intense solvent peak will obscure nearby protons, and the dynamic range problem will also... 

Figure 1 Example of a sample chromatogram with the analyte peak (11) eluting at 18.23 min, solvent peaks (1-3), matrix component peaks (4, 7-10, 12), and instrumental noise (5, 6,13)...

BIPS 7 in DMSO-[Pg.16]

Desorption of an analyte from the SPME fibre depends on the boiling point of the analyte, the thickness of the coating on the fibre, and the temperature of the injection port. The fibre can immediately be used for a successive analysis. Some modifications of the GC injector or addition of a desorption module are required. It is possible to automate SPME for routine analysis of many compounds by either GC-MS or HPLC. A significant advantage of SPME over LLE is the absence of the solvent peak in SPME chromatograms. SPME eliminates the separate concentration step from the SPE and LLE methods because the analytes diffuse directly into the coating of the SPME device and are concentrated there. 

Extraction or dissolution almost invariably will cause low-MW material in a polymer to be present to some extent in the solution to be chromatographed. Solvent peaks interfere especially in trace analysis solvent impurities also may interfere. For identification or determination of residual solvents in polymers it is mandatory to use solventless methods of analysis so as not to confuse solvents in which the sample is dissolved for analysis with residual solvents in the sample. Gas chromatographic methods for the analysis of some low-boiling substances in the manufacture of polyester polymers have been reviewed [129]. The contents of residual solvents (CH2C12, CgHsCI) and monomers (bisphenol A, dichlorodiphenyl sulfone) in commercial polycarbonates and polysulfones were determined. Also residual monomers in PVAc latices were analysed by GC methods [130]. GC was also... 

Diglycidyl ether of bisphenol A (DGEBA, MW 340 Da) and 4,4 -dihydroxy-diphenylmethane (DHDPM, MW 200 Da) were analysed by SEC-MALS [784]. DGEBA and DHDPM are the basic oligomers of epoxy resins and phenol-formaldehyde condensates, respectively, which are widely used in the electronic and automotive industries. Excellent reproducibility ( 1 %) and good accuracy (better than 10%) were observed. SEC has also been used for the determination of mineral oil in extended elastomers [785] and in PS [178]. With heptane containing 0.05% isopropanol as the mobile phase, mineral oil is completely unretained and elutes before the solvent via SEC all other components in a PS extract are retained on silica and elute after the solvent peak. 

Modifiers can be used very effectively in on-line SFE-GC to determine the concentration levels of the respective analytes. This presents an advantage in terms of the use of modifiers in SFE, since they appear as solvent peaks in GC separations and do not interfere with the target analyte determination. Although online SFE-GC is a simple technique, its applicability to real-life samples is limited compared to off-line SFE-GC. As a result, on-line SFE-GC requires suitable sample selection and appropriate setting of extraction conditions. If the goal is to determine the profile or matrix composition of a sample, it is required to use the fluid at the maximum solubility. For trace analysis it is best to choose a condition that separates the analytes from the matrix without interference. However, present SFE-GC techniques are not useful for samples... 

The main characteristics of on-line SPME-HPLC(-MS) are shown in Table 7.18. Most of the SPME fibres are compatible with HPLC solvents. SPME combined with HPLC provides a means by which simple, rapid concentration of analytes can be achieved together with a means of introduction of the concentrated analytes to the HPLC system. This eliminates the need for larger injection volumes, and avoids derivatisation if the analytes were to be detected by GC. An advantage of the SPME method over LLE methods is the absence of a solvent peak in chromatograms obtained after extraction by SPME. SPME is not suitable for organic solutions. As SPME is a microextraction technique, coupling to ft, HPLC may be envisaged. 

As mentioned in Chapter 3, we standardise our reporting of chemical shifts with reference to TMS or the residual solvent peak. Your spectrometer software should do this for you automatically. If it gets it wrong (which is possible if you have a mixed solvent or a spurious peak near TMS), then you can set it manually using your software. 

The spray paint can was inverted and a small amount of product was dispensed into a 20 mL glass headspace vial. The vial was immediately sealed and was incubated at 80°C for approximately 30 min. After this isothermal hold, a 0.5-mL portion of the headspace was injected into the GC/MS system. The GC-MS total ion chromatogram of the paint solvent mixture headspace is shown in Figure 15. Numerous solvent peaks were detected and identified via mass spectral library searching. The retention times, approximate percentages, and tentative identifications are shown in Table 8 for the solvent peaks. These peak identifications are considered tentative, as they are based solely on the library search. The mass spectral library search is often unable to differentiate with a high degree of confidence between positional isomers of branched aliphatic hydrocarbons or cycloaliphatic hydrocarbons. Therefore, the peak identifications in Table 8 may not be correct in all cases as to the exact isomer present (e.g., 1,2,3-cyclohexane versus 1,2,4-cyclohexane). However, the class of compound (cyclic versus branched versus linear aliphatic) and the total number of carbon atoms in the molecule should be correct for the majority of peaks. 

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