Background spectra

Every column (including chemically bonded columns) will have some column bleed. The amount of column bleed will increase with increasing column temperature, film thickness, column diameter, and column length. The base line starts to rise approximately 25-50° below the upper temperature limit of the stationary phase. After a column is installed in a GC/MS system, a background spectrum should be obtained for future reference. 

Background spectrum, tungsten, copper, and nickel lines in, 229 Backlash, error due to, 285-287 Bank notes, histograms from x-ray spec-trographic chart recordings of, 225-227... 

The potential of a tunable dye laser should not be overlooked. A tunable dye laser, employing an organic dye as lasing material allows one to choose any suitable excitation line within a particular region. This is in contrast to the case of a gas ion laser which has a limited number of emission lines at fixed wavelength. Nevertheless, a tunable dye laser has significant drawbacks such as poor resolution imposed by the dye laser linewidth (1.2 cm-1) and a continuous background spectrum which requires the use of a tunable filter 15-18). 

If preferred, the data system may be used to subtract the background spectrum (Figure 3.14) from that of the analyte (Figure 3.16). This manipulation yields the spectrum shown in Figure 3.17, in which the ions from the background are now totally absent. Care must be taken when adopting this procedure to ensure that any contribution from the analyte is not removed when ions at the same m/z value arise from both the background and the analyte of interest. 

Figure 9. Laser desorption FTMS mass spectra recorded following successive shots of the laser. In each spectrum, (a) shows the results following the first laser pulse, (b) is the second laser pulse at the same spot, (c) is after the third laser pulse, and (d) is the background spectrum (laser off).

Positive going bands indicate the consumption of species, which are present in higher concentration at the potential of the background spectrum ... 

All bands discussed here were also observed with 1 M CH3OH solutions. In order to check that the above discussed bands are due to bulk products accumulated in the thin layer, one series of experiments was performed stepping the potential from 1500 mV down to 450 mV after taking the background spectrum at 0 mV. In this case the bands are observed at all potentials showing that stable bulk products are accumulated in the interface. 

Catalyst Activation Gas phase activation of supported DENs was examined using in-situ FTIR spectroscopy and FTIR spectroscopy of adsorbed CO. For in-situ dendrimer decomposition studies, the spectra were collected under a gas flow composed of 20% 02/He or 20% H2/He. The supported DEN sample was pressed into a self-supporting wafer, loaded into a controlled atmosphere IR cell, and collected as the sample background. The temperature was raised stepwise and spectra were collected at each temperature until little or no change was observed. After oxidation, the sample was reduced in 20% H2/He flow with various time/temperature combinations. The sample was then flushed with He for lhr at the reduction temperature. After cooling under He flow, a background spectrum was collected at room temperature. A 5% CO/He mixture was flowed over the sample for 15 minutes, followed by pure He. IR spectra of CO adsorbed on the catalyst surface were collected after the gas phase CO had been purged from the cell. 

Flame background spectrum of an acetylene -oxygen flame containing an organic aerosol. 

FJciureJyT. (a) Mass spectrum at the top of the chromatographic peak (b) background spectrum (c) analyte spectrum after background subtraction (d) library spectrum of hexachlorobiphenyl (score 99%). 

UV Etching. A typical mass spectrum of the vaporized UV etching products is shown in Figure 4, together with a background spectrum obtained without UV irradiation. The comparison clearly shows that UV irradiation causes an increase in intensity for various mass peaks. For example, the intensity of the peaks of m/e=15, 31, 59 and m/e=41, 69 increased drastically by UV irradiation. The former three are due to side-chain scission caused by UV absorption at the C=0 unit, while the latter two are due to main-chain scission initiated by side-chain scission (11). The structure and mass numbers of typical vaporized species are shown in Table I. From here on, we use the spectral intensity after the background is subtracted. 

The detection difficulties were then accentuated by the several types of background which were superimposed on the x-ray spectrum of interest. This was overcome by the modelling and subtraction of the background spectrum from the acquired spectrum. 

The sampling station was equipped with an overhead DRIFTS accessory. The sample holder was used for the background spectra without KBr, and 256 coadded scans were taken for each sample from 4000 to 400 cm at a resolution of 16 cm L Single-beam spectra of the samples were obtained, and corrected against the background spectrum of the sample holder, to present the spectra in absorbance units. Spectra were collected in duplicate and used for multivariate analysis. 

Figure 5. Infrared spectrum at room temperature of VSil545 after evacuation at 500 C (a) and after contact at room temperature with 50 torr of propane (b). Reported in the inset is the expansion in the 1300-1550 cm region of spectrum b after subtraction of spectrum a. The background spectrum due to gaseous species has been subtracted.

But bremsstrahlung must also be considered as a part of the background spectrum.17 The main ionization processes of an analyte (M) in argon inductively coupled plasma are ... 

Beam Condensers.4c Beam condensers are used to focus the IR radiation from a beam that is typically 8 mm in diameter to one that is around 2 mm at the sample plane. This allows the analysis of 50-100 resin beads without KBr dilution. A diamond compression cell is used to flatten beads and to support the sample throughout the measurement. The same diamond cell without beads is then used to record a background spectrum. 

As far as we can see into the Universe, we don t observe any primordial antimatter. Within the limits of our present observational horizon the Universe is seen to contain only matter and no antimatter. The presence of cosmic antimatter would lead to observable traces of annihilation however the measurements of the extragalactic 7 ray flux indicate an absence of annihilation radiation, and the microwave background spectrum lacks a corresponding distortion. These findings preclude the existence of a significant amount of antimatter within tens of Megaparsecs, which is the scale of super-clusters of galaxies. 

IR spectrum of chemisorbed hexamethyl-disilazane on silica (---) the background spectrum in each case (-) new... 

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