Background continuum source

Instrumental correction for background absorption using a double beam instrument or a continuum source has already been discussed (p. 325). An alternative is to assess the background absorption on a non-resonance line two or three band-passes away from the analytical line and to correct the sample absorption accordingly. This method assumes the molecular absorption to be constant over several band passes. The elimination of spectral interference from the emission of radiation by the heated sample and matrix has been discussed on page 324 et seq. 

H. Becker-Ross, S. Florek, U. Heitmann, Observation, identification and correction of structured molecular background by means of continuum source AAS - determination of selenium and arsenic in human urine, J. Anal. Atom. Spectrom., 15 (2000), 137. 

In radio astronomy multichannel or autocorrelation (Fourier) spectrometers are used which simultaneously cover the whole line profile. Consider a molecular cloud observed against a source of continuum radiation of a given brightness temperature. The continuum brightness temperature is the sum of the 2.7 °K isotropic background radiation Tbh of a continuum source (such as an HII region or a supernova remnant) which may be in the line of sight and located behind the molecular cloud. A specific molecular transition with optical... 

It is readily seen from Eq. (25c) that if 7 jb + Tc > Tex, the molecular line will appear in absorption, whereas if Tht, + Tc < Tex, the line will appear in emission. If there is no continuum source in the line of sight, Tc = 0, and if collisional transitions are slow compared with radiative transitions induced by the isotropic background radiation, the molecules equilibrate with the 2.7 °K radiation,... 

Background correction is carried out with a continuum source, e.g. a hydrogen hollow-cathode lamp or a deuterium-arc lamp. 

Bismuth 223.1 air/acetylene Sample preparation. Dissolve 2.000 g of sample in 12 ml of hydrochloric acid, 6 ml of nitric acid and 20 ml of water in a PTFE beaker. Evaporate the solution to 10- 12 ml, cool, add 1 ml of hydrofluoric acid dropwise and boil for five minutes. Cool, add 5 ml of 1% boric acid solution and dilute to 50 ml. Background correction using a UV continuum source is advisable for bismuth... 

Background interference. Correction for non-specific absorption is sometimes essential in geochemical work (section I.D.) and is most conveniently carried out by means of a continuum source. However, not all systems available are completely effective, and this feature should be checked before purchase of an instrument. It is essential that the beams from the hollow-cathode lamp and the continuum lamp traverse exactly equivalent paths through the flame, and can be accurately balanced for energy. 

Simple procedures that require only a dilution of serum or urine have been reported by Schattenkirchner and Grobenski [95], and by Ward et al. [96]. The former diluted samples of sera 1 + 4 with 0.1% Triton X 100 and urine samples 1 + 9 with 0.01 M HC1 and the latter used a 1 + 9 dilution of serum in water. In both cases calibration was by standard additions to compensate for the considerable matrix interferences. Ward et al. [96] demonstrated an excellent correlation (r = 0.98) between neutron activation analysis (NAA) and ETA—AAS analysis of the total plasma Au and albumin bound Au, which contains up to 90% of the total. There was however, a bias towards higher values (10%) by NAA. This difference did not appear to be pre-atomisation losses during ETA—AAS, the recoveries of added Au ranged from 90—105%, nor over-correction by continuum source background corrector. 

High-pressure mercury lamp (ore) Radiation source containing mercury at a pressure of ca. 8 MPa (ca. 80 bar) or higher which emits hues over a background continuum between about 200 and 1400 nm. 

One of the main practical problems with the use of AAS is the occurrence of molecular species that coincide with the atomic signal. One approach to remove this molecular absorbance is by the use of background correction methods. Several approaches are possible, but the most common is based on the use of a continuum source, D2. In the atomization cell (e.g. flame) absorption is possible from both atomic species and from molecular species (unwanted interference). By measuring the absorption that occurs from the radiation source (HCL) and comparing it with the absorbance that occurs from the continuum source (D2) a corrected absorption signal can be obtained. This is because the atomic species of interest absorb the specific radiation associated with the HCL source, whereas the absorption of radiation by the continuum source for the same atomic species will be negligible. 

Continuum source background correction uses a deuterium lamp to obtain an estimate of the background absorbance. A hollow-cathode lamp obtains the total absorbance. The corrected absorbance is then obtained by calculating the difference between the two. 

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