Spectral Interference Control

Spectral line interference is less critical in atomic absorption than it is in flame emission. This is due to the fact that absorption is usually concerned with one spectral line only for each element and that, by proper modulation of the source signal, extraneous spectral lines that do not actually overlap the desired line are not detected. It is wise, however, to use as narrow a slit width as possible to keep the spectral band pass of the monochromator to a minimum. Actual spectral line overlap cannot be corrected by this means. If spectral line overlap occurs, as might happen, e.g., with palladium at 3404.6 A and cobalt at 3405.1 A, the only solutions are (1) to use another spectral line of the element or (2) remove the offending element from the analytical sample. 

Spectral bands or a general continuum can be troublesome for example, the copper line at 3274.0 A and the OH band with a band head at 3274.2 A mutually interfere. The best system for control of the OH band interference is to use a narrow slit and read the magnitude of the OH band contribution 

Spectral band interferences should, theoretically, be eliminated by proper modulation of the source however, a strong band or continuum may overload the photomultiplier and require treatment as explained above. 

---

Of the four strategies given above, the best condition for obtaining independent data for quality control (QC) are satisfied when INAA and RNAA results are compared, because the use of RNAA dramatically improves the selectivity of signal measurement and eliminates or greafiy reduces the measurement uncertainty sotuces, such as spectral interferences. A variety of radiochemical separations and... 

Quantum control beyond spectral interference and population control Can resonant intense laser pulses freeze the population ... 

In this contribution recent results [13] on the control of the quantum mechanical phase of an atomic state in strong laser fields studied using the Autler-Townes (AT) effect [14] in the photoionization of the K (4p) state are discussed. We demonstrate quantum control beyond (i) population control and (ii) spectral interference, (i) We show, that for suitable combinations of the laser intensity of the first pulse and the time delay the second resonant intense laser pulse leaves the excited state population unchanged. However, the knowledge of the... 

We demonstrate coherent control in strong fields beyond (i) population control and (ii) spectral interference, since (i) control is achieved without altering the population during the second intense laser pulse, i.e., the population during the second laser pulse is frozen, and (ii) the quantum mechanical phase is controlled without changing the spectrum of the pulse sequence. The control mechanism relies on the interplay of the quantum mechanical phase set by the intensity of the first pulse and the phase of the second pulse determined by the time delay. 

Fig. 1. Demonstration of the phase control of femtosecond chirped pulses. Solid lines spectral phase of the diffracted pulse for two delays X and -X between the writing pulses. Thin dotted lines spectral phase difference between the 2 writing pulses for the two cases x and -X. The thin dashed line represents the spectral amplitude of the diffracted pulse. Insert spectral interference fringes between the unchirped and chirped writing pulses at time delay equal 0 at 800nm. The chirp is formed by propagation through a SF58 glass plate of thickness 1.7 cm.

Spectral interferences from overlapping absorption lines may take place in FLAA analysis. They can be controlled by the proper selection of the instrument s optical system settings. 

Where applicable, the use of competitive cations for the control of anionic depressors appears to represent the method of choice. No spectral interference arises in atomic absorption from the addition of another cation, an objection often raised in emission. The concentrations of the added salt required for full anion control usually are less than 1%, a salt level well below that at which light scattering is observed. When working with serum, denaturation or precipitation of proteins may occur from the addition of high concentrations of lanthanum chloride or other salts, and the concomitant changes in solution properties should be taken into... 

In AAS and AFS, limitations to the analytical accuracy are mostly related to physical and chemical interferences and are due less to spectral interferences. In furnace AAS thermochemical processes limit the achievable accuracy and necessitate temperature programs to be carefully worked out in order to cope with errors arising from thermochemical effects. In AFS and also in LEI, it is necessary to control matrix influences relating to quenching when analyzing real samples. 

In flame emission, spectral interferences are common and affect accuracy. Spectral interferences occur because the different elements excited emit their radiation simultaneously and the monochromator may not have the resolution to isolate an analytical line from the effect of a very intense or a very close interfering line. Precision also suffers because the population of excited atoms is affected by flame fluctuations that are difficult to control. Flame emission is extremely sensitive for the determination of the alkali metals, the alkaline earth metals, and a few other metallic elements. 

Flame background or a continuum is a third type of spectral interference. It also can be controlled by use of an ac detection system. Random noise in the flame cell, since it contains a large number of ac components, cannot be entirely eliminated by use of an ac electronic system but the magnitude of this effect can be reduced substantially by use of an ac system, preferably the tuned (lock-in) type of system. 

---