Zeeman-correction

It was also shown that 2% nitric acid reduced the background to a level that can be handled by the Zeeman correction system. From 4% to 8% nitric acid, the changes in background signal shapes were not very large. 

Lum and Callaghan [140] determined down to 2 ng/1 of cadmium directly in seawater by atomic absorption spectrometry with Zeeman correction. 

Moffett [179] determined chromium in seawater by Zeeman corrected graphite tube atomisation atomic absorption spectrometry. The chromium is first complexed with a pentan-2,4 dione solution of ammonium 1 pyrrolidine carbodithioc acid, then this complex extracted from the water with a ketonic solvent such as methyl isobutyl ketone, 4-methylpentan-2-one or diisobutyl ketone. 

Moffett JH (1987) Varian Atomic Absorption No. AA69, Measurement of Varain Techitron Pty, Ltd., Mulgrave, Victoria, Australia. Chromium in environmental waters by Zeeman corrected graphite tube atomisation... 

Beam chopping corrects for flame emission but not for scattering. Most spectrometers provide an additional means to correct for scattering and broad background absorption. Deuterium lamps and Zeeman correction systems are most common. 

In this Hamiltonian (5) corresponds to the orbital angular momentum interacting with the external magnetic field, (6) represents the diamagnetic (second-order) response of the electrons to the magnetic field, (7) represents the interaction of the nuclear dipole with the electronic orbital motion, (8) is the electronic-nuclear Zeeman correction, the two terms in (9) represent direct nuclear dipole-dipole and electron coupled nuclear spin-spin interactions. The terms in (10) are responsible for spin-orbit and spin-other-orbit interactions and the terms in (11) are spin-orbit Zeeman gauge corrections. Finally, the terms in (12) correspond to Fermi contact and dipole-dipole interactions between the spin magnetic moments of nucleus N and an electron. Since... 

The term involving both the external field and the internal (dipolar) field is the electron-nuclear Zeeman correction... 

Almost no real samples can be run without background correction. After an instrument has been in service for some time, the continuum background correction lamps do not always remain in adjustment and correction can introduce errors. This is, beyond doubt, the major advantage of Zeeman correction. Since the same source and optical system are used for both analysis and correction, nothing can go out of adjustment. For this reason Zeeman corrected systems can accommodate much higher backgrounds which produces greater accuracy, as well as lower detection limits, in real samples. 

Continuum correction often introduces overcorrection errors for particular combinations of matrix and analyte. Dozens of these errors have been summarized in the literature by Slavin and Carnrick (1988). Fig. 9 shows the problem that arises in tissue samples (fish in this case) when Se is determined. There is a large negative signal caused by phosphate absorption bands in the gaseous phase when a continuum corrector is used. The upper line is background. There is no problem when Zeeman correction is used. 

How does one decide if Zeeman correction is necessary for some particular samples If you are serious about furnace analyses and accurate results are required at low concentrations, a Zeeman corrected system is close to mandatory. 

Antimony can be determined in blood and urine using simple STPF conditions. The presence of large amounts of Fe produces an interference in the determination of Sb at 217.6 nm using continuum correction (Fernandez and Giddings, 1982) and this will probably cause a small error for Sb in blood. The problem is avoided by using Zeeman background correction. Palladium alone, or with Mg(N03)2. has been found (Schlemmer and Welz, 1986) to be an effective modifier for Sb. Early furnace papers determining Sb in blood and urine found a variety of interferences that required separation of the matrix by extraction prior to deposition of the extract in the furnace. The use of STPF conditions with Zeeman correction avoids these problems. 

A good urinary As procedure has been developed by Paschal et al. (1986) using STPF technology and Zeeman background correction. Zeeman correction was judged to be critical to remove matrix interferences. The determination of As in many biological materials requires Zeeman correction but with this technology As becomes a simple determination. 

Cadmium is one of the most widely determined metals using the graphite furnace. A direct STPF method for Cd in urine detected less than 0.04 fig/L in the sample (Pruszkow-ska et al., 1983a). Zeeman correction was necessary because of the large background signals that accompanied the determination. The urine was diluted 1 + 4 in the matrix modifier. 

Serum and blood Cr is an important determination now being done frequently with STPF conditions and Zeeman correction (Schermaier et al., 1985). Serum is diluted 1 + 1... 

There is very little in the literature using modern furnace methods for Co in biological materials. Kimberly et al. (1987) determined Co in urine using mostly STPF conditions and Zeeman correction, except that the sample was deposited on the wall of the tube. They used 10, mL of a 1 -i- 1 dilution of urine and found no interferences. They reported a detection limit of 2.6, wg/L Co in the urine. We believe the detection limit can be reduced below 0.5, g/L if the platform and a somewhat larger sample are used. 

The determination of serum Pb with the furnace is difficult because the serum levels are very low. STPF methods and Zeeman correction are mandatory for serum Pb. If, as has been reported, normal serum Pb is less than 1 g/L, it will not be possible to measure these levels with confidence with a direct method. A 20- uL aliquot of a 1 -t- 1 dilution of serum in the diluent mentioned earlier will provide a detection limit a little lower than 1 IxqIL. For serum levels higher than this, the method can be used with confidence. 

Urine Pb down to the l- wg/L level can be measured in 20of a 1 + 1 dilution of urine in the matrix modifier. If a somewhat poorer detection limit is acceptable, a 1 -1- 3 dilution of urine is more reliably handled by the autosampler. Paschal and Kimberly (1985) used a very similar urine Pb method but altered the conditions to make the method applicable to non-Zeeman corrected instruments. 

Manganese is an ideal STPF analyte. The low levels of Mn that are often found in biological materials suggest that it should be determined in the furnace, usually by direct methods. The major problem with the determination of Mn is the control of contamination, which is discussed in an earlier section. Zeeman correction is particularly useful for Mn because, at the long wavelength used for Mn (279.5 nm) the continuum correctors are not very effective. 

Selenium is probably the furnace determination which most demands Zeeman correction STPF technology. Other methods are slow and prone to manipulative errors at the low concentrations that are typically of interest in biological materials. Nevertheless, the volatility of many Se compounds, especially organoselenium compounds, produces troubles. Both Fe and P cause severe overcorrection errors when Se is determined with continuum correction, making Zeeman correction mandatory for Se in biological materials. There are many papers in the literature that have not used Zeeman correction for Se but they rely on delicate timing of the thermal program so that Se is not volatilized at the same time as the interferent. The paper of Verlinden et al. (1981) on the MS determination of Se should be consulted. 

Silver is sensitively detected in the graphite furnace and is relatively free of interferences when STPF conditions are used. There is very little literature on biochemical applications but there is a growing literature on environmental materials. The experimental conditions for Ag with STPF and Zeeman correction were studied (Manning and Slavin. 1987) and it is recommended that Pd be used as a matrix modifier. 

Tellurium is rarely sought in biological materials but it will pose no problems when determined with STPF conditions. Like As and Se, there are problems in the presence of phosphorus if continuum correction is used and Zeeman correction is recommended for biological materials (Fernandez and Giddings, 1982). The preferred modifier is Pd. 

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