of Pixel at 196 nm
aAll values determined with HGA-500 graphite furnace atomizer (Perkin-Elmer, Norwalk, CT, USA). bCharacteristic mass.21 cComputed from
m as described in ref. 22. dSpectraspan III echelle (Spectrametrics) with 256 pixel LPDA and 25 mm pixel width.22 eSpectraspan III echelle
´ ´
0
(Spectrametrics) with 128 pixel LPDA and 50 mm pixel width.22 fH-20 monochromator with 128 pixel LPDA and 50 mm pixel width.23 gOptima
echelle (Perkin-Elmer) with 256 pixel LPDA and 25 mm pixel width.13 hPhysical width of pixel.
´
portional to the detection limit. The previous section demon- Table 4 CS-AAS detection limits
strated that the normalized, integrated absorbance was
Element Wave- HGA-500 furnace THGA furnace
independent of the source and detector characteristics.
length/
Consequently, the detection limit is directly proportional to nm LSa CS-LPDAb CS-SCDc LSd CS-DEMONe
the absorbance noise.
Eqn. (2) shows that the absorbance noise will grow smaller As 193.7 20 28 12 6 4
as the intensity increases or the read noise decreases. This Se 196.0 30 50 16 9 13
equation also indicates that the absorbance noise will decrease Zn 213.9 1 2 0.1 0.4 0.2
Pb 217.0 10 6 4 4 –
with increasing spectral bandwidth. For example, if the Sb 217.6 15 – 8 4 2.5
entrance slit width is doubled, the intensity will double, the Bi 223.1 6 – 5 – –
number of pixels necessary to cover the profile will double Sn 224.6 20 26 – 10 –
and sA will decrease by √2. The LPDA used previously with Cd 228.8 0.4 0.4 0.07 0.1 0.1
CS-AAS12 had a read noise of about 3000 e −. As a result, Ni 232.0 10 11 – 8 –
read noise was dominant at all intensity levels. The best Be 234.9 1 – – 0.1 0.08
Co 240.6 2 4 – 4 –
detection limits (Table 4) were obtained with the largest Fe 248.3 2 2 – 0.8 0.6
entrance slit width of the echelle, 500 mm. At the time, these
´
Si 251.6 40 – – 15 6
detection limits were the best ever achieved for CS-AAS, but Tl 276.8 10 – 1 9 3
they precluded operation in the high-resolution mode. Mn 279.5 21 0.5 0.2 0.6 0.3
The photon shot noise limited case, the ideal case, is achieved Pb 283.3 5 0.9 0.4 4 1
if the fluctuation noise is eliminated and the read noise is low. Al 309.3 4 – – 3 0.8
Mo 313.3 4 – – 1 2
A high quality CCD will typically have a read noise of less Cu 324.7 1.0 0.6 – 4 1
than 25 e−. Consequently, all but the lowest intensities Ag 328.1 0.5 – – 0.4 0.2
(625 e−) will be shot noise limited. The absorbance noise Cr 357.9 1 – – 0.4 0.8
for the shot noise limited case is aModel 5000 (Perkin-Elmer).21 bCS with linear photodiode array
0.43√I √n 1 0.43√n 1 (LPDA) detector.22cCS with segmented charge coupled array detector
sA (3) (SCD) of Optima (Perkin-Elmer).13 dSIMAA 6000 (Perkin-Elmer).25
I √I eCS with double echelle monochromator (DEMON).26
´
of Pixel at 196 nm
aAll values determined with HGA-500 graphite furnace atomizer (Perkin-Elmer, Norwalk, CT, USA). bCharacteristic mass.21 cComputed from
m as described in ref. 22. dSpectraspan III echelle (Spectrametrics) with 256 pixel LPDA and 25 mm pixel width.22 eSpectraspan III echelle
´ ´
0
(Spectrametrics) with 128 pixel LPDA and 50 mm pixel width.22 fH-20 monochromator with 128 pixel LPDA and 50 mm pixel width.23 gOptima
echelle (Perkin-Elmer) with 256 pixel LPDA and 25 mm pixel width.13 hPhysical width of pixel.
´
portional to the detection limit. The previous section demon- Table 4 CS-AAS detection limits
strated that the normalized, integrated absorbance was
Element Wave- HGA-500 furnace THGA furnace
independent of the source and detector characteristics.
length/
Consequently, the detection limit is directly proportional to nm LSa CS-LPDAb CS-SCDc LSd CS-DEMONe
the absorbance noise.
Eqn. (2) shows that the absorbance noise will grow smaller As 193.7 20 28 12 6 4
as the intensity increases or the read noise decreases. This Se 196.0 30 50 16 9 13
equation also indicates that the absorbance noise will decrease Zn 213.9 1 2 0.1 0.4 0.2
Pb 217.0 10 6 4 4 –
with increasing spectral bandwidth. For example, if the Sb 217.6 15 – 8 4 2.5
entrance slit width is doubled, the intensity will double, the Bi 223.1 6 – 5 – –
number of pixels necessary to cover the profile will double Sn 224.6 20 26 – 10 –
and sA will decrease by √2. The LPDA used previously with Cd 228.8 0.4 0.4 0.07 0.1 0.1
CS-AAS12 had a read noise of about 3000 e −. As a result, Ni 232.0 10 11 – 8 –
read noise was dominant at all intensity levels. The best Be 234.9 1 – – 0.1 0.08
Co 240.6 2 4 – 4 –
detection limits (Table 4) were obtained with the largest Fe 248.3 2 2 – 0.8 0.6
entrance slit width of the echelle, 500 mm. At the time, these
´
Si 251.6 40 – – 15 6
detection limits were the best ever achieved for CS-AAS, but Tl 276.8 10 – 1 9 3
they precluded operation in the high-resolution mode. Mn 279.5 21 0.5 0.2 0.6 0.3
The photon shot noise limited case, the ideal case, is achieved Pb 283.3 5 0.9 0.4 4 1
if the fluctuation noise is eliminated and the read noise is low. Al 309.3 4 – – 3 0.8
Mo 313.3 4 – – 1 2
A high quality CCD will typically have a read noise of less Cu 324.7 1.0 0.6 – 4 1
than 25 e−. Consequently, all but the lowest intensities Ag 328.1 0.5 – – 0.4 0.2
(625 e−) will be shot noise limited. The absorbance noise Cr 357.9 1 – – 0.4 0.8
for the shot noise limited case is aModel 5000 (Perkin-Elmer).21 bCS with linear photodiode array
0.43√I √n 1 0.43√n 1 (LPDA) detector.22cCS with segmented charge coupled array detector
sA (3) (SCD) of Optima (Perkin-Elmer).13 dSIMAA 6000 (Perkin-Elmer).25
I √I eCS with double echelle monochromator (DEMON).26
´
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