REPORT FOR ANALYTICAL CHEMISTS
ACI
TEFLON* LINED COATED STAINLESS STEEL
LAB W A R E for those
Table IV. Precision of chemical and AAS methods used for the analysis of a mineral (6).
9.78 2.30
9.90 0.48
9.86 0.83
Cobalt Mean: Coeff. of var, %:
0.454 2.18
0.456 1.13
0.433 0.71
0.429 0.91
Copper Mean: Coeff. of var, %:
1.333 0.71
1.510 3.57
1.417 0.88
1.418 0.56
DIFFICULT LAB JOBS
GRIFFIN BEAKERS Seamless stainless steel. Non-stick prop erties of Teflon* lin ing makes cleaning easy. In 8 sizes from 50 ml to 4000 ml capacity.
CHROMATOGRAPHY CLIPS Assure firm grip to chromatograms on anti-siphon and hold ing rods. Smooth coating of chemically inert Teflon on jaws permits easy removal of wet c h r o m a t o grams without dam age.
Teflon coated stainless steel mixer stirs and blends even the most viscous liquids. Smooth, quick, no splashing. VA" χ 10V2" long or 2 5 /e"x IOV2" long.
Mean: Coeff. of var, %:
36.96 0.29
ceptable values for this silicate rock can be obtained by AAS methods. As indicated earlier, we should be embarrassed because of the dearth of interlaboratory precision studies. In one of the few studies on the precision of chemical and AAS methods, Meddings and Kaiser (6) concluded that the coefficient of variation of the most careful gravimetric and titrimetric methods was about 0.1 per cent, and that the corresponding figure for most rou tine analyses is from 1 to 2 per cent. Their experience with AAS equipment that had a digital read out system and high-brightness lamps indicated that the coefficient of variation of routine analyses by
15
SPEED MIXER
Mean: Coeff. of var, %:
Atomic Absorption Lab A Lab Β
9.89 1.22
Nickel
Iron
• CHEMICALLY INERT • NON-CONTAMINATING • LONG LIFE • EASY TO CLEAN
Ch emical Lab A Lab Β
Element
38.66 0.37
38.25 0.33
38.46 0.80
AAS can be from 0.3 to 0.9 per cent. These conclusions are supported by their data given in Table IV on the analysis of a mineral containing nickel, cobalt, copper, and iron. (These data are on the "overall pre cision" of the methods, which in cludes errors arising from sampling, sample dissolution, etc.) Errors from Losses and Contamina tion. I now want to discuss briefly something that is seldom men tioned in AAS, but which I con sider to be quite serious. This con cerns errors from losses and con tamination. Because of the inher ently low limits of detection of AAS, dilute solutions are used not only for determining substances at
1—1—ι ι ι ι 111 60—1—1—1 1 1 1 11| 13.3 ppb Cobalt (Plus Co
65 Zinc (Plus Zn
1—1—rr
) in Borosilicate Glass
) Mercury (Plus Hg
190 )
c ± 2%
Borosilicate Glass
D ± 1% And in Polyethylene
*Tefton, ® Du Pont Co.
In Glass (Leuhvein)
Coatings to your specifications, any quantity and size. Send us your requirements.
Β ± 20%
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·
ANALYTICAL CHEMISTRY
J
3
6
10
30
60
100
I
300
L_L
600
Time (Days) (Courtesy John Wiley & Sons, Inc.)
Figure 2. Stability of dilute solutions
