Hach DR/850, Procedures Manual, Page: 51 / 460

51
CHEMICAL ANALYSIS INFORMATION
, continued
Absorbance Versus Concentration Calibration
To read concentration values directly from the instrument, create a user-
entered program. See the instrument manual for more information.
If absorbance values are measured, plot the results on linear graph paper.
Plot the absorbance value on the vertical axis and the concentration on the
horizontal axis.
Plot increasing absorbance values from bottom to top. Plot increasing
concentration values from left to right. Values of 0.000 absorbance units
and 0 concentration will begin at the bottom left corner of the graph. A
calibration table can be extrapolated from the curve or the concentration
values can be read directly from the graph for determining an equation for
the line using the slope and the y-intercept.
USEPA Approved and Accepted Definitions
The United States Environmental Protection Agency (USEPA) establishes
limits for maximum contamination levels of certain constituents in water.
It also requires that specific methodology be used to analyze for these
constituents. These methods originate from several sources. The USEPA
has developed some of these methods. In other cases, the USEPA has
evaluated and approved methods developed by manufacturers,
professional groups and public agencies such as:
•
American Public Health Association
Table 7 Calibration Table
%T
Tens
%T Units
0 1 2 3 4 5 6 7 8 9
0
10 2.30 2.21 2.12 2.04 1.97 1.90 1.83 1.77 1.72 1.66
20 1.61 1.56 1.51 1.47 1.43 1.39 1.35 1.31 1.27 1.24
30 1.20 1.17 1.14 1.11 1.08 1.04 1.02 .99 .97 .94
40 .92 .89 .87 .84 .82. .80 .78 .76 .73 .71
50 .69 .67 .65 .64 .62 .60 .58 .56 .55 .53
60 .51 .49 .48 .46 .45 .43 .42 .40 .39 .37
70 .36 .34 .33 .32 .30 .29 .28 .26 .25 .24
80 .22 .21 .20 .19 .17 .16 .15 .14 .13 .12
90 .11 .09 .08 .07 .06 .05 .04 .03 .02 .01