Hach Lange 2100AN, Инструкция по эксплуатации инструмента

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SECTION 2,
continued
2.3.7 Measuring Over-Range Samples
The nephelometric method of turbidity measurement depends on light scattering
from suspended particles. If turbidity is very high, significant amounts of light may
be absorbed by the particles, and thus little light is available for scattering. This
results in a negative interference; the measured turbidity is lower than the actual
turbidity. This condition is called “going blind.” If a sample causes the 2100AN
Turbidimeter to “go blind,” the sample may be diluted and re-measured. Or, use a cell
adapter and a smaller diameter sample cell to shorten the length of the light path.
Light absorbing particles, such as activated carbon and significant amounts of true
color, also may cause an instrument to “go blind.” Dilution may not be effective in
correcting for these interferences. The Ratio mode can minimize the effects of
light absorbing particles, color, absorbance and high turbidity interferences.
When too much light is absorbed by the sample matrix, sufficient light may not be
available for measurement. If this condition occurs, the lamp symbol on the
instrument display flashes to warn the user.
2.3.7.1 Sample Dilution
High turbidity samples may be diluted, but avoid this when possible because
dilution may alter the characteristics of the suspended particles and produce
erroneous results.
When necessary, dilute the sample with a portion of filtered sample. (Diluting
with distilled or deionized water may dissolve some of the turbidity.)
Filter samples with the Sample Filtration and Degassing Kit (Cat. No. 43975-10)
shown in Figure 3. If the filters in this kit plug too rapidly, use a standard
47 mm filtration apparatus illustrated in Figure 4 with a membrane filter
(Cat. No. 13530-01), or use a glass-fiber filter (Cat No. 2530-00) for very high
solids. After dilution and measurement, calculate the actual result as follows:
1. Calculate the dilution factor
Where total volume = dilution water
Example: 20 mL of 80 mL of dilution water = 100 mL total
2. Calculate the Final Turbidity Value:
Measured Result x Dilution Factor = Actual NTU
For example, if the measured turbidity value is 2450 NTU, the final turbidity
value is calculated as:
Dilution Factor
Total Volume
Sample Volume
------------------------------------------ =
Dilution Factor
100
20
---------- 5 = =
2450 5
×
12250
=