Hanna Instruments LP 2000 - Manual (Page 5)

9 8
TIPS TO OBTAIN BEST ACCURACY
• Each time the cuvette is used, tighten the cap to the same
degree.
• Discard the sample immediately after the reading is taken to
prevent permanent clouding of the glass.
• All glassware used to contain the standards and the samples
should be kept clean, washed with HI 93703-50 cleaning
solution and rinsed with HI 93703-0 or turbidity-free water.
• Samples should be collected in clean glass or plastic bottles with
appropriate stoppers. Analysis should be performed shortly after.
If the sample requires storage, it should be kept in a cool dark
place. Stored samples should be restored to room temperature
prior to analysis. Samples may not be stored for longer than 24
hours.
• To obtain a representative sample, gently and thoroughly, stir
the solution. To prevent air bubbles from forming do not shake or
let the solution settle prior to sampling.
• Monthly calibration of the meter, using HI 93703-10 @ 10 FTU
standard is recommended.
• Before inserting cuvettes into the instru-
ment, wipe them with HI 93703-70 or a
soft, lint-free tissue. Handle vials so that
no fingerprints are left on the areas where
light passes through, i.e. the bottom 2 cm
(3/4”) of the cuvette.
If you experience any problems in taking measurements, please
contact your dealer or the nearest Hanna Customer Service Depart-
ment.
SOURCES OF INTERFERENCE
• The presence of floating debris and coarse sediments which may
settle rapidly will give false readings.
• The infrared light source of LP 2000 can effectively minimize
errors due to colored substances found dissolved in solution. This
“True Color” effect is the most common interference found in
commercial instruments operating in the visible light range.
• Air bubbles and the effect of vibrations that disturb the surface of
the sample may produce false results.
• Dirty, scratched, or etched glassware will also affect readings.
• The mark on the cuvette cap should point
towards the keyboard.
• Press the READ/ ▲ key and the LCD will display an intermittent
“SIP” (Sampling In Process).
• The turbidity value will appear after ap-
proximately half a minute.
• Though LP 2000 covers a wide turbidity range, highly accurate
readings exceeding 40 FTU require dilution as recommended by
the Standard Methods.
Use the formula below to calculate the amount of HI 93703-0 or
turbidity-free water needed for accurate dilution.
The total volume = 100 mL.
Vos = 3000 / T
where:
Vos = volume of original sample (mL) to be added to HI 93703-0
to obtain the total diluted volume of 100 mL.
T = LP 2000 reading (exceeding 40 FTU)
E.g.: LP 2000 reading = 200 FTU
3000 / 200 = 15 mL (Vos)
15 mL (Vos)+85 mL (HI 93703-0) = 100 mL
At this point, take a sample of this diluted solution and measure its
turbidity.
The correct turbidity value of the original sample is derived by:
Ta= Tn x 100 mL / Vos
where:
T
a
= actual turbidity value of the original sample
T
n
= LP 2000 reading of the diluted solution
E.g. If T
n
= 27
T
a
= 27 x 100 mL / 15 mL = 180 FTU