18
PFP7/REV C/01-08
Figure 4.3.2
: Typical calibration curve measuring ppm.
Customers working in medical environments are quite likely to be using the S.I. unit of mmol/l to
report their results. The relationship between mmol/l and ppm is defined below:
Sodium
Na
1ppm = 0.0435mmol/l
1mmol/l = 23ppm
Potassium
K
1ppm = 0.0256mmol/l
1mmol/l = 39ppm
Lithium
Li
1ppm = 0.1441mmol/l
1mmol/l = 7ppm
Calcium
Ca
1ppm = 0.0250mmol/l
1mmol/l = 40ppm
This relationship means that Na and K samples in the normal clinical range of 136-145mmol/l
Na and 3.5-5.0mmol/l K should be pre-diluted 1 in 100 or 1 in 200 to get optimum results from
the flame photometer.
1. Aspirate a blank solution and set the readout to 000 using the
blank
control.
2. Aspirate the highest standard solution and set the readout to an appropriate reading
using the
fine
and
coarse
sensitivity controls. Re-check the blank setting and adjust if
necessary.
3. Aspirate the remaining standard solutions (if used) to construct the calibration curve and
note the results.
4. When the blank and standards are set, unknown samples can be aspirated and the
results noted, either directly from the instrument readout, or by deriving the
concentrations from the calibration curve.
5. Calibration needs to be checked periodically by aspirating the blank and standard
solutions. Initially this check should be carried out after every 10 samples. Experience
and increased confidence in the PFP7 will enable you to best judge the frequency of
this check.
6. The decimal point (
d.p.
) switch can be set to illuminate the decimal point in any
significant position. This should be chosen to give sufficient resolution for the test
required.
0
5
5
10
10
15
15
20
20
25
25
ppm
R
e
a
d
o
u
t
Unknown sample
reads 20 and can
be seen to have a
concentration of
approx. 16.5ppm
Calibration points
at 5,10,15,20 and
25ppm
0
5
5
10
10
15
15
20
20
25
25
ppm
R
e
a
d
o
u
t
0
5
5
10
10
15
15
20
20
25
25
ppm
R
e
a
d
o
u
t
Unknown sample
reads 20 and can
be seen to have a
concentration of
approx. 16.5ppm
Calibration points
at 5,10,15,20 and
25ppm