Metrohm 750 Autosampler - Manual (Page 6)

1.2 Theory of operation
750 Autosampler
3
Number of injections
The number of injections per sample with the 750 Autosampler de-
pends on the sample loop size. With sample loops > 10 µ L max. 3,
with sample loops ≤ 10 µ L max. 4 injections are possible. Fig. 3 details
the needle position and displacement volume at the sample delivery
action. Care should always be taken that the injection volume is at least
three times greater than the volume of the sample loop. This is why only
a maximum of 2 injections per sample should be made with 100 µ L
loops; the minimum sample volume is 300 µ L for 1 and 600 µ L for 2 in-
jections. For sample loops with a volume ≤ 10 µ L up to 4 injections per
sample are possible. The minimum sample volume required is 150 µ L
for 1, 300 µ L for 2, 450 µ L for 3 and 600 µ L for 4 injections.
Rinsing
Rinsing will be necessary for highly concentrated samples or for sam-
ples that may absorb in the tubing or in the injection valve. Rinse vials
are filled with eluent or other suitable solvent. The Rinse process is
shown in Fig. 3. Rinse vials can be used either after each vial (every
even numbered or odd numbered vial) or at programmed vial intervals.
There are two types of Rinses, the Normal Rinse and the Quick Rinse.
The Normal Rinse occurs after all the injections have been made from
the sample vial and the run time has elapsed. A Quick Rinse occurs
immediately after an injection and is used in applications where the
sample solution must not be left in the needle, transfer tubing or valve
for whatever reason. Only one injection per vial can be programmed
when using a Quick Rinse.
Injection
1 Injection
per vial
2 Injections
per vial
3 Injections
per vial
4 Injections
per vial Rinse
1
2
3
4
2.65 cm
730
µL
1.63 cm
450
µL
1.02 cm
280
µL
1.63 cm
450
µL
0.51 cm
140
µL
0.51 cm
140
µL
1.12 cm
310
µL
0.51 cm
140
µL
0.51 cm
140
µL
0.51 cm
140
µL
2.65 cm
730
µL
Fig. 3: Displacement volume versus needle position