58-11Chromatography Composition Measurement
pressures up to 48,263 kPa (7000 psi). The flow rate must be precisely controlled and the outlet
st
ream
mu
st
be pu
lse-free
. Me
tered
mi
xing
of up to fo
ur
so
lvent
st
reams
ma
y
be re
quired
fo
r
gr
adi-
ent
el
ution
an
d
co
lumn
wa
shing
. HP
LC
pu
mps
mu
st
be ca
pable
of de
livering
a pu
lse-free
st
ream
of mo
bile
ph
ase,
at pr
essures
up to 48
,263
kP
a
(7
000
ps
i)
.
Va
riations
in mo
bile-phase
fl
ow
ra
te
le
ad
to ir
reproducibility
in ch
romatographic
re
tention
ti
mes,
an
d
pu
lses
in th
e
fl
ow
gi
ve
no
ise
in th
e
de
tector
ba
seline
.
To en
sure
opt
imum
pu
mp
pe
rformance
an
d
to re
move
di
ssolved
ox
ygen,
th
e
mo
bile
ph
ase
mu
st
be
degassed. Degassing can be by vacuum, but periodic purging with helium is more usual. Dissolved oxy-
gen
ca
use ...