parameter to separation efficiency!) is described by three additive terms. Two terms
are influenced by the linear gas velocity, one with a linear correlation, one with an
opposite working inverse correlation. As a consequence, the equation exhibits a
minimum representing a maximum of separation efficiency as illustrated by the
Van-Deemter graphs (see Fig. 4.6). This implies different ideal gas velocities for the
common phases for gas chromatography
OV1, DB-1, SE30,
CP-Sil 5, ZB1
Permethylated polysiloxane
BPX5, SE52, DB5,
SPB-5 , ZB5
Permethylated polysiloxane
with 5% phenyl subsƟtuƟon
SE54
Permethylated polysiloxane
with 5% phenyl and 1% vinyl
subsƟtuƟon
OV1701, DB5, SPB7, CP-Sil19
Permethylated polysiloxane
with 7% phenyl and 7% cyano
subsƟtuƟon
DBWax, CW20M,
BP-20
Polyethylene glycol (MW
20000)
FFAP
Polyethylene glycol (MW
20000) parƟally esterified with
2 - nitro terephthalic acid
O
n
O Si
Si
O
Si
(C H
2
)
3
(C H
2
)
3
C N
C N
n
m
O
Si
Si
O
Si
m
n
Si
O
Si
O
n
O Si
Si
O Si
CH
CH 2
n
m
Fig. 4.3 Chemical composition of some typical films used in gas chromatography
42
4 Instrumental Analysis