Rheodyne manufactures a wide array of manual platforms for
both laboratory users and instrument manufacturers. Manual
platforms include manual sample
injectors and high-pressure
switching platforms. In addition to functions and capabilities,
most platforms are available with different liquid contact
materials to accommodate sample pH ranges and the retention
of biological activity.
Each of the following manual applications contains a full-color
system application illustration including flow path, columns,
valves, autosamplers, and detectors.
 Manual
Sample Injection
The injection of a sample (at low pressure) into the system
(at high pressure) is a critical step in the analytical process.
Manual sample injectors have two positions, LOAD and INJECT.
The LOAD position allows sample loading into the sample loop
or sample chamber. A syringe is commonly used to load sample
into the sample injector. After loading, manual rotation of
the sample injector's handle to the INJECT position permits
the flushing of loaded sample onto a column.
Various sample injection platforms are available for micro-,
analytical-, and preparative-scale applications.
Two-Column Selection
A column switching platform allows immediate selection of
a column without having to disconnect and reconnect columns.
There are several reasons for column selection:
 To
change columns for a different analytical method. - To use the same column for two different methods. Dedicating
a separated column to each method eliminates column equilibration
delays when the mobile phase is changed. It also avoids
the chance that highly retained sample components for the
previous method will interfere with the analysis when using
the next method.
- To dedicate a separate column for method development to
avoid the chance that new sample components or mobile phase
will change the column used for an established method.
- To segregate columns used by different operators so each
remains personally familiar with the column's history.
The illustration shows a typical two-column selection situation.
In Position A, flow from the injector goes through Column
B to the detector. Meanwhile, Column A is sealed at both ends
for convenient storage. When the platform is switched to Position
B, Column A is now in line between the injector and the detector
and Column B is off-line.
Sample Enrichment
In enrichment methods, the analytes of interest are retained
and concentrated onto a pre-column while undesirable sample
components are directed to waste. The valve is then switched
to backflush the analytes from the pre-column onto the analytical
column. Typically, the pre-column is a reversed-phase column
with a mobile phase causing strong retention of analytes.
A large sample volume can be injected onto the pre-column,
resulting in a highly concentrated sample at the pre-column
inlet. In enrichment, samples are both cleaned-up and concentrated.
Enrichments can range from a factor of ten to several thousand,
significantly improving the limit of detection.
Two popular applications illustrate the versatility of enrichment
methods. One is the LC–MS analysis of drugs and metabolites
by direct injection of plasma with minimal previous work-up.
By using a restricted access media (RAM) pre-column, the analytes
are tightly bound and the plasma proteins, which could otherwise
destroy the analytical column, pass through the pre-column
to waste.
Another popular application is the LC–MS analysis of
protein tryptic digests. A very small pre-column (trap column)
allows the injection of several microliters of digest under
conditions where the peptides are highly retained. The resulting
small volume, concentrated sample is transferred by a switching
platform to a microbore or a packed capillary column. Sample
volumes are large enough for convenient handling, yet enrichment
allows the actual gradient elution separation of the peptides
to take place on microcolumns using low flow rates compatible
with MS instruments.
 A
Two-Position, Ten-Port high pressure switching platform can
function as a combined sample injection and enrichment system.
In Position A, sample is loaded into the loop. Meanwhile,
Pump B backflushes the cleaned-up and concentrated analytes
of the previous sample from the pre-column onto the analytical
column.
In Position B, the analysis of the previous sample is carried
out on the analytical column using the mobile phase from Pump
B. Mobile phase from Pump A flushes the sample from the loop
onto the pre-column, where the sample is concentrated and
undesired components are directed to waste.
|
 |
Manual Applications
