Frequently Asked Questions
How
long does an extraction take with an automated SPE system?
How
much solvent is used during an extraction process?
My laboratory is concerned with solvent
exposure.
What solvents are compatible with the automated
extractors?
How are solvent volumes determined?
Does
the Controller come pre-programmed with EPA methods?
Can I create my own methods in the 4700
Controller?
What are the differences between the SPE-DEX
4790 Extractors, the Spe-Dex 4770, and the Spe-Dex 4750
Extractors?
What are typical Background values for
the extractors?
I have difficulties with sample flow rates
when using 3M Empore™ Oil & Grease disks. Is there
anything that I can do?
__________________________________________________________________________
Q:
How long does an extraction take with an automated SPE
(Solid Phase Extraction) system?
A:
On average, an extraction can take anywhere from 15
- 20 minutes, with dirtier samples taking longer.
The total run time will also be a function of the number
of Pre-wet and Rinse steps that have been programmed
into the method.
Q:
How much solvent is used during an extraction process?
A: Horizon Technology’s Automated Extractors
use approximately 1/3 less solvent than with conventional
LLE (liquid-liquid extractions). For a typical method,
using a 47 mm disk, the total amount of solvent would
be approximately 10 - 20 mLs for Prewetting and 15 -
20 mLs for final Rinsing. A typical method using
a 90 mm disk will use about twice that volume.
Q:
My laboratory is concerned with solvent exposure.
A: The 1000XL and 3000XL Oil & Grease Machines
come standard with an internal fan and hose ducting. This
permits the systems to be operated directly on the lab
bench. The Sep-Dex 4790 system has an internal fan,
but the Vent Hose Kit is an option. If you plan to operate
Spe-Dex 4790's on the bench, we recommend ordering the
optional Vent Hose Kit at the time of purchase.
The
fan pulls solvent fumes away from the technician and
can be vented into a fume hood. This minimizes exposure
to solvent fumes. Because the extraction process is
automated, all of the solvents are contained in 2.5
Liter solvent bottles. Therefore, there is minimal handling
of the solvents by the technician. Exposure levels have
been tested and fall below the OSHA limits.
Q:
What solvents are compatible with the automated extractors?
A: Because the Spe-Dex® 1000XL &
3000XL Oil & Grease Machines are designed specifically
for Method 1664A they can only be used with hexane and
methanol. The use of other solvents will damage the
extractors. Since the Spe-Dex 4790 was designed to perform
all EPA approved SPE methods, it can handle all solvents.
Some customers even use the Spe-Dex 4790 system for
other internal R&D applications.
Q:
How are solvent volumes determined?
A:
The
volume of solvent delivered to the system is a function
of the solvent bottle pressure; the length of time the
internal solvent delivery valve (solenoid) stays open;
the diameter of the solenoid valve opening; the diameter
of the rinse tube and the number of Pre-wet and Rinse
steps programmed. On the Spe-Dex® 4790
Extractors, an IR sensor regulates dispense time (or
time the solenoid valve stays open) depending on whether
a 47 mm or 90 mm disk is being used. For the 1000/3000XL
Systems the dispense time is programmed into the Controller
method.
Q:
Does
the Controller come pre-programmed with EPA methods?
A: Yes. All of the currently approved EPA methods
are pre-programmed into the Controller. These methods
are simply called up by the operator, (EXAMPLE 525.2)
and downloaded to the individual extractors.
Q:
Can I create my own methods in the 4700 Controller?
A: Yes. The 4700 Controller allows you to modify
the pre-programmed EPA methods to create your own methods. The
Controller simply asks which solvents will be used and
the various times for soaking, air drying and rinsing
the disk. The Controller can safely store about
200 individual methods in its non-volatile memory.
Q:
What
are the differences between the SPE-DEX®
4790 Extractors, the Spe-Dex® 4770, and the
Spe-Dex® 4750 Extractors?
A:
1) Water Bottle Holder: Unlike the
4770 & 4750 Extractors in which the sample bottle
sat loosely in the bottle holder, the 4790 requires
a tight seal between the bottle holder and the sample
bottle cap adapter. This is required, as the Water
Inlet Valve now remains open during the entire
water sample. In comparison, the 4770 &
4750 Water Inlet Valves opened and closed to introduce
the water sample.
Therefore, since the Water Inlet Valve remains open
until all of the water has been filtered, the sample bottle
and cap adapter need to be firmly attached together to
prevent air leaks. If you look into the bottle
holder, you will notice a black o-ring. This
o-ring provides the seal between the cap adapter and
the bottle holder. As long as a good seal is maintained
between the sample bottle/cap adapter and the bottle
holder, the water sample can only flow out, as air is
introduced into the bottle.
2)
Loading the Sample Bottle: 4790 - Once
the aluminum foil and cap adapter are in place, follow
the procedures in the manual to load the sample bottle.
Once the bottle is loaded into position, it is important
to use a "clockwise" rotation to open the
foil. If the bottle is rotated "counterclockwise"
the cap adapter could be loosened from the bottle and
allow an air leak to develop. This would cause
an overflow of the water sample. Also, to prevent
the aluminum foil from covering the solvent rinse opening,
only rotate the bottle 3/4 of the way. Again,
practice with the unit first - use an empty bottle with
foil and observe how the foil opens. 4770 & 4750
– The rinse cone breaks the aluminum foil when loading
the sample bottle.
3)
Liquid Level Sensors: Unlike the 4770
& 4750 Extractors, which had fixed sensors, the
4790 sensors can be adjusted. This design was
used in order to handle dirty samples that contain great
amounts of particulate matter. Being able to move
the sensors up (or down) is very useful.
Before running a water sample, inspect and adjust
the height of the sensors. It is recommended to
run a Purge method and visually inspecting the volume
of Prewet solvent dispensed. Also, based on the
vacuum setting, inspect the disk to ensure sufficient
volume is left on the disk during the soaking cycle.
The sensor assembly can be moved up or down until
the desired Prewet volume is obtained. Once this
sensor height is adjusted, it does not need to be changed, unless
the operator elects to.
4)
Water Inlet Valve: The 4790 Water Inlet
Valve uses air pressure to open the valve. It is designed
similar to a stopcock on a separatory funnel. The opening
of the Water Inlet Valve is ½ “ in diameter. This is
ideal for processing dirty samples that may not only
be high in suspended solids but may have larger particles
or chunks. The Water Inlet Valve opens during the sample-processing
step and remains open until the entire extraction is
complete. The Water Inlet Valve on the 4770 & 4750
Extractors operate on vacuum and have a diaphragm assembly
that opens when vacuum is supplied to the valve. In
this system, the Water Inlet Valve alternates between
the open and closed positions during the sample-processing
step to prevent the Disk Assembly from over filling.
The diameter of the water path opening on this valve
is 0.24 “. Therefore, the extraction of dirty samples
with particulate material could be a problem causing
the diaphragm to not seal properly and result in sample
overflows. The 4770 Extractors were designed for the
extraction of clean drinking water samples. The 4750
Extractors are similar in design to the 4770 Extractors.
Although the 4750 Extractors were designed for Oil &
Grease extractions, samples that are very dirty will
be problematic. The 4790 Extractors were design to overcome
this limitation.
5)
Disk Holder Assemblies: The 4770 &
4750 Extractors have Disk Assemblies that can only accommodate
47 mm disks. The 4790 Extractors can accommodate two
different size Disk Holder Assemblies. When running
clean samples, the 47 mm Disk Holder Assembly is loaded
onto the extractor platform and is used with 47 mm disks.
For running dirty samples, the 90 mm Disk Holder Assembly
is mounted on the platform and used with 90 mm disks.
The Bakerbond Speedisks® can be used on all
three extractors.
These
are the main changes to the 4790. Internally,
the main circuit board is now located in a higher position
- not on the bottom. Also, the keypad is a membrane
design so as to be impervious to liquids, plus, it is
mounted higher up on the chassis. Two of the check
valves have also been removed, which will make daily
operation more reliable and user friendly.
Q:
What are typical Background values for the extractors?
A: First, let's discuss the background values typically
found with method 1664A. A clean extractor system
with clean solvents (and no disk), should give a background
value of 0.5 - 0.75 mg. Based on the particular
disk used, and the size of the disk (47 or 90 mm), the
background value could range from 0.75 - 1.5 mg. Most
of the higher backgrounds are a result of the SPE disk.
Various steps can be taken to reduce these higher values.
With
regards to background values for organic contaminates,
the Spe-Dex 4790 model uses all PTFE, PEEK, and Kalrez
components. Again, as long as the solvents are
clean and no contaminating materials are used in the
extractor, such as O-Rings, the background values are
well below standard EPA method requirements.
Q:
I have difficulties with sample flow rates when using
3M Empore™ Oil & Grease disks. Is there anything
that I can do?
A: Yes. There has been three generations of Disk
Holder Assemblies. The old style snap fit assembly required
one o-ring on the groove of the Insert that would hold
the disk in place and form a tight seal. The second
generation of Disk Holder Assemblies came in three parts,
the Base Cup, the Riser and the Aluminum Locking Ring.
No o-ring is needed when using a flat disk. However,
when using the 3M Empore™ Oil & Grease disks the
two o-rings are needed to provide a tight seal for optimal
flow rates. The larger diameter, thicker o-ring is placed
in the bottom outer groove of the Cup and the smaller
diameter, thinner, o-ring is placed in the groove of
the Riser, which is inserted into the Base Cup to hold
the disk in place. The orientation of the Riser is such
that the groove with the o-ring is face up and the flat
edge is face down on the disk. The Aluminum Locking
Ring is then screwed tightly onto this assembly.
If the assembly is not tight, when vacuum is pulling,
air will flow through the parts and slow the flow rates.
A high amount of residual water may also be left on
the disk after the Air Dry Time which can adversely
effect recoveries.
The latest style of Disk Holder Assemblies also come
in three parts but have been redesigned such that the
o-rings are no longer used with the 3M disks. Instead,
a red gasket is used to provide a better seal. The support
screen is placed in the center of the Base Cup. The
gasket is then placed into the Cup with the flat even
side face down. The 3M Oil & Grease disk is placed
into the center recess of the gasket. For the 90 mm
assemblies, the Riser is inserted into the Cup with
the grooved side face down on the disk. For the 47 mm
assemblies, the side with the thin lip is inserted face
down on the disk and the flat edge face up. Finally,
tightly screw on the Aluminum Locking Ring. This design
provides a better seal when using the 3M disks. For
the flat disks, the gasket is eliminated and the orientation
of the Riser in the Cup is reversed (flip over).
Refer to the Operator Manual for detailed instructions
and photos.
