Bio-Rad Mini-PROTEAN Tetra Cell User Manual

Mini-PROTEAN
Tetra Cell

Instruction Manual

Catalog Numbers

165-8000 165-8004
165-8001 165-8005
165-8002 165-8006
165-8003 165-8007

®

Table of Contents

Section 1 General Information 1

1.1 Introduction 1

1.2 Components 1

1.3 Specifications 4

1.4 Safety 5

Section 2 Setup and Basic Operation 6

2.1 Gel Cassette Preparation 6

2.2 Electophoresis Module Assembly and
Sample Loading 9

Section 3 Separation Theory and Optimization 15

3.1 Introduction 15

3.2 SDS-PAGE (Laemmli) Buffer System 16

3.3 Native PAGE 17

Section 4 Reagent Preparation and Stock Solutions 19

4.1 Volumes Required per Gel 19

4.2 SDS-PAGE (Laemmli) Buffer System 19

4.3 Discontinuous Native PAGE (Ornstein-Davis) 22

4.4 Continuous Native PAGE 24

Section 5 References 27

Section 6 Maintenance 27

Section 7 Troubleshooting Guide 28

Section 8 Product Information and Accessories 31

Section 9 Warranty Information 35

Section 1
General Information

1.1 Introduction

The Mini-PROTEAN® Tetra cell runs both handcast gels and Ready
Gel® precast gels interchangeably. The Mini-PROTEAN Tetra
system includes a casting stand and glass plates with permanently
bonded gel spacers that simplify handcasting and eliminate leaking
during casting. The cell can run one or four gels, and the mini
tank is compatible with other Bio-Rad electrode modules for tank
blotting, 2-D electrophoresis, and electroelution.

1.2 Components

To get the best performance from your Mini-PROTEAN Tetra
Cell, familiarize yourself with the components by assembling and
disassembling the cell before using it (refer to Figures 1 and 2).

Spacer Plate The spacer plate is the taller glass plate

Short Plate The short plate is the shorter, flat glass

Casting Frame The casting frame, when placed on the

Gel Cassette Assembly One casting frame, a spacer plate, and a

Casting Stand The casting stand secures the gel cassette

Gel Cassette Sandwich A spacer plate and short plate with

Buffer Dam The molded, one-piece buffer dam is used

with permanently bonded gel spacers.
Spacer plates are available in 0.75 mm, 1.0
mm, and 1.5 mm thicknesses, which are
marked directly on each spacer plate.

plate that combines with the spacer plate
to form the gel cassette sandwich.

benchtop, evenly aligns and secures the
spacer plate and the short plate together
to form the gel cassette sandwich prior to
casting.

short plate form one gel cassette assembly.

assembly during gel casting. It contains
pressure levers that seal the gel cassette
assembly against the casting gaskets.

polymerized gel form a gel sandwich.

when running only one or three gels.

1

Electrode Assembly The electrode assembly holds the gel

Companion Assembly The companion assembly allows you to run

Mini Tank and Lid The mini tank and lid combine to fully

sandwich. It houses the sealing gasket,
the upper and lower electrodes, and the
connecting banana plugs. The anode
(lower electrode) banana plug is identified
with a red marker and the cathode (upper
electrode) banana plug with a black marker.

gels 3 and 4. It holds the gel sandwich and
houses the sealing gasket.

enclose the inner chamber during
electrophoresis. The lid cannot be removed
without disrupting the electrical circuit.
The mini tank and lid are also compatible
with other Bio-Rad electrode modules
for blotting, first-dimension of 2-D
electrophoresis, and electroelution.

2

Lid

Electrode
assembly

Banana plug jacks

Gel cassette

Notch on

U-shaped gasket

Mini tank

Fig. 1. Assembling the Mini-PROTEAN Tetra Cell.

Fig. 2. Assembling the Mini-PROTEAN Tetra Cell casting frame and
casting stand

3

1.3 Specifications

Casting Stand* Polycarbonate

Pin, retaining ring, and spring Stainless steel

Casting Frames* Polysulfone

Gray gaskets Thermoplastic rubber (gray)

Electrode Assembly Glass-filled polybutylene

terephthalate

Electrodes Platinum wire, 0.010 inches diameter

Gasket, electrode inner core Silicone rubber (green)

Mini Tank and Lid Polycarbonate

Sample Loading Guides** Delrin

Combs* Polycarbonate

Overall Size (W x L x H, cm) 12 x 16 x 18

Precast Gel Compatibility Ready Gel and Mini-PROTEAN

precast gels (for more information,
go to www.bio-rad.com/mpgels)

Voltage Limit 600 V DC and 500 W

Shipping Weight 2.0 kg

Maximum Sample Volume per Well

# Wells Well Width 0.75 mm 1.0 mm 1.5 mm

5 12.7 mm 20 µl 105 µl 160 µl

9 5.08 mm 33 µl 44 µl 66 µl

10 5.08 mm 33 µl 44 µl 66 µl

15 3.35 mm 20 µl 26 µl 40 µl

IPG 6.2 mm – 420 µl 730 µl

Prep/2-D

Reference well 3.1 mm 13 µl 17 µl 30 µl

Sample well 71.1 mm 310 µl 400 µl 680 µl

* US patent No. 6,162,342
** US patent No. 5,656,145

4

Chemical Compatibility

Mini-PROTEAN Tetra cell components are not compatible with
acetone or ethanol. Use of organic solvents voids all warranties.
Call 1-800-4-BIORAD (US) or your local Bio-Rad representative for
technical information regarding chemical compatibility of the
Mini-PROTEAN Tetra cell with various laboratory reagents.
The Mini-PROTEAN are not compatible with repeated exposure to
100% TEMED. Rubbing the combs with TEMED prior to casting
will destroy the structural integrity of the combs over time.

1.4 Safety

Power to the Mini-PROTEAN Tetra cell is supplied by an external
DC voltage power supply (not included). The output of this power
supply must be isolated from external ground to ensure that the
DC voltage output floats with respect to ground. All Bio-Rad power
supplies meet this important safety requirement. Regardless of the
power supply used, the maximum specified operating parameters
for the Mini-PROTEAN Tetra cell are as follows

• 600 V DC maximum voltage limit

• 500 W maximum power limit

• 40°C maximum ambient temperature limit

The current to the cell enters the unit through the lid assembly,
which provides a safety interlock to the user. The current to the
cell is broken when the lid is removed. Always turn off the power
supply before removing the lid. Do not attempt to use the cell

without the safety lid.
Important: This Bio-Rad product is designed and certified to meet

IEC61010-1 and EN61010-1* safety standards. Certified products
are safe to use when operated in accordance with the instruction
manual. This instrument should not be modified or altered in any
way. Alteration of this instrument will

• Void the warranty

• Void the IEC61010-1 and EN61010-1 certifications, and

• Create a potential safety hazard

Bio-Rad is not responsible for any injury or damage caused by
use of this instrument for purposes other than those for which it is
intended or by modifications of the instrument not performed by
Bio-Rad or an authorized agent.

*IEC61010-1 and EN61010-1 are internationally accepted electrical safety
standards for laboratory instruments.

5

Section 2
Setup and Basic Operation

2.1 Gel Cassette Preparation

Handcast Gels

1. Glass Cassette and Casting Stand Assembly

Note: All glass plates should be clean and dry.

a. Place the casting frame upright with the pressure cams in

the open position and facing forward on a flat surface.

b. Select a spacer plate of the desired gel thickness and place
a short plate on top of it (see Figure 3a).

c. Orient the spacer plate so that the labeling is up. Slide the
two glass plates into the casting frame, keeping the short
plate facing the front of the frame (side with pressure cams)
(see Figure 3b).

Note: Ensure that both plates are flush on a level surface and
that the labels on the spacer plate are oriented correctly. Leaking
may occur if the plates are misaligned or oriented incorrectly.

d. When the glass plates are in place, engage the pressure
cams to secure the glass cassette sandwich in the casting
frame (see Figure 3c). Check that both plates are flush at
the bottom.

e. Place the casting frame into the casting stand by positioning
the casting frame (with the locked pressure cams facing out)
onto the casting gasket while engaging the spring-loaded
lever of the casting stand onto the spacer plate (see Figure
3d).

Note: The gray casting stand gaskets must be clean and dry.
The casting stand gaskets are made of a special thermoplastic
material that swells when soaked in water, so we recommend
that you do not soak the gaskets for prolonged periods prior to
casting. If the gaskets do get accidentally soaked and display
swelling and/or deformation, just allow them to air dry and they
will regain their original shape, size and performance.

6

f. Repeat steps a–e for additional gels.

3a 3b

3c 3d

Fig. 3. Assembling the Mini-PROTEAN casting stand and frame.

2.0 Gel Casting

a. Discontinuous Polyacrylamide Gels

i. Place a comb completely into the assembled gel cassette.
Mark the glass plate 1 cm below the comb teeth. This is the
level to which the resolving gel is poured. Remove the comb.

ii. Prepare the resolving gel monomer solution by combining all
reagents except APS and TEMED. (Refer to section 4 for
gel formulations.) Degas the solution under vacuum for at
least 15 min. Do not use a sink water aspirator.

iii. Add APS and TEMED to the degassed monomer solution
and pour to the mark using a glass or disposable plastic
pipet. Pour the solution smoothly to prevent it from mixing
with air.

7

iv. Immediately overlay the monomer solution with water or
t-amyl alcohol.

Note: If water is used, add it slowly and evenly to prevent mixing.
Do not overlay with butanol or isobutanol.

v. Allow the gel to polymerize for 45 min to 1 hr. Rinse
the gel surface completely with distilled water. Do not leave
the alcohol overlay on the gel for more than 1 hr because
it will dehydrate the top of the gel.

Note: At this point the resolving gel can be stored at room
temperature overnight. Add 5 ml of 1:4 dilution of 1.5 M
Tris-HCl, pH 8.8 buffer (for Laemmli system) to the resolving gel
to keep it hydrated. If using another buffer system, add 5
ml 1x resolving gel buffer for storage.

vi. Prepare the stacking gel monomer solution. Combine all
reagents except APS and TEMED. Degas under vacuum for
at least 15 min.

vii. Dry the top of the resolving gel with filter paper before
pouring the stacking gel.

viii. Add APS and TEMED to the degassed stacking gel
monomer solution and pour the solution between the glass
plates. Continue to pour until the top of the short plate is
reached.

b. Continuous Polyacrylamide Gels

i. Prepare the monomer solution by combining all reagents
except the APS and the TEMED. Degas under vacuum for
15 min (refer to section 4 for gel formulations).

ii. Add APS and TEMED to the degassed monomer solution
and pour the solution between the glass plates. Continue to
pour until the top of the short plate is reached.

iii. Insert the desired comb between the spacers starting at the
top of the spacer plate, making sure that the tabs at the
ends of each comb are guided between the spacers. Seat
the comb in the gel cassette by aligning the comb ridge with
the top of the short plate.

iv. Rinse the casting frame(s) and stand with distilled,
deionized water after use.

8

®

Ready Gel

Precast Gels

1. Ready Gel Cassette Preparation

Note: The Mini-PROTEAN Tetra cell is guaranteed for use with

Bio-Rad’s Ready Gel and Mini-PROTEAN® precast gels. For
more information, go to www.bio-rad.com/mpgels.

a. Remove the Ready Gel from the storage pouch.

b. Gently remove the comb and rinse the wells thoroughly with
distilled water or running buffer.

c. Cut along the dotted line at the bottom of the Ready Gel
cassette with a razor blade.

d. Pull the clear tape at the bottom of the Ready Gel cassette
to expose the bottom edge of the gel.

e. Repeat for second Ready Gel.

Note: If only one or three gels are to be run, use the mini cell
buffer dam.

2.2 Electrophoresis Module Assembly and Sample Loading

Required materials:

• Clean and dry Mini-PROTEAN Tetra cell tank

• Electrophoresis module (electrode assembly module only for

1 or 2 gels; for 3 or 4 gels also use the companion running
module)

• Running buffer (700 ml for 2 gels; 1000 ml for 4 gels)

• Ready Gel precast gels or hand-cast gels

• PowerPac™ Basic power supply

1. Assembly

Note: When running 2 gels only, use the electrode assembly (the

one with the banana plugs), not the companion running module
(the one without the banana plugs). When running 4 gels, both
the electrode assembly and the companion running module
must be used, for a total of 4 gels (2 gels per assembly).

9

a. Set the clamping frame to the open position on a clean flat
surface (see Figure 4a).

b. Place the first gel sandwich or gel cassette (with the short
plate facing inward) onto the gel supports; gel supports are
molded into the bottom of the clamping frame assembly;
there are two supports in each side of the assembly. Note
that the gel will now rest at a 30° angle, tilting away from the
center of the clamping frame.Please use caution when

placing the first gel, making sure that the clamping frame
remains balanced and does not tip over. Now, place the

second gel on the other side of the clamping frame, again by
resting the gel onto the supports. At this point there will be
two gels resting at an angle, one on either side of the
clamping frame, tilting away from the center of the frame (see
Figure 4b).

Note: It is critical that gel cassettes are placed into the clamping
frame with the short plate facing inward. Also, the clamping
frame requires 2 gels to create a functioning assembly. If an odd
number of gels (1 or 3) is being run, you must use the buffer dam
(see Figure 4b).

c. Using one hand, gently pull both gels towards each other,
making sure that they rest firmly and squarely against the
green gaskets that are built into the clamping frame; make
certain that the short plates sit just below the notch at the
top of the green gasket.

d. While gently squeezing the gel sandwiches or cassettes
against the green gaskets with one hand (keeping constant
pressure and both gels firmly held in place), slide the green
arms of the clamping frame over the gels, locking them
into place. Alternatively, you may choose to pickup the
entire assembly with both hands, making sure that the
gels do not shift, and simultaneously sliding both arms of
the clamping frame into place (see Figure 4c).

The arms of the clamping frame push the short plates of each
gel cassette up against the notch in the green gasket, creating a
leak-proof seal (check again to make certain that the short plates
sit just below the notch at the top of the green gasket). At this
point, the sample wells can be washedout with running buffer,
and sample can be loaded (Figure 4d).

Note: If running more than 2 gels, repeat steps 1a–d with the
companion running module

10

Important Note: Do not attempt to lock the green arms of the
clamping frame, without first ensuring that the gel cassettes are
perfectly aligned and stabilized against the notches on the green
gaskets of the module. To prevent the gels from shifting during
the locking step, firmly and evenly grip them in place against the
core of the module with one hand.

Caution: When running 1 or 2 gels only, do not place the
companion running Module in the tank. Doing so will cause
excessive heat generation and prevent electrophoretic
separation.

4a 4b

4c

4e

Fig. 4. Assembling the Mini-PROTEAN Tetra cell electrophoresis module.

4d

11

2. Sample Loading

a. Fill the assembly (upper chamber) with buffer to just under
the edge of the outer gel plate.

b. Load samples into each of the assemblies while they are
sitting on a flat surface, outside of the tank.

c. Load the samples into the wells with a Hamilton syringe or a
pipet using gel loading tips.

d. If using Bio-Rad’s patented sample loading guide, place
it between the two gels in the electrode assembly. Sample
loading guides are available for 9, 10, 12, and 15-well
formats.

e. Use the sample loading guide to locate the sample wells.
Insert the Hamilton syringe or pipet tip into the slots of the
guide and fill the corresponding wells.

Note: Load samples slowly to allow them to settle evenly on the
bottom of the well. Be careful not to puncture the bottom of the
well with the syringe needle or pipet.

Note: Samples may be loaded in the modules prior to placing
the modules into the tank. Samples may also be loaded in the
modules after the modules have been placed into the tank. Both
methods will produce acceptable results. In both instances, the
assembly (upper chamber) and the tank (lower chamber) should
be filled with buffer according to the instructions under 2.2.2a
and 2.2.3d.

3. Placement of the Electrode Assemblies in the
Mini-PROTEAN Tetra Tank

Note: required total buffer volume, 700 ml for 2 gels; 1000 ml

for 4 gels.

The Mini-PROTEAN Tetra tank has two positions in which to
place two assemblies: the electrode assembly (back position)
and the companion running module (front position).

a. Begin by placing the tank on a flat surface, with the front of
the tank facing you (the front of the tank is the face that has
the 2-Gels and 4-Gels line markings); when oriented
properly, the red marking on the top inside edge of the tank
will be on your right, and the black marking on the top
inside edge of the tank will be on your left.

12

b. If running 2 gels only, you will be using just the electrode
assembly, so place this assembly in the back position of the
cell, making sure that the red (+) electrode jack matches the
red marking on the top right inside edge of the tank.

c. If running 4 gels, place the electrode assembly (banana
plugs) in the back position (as detailed in 2.2.3b.) and
the companion running module (no banana plugs) in the
front position. Make sure that in both instances the red (+)
electrode is matching with the red marking on the top inside
right edge of the tank. Note that incorrect orientation will not
permit proper placement of the lid.

d. Fill the tank (lower chamber) with buffer to the indicated level
(550 ml for 2 gels and 680 ml for 4 gels).

4. Mini-PROTEAN Tetra Tank Assembly

a. Place the lid on the Mini-PROTEAN Tetra tank. Make sure
to align the color-coded banana plugs and jacks. The
correct orientation is made by matching the jacks on the
lid with the banana plugs on the electrode assembly. A stop
on the lid prevents incorrect orientation. Note that the raised
tabs on each side of the tank will now slide through the
slots in the lid, guiding the lid to a proper close. At this
point, firmly, yet gently, press down on the lid with your
thumbs using even pressure, till the lid is securely and tightly
positioned on the tank.

Caution: When running 1 or 2 gels only, do not place the
companion running module in the tank. Doing so will cause
excessive heat generation and will prevent electrophoretic
separation.

5. Power Conditions

a. Insert the electrical leads into a suitable power supply with
the proper polarity.

b. Apply power to the Mini-PROTEAN Tetra cell and begin
electrophoresis; 200 V constant is recommended for
SDS-PAGE and most native gel applications. The same
voltage (200 V) is used for both 2 and 4 gels. The optimal
voltage for your application may differ. Run time is
approximately 35 min* at 200 V for SDS-PAGE.

* Electrophoresis time will vary between 35 and 45 min for Tris-HCl gels, depending on
acrylamide percentage levels.

13

6. Gel Removal

a. After electrophoresis is complete, turn off the power supply
and disconnect the electrical leads.

b. Remove the tank lid and carefully lift out the electrode
assemblies. Pour off and discard the running buffer.

Note: Always pour off the buffer before opening the arms of the
assembly, to avoid spilling the buffer.

c. Open the arms of the assembly and remove the gel cassettes.

d. Remove the gels from the gel cassette by gently separating
the two plates of the gel cassette.

Note: To remove the gel from a Ready Gel cassette, first slice
the tape along the sides of the Ready Gel cassette where the
inner glass plate meets the outer plastic plate.

e. Remove the gel by floating it off the plate by inverting the gel
and plate under fixative or transfer solution, agitating gently
until the gel separates from the plate.

f. Rinse the Mini-PROTEAN Tetra cell electrode assembly,
clamping frame, and mini tank with distilled, deionized water
after use.

14

Section 3
Separation Theory and Optimization

3.1 Introduction

Polyacrylamide gel electrophoresis separates molecules in complex
mixtures according to size and charge. During electrophoresis
there is an intricate interaction of samples, gel matrix buffers, and
electric current resulting in separate bands of individual molecules.
Hence the variables that must be considered in electrophoresis
are gel pore size, gel buffer systems, and the properties of the
molecule of interest.

Gel Pore Size

Gel pores are created by the crosslinking of polyacrylamide with
bis-acrylamide (bis) to create a network of pores. This structure
allows the molecular sieving of molecules through the gel
matrix. Gel pore size is a function of the acrylamide monomer
concentration used (%T). By convention, polyacrylamide gels are
characterized by %T, which is the weight percentage of the total
monomer including the crosslinker. The %T gives an indication of
the relative pore size of the gel. In general, pore size decreases
with increasing %T.

%T is calculated using the following equation.

%T = g acrylamide + g crosslinker x 100%
total volume (ml)

%C is the ratio of the crosslinker to the acrylamide monomer ratio
in the monomer solution. %C is calculated using the following
equation.

%C = g crosslinker x 100%
g acrylamide + g crosslinker

2.67% C is traditionally used for most analytical gels.

Gels can be made as a single continuous percentage throughout
the gel, or can be cast as a gradient %T through the gel. Typical
compositions are from 7.5% up to 20% for single percentage gels,
or gradients ranging from 4–15% to 10–20%.

15

The total monomer concentration for optimal separation is referred
to as optimal %T. Optimal %T will vary depending on the molecular
weight of the molecule of interest. Empirically the pore size
providing optimum resolution for proteins is that which results in a
relative mobility (Rf) value between 0.55–0.6. Rf values for specific
proteins are calculated as follows.

Rf = Distance migrated by the protein of interest

Distance migrated by the ion front

Gel Buffer System

The buffer system determines the power requirements and
affects separation. The buffer system is composed of the buffer
used in the gel and the running buffer. There are continuous and
discontinuous buffer systems.

Continuous Buffer Systems

In continuous buffer systems, the same buffer ions are present at
constant pH in the gel and electrode reservoirs. The gel is typically
made of one continuous %T and the sample is loaded directly into
the part of the gel where separation will occur. The band width is
determined in part by the height of the sample load, so samples
should be concentrated and volumes small for best results.

Discontinuous Buffer Systems

In discontinuous buffer systems different buffer ions are present
in the gel and electrode reservoirs. By using different buffers in
the gel and in the electrode solutions and adding a stacking gel
to the resolving gel, samples are compressed into a thin starting
band and individual proteins are finely resolved and separated.
Discontinuous buffer systems were devised initially for use with
undenatured, or native proteins; however the most popular
discontinuous system employed is the SDS-PAGE buffer system
by Laemmli (1970). Formulations for this system are included in
section 4.1.

3.2 SDS-PAGE (Laemmli) Buffer System

The Laemmli buffer system is a discontinuous buffer system
that incorporates SDS in the buffer. In this system, proteins
are denatured by heating them in buffer containing sodium
dodecyl sulfate (SDS) and a thiol reducing agent such as
2-mercaptoethanol. The resultant denatured polypeptides take on
a rod-like shape and a uniform charge-to-mass ratio proportional

16

to their molecular weights. Proteins are separated according to
their molecular weights, making this system extremely useful for
calculating molecular weights.

3.3 Native PAGE

Native PAGE is a technique for separating biologically active
proteins. In contrast to SDS-PAGE, the mobilities of proteins in a
native PAGE system depend on both size and charge. There is
no single electrophoresis buffer system that will optimally purify all
native proteins. Key parameters for separating proteins in a native
PAGE system are isoelectric point (pI) of the protein of interest and
the pH of the electrophoresis buffer.

pH and pI

The pH of the electrophoresis buffer must be within the pH range
over which the protein of interest is stable and retains biological
activity. In addition, the pH of the buffer must impart sufficient
charge to the protein for it to move through the gel. Changes in
pH will affect both the charge and size (hydrodynamic volume) of
the protein of interest and will affect migration rates. For example,
a buffer with a pH greater than the pI of the protein will impart
a negative charge on the protein and it will migrate toward the
positive electrode (anode). Conversely, a buffer with a pH lower
than the pI of the protein will impart a positive charge and the
protein will migrate to the negative electrode (cathode). A pH equal
to the pI will result in no net charge in the protein and it will not
migrate in an electric field.

Protein mobilities are best modified by the buffer’s pH. Buffers with
a pH closer to the pI will provide the best resolution. However run
times may be lengthy. Conversely, buffers with a pH further from
the pI will migrate quickly but resolution may be compromised. The
choice of pH becomes a tradeoff between separation and speed.

How to Choose a Native PAGE System

1. Discontinuous Buffer Systems (Ornstein and Davis

1964)

This discontinuous buffer system should be the first
nondenaturing gel system tried. Detailed protocols are provided
in section 4.2. The advantage of a discontinuous system is the
use of a stacking gel to concentrate dilute protein samples.
However, the stacking phenomena can also cause aggregation
of some proteins and interfere with resolution. If protein
aggregation occurs, a continuous buffer system should be used.

17

Note: The pH attained in the resolving gel of the Ornstein-Davis
system approaches pH 9.5, which may be outside the range of
stability for some proteins, causing denaturation. Additionally,
the pI of the protein of interest may be too close to or above the
Ornstein-Davis buffer pH (9.5), which may result in a very low net
charge or a positive net charge that may significantly reduce or
even prohibit migration to the anode. Alternative discontinuous
systems can be found in an article by Chrambach and Jovin
(1983).

Note: It is very desirable to know the pI of the protein of interest
before selecting a buffer system.

2. Continuous Buffer Systems

A continuous buffer system will be required if discontinuous
systems cannot be used due to stacking-induced protein
aggregation. In a continuous system the same buffer is used
in the upper and lower electrode chambers as in the gel. Since
stacking does not occur, proteins migrate in bands at least as
wide as the applied sample. Consequently, sample volumes
should be minimized. The mobility of proteins in a continuous
system is dictated by pH rather than by sieving through the
polyacrylamide gel. For this reason, 6% polyacrylamide gels are
recommended for most applications. For very large proteins, 4%
or 5% gels may be used. McLellan describes various continuous
buffer systems from pH 3.8–10.2. Detailed protocols are
provided in section 4.3.

18

Section 4
Reagent Preparation and Stock Solutions

4.1 Volumes Required Per Gel

The volumes listed are required to completely fill a gel cassette.
Amounts may be adjusted depending on the application (with or
without comb, with or without stacking gel, etc.).

Gel Thickness (mm) Volume (ml)

0.5 2.8

0.75 4.2

1.0 5.6

1.5 8.4

Note: 10 ml of monomer solution is sufficient for two stacking gels
of any thickness.

4.2 SDS-PAGE (Laemmli) Buffer System Stock Solutions and
Buffers

1. Acrylamide/Bis (30%T, 2.67%C)

87.6 g acrylamide (29.2 g/100 ml)

2.4 g N’N’-bis-methylene-acrylamide (0.8 g/100 ml)

Make to 300 ml with deionized water. Filter and store at 4°C in
the dark (30 days maximum).
Or use:
Preweighed acrylamide/bis, 37.5:1 mixture (30%T, 2.67% C)
(Bio-Rad catalog #161-0125, 150 g)
30% acrylamide/bis solution, 37.5:1 mixture (30%T, 2.67% C)
(Bio-Rad catalog #161-0158, 500 ml)
(Bio-Rad catalog #161-0159, 2 x 500 ml)

2. 10% (w/v) SDS

Dissolve 10 g SDS in 90 ml water with gentle stirring and
bring to 100 ml with deionized water. Alternatively, 10% SDS
solution (250 ml) can be used (Bio-Rad catalog #161-0416).

3. 1.5 M Tris-HCl, pH 8.8

27.23 g Tris base (18.15 g/100 ml)
80 ml deionized water

19

Adjust to pH 8.8 with 6 N HCl. Bring total volume to 150 ml
with deionized water and store at 4°C. Alternatively, 1.5 M
Tris-HCl, pH 8.8 (1 L) premixed buffer can be used (Bio-Rad
catalog #161-0798).

4. 0.5 M Tris-HCl, pH 6.8

6 g Tris base
60 ml deionized water

Adjust to pH 6.8 with 6 N HCl. Bring total volume to 100 ml
with deionized water and store at 4°C. Alternatively, 0.5 M
Tris-HCl, pH 6.8 (1 L) premixed buffer can be used (Bio-Rad
catalog #161-0799).

5. Sample buffer (SDS reducing buffer)

3.55 ml deionized water

1.25 ml 0.5 M Tris-HCl, pH 6.8

2.5 ml glycerol

2.0 ml 10% (w/v) SDS

0.2 ml 0.5% (w/v) Bromophenol Blue

9.5 ml total volume

Store at room temperature.
Use: Add 50 µl ß-mercaptoethanol to 950 µl sample buffer
prior to use. Dilute the sample at least 1:2 with sample buffer
and heat at 95°C for 4 min.

6. 10x electrode (running) buffer, pH 8.3 (makes 1 L)

30.3 g Tris base

144.0 g glycine

10.0 g SDS

Dissolve and bring total volume up to 1,000 ml with deionized
water. Do not adjust pH with acid or base. Store at 4°C. If
precipitation occurs, warm to room temperature before use.
Alternatively, electrophoresis running buffer 10x Tris/glycine/
SDS, 5 L cube (Bio-Rad catalog #161-0772) can be used.
Use: Dilute 50 ml of 10x stock with 450 ml deionized water for
each electrophoresis run. Mix thoroughly before use.

7. 10% (w/v) APS (fresh daily)

100 mg ammonium persulfate
Dissolve in 1 ml of deionized water.

20

Gel Formulations (10 ml)

1. Prepare the monomer solution by mixing all reagents except
the TEMED and 10% APS. Degas the mixture for 15 min.

30 % Degassed

Percent DDI H

gel (ml) (ml) (ml) (ml)

4% 6.1 1.3 2.5 0.1

5% 5.7 1.7 2.5 0.1

6% 5.4 2.0 2.5 0.1

7% 5.1 2.3 2.5 0.1

8% 4.7 2.7 2.5 0.1

9% 4.4 3.0 2.5 0.1

10% 4.1 3.3 2.5 0.1

11% 3.7 3.7 2.5 0.1

12% 3.4 4.0 2.5 0.1

13% 3.1 4.3 2.5 0.1

14% 2.7 4.7 2.5 0.1

15% 2.4 5.0 2.5 0.1

16% 2.1 5.3 2.5 0.1

17% 1.7 5.7 2.5 0.1

O Acrylamide/Bis Gel buffer 10% w/v SDS

2

* Resolving Gel Buffer – 1.5 M Tris-HCl, pH 8.8
* Stacking Gel Buffer – 0.5 M Tris-HCl, pH 6.8

2. Immediately prior to pouring the gel, add:

For 10 ml monomer solution:
Resolving gel: 50 µl 10% APS and 5 µl TEMED
Stacking gel: 50 µl 10% APS and 10 µl TEMED
Swirl gently to initiate polymerization.
Note: Prepare any desired volume of monomer solution by

using multiples of the 10 ml recipe. The volumes of APS and
TEMED must be adjusted accordingly.

Warning: The catalyst concentration is very important!
Webbing and incomplete well formulation can result from
inaccurate catalyst concentration.

21

4.3 Discontinuous Native PAGE (Ornstein-Davis) Stock

Solutions and Buffers

1. Acrylamide/Bis (30%T, 2.67%C)

87.6 g acrylamide (29.2 g/100 ml)

2.4 g N’N’-bis-methylene-acrylamide (0.8 g/100 ml)

Make to 300 ml with deionized water. Filter and store at 4°C in
the dark (30 days maximum).
Or, use:
Preweighed acrylamide/bis, 37.5:1 mixture
(Bio-Rad catalog #161-0125, 150 g)
30% acrylamide/bis solution, 37.5:1 mixture
(Bio-Rad catalog #161-0158, 500 ml)
(Bio-Rad catalog #161-0159, 2 x 500 ml)

2. 1.5 M Tris-HCl, pH 8.8

27.23 g Tris base (18.15 g/100 ml)
80 ml deionized water

Adjust to pH 8.8 with 6 N HCl. Bring total volume up to 150
ml with deionized water and store at 4°C. Alternatively, 1.5 M
Tris-HCl, pH 8.8 (1 L) premixed buffer can be used (Bio-Rad
catalog #161-0798).

3. 0.5 M Tris-HCl, pH 6.8

6 g Tris base
60 ml deionized water

Adjust to pH 6.8 with 6 N HCl. Bring total volume up to 100
ml with deionized water and store at 4°C. Alternatively, 0.5 M
Tris-HCl, pH 6.8 (1 L) premixed buffer can be used (Bio-Rad
catalog #161-0799).

4. Sample Buffer

5.55 ml deionized water

1.25 ml 0.5 M Tris-HCl, pH 6.8

3.0 ml glycerol

0.2 ml 0.5% (w/v) Bromophenol Blue

10.0 ml Total volume

Store at room temperature.
Use: Dilute the sample at least 1:2 with sample buffer.

22

5. 10x electrode (running) buffer, pH 8.3

30.3 g Tris base (15 g/L)

144.1 g glycine (72 g/L)

Bring total volume up to 1,000 ml with deionized water. Do not
adjust pH. Alternatively, electrophoresis running buffer 10x Tris/
glycine, 1 L (Bio-Rad catalog #161-0734) can be used.

Usage: Dilute 100 ml of 10x stock with 900 ml deionized water
for each electrophoresis run.

Gel Formulations (10 ml)

1. Prepare the monomer solution by mixing all reagents except
the TEMED and 10% APS. Degas the mixture for 15 min.

30 % Degassed

Percent DDI H

gel (ml) (ml) (ml)

4% 6.2 1.3 2.5

5% 5.8 1.7 2.5

6% 5.5 2.0 2.5

7% 5.2 2.3 2.5

8% 4.8 2.7 2.5

9% 4.5 3.0 2.5

10% 4.2 3.3 2.5

*Resolving Gel Buffer – 1.5 M Tris-HCl, pH 8.8
*Stacking Gel Buffer – 0.5 M Tris-HCl, pH

O Acrylamide/Bis Gel buffer

2

2. Immediately prior to pouring the gel, add:

50 ml APS and TEMED (5 µl for resolving gels; 10 µl TEMED
for stacking gels)
Swirl gently to initiate polymerization.

Note: Prepare any desired volume of monomer solution by
using multiples of the 10 ml recipe. The volumes of APS and
TEMED must be adjusted accordingly.

23

4.4 Continuous Native PAGE Stock Solutions and Buffers

1. Acrylamide/Bis (30%T, 2.67%C)

87.6 g acrylamide (29.2 g/100 ml)

2.4 g N’N’-bis-methylene-acrylamide (0.8 g/100 ml)

Make to 300 ml with deionized water. Filter and store at 4°C in
the dark (30 days maximum)
Or use:
Preweighed acrylamide/bis, 37.5:1 mixture
(Bio-Rad catalog #161-0125, 150 g)
30% acrylamide/bis solution, 37.5:1 mixture
(Bio-Rad catalog #161-0158, 500 ml)
(Bio-Rad catalog #161-0159, 2 x 500 ml)

2. Sample Buffer

1.0 ml electrophoresis buffer

3.0 ml glycerol

0.2 ml 0.5% Bromophenol Blue

5.8 ml deionized water

10.0 ml total volume

3. Continuous Buffers (McLellan)

McLellan describes various continuous buffer systems from
pH 3.8 to pH 10.2. Use the table on the page to prepare 5x
continuous non-denaturing PAGE electrophoresis buffers. Add
both the acidic and basic component to 1 L of water. Do not
adjust the pH. If the final pH is outside the listed range discard
the buffer and remake.

24

Basic
pH

3.8

Acidic
Component

ß-Alanine

(MW 89.09) 85% solution

5x Solution Component 5x Solution

13.36 g/L Lactic acid 7.45 ml/L

4.4

4.8 GABA 41.24 g/L Acetic acid 5.75 ml/L

6.1 Histidine 23.28 g/L MES 29.5 g/L

6.6 Imidazole 19.94 g/L MOPS 31.4 g/L

7.4 Tris 14.64 g/L HEPES 41.7 g/L

8.1 Tris 19.38 g/L EPPS 37.85 g/L

8.7 Tris 30.28 g/L Boric acid 7.73 g/L

9.4 Tris 36.34 g/L CAPS 44.26 g/L

1.0 Ammonia 12.5 ml/L CAPS 22.13 g/L

ß-Alanine

(MW 89.09) 17.4 M

(MW 103.1) 17.4 M

(MW 155.2) (MW 195.2)

(MW 68.08) (MW 209.3)

(MW 121.14) (MW 238.33)

(MW 121.14) (MW 252.2)

(MW 121.14) 9MW 61.83)

(MW 121.14) (MW 221.3)

35.64 g/L Acetic acid 11.5 ml/L

(14.8 M) (MW 221.3)

25

Dilute 200 ml of 5x buffer with 800 ml deionized water to prepare
1x electrophoresis buffer. The final concentrations of buffer
components will be.

pH Basic component Acidic component

3.8

4.4

4.8 80 mM GABA 20 mM Acetic Acid

6.1 30 mM Histidine 30 mM MES

6.6 25 mM Histidine 30 mM MOPS

7.4 43 mM Histidine 35 mM HEPES

8.1 32 mM Tris 30 mM EPPS

8.7 50 mM Tris 25 mM Boric acid

9.4 60 mM Tris 40 mM CHAPS

10.2 37 mM Ammonia 20 mM CAPS

30 mM

80 mM

ß-Alanine

ß-Alanine

20 mM Lactic acid

40 mM Acetic acid

Gel Formulations (10 ml)

1. Prepare the monomer solution by mixing all reagents except
the TEMED and 10% APS. Degas the mixture for 15 minutes.

30 % Degassed

Percent DDI H

gel (ml) (ml) (ml)

4% 6.7 1.3 2.0

5% 6.3 1.7 2.0

6% 6.05 2.0 2.0

O Acrylamide/Bis Gel buffer

2

Note: Prepare any desired volume of monomer solution by using

multiples of the 10 ml recipe.

2. Immediately prior to pouring the gel, for 10 ml monomer
solution add:

50 µl 10% APS
10 µl TEMED
Swirl gently to initiate polymerization.

Note: Below pH 6, TEMED becomes a less effective catalyst.
Increase the concentration of TEMED 5-fold to polymerize gels
with a pH range between 4 and 6.

26

Section 5
References

Laemmli UK (1970). Cleavage of structural proteins during the
assembly of the head of bacteriophage t4. Nature 227, 680-685.

Ornstein L (1964). Disc electrophoresis. I. Background and theory.
Ann N Y Acad Sci 121, 321-349.

Chrambach (1983). A and Jovin, T M, Electrophoresis, 4, 190–204

McLellan T (1982). Electrophoresis buffers for polyacrylamide gels
at various ph. Anal Biochem 126, 94-99.

Section 6
Maintenance

Mini-PROTEAN Tetra tank and lid,
Rinse thoroughly with distilled water
electrode assembly, companion after
every use. assembly, casting stand,
and frame

Glass plates and combs Wash with a laboratory detergent, then

Rinse thoroughly with distilled water
electrode after every use

rinse thoroughly with distilled water.
Limit submersion of spacer plates
in strongly basic solutions, such as
>100 mM NaOH, to less than 24 hr.
Limit submersion in chromic-sulfuric
acid glass cleaning solution to 2–3 hr.
Prolonged submersion compromises
the integrity of the adhesive.

To preserve the longevity of the
adhesive bond, avoid extended
submersion (>5 days) in cleaning
solution made from Bio-Rad cleaning
concentrate (catalog #161-0722) or
other strongly basic detergents.

27

Section 7
Troubleshooting Guide

Problem Cause Solution

Smile effect – band
pattern curves
upward at both
sides of the gel

Vertical streaking of
protein

Lateral band
spreading

Skewed or distorted
band

Center of the gel
running hotter than
either end

Power conditions
excessive

Sample overloaded

Sample
precipitation

Diffusion of the
wells prior to
turning on the
current

Ionic strength of
the sample lower
than that of the gel

Poor
polymerization
around wells

Buffer not mixed well or
buffer in upper chamber too
concentrated. Remake buffer,
ensuring thorough mixing,
especially when diluting 5x or 10x
stock

Decrease the power setting from
200 V to 150 V or fill lower chamber
to within 1 cm of top of short plate

Dilute sample, selectively
remove predominant protein in
sample, or reduce the voltage
about 25% to minimize streaking

Centrifuge sample before
addition of SDS sample
buffer, or decrease %T of the gel*

The ratio of SDS to protein should
be enough to coat each protein
molecule with SDS, generally 1.4:1.
It may require more SDS for some
membrane protein samples

Minimize the time between sample
application and turning on the
power startup

Use same buffer in sample as in the
gel or the stacking gel

Degas stacking gel solution
completely prior to casting;
increase ammonium persulfate and
TEMED concentrations by 25%, for
stacking gel or low %T, leave APS
the same and double the TEMED
concentration

Salts in sample

Uneven gel
interface

Remove the salts by dialysis,
desalting, column, Micro Bio­Spin™ columns, etc.

Descrease the polymerization rate.
Overlay gels very carefully

28

Troubleshooting Guide (cont.)

Problem Cause Solution

Lanes constricted at
the bottom of the gel

Run taking unusually
long

Run too fast Running or reservoir

Doublets observed
where single protein
species is expected
(SDS-PAGE)

Fewer bands than
expected and one
heavy band at the
dry front

Upper buffer
chnamber leaks

Leaking during hand
casting

Ionic strength of
sample higher than
the surrounding gel

Running buffer too
concentrated

Excessive salt in
sample

buffer too dilute

Voltage too high

A portion of the
protein may have
been reoxidized
during the run or
may not have been
fully reduced prior to
the run

Protein(s) migrating
at the dye front

Protein degradation

Upper buffer
chamber overfilled

Improper assembly

Chipped glass plates

Spacer plate and
short plate not level

Csating stand gasket
is dirty, flawed, or
worn out.

Desalt sample and neighboring
samples

Check buffer protocol, dilute if
necessary

Desalt sample

Check buffer protocol, dilute if
necessary

Decrease voltage by 25–58%

Prepare fresh sample buffer
solution if over 30 days old;
increase concentration in the
sample buffer; sustitute DTT for
BME

Increase the %T of the resolving
gel*

Use protease inhibitors, e.g.,
PMSF, etc.

Keep buffer level below the top of
the spacer plate

Be sure U-shaped electrode core
gasket is clean, free of cuts, and
lubricated with buffer

Be sure short plate is under the
notch on the gasket, not on top
of it

Ensure glass plates are free of
flaws

Ensure plates are aligned
correctly

Wash the gasket if it is dirty,
replace casting stand gaskets if
flawed or worn out

29

Troubleshooting Guide (cont.)

Problem Cause Solution

Poor end well
formation

Webbing/excess
acrylamide behind
the comb

The pressure cams
on the casting frame
are difficult to close
or make noise when
closed

Incorrect catalyst
formation

Monomer solution
not degassed.
Oxygen inhibits
polymerization

Incorrect catalyst
concentration

Powder residue has
built up at the pivot
of the pressure cams

Prepare fresh catalyst solution,
or increase the catalyst
concentration of the stacking
gel to 0.06% APS and 0.12%
TEMED

Degas monomer solution
immediately prior to casting the
stacking gel

Prepare fresh catalyst solution,
or increase the catalyst
concentration of the stacking
gel to 0.06% APS and 0.12%
TEMED

Rinse or wipe off the powder
residue before each use

*Polyacrylamide gels are described by reference to two
characteristics:

1. The total monomer concentration, (%T) and

2. The crosslinking monomer concentration (%C).

g acrylamide + bis-acrylamide x 100%

Total Volume

g bis-acrylamide x 100%

g acrylamide + bis-acrylamide

30

Section 8
Product Information and Accessories

Mini PROTEAN Tetra Systems

Catalog
Number Descriptions

165-8000 Mini-PROTEAN Tetra Cell, 10 well, 0.75 mm thickness, complete

165-8001 Mini-PROTEAN Tetra Cell, 10 well, 1.0 mm thickness, complete

165-8002* Mini-PROTEAN Tetra Cell, 10 well, 0.75 mm thickness; 2-gel

165-8003* Mini-PROTEAN Tetra Cell, 10 well, 1.0 mm thickness; 2-gel

165-8004 Mini-PROTEAN Tetra Cell for Ready Gel

165-8005* Mini-PROTEAN Tetra Cell for Mini Precast Gels, 2-gel system

165-8006 Mini-PROTEAN Tetra Cell, 10 well, 1.5 mm thickness; 4-gel

165-8007* Mini-PROTEAN Tetra Cell, 10 well, 1.5 mm thickness; 2-gel

165-8025 Mini-PROTEAN Tetra Cell and PowerPac Basic Power Supply,

165-8026 Mini-PROTEAN Tetra Cell and PowerPac Universal Power

system includes 5 combs, 5 sets of glass plates, 2 casting
stands, casting clamp assembly, sample loading guide, electrode
assembly, companion running module, tank, lid with power cables,
mini cell buffer dam

system, includes 5 combs, 5 sets of glass plates, 2 casting
stands, casting clamp assembly, sample loading guide, electrode
assembly, companion running module, tank, lid with power cables,
mini cell buffer dam

system includes 5 combs, 5 sets of glass plates, casting stand, 2
casting frames, sample loading guide, electrode assembly, tank, lid
with power cables, mini cell buffer dam

system includes 5 combs, 5 sets of glass plates, casting stand, 2
casting frames, sample loading guide, electrode assembly, tank,
lid with power cables, mini cell buffer dam

®

assembly, companion running module, clamping frame, tank, lid
with power cables, mini cell buffer dam

includes electrode assembly, clamping frame, tank, lid with power
cables, mini cell buffer dam

system includes 5 combs, 5 sets of glass plates, 2 casting stands,
4 casting frames, sample loading guide, electrode assembly,
companion running module, tank, lid with power cables, mini cell
buffer dam

system includes 5 combs, 5 sets of glass plates, casting stand, 2
casting frames, sample loading guide, electrode assembly, tank, lid
with power cables, mini cell buffer dam

includes 165-8001 and 164-5050

Supply, includes 165-8001 and 164-5070

precast gels, electrode

31

Catalog
Number Descriptions

165-8027 Mini-PROTEAN Tetra Cell and PowerPac HC Power Supply,

includes 165-8001 and 164-5052

165-8028 Mini-PROTEAN Tetra Cell and PowerPac HV Power Supply,

165-8029 Mini-PROTEAN Tetra Cell and Mini Trans-Blot Module, includes

165-8030 Mini-PROTEAN Tetra Cell (for Ready Gel Precast Gels) and

165-8033 Mini-PROTEAN Tetra Cell, Mini Trans-Blot Module, and

165-8034 Mini-PROTEAN Tetra Cell (for Ready Gel Precast Gels), Mini

165-8035 Mini-PROTEAN Tetra Cell, Mini Trans-Blot Module, and

165-8036 Mini-PROTEAN Tetra Cell (for Ready Gel precast gels), Mini

*The 2-gel systems do not include the companion running module.

includes 165-8001 and 164-5056

165-8001 and 170-3935

Mini Trans-Blot Module, includes 165-8004 and 170-3935

PowerPac Basic Power Supply, includes 165-8001, 170-3935,

and 164-5050

Trans-Blot Module, and PowerPac Basic Power Supply,
includes 165-8004, 170-3935, and 164-5050

PowerPac HC Power Supply, includes 165-8001, 170-3935, and
164-5052

Trans-Blot Module, and PowerPac HC Power Supply, includes
165-8004, 170-3935, and 164-5052

Casting Modules

Each casting module includes 2 combs, 5 sets of glass plates,
2 casting stands, 4 casting frames, and the appropriate sample
loading buffer.

0.75 mm Spacer 1.0 mm Spacer 1.5 mm Spacer

5–well 165-8008 165-8013 165-8019

9–well 165-8009 165-8014 165-8020

10–well 165-8010 165-8015 165-8021

15–well 165-8011 165-8016 165-8022

Prep/2–D well 165-8012 165-8017 165-8023

IPG well N/A 165-8018 165-8024

32

Handcast Gel Accesories and Replacement Parts

Catalog
Number Descriptions

165-3303 Mini-PROTEAN Casting Stand

165-3304 Mini-PROTEAN Casting Frame

165-3305 Mini-PROTEAN Casting Stand Gaskets, 2

165-3308 Short Plates, 5

165-3310 Spacer Plates with 0.75 mm Internal Spacers, 5

165-3311 Spacer Plates with 1.0 mm Internal Spacers, 5

165-3312 Spacer Plates with 1.5 mm Internal Spacers, 5

Other Replacements Parts

Catalog
Number Descriptions

165-8037 Mini-PROTEAN Tetra Electrode Assembly

165-8038 Mini-PROTEAN Tetra Companion Running Module

165-8039 Buffer Tank, replacement

165-8040 Buffer Tank and Lid, replacement

165-8041 Cell Lid with Power Cables

165-3201 Sample Loading Guide, 9 well (red)

165-3146 Sample Loading Guide, 10 well (yellow)

165-3203 Sample Loading Guide, 12 well (green)

165-3132 Sample Loading Guide, 15 well (blue)

165-3130 Mini Cell Buffer Dams, 2

165-3149 Replacement Gaskets for Electrophoresis Assembly, green, 2

161-0990 Empty Ready Gel Cassettes, 10

33

Combs

0.75 mm 1.0 mm 1.5 mm

5–well 165-3352 165-3357 165-3363

9–well 165-3353 165-3358 165-3364

10–well 165-3354 165-3359 165-3365

15–well 165-3355 165-3360 165-3366

Prep/2–D well 165-3356 165-3361 165-3367

IPG well N/A 165-3362 165-3368

34

Section 9
Warranty Information

The Mini-PROTEAN Tetra cell is warranted for one year against
defects in materials and workmanship. If any defects should occur
during this warranty period, Bio-Rad Laboratories will replace the
defective parts without charge. However, the following defects are
specifically excluded.

1. Defects caused by improper operation

2. Repairs or modifications done by anyone other than Bio-Rad
Laboratories or their authorized agent

3. Damage caused by accidental misuse

4. Damage caused by disaster

5. Common replacement parts including platinum wire, the
rubber gaskets, and glass plates

6. Damage caused by the use of organic solvents

For inquiries or requests for repair service, contact your local Bio­Rad office.

Warranty Information

Model____________________________________________________
Catalog number____________________________________________
Date of delivery____________________________________________
Serial number______________________________________________
Invoice number____________________________________________
Purchase order number_____________________________________

* US Patent No. 6,162,342
** US patent No. 5,656,145

35

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Group

Sig 121110007296 Rev D US/EG

Bio-Rad
Laboratories, Inc.

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