Viscotek TDA 302 User manual

1
The Leader in Polymer Characterization
Model 302 TDA Detectors
Instrument Manual
1002
Revision 2.00
15600 West Hardy Road
Houston, Texas 77060
Telephone: [phone]
Facsimile: [phone]

2
TABLE OF CONTENTS
A. DESCRIPTION OF INSTRUMENT
1. General Description And Notices. . . . . . . . . . . . . . . . . . . . . . . 5
a) Purpose and Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
b) General Layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
2. Light Scattering Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
a) Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
b) Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26
c) Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
3. Refractometer Detector/Vapor Sensor . . . . . . . . . . . . . . . . . . . 28
a) Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
b) Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
c) Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
4. Viscometer Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
a) Theory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
b) Components . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
c) Specifications. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
B. INSTALLATION
1. Installation Kit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
2. Connection to SEC System . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
3. Connection with External Detectors . . . . . . . . . . . . . . . . . . . 42
4. Solvent Compatibility with Instrument . . . . . . . . . . . . . . . . . . 42
C. OPERATION
1. Solvent Purging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
a) Air bubbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
b) Changing Mobile Phase Solvents. . . . . . . . . . . . . . . . . . . . . . . 43
2. Adjusting Zero Offsets of Detector Signals . . . . . . . . . . . . . . 44
a) Adjusting IP Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
b) Adjusting LS Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
c) Adjusting RI Zero . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

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3. Checking Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
a) Measuring Capillary Bridge Balance . . . . . . . . . . . . . . . . . . . . 45
b) Measuring Baseline Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
c) Computing Pump Pulsation Noise . . . . . . . . . . . . . . . . . . . . . . 46
d) Checking Background Light Scattering . . . . . . . . . . . . . . . . . . 47
e) Standard Sample Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47
D. TROUBLESHOOTING
1. Problems in the Viscometer Baseline . . . . . . . . . . . . . . . . . . . 48
a) Pulsation Noise in the DP Baseline . . . . . . . . . . . . . . . . . . . . . 48
b) Random (White) Noise in the DP Baseline . . . . . . . . . . . . . . . . 49
c) Sporadic Noise in the DP Baseline . . . . . . . . . . . . . . . . . . . . . . 49
2. Problems in the Light Scattering Baseline . . . . . . . . . . . . . . . 49
a) General Instrument Function . . . . . . . . . . . . . . . . . . . . . . . . . . 49
b) Baseline Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49
3. Problems in the Refractometer Baseline . . . . . . . . . . . . . . . . 50
a) General Instrument Function . . . . . . . . . . . . . . . . . . . . . . . . . . 50
b) Baseline Noise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50
APPENDICES
I. Changing the Internal Viscometer Delay Column . . . . . . . . . . 51
II. Cleaning the Viscometer Detector in Situ. . . . . . . . . . . . . . . . .52
III. Solvent Changeover Procedure . . . . . . . . . . . . . . . . . . . . . . . . 53
IV. Warranty Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53
TO THE CUSTOMER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

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LIST OF ILLUSTRATIONS AND DRAWINGS
PAGE FIGURE DESCRIPTION
9 1 TYPICAL NARROW STANDARD UNIVERSAL CALIBRATION CURVE
10 2 TYPICAL PLOT OF INTRINSIC VISCOSITY VERSUS RETENTION VOLUME FOR BROAD
SAMPLE
13 3 VISCOMETER, REFRACTIVE INDEX, AND LIGHT SCATTERING DETECTORS
PLUMBING DIAGRAM
14 4 FRONT PANEL OF MODEL 302 TDA
17 5 BACK PANEL OF MODEL 302 TDA
23 6 RALLS DIAGRAM
27 7 LIGHT SCATTERING DETECTOR DETAIL
29 8 OPTICAL SCHEMATIC OF REFRACTOMETER DETECTOR
30 9 VAPOR SENSOR, LIGHT SCATTERING AND REFRACTIVE INDEX DETECTORS
31 10 CELL/MIRROR ENDOF REFRACTOMETER BLOCK
31 11 SOURCE/DETECTOR ENDOF RI BLOCK ASSEMBLY
34 12 FOUR CAPILLARY BRIDGE
35 13 SOURCE/DETECTOR ENDOF REFRACTOMETER BLOCK
36 14 DP CHROMATOGRAM SHOWING DELAY VOLUME TOO SMALL
37 15 VISCOMETER COMPONENTS
41 16 LIGHT SCATTERING FILTER ASSEMBLY
41 17 PNUMATIC PULSE DAMPENER ASSEMBLY
46 19 METHOD OF ESTIMATING BASELINE NOISE
47 20 MEASUREMENT OF PUMP PULSATION FROM THE INET PRESSURE SIGNAL/NOISE
LIST OF TABLES
PAGE TABLE DESCRIPTION
24 A2-1 ACCURATE MOLECULAR WEIGHT AND RADIUS OF GYRATION DETERMINATION BY
TRIPLE DETECTOR SEC OF POLYBUTADIENE STANDARDS IN THF
26 A2-2 UNPRECEDENTED PRECISION OF SEC VISCOMETRY-RALLS IN DETERMING
POLYMER CONFORMAION OF POLYSYRENE STANDAD (NBS706) IN TOLUENE

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NOTICES AND WARNINGS
The information contained in this manual is subject to change without notice. Viscotek
Corporation assumes no responsibility for errors that may appear in this document. The
manual is believed to be accurate at the time of printing. Viscotek Corporation shall not
be liable for damages resulting from the use of this document.
ATTENTION: This detector is a highly sensitive instrument. Read the manual before
using, and follow appropriate safety procedures.
To avoid the risk of electrical shock, disconnect the power cord before
removing top cover.
To avoid possible damage to electrical components, power off the TDA before removing
detector module.
WARNING: Set fuse module and switch (sw-6) for correct line voltage (110/240 VAC
50/60 Hz) to avoid damage and possible fire hazard. When fuse replacement is
necessary, use only the fuse specified on the chassis rear cover (5.0 Amperes 250V
type T).
WARNING: HOT surfaces inside. Wear appropriate protection when handling detector
module.
When connecting power cord to detector, use a properly grounded receptacle.
Attention: The detector has two flow cells that are pressure rated at 150 psi. Do not
connect any tubing or device that might cause the back pressure to exceed the above
pressure rating.

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Note: The operating temperature of the instrument is from 5 to 30 degrees centigrade.
The maximum operating humidity rating is 80% non-condensing. The current draw for
the unit is 3.5 amperes.
The laser diode used in this product has been classified as a Class 1 Laser Product that
complies with 21 CFR 1040.10 and 21 CFR 1040.11
The Light Scattering Detector assembly contains no user serviceable parts. Contact the
Viscotek Corporation if service is needed.
This product has been tested for and is in compliance with low voltage safety, EMC, and
laser safety according the directives of
If further information is needed about these or any other notices or warnings, please
contact Viscotek Corporation Technical Service and Support Department.

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A. DESCRIPTION OF INSTRUMENT
A.1 GENERAL DESCRIPTION
A.1.a Purpose and Applications
The Model 302 TDA Differential Refractometer is the basic detector component of a
system for polymer analysis by gel permeation chromatography (GPC), also called size
exclusion chromatography (SEC). SEC involves separation through the hydrodynamic volume
of the molecular distribution. The refractometer can also be used to determine the
concentration of solutions after calibration.
SEC SEPARATION
In SEC, columns are packed with porous packing material. Molecules which are smaller
than the pores are trapped for short periods of time within the pores with which they come in
contact. A common term for this is that “the molecules are totally included.” Molecules larger
than the size of the pores are not trapped at all, and will elute earliest. These molecules are
said to be “totally excluded.” In these two cases, the column has little or no separation as a
function of molecular weight and the values fall on a non-linear section of the calibration curve
(log Hydrodynamic Volume (Vh) vs. Retention Volume). Within a given column, there is a
distribution of pore sizes which allows most molecules to stay resident in many of the pores
while being excluded from many others. Molecules in this size range, generally will fall on a
fairly linear calibration range of the calibration curve.
MEASURING THE INTRINSIC VISCOSITY DISTRIBUTION
The Model 302 TDA is specifically designed for polymer analysis by SEC3or FIPA.
In an SEC3system, the Deflection-type refractometers are the most common type used in SEC
separation; they operate by measuring the deflection of a light source caused by a difference in
the refractive index of a sample-solvent mixture and pure solvent. Because different polymer
types have different differential refractive index responses with concentration (dn/dc), each
polymer type must have a unique RI response factor. Therefore, the area of the RI is
proportional to the product of the concentration, injection volume and inverse flowrate of the
sample only across a single sample type. The RI area is exactly proportional to the quantity of
the mass injected of the sample and its dn/dc value.
Thus, the refractometer provides a signal which is generally proportional to concentration of
sample as it elutes from the column.
[A.1-1] Yk
dn
dc C
iri i
=where for species i,
k
ri = Refractometer response constant
dn
dc
= Polymer refractive index increment
Ci= Concentration
If the usual assumption is made that all of the sample injected into the column elutes from the
column, the sum can be taken over all data points in the concentration chromatogram. Then
Equation [A.1-1] can be normalized, yielding a cancellation of constants.

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[A.1-2] Y
Y
C
C
i
i
i
i
∑∑
=
But,
[A.1-2a] CCV
V
i
ss
∑=∆where,
C
s
= Concentration of sample injected
V
s
= Volume of sample injected
∆
V
= Elution volume increment
Therefore it can be written that,
[A.1-2b] CY
Y
CV
V
i
i
i
ss
=∑∆
The viscometer provides a signal likewise proportional to the specific viscosity of the sample.
[A.1-3]
η
sp
DP
IP
D
P
=−
4
2
where,
η
sp = Specific viscosity
DP= Differential pressure
IP= Inlet pressure
Equation [A.1-3] can easily be solved for the differential pressure value, DP:
( )
η
sp IP DP DP−
=
24
η
η
sp sp
I
PDPDP=
+
42
(
)
ηη
sp sp
IP DP=+22
[A.1-3a] DP IP
i
sp i
sp i
i
=+





1
22
η
η
These are the two primary pieces of information provided by the refractometer and
viscometer detectors. Taken together, the specific viscosity and concentration permit the
calculation of intrinsic viscosity of the sample at every elution point.1
1Equation [A.1-4] is exact only in the limiting case of infinite dilution of the sample. At normal
concentrations encountered in SEC, it is usually adequate. However, the Viscotek TriSEC software
actually uses an empirical improvement called the Soloman-Gottesman equation to calculate more
accurate intrinsic viscosities. See the TriSEC manual, Part 2.e (Further Derivations) for more details.

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[A.1-4]
[]
η
η
i
sp i
i
C
≅where
[
]
η
= intrinsic viscosity
The set of data points {Ci, [
η ]i, Vi} is thus obtained across the entire chromatogram. The first
pair of this set constitutes the Intrinsic Viscosity Distribution (IVD) of the polymer sample. Note
that it is obtained directly from the detector responses of the detector.
DERIVING MOLECULAR WEIGHT DISTRIBUTION
The Molecular Weight Distribution (MWD) can be obtained at least 3 ways:
(1) Conventional Calibration
Conventional calibration generally calibrates the molecular weight or intrinsic viscosity of
a given substance to the retention volume. The only case where this can be rigorously held true
is when there is no variation of structure (including branching, conformation, etc.) between the
standards and the unknowns. Therefore, for each different structure or substance, a new
calibration curve must be made to obtain a true molecular weight or intrinsic viscosity
distribution. “Apparent molecular weights” referenced to standards such as polystyrene are
commonly used; however, this leads to disproportionate information if there are major structural
differences within the sample such as branching. This type of error can cause gross
underestimation of sample polydispersity.
In conventional calibration techniques, the absolute concentration is not required for the
sample measurement. The overriding concern is the ability to measure relative concentrations
along the elution profile. Therefore, the RI detector is often used to determine relative mass.
(2) Universal Calibration
By calibrating the column with primary molecular weight standards, one can convert the
intrinsic viscosity distribution into the molecular weight distribution via the Universal Calibration
Curve. This is usually accomplished by measuring the retention volumes Viand intrinsic
viscosities [
η ]ifor a set of narrow distribution polymer standards. The product of intrinsic
viscosity and molecular weight for each of the standards is then plotted against the retention
volumes, obtaining a smooth curve.
R etention V olum e (m l)
U nive rsa l C alibra tio n
0.86
2.41
3.95
5.50
7.05
8.60
9.3 11.7 16.5 18.9 21.3
14.1
Figure 1 Typical Narrow Standard Universal Calibration Curve
Log (IVxMW)

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Then for an unknown the data set {[
η ]i, Vi} is also measured.
Intrinsic Viscosity Results
9.7 11.9 14.1 16.2 18.4 20.5
-1.33
-0.91
-0.48
-0.05
0.37
0.80
R etention V olum e (m l)
Figure 2 Typical Plot of Intrinsic Viscosity versus Retention Volume for Broad Sample
It is clear that the data set {Mi,Vi} for the unknown sample can be mathematically extracted by
dividing the data of Figure 2 into that of Figure 1. The full data set {Ci, [
η ]i, Mi,V
i} for the
unknown sample could then be constructed, the first and third terms of which constitute the
desired MWD.
Universal Calibration is the best means of column calibration in SEC. It is applicable to
a wide range of polymers, the polymer standards do not have to be the same type as the
unknown, and it applies to copolymers as well as to both linear and branched samples.
However, it necessarily assumes that the mechanism of retention on the columns for both
sample and standards is pure size exclusion.
(3) SEC3
The molecular weight distribution can be obtained directly from an on-line light scattering
detector connected in series before the refractometer and viscometer detectors. This is the
SEC3system. The data set {Ci, [
η ]i, Mi,V
i} is obtained just as with Universal Calibration.
However, the Mivalues are calculated directly from the LS detector signal, not derived through
the column calibration. In addition to the convenience of not having to run calibration standards,
SEC3offers the real advantage of not being constrained by the size exclusion separation
mechanism.
MOLECULAR SIZE AND BRANCHING
Regardless of how one determines MWD, whether by Universal Calibration or Triple
Detection, the viscometer detector is useful for determining the size of molecules in solution.
The molecular size can then be related to the secondary structure of the polymer, either in
terms of chain stiffness, conformation, or branching.
Molecular size is commonly computed as the radius of gyration, Rg, which can be
determined rigorously only from the initial slope of multi-angle light scattering measurements.
Unfortunately, the multi-angle slope approach has only a limited range of applicability, as the
Log IV

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precision of measurement suffers greatly below Rgof 20 nm (MW ≈250K for flexible coils) and
becomes impossible below 10 nm (MW ≈80K).
The radius of gyration can be computed from the intrinsic viscosity and molecular weight
via the Ptitsyn-Eizner modification of the Flory-Fox equation.
[A.1-5]
[]
( )
(
)
ηεε MR
g
=− +Θ0
23
1263 286 6..
where
ε =
−
21
3
aand with
a= Mark-Houwink exponent.
Although this viscometry approach is certainly non-rigorous and would likely be
inaccurate for polymer molecules deviating significantly from the flexible coil model, it has the
necessary virtue of excellent precision over all ranges of molecular size and weight. Precision
and range of applicability are most important because it turns out that any subsequent
calculations of secondary structural effects, e.g., branching, are only suitable for relative
measurements. This is because those theoretical calculations involve the same type of
assumptions that affect Equation [A.1-5].
A.1.b General Layout
LIGHT SCATTERING PLUMBING AND FLOW PATH
Refer to the Detector Plumbing Diagram in Figure 3 for the flow through the system.
Flow enters the light scattering cell from the in-line RALLS filter and then exits to the
refractometer detector of the 302TDA. A laser beam is focused on the end of the cell and
scattered light is measured at 90 degrees and at 7 degrees.
REFRACTOMETER PLUMBING AND FLOW PATH
Refer to the Detector Plumbing Diagram Figure 3 for a schematic of the flow through the
refractometer. Note that the diameter of the tubing is not the same throughout the
refractometer. The tubing from the inlet through to the sample side of the cell is 0.01”id; all
other tubing is 0.04”id, from the bottom of the reference cell and out to the RI Purge solenoid.
Although the pressure drop also depends on length, the strong dependence on bore radius or
diameter means that the wide bore tubes shown have small resistance compared to the narrow
bore tubes. Only with this relationship clearly in mind can one understand the flow patterns
described below.
The reference cell of the refractometer is filled with mobile phase solvent by opening the
RI purge valve. Solvent flow is then diverted from the Viscometer to the Reference side of the
RI flow cell. Solvent then passes through a 20 micron filter, the positive Inlet Pressure
transducer cavity and Cross 3. It then flows through the negative Inlet Pressure transducer
cavity, Cross 2 and finally exits to waste via the Outlet bulkhead port fitting.
VAPOR SENSOR DETECTOR
Refer to Figure 9 for the location of the vapor sensor in the Model 302. The sensor is
mounted in the rear of the TDA module. The 4-lead sensor plugs into a socket for easy
replacement. Note that the socket has a notch cut for the sensor key alignment. Hence, the

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socket’s notch should be aligned with the sensor’s orientation tab. Should a solvent leak occur
in the TDA module, the chemical sensor’s output signal will increase and exceed a set threshold
level. This will cause the vapor bar LED on the front panel to flash and it turn activate a solid-
state relay. This relay will provide a contact closure to shut down the external solvent pump.
VISCOMETER PLUMBING AND FLOW PATH
Refer to the Viscometer Plumbing Diagram in Figure 3 for the flow through the system.
Poiseulle’s Law of flow through tubes requires that the pressure drop across any tube is
inversely proportional to the diameter raised to the fourth power.
[A.1-6] PLQ
R
∝8
4
π
where
L= length, Q= flowrate, and R= radius
Note that some of the tubing shown in Figure 3 is small bore (shown with fine line width)
and other tubing is wide bore (shown with wide line width). The wide bore tubing is 0.040”
diameter and the fine bore tubing is 0.010” diameter. Although the pressure drop also depends
on length, the strong dependence on bore radius or diameter means that the wide bore tubes
shown have negligible resistance compared to the narrow bore tubes. Only with this
relationship clearly in mind can one understand the flow patterns described below.
The viscometer differential pressure transducers, having positive and negative cavities,
are purged using electronic solenoids from the front panel of the instrument. These purge
procedures must be carried out independently to properly redirect the flow through the
transducer cavities and remove air bubbles and/or purge the cavities with new mobile phase
solvent. Normal flow is directed into the viscometer and split at a tee connecting capillaries R1
and R2. After closing the DP purge ports, the flow is directed only through the four capillary
bridge R1- R4. The IP+cavity is in series before the bridge and is purged by the Refractometer
Purge valve. The IP-cavity is in series after the bridge and is continuously purged by the
viscometer waste flow.

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Figure 3 Viscometer, RI and LS Plumbing Diagram

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FRONT PANEL
Figure 4 Front Panel of the Model 301/302 TDA
Located in the center at the top of the electronics module is the LED voltage display of
the signal (FIGURE 4), which is indicated as DP, IP, RALS, LALS, RI or UV by the appropriate
light on the left of the electronics module. Readout shown on the meter is in units of millivolts,
which matches the analog output voltages available on the back panel. For the DP signal, 1.0
mV corresponds to a pressure of 1 Pa. For the IP signal, 10 mV corresponds to 1 kPa. The LS
signal corresponds to mV from the photodiode amplifier of the light scattering detector and the
refractometer signal corresponds to the mV output of the refractometer. Full scale data ranges
are established in the TriSEC software package for each channel between 100mV, 500mV, and
2500mV FS. Default ranges are 2500mV FS for IP, 500mV FS for DP, 2500mV FS for LS and
500mV FS for RI.
In the center of the module is a set of five push-buttons: two for SELECT, ZERO,
TRIGGER, and LASER:
ELECTRONICS MODULE
OVEN MODULE

15
•The SELECT button is a selection switch to choose the signal displayed on the LED
display meter. You can cycle up or down through the display using either the up button
or the down button.
•The ZERO button is an electronic zeroing adjustment control for offsetting the IP and the
LS signals only. DP, RI and LS are strictly baseline signals, that is, measurements are
made in the computer after subtracting the baseline. Zeroing these signals is primarily a
matter of convenience or visual reference. On the other hand, the IP signal is read by
the computer as an absolute pressure, so it is critical that the IP signal be zeroed only
when the flow is off.
•The TRIGGER button can be used to start an acquisition with a manual injector.
Remember to connect a contact closure signal cable output to the VAC terminal strip if
using an auto-sampler.
•The LASER button turns the power on to the laser diode. When this button is depressed
for the first time, it illuminates, indicating that the power is on. The power to the laser
diode is turned off by depressing this button a second time. The light will go off
indicating that the power is off to the laser diode.
On the right is another bank of lights, which indicates the status of operation: LASER,
IDLE, ACQUIRE, ZERO, VAPOR and SERIAL I/O:
•The LASER light indicates whether or not the power to the laser diode is on. It is
recommended that this switch be left ON at all times since a warm-up period is
required for the LASER source to become stable. NOTE: The laser operates in a
constant optical power output mode. This is not a pulsed laser unit.
•When the IDLE indicator light is illuminated, the instrument is ready to communicate
to the host computer. This light also serves as an indicator light for the self
diagnostic routine during the power up routine. At unit power up, this LED is off until
self diagnosis is completed. Should the unit fail self diagnosis, the LED will not be
properly set.
Note: An improper set may be indicated by either none or several of the LEDS being lit.
•When the ACQUIRE indicator light is illuminated, the instrument is in the process of
acquiring data from the analog inputs. This diode will turn off after each runtime
cycle.
•The ZERO indicator light is only illuminated when either the RALS, LALS, or IP
signal is selected and the ZERO switch is pushed.
•The VAPOR light will only illuminate when the vapor sensor is activated by a leak in
the detector module. This will also shut off the solvent delivery system if a shut off
cable is attached to the terminal strip on the back of the detector. The connector is
polarity sensitive! Pin #1 must be connected to the pump stop and pin #2
connects to pump ground.
•When the SERIAL I/O light is on serial data is being received from the computer.

16
Below the Viscotek Corporation Logo On the lower portion of the electronics module
is a smoked plastic cover that encloses several switches and a push-button used for
operating the Model 300TDA. They include: MAIN POWER button, REFRACTOMETER
and VISCOMETER PURGE, REFRACTOMETER ZERO, as well as a DC POWER
RESET switch.
•The MAIN POWER push-button turns the AC power On/Off. This switch will disable
all electronic components including the heater circuit. This switch is always left ON
during data acquisition.
•The REFRACTOMETER PURGE switch is used to control an electronic valve that is
used to purge the reference side of the cell with fresh solvent. Normal HPLC pump
flow-rate is required for a period of approximately 5 minutes (or until a stable Display
Meter reading is achieved) to adequately purge the Refractometer. Additionally, the
positive signal side of the Inlet Pressure transducer is purged simultaneously. This
switch must be in the OFF position for data acquisition.
•The VISCOMETER PURGE switch is used to control a pair of electronic valves that
are used to purge the two halves of the Differential Pressure transducer. Again,
normal HPLC flow is required for approximately 5 minutes (or until a stable Display
Meter reading is achieved) to adequately purge the viscometer. The negative signal
side of the Inlet Pressure transducer is continuously purged during normal operation
of the Model 300TDA.
•The REFRACTOMETER ZERO switch is used to adjust the optical alignment of the
Refractometer signal during the initial setup and upon solvent change-over. To
make adjustments hold the switch either up or push down depending upon the
algebraic sign of the signal displayed. NOTE: Once the zero has been obtained, do
not change or re-zero the signal while running samples. If it is necessary to re-zero
the signal, you may need to re-calibrate the RI detector. See the TriSEC 3.0
Software manual for this procedure.
•The DC POWER RESET switch is used to reestablish serial communication between
Model 302TDA and its data station. If either power surges or signal saturation are
experienced during normal data acquisition result in an apparent “lock-up” of the data
stream it will be necessary to STOP data acquisition and use this switch to reset the
internal CPU for proper operation. Use of this switch does not effect proper
temperature control.
Located to the left hand side of the electronics module is the Oven Compartment that
contains space for up to 3 separation columns and the Model 302TDA detectors. This
compartment may be removed from its housing by loosening the two panel screws
located at the center top and bottom of the compartment front panel. A handle is
provided in the front and rear of the drawer as an aid in removal.
Note: No locking mechanism is provided for sliding the detector drawer out of the
oven chamber. Also, HOT surfaces will be encountered upon removal.

17
On the outside and to the bottom of the oven compartment are the Sample In/Out
Flow Ports. These are used to connect the Model 302TDA to the HPLC system.
NOTE: An optional manual sample injection valve may also be located on the front
panel of the Oven Module. This is often used in the FIPA application. This option may
also be selected for GPC applications not requiring auto-sampler capabilities.
BACK PANEL
Figure 5 Back Panel of the Model 301/302 TDA
The back panel, Figure 5, contains the fused A/C power module. This module contains
the receptacle, a fuse holder and a voltage selector switch. The voltage is selectable for either
100, 120, 220 or 240 VAC. An additional HEATER POWER switch is located above the A/C
power module. It may either be selected for 110 or 220 VAC. The main power on/off push-
button is wired directly to the AC power supply.
The back panel also contains the analog signal input/output connector and the auto-
sampler trigger input. This includes inputs for an external UV detector, and a RI detector as well
as an output for one detector signal. Connections to the barrier strip may be made by using a
small flat-head screwdriver supplied with the instrument. The maximum level of signal inputs is
2.5 VDC. The device may be damaged by voltages exceeding 12VDC
A/C Power Module
9 pin Serial Connector
Analog Signal/Trigger Connector
Heater Power Switch
Vapor Detector Connector

18
A nine-pin serial connection port is located on the rear of the instrument. This
communication socket allows the instrument to be connected directly to a PC through the
standard RS232 serial port. The nine-pin connector cable may be oriented in one direction only.
The back panel also contains the vapor detector connector. A two wire connector can
be connected here and to the back of the solvent delivery unit to the pump stop or shut down
terminal. When the vapor sensor is activated by a leak, the detector will send out a contact
closure signal to the pump to shut off flow to the system. The connector is polarity sensitive!
Pin #1 must connect to the pump stop and pin #2 must connect to pump ground.
DC POWER SUPPLY
The DC power supply is located toward the back of the detector. It provides ±15 volts
and ±5 volts to the electronic components of the detector. The primary side of its transformer is
wired directly to the AC power module on the back panel.
DATA ACQUISITION
A separate data acquisition device is not necessary for either of the Model 302TDA. The
data acquisition device (DAD) has been integrated into each T model detector, available
through the serial interface located on the back panel.
The DAD system is more than a simple chromatography board, which only converts
analog voltage signals from GPC detectors into digital values for processing by a computer. It
is designed for unattended data acquisition, leaving the computer free to run other applications.
The DAD collects and stores analog data and controls linked accessories. On request, data can
be transferred to the host PC for further evaluation with the TriSEC GPC Windows Modules.
A.2 LIGHT SCATTERING DETECTOR
A.2.a Theory
LIGHT SCATTERING THEORY
Light scattering is a well established technique for determining weight-average molecular
weights (MW) of polymers in solution. When light interacts with a molecule, it induces a
temporary dipole moment which oscillates in phase with the incident beam. In fact, the
molecule acts as an antenna and re-radiates light in all directions. This scattered light is
referred to as Rayleigh scattering and is of the same wavelength as the incident beam.
Due to thermal fluctuation, pure solvent also scatters light, although to a lesser degree
than the polymer solution. The information about the size and molecular weight of polymer is
experimentally derived from the excess light scattering intensity above the solvent background.
The excess light scattering intensity caused by the presence of polymer molecules in the
sample solution is directly proportional to polymer MW and sample concentration:

19
[A.2-1]
( )
KC
RMP AC
w θ
θ
=+
122
where Cis the sample concentration, Mwis the weight average MW, and A2is the second virial
coefficient. The term P(
θ ) is the particle scattering function2,3 which describes the angular
dependence of light scattering intensity. The term P(
θ ) is a function of the geometry and size of
the polymer molecules with respect to wavelength of the incident light. The Kterm in Equation
[A.2-1] is an optical constant:
[A.2-2] Kn
N
dn
dc
A
=








22
0
2
0
4
2
π
λ
where nis the refractive index of the medium,
λ
0is the wavelength of the incident beam, NAis
Avagadro’s number (6.023 x 1023), and dn/dc is the refractive index increment. The excess
Rayleigh ration R
θ
in Equation [A.3-1] gives the normalized scattering intensity with respect to
the scattered volume v, distance r, and incident intensity I0:
[A.2-3]
( )
RI I r
Iv
θθ θ
=−





solution solvent
2
0
where I
θ solution and I θ solvent represent the scattering intensity observed at the scattered angle
θ , for
the polymer solution respectively.
Experimentally, the P(
θ ) value can be determined as the ratio of scattering intensity at
the scattering angle
θ , versus the scattering intensity at θ = 0°:
[A.2-4]
( )
PI
I
θ
θ
θ
=
=
solution
solution0o
Due to the dissymmetry and depending on the size of the polymer molecule, the P(
θ ) function
can take on values that are equal to, or less than unity.
The angular dependence of light scattering intensity is the consequence of the
destructive interference of the scattered radiations.4When a scattering particle has its sizes
comparable to the wavelength of the incident beam, the scattering radiation from different parts
of the particle may get out of phase when they reach the detector. The extent of this phase
mismatch varies with the scattering angle. For example, due to the difference in the optical path
distances, the radiations from scattering point A and B would be more out of phase as they
reach detector 2 than detector 1. Because of this destructive radiation field interference, a lower
scattering intensity would be observed at the larger scattering angles, such as the case for
2P. Kratochvil, “Classical Light Scattering from Polymer Solutions”, Elsevier, Amsterdam, 1987.
3P. Kratochvil, in “Light Scattering of Polymer Solutions”, M. B. Huglin (Ed.), Academic Press, New York,
1967, Ch. 7.
4B. H. Zimm, R. S. Stein, and P. Doty, Polymer Bulletin, 1, 90, (1945).

20
detector 2. This angular dependency of light scattering intensity is represented by the particle
scattering function P(
θ )in light scattering theory, see Equation [A.2-1].
Quantitative theories of P(
θ ) for the solute shape models of hard-sphere, random-coil,
and rigid-rod types have long been worked out and published.4For example, the P(
θ ) function
according to Debye’s theory for random coil polymers5gives:
[A.2-5]
( ) ( )
[]
P
X
eX
X
θ =−−
−
21
2
or,
[A.2-6]
( )
PXX θ =− + −1312
2
. . .
where,
[A.2-7]
2
2
sin
3
8










=
θ
λ
π n
RX g
Equation [A.2-6] shows that it is the initial slope of the P(
θ ) function which is proportional to the
square of the polymer radius of gyration, Rg, value. In this manner a light scattering instrument
can be used to determine the Rgof the polymer samples.
Since there are two variables,
θ and Cin Equation [A.2-1], a double-extrapolation
procedure is used to obtain Mwas well as Rgand A2. This is done by plotting Kc /Rgversus sin2
( θ /2) and C, known as the Zimm plot method.6
SEC LIGHT SCATTERING DETECTOR
Potentially, the coupling of an on-line light scattering detector can give a very powerful
polymer characterization capability. Considerable efforts have been invested in the past two
decades or more in the attempt to develop an on-line light scattering detector for SEC to
achieve absolute molecular weight distribution determination of polymer samples. Earlier
commercial light scattering detectors for SEC were far less than satisfactory because of the lack
of detection precision.7,8 The concentration of the polymer solution eluting from an SEC column
is extremely dilute. The polymer concentration level in an SEC effluent is typically an order of
magnitude less than the sample concentration commonly used in classical light scattering
experiments. The signal-to-noise of a light scattering instrument is the most important
consideration in the SEC detector application.
Viscotek’s choice of the 90° right angle in the light scattering instrument is for the reason
of optimum signal-to-noise performance in the SEC-LS detection. Compared to the other
scattering angles, the 90° scattering intensity is the least affected by the problems of stray-light,
5P. Debye, Technical Report CR-637, Private Communication to Reconstruction Finance Corporation,
Office of Rubber Reserve (1945). Reprinted in “Light Scattering from Dilute Polymer Solutions”, (D.
McIntyre, and F. Fornick, eds.) pp. 139-147, Cordon and Breach, New York (1964).
6B. H. Zimm, J. Chem. Phys., 16, 1093 (1948).
7Grinshpun, O’Driscoll, and Rudin, ACS Symposium SER., 245, 273 (1984).
8S. Kim, P. M. Cotts, and W. Volksen, J. Polymer Science, Part B: Polymer Physics, 30, 177 (1992).