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Viscotek TDA 302 Instrument Manual Download Page 43

 
 

43

C.  OPERATION

 

 
 

 

C.1  PURGING THE SYSTEM

 

 

 

 

C.1.a  Air Bubbles

 

 
 

The presence of air bubbles in any of the detectors will greatly increase the level of 

baseline noise in the signal.  It is imperative that bubbles be kept out of the detectors. There are 
basically two ways for air bubbles to get into the system: Purging is accomplished by operation 
of the Refractometer and Viscometer Purge valves as previously described. 
 
1. 

By Entry from the Outside

 

 

This ordinarily happens only when the detector is disconnected and then reconnected.  

Air may enter by siphoning of solvent from the detector, or from air in the connecting tubing.  
To minimize this, always immediately plug off the Sample In port when disconnecting the 
connecting tubing.  Then before reconnecting the tubing, be sure to purge the tubing of any 
air that may have entered. 

 

2. 

By Spontaneous Bubble Formation in the Solvent 

 

If the solvent is not thoroughly degassed before use, it can occasionally form bubbles 

spontaneously on the wall of any static cavity.  The best way to prevent this from happening 
is to use only filtered / vacuum degassed mobile phase solvent.  For this purpose,

 

an in-line 

solvent degasser before the HPLC pump is most convenient and highly 
recommended.

  Air bubble problems seldom occur in systems operating with an in-line 

degasser.  Sparging is not a recommended method for degassing solvent. 

 
 

 

 

C.1.b  Changing Mobile Phase Solvent 

 
 

The other reason for purging is upon changing mobile phase solvent composition. 

 
1.  Be certain that the new mobile phase is miscible with the old solvent that is in the detector.  

In most cases, the detector is shipped in THF, which is miscible with virtually all organic 
solvents and also with water.  However, it is not miscible with all aqueous salt solutions.  
The best practice when going from THF to an aqueous salt solution is to go through an 
intermediate flush with distilled/deionized water. 

2.  To make a change of mobile phase in the columns, disconnect the detector from the system 

while making the solvent changeover in the columns.  Reconnect the detector only after the 
columns are sufficiently purged and equilibrated with the new mobile phase.  The reason for 
this is that columns frequently discharge residues upon solvent changeover and these 
residues can sometimes coat the capillary walls of the viscometer bridge and deposit debris 
on the surface of light walls causing high background and noise. 

3.  To replace the columns with another set that is already equilibrated to the new mobile phase 

solvent: 

Summary of Contents for TDA 302

Page 1: ...1 The Leader in Polymer Characterization Model 302 TDA Detectors Instrument Manual 1002 Revision 2 00 15600 West Hardy Road Houston Texas 77060 Telephone 281 445 5966 Facsimile 281 931 4336 ...

Page 2: ...8 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 Adj...

Page 3: ...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 S...

Page 4: ...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 FRO...

Page 5: ...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 surface...

Page 6: ...roduct 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 ...

Page 7: ...les 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 SEC3 or FIPA In an SEC3 system the Deflection type refractometers are the most common type used in SEC separation they operate by measuring the deflection of a light source caused b...

Page 8: ...p IP DP DP 4 2 η η sp sp IP DP 2 2 A 1 3a DP IP i sp i sp i i 1 2 2 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 1 Equation A 1 4 is exact only in the limiting case of infinite dilution of the samp...

Page 9: ...ed 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 ...

Page 10: ...ular 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 SEC3 system The data set Ci η i Mi Vi is obtained just as with Universal Calibration However the Mi values are calculated directly from the LS detector signal not derived through the column calibration In addition to the conve...

Page 11: ...cattered 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 o...

Page 12: ...iameter 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...

Page 13: ...13 Figure 3 Viscometer RI and LS Plumbing Diagram ...

Page 14: ...he 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 Defaul...

Page 15: ... 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 ho...

Page 16: ... 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 t...

Page 17: ...e 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 detec...

Page 18: ...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 furthe...

Page 19: ...scattering intensity at the scattering angle θ versus the scattering intensity at θ 0 A 2 4 P I I θ θ θ solution solution 0o 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 radiatio...

Page 20: ...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 l...

Page 21: ...negligible in the SEC application A 2 8 θ θ P M R KC w 1 In theory the polymer size parameter can be derived from the P θ function Again in theory the P θ function and therefore the polymer Rg value can be determined by a multi angle approach to light scattering detection However the molecular size measurement by SEC and multi angle LS has may severe practical limitations The P θ function approach...

Page 22: ... 1 3 π η For linear flexible chain polymers this can be related to the radius of gyration using the Flory Fox and Ptitsyn Eizner equations 12 13 where A 2 12 3 1 2 1 6 1 Φ M Rg η A 2 13 Φ 2 55 10 1 2 63 2 86 21 2 ε ε A 2 14 ε 2 1 3 a where a is the exponent of the Mark Houwink equation A 2 15 η KM a SEC VISCOMETRY RALLS LALLS In this triple detector method the angular dissymmetry in the scattered ...

Page 23: ...lated directly from the RALLS intensity R90 from Equation A 2 10 that is A 2 16 KC R Mest D 90 θ where K is the optical constant defined earlier 2 A Flory Fox radius RFF is then calculated from the above Mest and the experimental intrinsic viscosity value η A 2 17 R M FF est est 1 6 1 2 1 3 η Φ where Φ is the Flory viscosity constant defined earlier in Equations A 2 12 and A 2 13 that take into ac...

Page 24: ...iple Detector SEC of Polybutadiene Standards in THF The P 90 values in the fourth column are the angular dissymmetry factor of the particle scattering function measured at the 90 scattering angle Remember that the P 90 value equals the ration of the scattering intensity at the 0 scattering angle The P 90 factor can be 1 00 or less A P 90 value of 1 00 is indicative of the fat that there is no angu...

Page 25: ...Viscotek LALLS detector measures signal response at an angle of 7 degrees having virtually no background noise and a high signal to noise ratio compared to earlier low angle instruments The remarkable ability of triple detector SEC to detect polymer branching has been illustrated for an experimental bimodal polymer The RALLS detected a very high MW species in the prepeak while the viscometer showe...

Page 26: ...distribution of polymer samples over the widest range of molecular weights The technique provides extra sensitivity at low molecular weights The triple detector combination also eliminates the need of SEC column calibration and instrumental band broadening correction 14 In addition the low angle LALLS detector can confirm the molecular weight calculations of odd shaped species where the angular di...

Page 27: ...ght Scattering Detector Detail A 2 c Specifications Measuring Angle 90 and 7 Light Source Constant optical power output laser diode Wavelength 670 nm Output Power 3 mW Detectors Photodiode Amplifier Cell Volume 10 µL ...

Page 28: ...ror is then aligned so that near zero signal is output Now when the sample elutes into the sample side of the dual cell the light beam is refracted deflected according to Snell s Law of Refraction sin sin n n 1 A 3 s r r s θ θ where q is the angle of incidence with respect to the normal of the plane separating the two liquids and r and s refer to the reference and sample liquids respectively The R...

Page 29: ...termined by calibration it should remain constant for an indefinite period of time unless the solvent is changed some optical re alignment is made or the cell is discolored due to residue accumulating on its surface Prism Detector Detector Amplifier Rf VOUTPUT Source S R Cell Mirror n n S R d L θ Figure 8 Optical Schematic of RI detector A 3 b Components The RI detector is fully contained within t...

Page 30: ... block is used to assemble these components A slit diaphragm is attached to the inside of the cell block The slit diaphragm defines the reflected beam before it leaves the cell on its path back toward the detector The dual RI cell is dropped into the cell block on top of the lower seal mount containing two TFE seals Seals are placed on the upper seal mount and it is placed on top of the cell and t...

Page 31: ...y SOURCE DETECTOR END The light source and detector are mounted on the detector end plate which is mounted with three screws to the end of the RI cylinder block The source is mounted in a clamp which Figure 11 Source Detector End of the RI Block Assembly ...

Page 32: ...g the front panel switch to adjust the zero glass assembly Please see section A 1 b General Layout for operation REFERENCE PURGE The reference cell can be purged under normal flow conditions by switching ON the RI purge valve Continue solvent flow for several minutes or until a stable RI signal is obtained The flow path during purge condition can be followed from the flow diagram Flow is always fi...

Page 33: ...me µL 12 Maximum backpressure on cell 30 kPa 5 psi Maximum Signal V 10 nom Baseline Noise mV 0 10 Baseline Noise RIU 15 2 x 10 8 Baseline Drift mV hr 16 5 0 15 Refractive Index Units 16 Measured under no flow or reference purge conditions ...

Page 34: ...fferential pressure DP P2 P2 will be zero or have some near zero baseline value Then as the polymer solution elutes through the bridge the viscosity in capillaries R1 R2 and R3 will increase to η while the pure solvent remains flowing through capillary R4 due to the delay volume column Now it is found that DP is no longer zero but increases in approximate proportion to the specific viscosity of th...

Page 35: ...The full power of the bridge to cancel flow rate pulsation and noise is seen in the DP signal DELAY COLUMNS It is clear that the delay column is an important component of the bridge as it provides the reference solvent to the reference capillary R4 during the period of elution of the polymer If the delay volume provided by the delay column is well matched to the elution profile chromatogram the po...

Page 36: ...gh negative DP peak with the chromatogram of a subsequent injection This may always be prevented by delaying the start of the next injection but at a loss in sample throughput So it is important that the delay volume be matched to the chromatographic columns being used for the separation Viscotek provides two columns for this purpose small one to two columns and large three to four columns They ar...

Page 37: ...etic reluctance type They are mounted on the inside center panel of the detector module Connections via 0 04 id ss tubing go to the transducers and to the purge valves The IP transducer is positioned in series with the RI reference purge and is thus purged with the RI PURGE SOLENOIDS The transducers must be purged completely of air bubbles in order to obtain an optimum baseline This is accomplishe...

Page 38: ...g a length of 0 04 id tubing and a 1 16 union U1 Any air bubbles in the delay column will affect the DP signal stability the same as if they were in the DP transducer Therefore it is equally essential that the delay column be purged of any air Normally the continuing flow of mobile phase will keep the column free of air bubbles However if some air is introduced into the system it will take the equ...

Page 39: ...ge Balance 1 Maximum Flow Rate H2O 1 5 mL min Maximum Flow Rate THF 3 mL min DP Noise Maximum 0 3 mV 0 3Pa DP Noise Typical 0 2 mV 0 2Pa DP Drift Typical 1 5 mV hr Assuming variations in IP of less than 1 With flow off or with negligible variation in solvent composition and IP ...

Page 40: ... 10 Ft Trigger Cable 1 Pr 1 10 Ft Serial Cable 1 10 Ft Diagnostic Cable B 2 CONNECTION TO SEC SYSTEM The Model 302 TDA is designed to be directly to the outlet of a properly functioning HPLC pump by the minimum length possible of 0 01 id SS tubing 1 Check the power receptacle on the back and make sure that the voltage set is correct for the AC power source 110V 220V being used Connect the power co...

Page 41: ...in from the tube See Figure 17 for proper assembly Valco T Fitting 0 04 i d Tubing 0 01 i d Tubing 0 01 i d Tubing To Detectors From Column or LS Filter Figure 17 Pneumatic Pulse Dampener 6 Connect a waste line to the outlet connection on the front of the detector 7 With the solvent flowing slowly install the separation columns Increase the solvent flow to normal flow rate for at least three colum...

Page 42: ...y other detector can be plumbed after the 302 TDA module Connect any analog signal cables to the analog signal terminal strip located on the back of the 302 TDA B 4 CORROSIVITY OF SOLVENT AND COMPATIBILITY WITH INSTRUMENT The Model 302 TDA detector array will not function properly for prolonged periods of time in the presence of aqueous halides at low pH values If the mobile phase involves a salt ...

Page 43: ...asser before the HPLC pump is most convenient and highly recommended Air bubble problems seldom occur in systems operating with an in line degasser Sparging is not a recommended method for degassing solvent C 1 b Changing Mobile Phase Solvent The other reason for purging is upon changing mobile phase solvent composition 1 Be certain that the new mobile phase is miscible with the old solvent that i...

Page 44: ...d as an absolute measurement by the data system unlike the RI and DP signals which are baseline corrected For this reason the IP must never be zeroed with the flow on C 2c Adjusting LS Zero The LS zero can also be adjusted by selecting the LS signal with the select button on the front panel and pushing the zero button This provides offset up to the full scale collection setting established in the ...

Page 45: ...nal 3 Turn the flow back on again Record the initial jump of the DP signal and its settling value Pa An initial jump value greater than 150 Pa indicates air is in the system Record the IP value kPa If air in the system has been ruled out as the problem compute the balance as below For example if the inlet pressure IP is 30 kPa and DP reads 20 mV 40Pa with a sensitivity of 0 5mV Pa the apparent spe...

Page 46: ...actual pulsation noise of the pump would have to be measured at the pump head itself using the pressure transducer normally provided with the pump This may be a very desirable thing to do but it is not necessarily a good measure of the pulsation that is transmitted to the detectors The columns absorb some of the pump pulsation for example If the pneumatic pulse dampener is installed in front of th...

Page 47: ...r signals The LS calibration constant for the LALLS detector should be 50 less that the RALLS detector If either of these values are significantly different then you may have a contaminated optics system Please contact the Viscotek Technical Service and Support department for further instructions C 3 e Standard Sample Analysis Periodically it is a good idea to check the performance of the detector...

Page 48: ...ump pulsation but it may possibly come from electronic sources To eliminate the latter possibility turn off the pump flow If the pulsation noise on the DP goes away electronic sources are clearly eliminated Assuming it is pump related there are three possible causes to consider 1 Air bubbles in the DP transducer and or the delay column Any air in the DP transducer cavities or in the delay column w...

Page 49: ...need to be replaced If the noise does not disappear electronic noise elsewhere in the output board circuit is indicated D 1 c Sporadic Noise in the DP Baseline Sporadic noise in the DP baseline such as a sudden decrease in the baseline or a spike etc is usually caused by flow problems such as a faulty pump seal check valve or bad column frit or occasionally by the passage of an air bubble through ...

Page 50: ...scometer signal has already become unusable since it is much more sensitive to solvent compressibility changes than even the RI The most frequently encountered form of baseline noise in the RI signal is that of drift The RI is extremely sensitive to compositional changes in the solvent and to thermal variation Often when mixed solvent systems are used it is necessary to continuously stir the mixtu...

Page 51: ...lical cord 7 Set the SEC Pump flow to 0 2 mL min 8 Remove the delay column from the clamp ring holders 9 Place a towel underneath the delay column 10 Disconnect the delay column by removing the 1 4 fittings with a wrench 11 Replace the delay column with the new one being careful not to allow any air into the system 12 Cap off the old delay column so that no air will be introduced to it during stor...

Page 52: ...place it with a union 5 Likewise bypass the SEC columns LS and RI dectectors from the chromatographic circuit replacing them also with a shunt of clean tubing It is very important that both the RI and LS detectors be bypassed when using dilute acid for cleaning Failure to do this could damage the detectors 6 Exchange the mobile phase with a miscible solvent and eventually distilled H2O Purge the d...

Page 53: ...e flow and replace the solvent reservoir with whatever new solvent is to be used 7 Flow the solvent through the system at 1 0 ml min Pump at least 200 ml through the system 8 Purge both the RI and DP with at least 20 ml of solution 9 Examine the signals from the TDA through the front panel They should be stable If not repeat steps 7 and 8 until stable 10 Connect the analytical column but run the c...

Page 54: ... Failure of parts due to chemical decomposition poor facilities or environment Any expendable items such as filters gaskets frits and fittings Warranty Period The warranty begins when the product is installed by a qualified Viscotek technician or in the case of customer installation 21 days after shipment from the Viscotek facility The Model 302 TDA will be warranted free of defects for a period o...

Page 55: ...anual or if there are any questions in general about the instrumentation or the ability of the instrumentation to perform sample analyses please do not hesitate to call us at 800 375 5966 or fax us at 281 931 4336 Furthermore Viscotek gladly welcomes any comments from users either positive or negative which can be forwarded directly to our Technical Service and Support department These comments ar...

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