Laboratory Robotics To Automate High-Temperature Gel Permeation

3 Laboratory Robotics To Automate

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High-Temperature Gel Permeation Chromatography Daniel G . Moldovan and Steve C. Polemenakos Dow Chemical U.S.A., Polyethylene Research, B-3827, Freeport, TX 77541

This chapter presents the use of a commercial robotic system (PerkinElmer Masterlab) to automate the preparation of polyethylene samples for high-temperature gel permeation chromatography (GPC). The robotic system weighs the samples, calculates the appropriate volume of solvent, adds the solvent, caps the sample bottle, heats the sample for dissolution, and prepares the sample carrousel for the GPC autosampler. The advantages of this system include freeing technicians from tedious, repetitive tasks and from handling hot, hazardous materials.

I N T E R E S T I N L A B O R A T O R Y A U T O M A T I O N has g r o w n i n t h e past f e w years because o f t h e i n c r e a s i n g c o m p l e x i t y , d i v e r s i t y , a n d n u m b e r o f analytical t e c h n i q u e s . " H a r d " a u t o m a t i o n is u s e d i n areas w h e r e a single o p e r a t i o n is p e r f o r m e d . T h e use o f "soft" a u t o m a t i o n (laboratory robotics) is i m p l e m e n t e d where

flexibility

a n d a range o f operations is r e q u i r e d .

T h e most r e p e t i t i o u s a n d l a b o r - i n t e n s i v e task for t h e c h r o m a t o g r a p h e r i n h i g h - t e m p e r a t u r e g e l p e r m e a t i o n c h r o m a t o g r a p h y ( G P C ) is sample p r e p aration. T h e o t h e r steps i n t h e analysis have b e e n a u t o m a t e d w i t h a h i g h t e m p e r a t u r e (150 °C) G P C system (Waters) that w i l l automatically analyze 16 samples a n d a c o m p u t e r system that w i l l collect a n d r e d u c e t h e data. T h e sample p r e p a r a t i o n step is t h e o n l y p r o c e d u r e i n t h e G P C analysis that is n o t a u t o m a t e d a n d therefore is t h e b o t t l e n e c k i n t h e h i g h - t e m p e r a t u r e G P C analysis. I n this c h a p t e r , w e r e p o r t a p r o c e d u r e that has b e e n d e v e l o p e d 0065-2393/90/0227-0045$06.00/0 © 1990 American Chemical Society

In Polymer Characterization; Craver, C., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1990.

46

POLYMER CHARACTERIZATION


a n d uses a c o m m e r c i a l robotic system (the P e r k i n - E l m e r M a s t e r l a b ) to a u tomate the sample p r e p a r a t i o n p r o c e d u r e for the h i g h - t e m p e r a t u r e G P C analysis. T h e first step i n d e v e l o p i n g this p r o c e d u r e or any robotic m e t h o d is to define each o f the laboratory u n i t operations ( L U O s ) (I). L U O s are c o m m o n steps or b u i l d i n g blocks of a laboratory p r o c e d u r e . E x a m p l e s of some L U O s are w e i g h i n g , m a n i p u l a t i o n , l i q u i d h a n d l i n g , c o n t r o l , a n d d o c u m e n t a t i o n . T h e s e major L U O s can t h e n b e b r o k e n d o w n i n t o m u c h s m a l l e r subclasses such as d i s p e n s i n g solvent a n d u n c a p p i n g the bottle. A f t e r each of these smaller subclasses is d e f i n e d , a flow d i a g r a m of the sequence of events is m a p p e d out ( F i g u r e 1). A t this p o i n t , i n d i v i d u a l robotic p r o c e d u r e s can be w r i t t e n for each of the subclass L U O s . It is advantageous to m a k e these robotic p r o c e d u r e s as s m a l l as possible a n d to call t h e m u p i n d i v i d u a l l y i n the m a i n p r o g r a m o r o v e r a l l p r o c e d u r e . T h i s approach allows one to access the i n d i v i d u a l procedures to m a k e changes w i t h o u t h a v i n g to o v e r h a u l the whole procedure.

Experimental Details The Perkin-Elmer Masterlab robotic system used for the high-temperature GPC preparation consists of the Mitsubishi Move Master II model RM-501 robot equipped with a 0.7-m custom hand, a master syringe, symbol bar code reader, capper, Sartorius analytical balance (model A 200S), device interface, gas controller, custom racks, aluminum heat blocks, regripping station, and an IBM AT personal computer with a printer. The layout for our system is mounted on a 5- X 10-ft table and is shown in Figure 2. In an effort to retain the integrity of our sample preparation procedure, the 50-mL glass sample bottles that were used for the manual sample preparation procedure are used for the automated sample procedure. A set of custom racks that will hold 18 glass bottles was fabricated by the Perkin-Elmer Corporation. Also, two nine-hole anodized aluminum heat blocks were specially fabricated inhouse to hold the bottles. The holes in the heat blocks were made deep enough to completely encompass the bottles and have a spherical clearance of 1 mm in order to provide good heat transfer to the bottles. To begin the procedure, the operator fills the bottle rack with the appropriate number of 50-mL glass bottles. The operator then types the number of samples that need to be prepared. The robot tares each bottle. After all of the bottles have been tared on the Sartorius balance, the robot rings an alarm to let the operator know it has completed that part of the task. The robot then waits until the operator has added a representative amount of sample that consists of either pellets, film, or powder. The operator tells the robot to continue the task of sample preparation by hitting any key on the IBM AT keyboard. The robot reweighs each bottle and obtains the weight of the sample added. The robot calculates the amount of solvent that needs to be dispensed to the bottle to obtain a concentration of 0.3% (w/w). The robot next takes the bottle to the regrip station, where it grips the middle of the bottle so that the bottle can be uncapped by the capper. While the robot is uncapping the bottle, the bar code reader reads the sample number from the bottle label that has been attached to the bottle. After removing the cap, the robot takes the sample bottle over to the dispensing station, where the syringe dispenses the required allotment of solvent to meet the concentration specification.


MOLDOVAN

& POLEMENAKOS

Laboratory Robotics To Automate GPC

I Retrieve empty bottlefromrack)

i [Weigh empty bottle]

i Downloaded by KTH ROYAL INST OF TECHNOLOGY on November 19, 2015 | http://pubs.acs.org Publication Date: May 5, 1990 | doi: 10.1021/ba-1990-0227.ch003

I Return bottle to rack]

i |Add samplel

i [Retrieve bottle with samplel i

[Reweigh sample)

i I Calculate amount of solvent needed |

i [Regrip low|

i [Uncapl

i I Dispense amount of calculated solventi

i fcipl I

[Regrip highl

1 fReweighl

i I Print sample number and concentration!

i [Place sample in heating block|

i I Shake sample! Sample is now ready for GPC analysis. Figure 1. Flow diagram of sequence of events in sample preparation.

American Chemical Society Library Craver, C., et al.; In Polymer Characterization;

Advances in Chemistry; American Chemical Society: Washington, DC, 1990.

48


•• D

Sample B o t t l e Storage Racks


Track

BaH Code

Reader

pping S t a t i o n Cx p P a r k i n g S t a t i o n

Sample B o t t l e R a c k Heating B l o c k s

spense Station

Personal

Computer

Printer Sartorius Analytical Balance Figure 2. Robot table layout. A 10-mL syringe is used for our application for dispensing the solvent because the solvent routinely used for high-temperature G P C is 1,2,4-trichlorobenzene. This solvent is very viscous at ambient temperature; therefore, it is difficult for the syringe mechanism to dispense large volumes accurately. The syringe must do repetitive fills for each bottle to obtain the correct concentration because of this limitation. The robot takes the bottle back to the capper station, where it recaps the filled sample bottle. The capper turns a quarter of a turn counterclockwise to catch the lip of the botde before turning clockwise to tighten the cap onto the bottle. The robot takes the bottle back to the balance, where it obtains the exact weight of solvent added; this step allows a more precise concentration calculation. The concentration, the sample weight, and the volume of solvent are printed for each sample prepared. The robot again takes the bottle to the regrip station where it regrips the bottle by the cap so that it can place the bottle in the heat block, which is maintained at a temperature of 160 ° C for 8 h for dissolution. The temperature in the heat block is monitored by a thermocouple that is inserted into the middle of the block. The temperature of the solution in the bottle is checked manually with a mercury thermometer during the setup of the system. (We found that the temperature of the solution in the bottle reached the target temperature of 160 ° C after 35 min.) The robot shakes the sample bottle once during this period to help the dissolution process. The sample is now ready for high-temperature G P C analysis on a 150 ° C G P C system.

Results and Discussion T h e sample p r e p a r a t i o n i n most analytical p r o c e d u r e s is c o n s i d e r e d the w e a k l i n k i n the analysis for a n u m b e r of reasons. S a m p l e p r e p a r a t i o n is a major source of errors because i t is subject to h u m a n variability. I n o u r laboratory, a n u m b e r of technicians p e r f o r m the sample p r e p a r a t i o n , a n d each t e c h n i c i a n


3.

MOLDOVAN & POLEMENAKOS

Laboratory Robotics To Automate GPC

does it j u s t a little b i t differently from t h e others; t h e result is a variance i n the concentration o f the samples. E v e n a n i n d i v i d u a l ' s laboratory p e r f o r m ance changes from d a y to day, d e p e n d i n g o n the p e r s o n s m o o d . T a b l e I compares the weights a n d t h e v o l u m e s o f the m a n u a l m e t h o d versus t h e automated m e t h o d . I n t h e m a n u a l m e t h o d , t h e v o l u m e o f the solvent is set b y a r e p e a t i n g


p i p e t (repipet); therefore, a target w e i g h t o f 0.25 g is r e q u i r e d for the sample to achieve a 0 . 3 % ( w / w ) concentration. A s s h o w n i n T a b l e I, t h e range o f the actual sample w e i g h t is w i d e ; thus a greater e r r o r i n t h e G P C analysis results. Table I. Manual versus Automated High-Temperature GPC Method Sample Weight (g)

Method Manual Automated

Solvent Volume (mL)

Cone. (% w/w)

Standard Deviation (%)

0.25 ±

0.0025

50 ±

0.5

0.03

10

0.15-0.25 ±

0.0001

30-50 ±

0.1

0.03

0.8

A n o t h e r reason that sample p r e p a r a t i o n is c o n s i d e r e d t h e weak l i n k is that t h e sample p r e p a r a t i o n p r o c e d u r e is labor intense a n d therefore exp e n s i v e . I n t h e m a n u a l G P C sample p r e p a r a t i o n , t h e laboratory p e r s o n n e l have to w e i g h o u t a p p r o x i m a t e l y 0.25 g o f sample. M o s t o f the sample is i n the f o r m o f p o l y e t h y l e n e p e l l e t s , w h i c h the technicians m u s t cut i n t o s m a l l pieces to get 0.25 g. A f t e r the 0.25-g sample is a d d e d to the 5 0 - m L b o t t l e , 50 m L o f 1,2,4-trichlorobenzene is r e p i p e t e d into the bottle. T h e m a n u a l m e t h o d r e q u i r e s f r o m 4 to 6 h each m o r n i n g , d e p e n d i n g o n the sample l o a d , i n o r d e r to have samples ready for o v e r n i g h t analysis o n t h e 150 °C G P C system. T h e t y p i c a l sample load for the laboratory is from 16 to 48 samples p e r day. T h e a u t o m a t e d m e t h o d r e q u i r e s o n l y 5 - 1 0 m i n o f a technician's t i m e to achieve t h e same task. T h i s automated m e t h o d therefore r e s u l t e d i n a n i m m e d i a t e saving o f h a l f a w o r k e r - y e a r . F u r t h e r m o r e , sample p r e p a r a t i o n is t i m e c o n s u m i n g , so sample t u r n a r o u n d t i m e is slow. A p e r s o n c o u l d p r e p a r e o n e , t w o , o r m o r e samples faster t h a n t h e robot for t h e G P C sample p r e p a r a t i o n p r o c e d u r e , b u t o n a daily basis t h e robot does n o t have to d e a l w i t h meetings, a n s w e r i n g t h e p h o n e , a n d other tasks that distract the technicians from p e r f o r m i n g t h e sample p r e p a r a t i o n p r o c e d u r e . F i n a l l y , sample p r e p a r a t i o n often exposes the p e r s o n n e l to a hazardous e n v i r o n m e n t . T h e m a n u a l G P C sample p r e p a r a t i o n p r o c e d u r e r e q u i r e s t h e t e c h n i c i a n to w e a r b o t h r u b b e r a n d cotton gloves along w i t h face shields a n d aprons to p r e v e n t exposure to h o t 1,2,4-trichlorobenzene. W i t h t h e automated m e t h o d , o n l y t h e robot is exposed to these hazards. T h e automated system for h i g h - t e m p e r a t u r e G P C p r e p a r a t i o n was successful i n e l i m i n a t i n g a v e r y l a b o r - i n t e n s i v e task r e q u i r i n g 4 - 6 h each d a y a n d r e p l a c i n g it w i t h a 5 - 1 0 - m i n c o m p u t e r interfacing task. I n a d d i t i o n , the automated p r o c e d u r e has r e s u l t e d i n faster sample t u r n a r o u n d t i m e a n d


50



m o r e r e p r o d u c i b l e data for the h i g h - t e m p e r a t u r e G P C analysis. T h e m a n u a l G P C p r e p a r a t i o n p r o c e d u r e h a d a standard deviation of 10%, b u t w i t h the automated p r o c e d u r e , a standard d e v i a t i o n of 0.8% was attained. B e s i d e s p r o v i d i n g a l l of these advantages, the automated sample p r o c e d u r e has r e m o v e d the solvent exposure a n d hot m a t e r i a l h a n d l i n g hazards that w e r e part of the m a n u a l p r o c e d u r e .

Conclusions T h e automation of the sample p r e p a r a t i o n p r o c e d u r e for h i g h - t e m p e r a t u r e G P C analysis u s i n g a P e r k i n - E l m e r M a s t e r l a b robotic system has r e m o v e d the major bottleneck i n the G P C analysis a n d therefore a l l o w e d essentially c o m p l e t e automation of the h i g h - t e m p e r a t u r e G P C analysis.

References 1. Hurst, W. J.; Martimer, J. W. Laboratory Robotics: A Guide to Planning, Programming, and Applications; V C H : New York, 1987; pp 15-23. RECEIVED

1989.

for review February 14, 1989.

ACCEPTED

revised manuscript August 16,


Laboratory Robotics To Automate High-Temperature Gel Permeation

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