Liquid Handling
Application Note LHA-021
Automated Gravimetric Performance
Evaluation Option
®
for the MultiPROBE II and MultiPROBE II HT
By Patricia Ahrweiler Ph.D., Peng Li, and Ami Bilimoria,
Packard BioScience Company, Downers Grove, Illinois
Abstract
FDA guidelines require periodic verification of precision and
accuracy performance of automated liquid handling instruments. Spectrophotometric methods are common but
require calibration curves for measurement of pipetting
accuracy with dye solutions. Gravimetric analysis is the verification technique of choice but when performed manually
can involve tedious and error-prone vial handling and data
collection. To better meet the needs of the automated laboratory, an integrated accessory kit for Packard Instrument
Company’s MultiPROBE II and MultiPROBE II HT was
developed for gravimetric determination of pipetting precision and accuracy on these two instruments. The kit
includes a user-friendly, error-minimizing WinPREP 
program with an interactive user-interface for recording key
information about the run. The data report meets FDA documentation standards. An integrated Mettler SAG285/L
balance on the MultiPROBE II deck, automated data
collection, evaporation-reducing humidity chamber, and
automated report generation all work to overcome previous
difficulties in using gravimetric analysis for precision and
accuracy verifications.
Introduction
A critical need for an automated gravimetric performance
evaluation test for the MultiPROBE II and MultiPROBE II HT
for in-house and customer use prompted the development
of a user-friendly, automated test that also meets FDA documentation standards. The product development team identified the following user-friendliness and FDA documentation standards as targets for a “Gravimetric Performance
Evaluation Option” accessory kit (P/N 7601822, 110 V; P/N
7601823, 220 V).
Figure 1.
A MultiPROBE II is shown that has a Mettler SAG285/L balance and humidity chamber
placed on the liquid handler deck. The balance pan is connected to a balance control
touchpad and the MultiPROBE II computer by communication cables
800 Research Parkway Meriden, CT 06450 Tel: 203-639-2598 1-800-323-1891 Fax: 203-639-2172
Web site: http://www.packardbioscience.com E-mail: [email protected]
Figure 2.
WinPREP test outline for the Gravimetric Performance Evaluation Option using disposable tips
User-friendliness Development Goals:
• Easy installation of the Gravimetric Performance Evaluation Option on the MultiPROBE II or MultiPROBE II HT.
• Can be used with fixed tips, VersaTips , and disposable
tips.
• Use of a low profile, five-place analytical balance with no
risk of collision with the MultiPROBE automated pipetting
arm on the MultiPROBE deck.
• Draft isolation and evaporation control for the balance
sample collection vessel to minimize sample evaporation
contributions to weight data.
• User-interface for quick entry of volumes to be tested,
number of tips to be tested, and the number of data points
to collect per tip.
• Automated data collection and report generation by
WinPREP.
• Automatic display of the run report for easy printing by
operator.
• Graph of pipetting data for visual inspection of run.
• Automatic emptying of sample collection vessel when full.
FDA Report Documentation Criteria:
• Automatic report file saving and file naming scheme to
prevent overwriting of report files.
• Date of run, operator ID, and other important details must
appear on the report.
• Run will not commence unless ALL information is entered
in the user-interface screen, assuring appropriate
information is recorded for each run.
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• Automatic retrieval of the MultiPROBE serial number,
WinPREP version, MultiPROBE model from WinPREP,
and the date from the instrument computer.
• Automatic data graphing and calculation of pipetting
performance based on data collected.
• Read-only report file preventing overwriting or editing of
report details.
Using the above criteria, a “Gravimetric Performance Evaluation Option” accessory kit for the MultiPROBE II was
developed, meeting these requirements. This application
note reports the salient features of this accessory that make
it suitable for use in labs subject to FDA guidelines. The
Gravimetric Performance Evaluation Option WinPREP test,
user-interface, and report format are discussed.
Materials and Methods
A Mettler SAG285 balance (Mettler-Toledo, Columbus, OH)
was selected for use in the “Gravimetric Performance
Evaluation Option” accessory kit due to its precision (81 g
capacity and 0.01 mg readability), low profile, and RS232
capability. A humidity chamber was developed for use with
the balance.
Mounting hardware was designed to place the SAG285
balance directly on the deck of the MultiPROBE II or
MultiPROBE II HT using existing locator holes for labware
holders. A user-interface was developed using Visual C++
(Microsoft, Seattle, WA).
The accessory kit’s performance was tested on a
MultiPROBE II using distilled, filtered water as system
liquid. Dissolved air was eliminated from the system liquid
immediately prior to the experiment by applying a vacuum
to the system liquid bottle with stirring. Distilled and filtered
water was used as the pipetted sample for precision and
accuracy determinations.
Results
WinPREP Test for Automated Gravimetric
Data Collection on the MultiPROBE II
Installation of the Gravimetric Performance Evaluation
Option on the MultiPROBE II is straightforward. The Mettler
SAG285 mounted on a MultiPROBE II is shown in Figure 1,
corresponding to the deckview in the WinPREP test. The
humidity chamber assembly replaces the balance pan in
plug and play fashion. The balance is then connected to the
MultiPROBE computer via a RS232 cable and is ready to
use. Placement of the wash station, reagent trough, and tip
racks (if applicable) prepares the MultiPROBE II or
MultiPROBE II HT for the run.
The WinPREP test outline for the Balance Test Option
using disposable tips is shown in Figure 2.
Figure 3.
WinPREP test features:
• Labware definition for the Mettler SAG285/L balance
displayed in the deck view of the test outline.
• User-Interface screen to enter information about the run
(see below).
• Automatic volume checking of the humidity chamber
collection vial is accomplished using liquid level sensing.
• Humidity chamber vial is automatically emptied before a
run or between tips during the run, with no intervention
required from the operator.
• Sample is aspirated from a reagent trough and dispensed
directly onto the humidity chamber collection vial.
• Tip wash before every transfer.
• User Programs to communicate with the balance for
automatic tare before each sample transfer and automatic
sample weight data collection.
• User Program to automatically generate a report in
Microsoft  Excel.
User-Interface Screen
Running the WinPREP test automatically displays a userinterface text box prompting the operator to enter important
information describing the run details. The user-interface
screen is shown in Figure 3.
Grayed out boxes indicate the information is automatically
read from data entered into WinPREP at installation of the
instrument, or is read from the instrument computer, and is
not accessible to change by the operator either in WinPREP
or in the Balance Test.
Hard-coded information (grayed out boxes) includes:
•
•
•
•
Date of run
MultiPROBE Model
WinPREP Version
MultiPROBE S/N
User-interface text box prompting the operator
to enter run details
Information entered by the Operator (shown in white text
boxes) includes:
•
•
•
•
•
•
•
Test Volumes (2 volumes can be tested per run)
# Replicates per tip
System Liquid type (Water, DMSO, etc.)
Technician ID
Tip Type (Fixed Tips, Disposable Tip/Size)
Sample Type (description entered by operator)
Density of Sample – weights are automatically converted
into volumes on the report
• Performance File (entered by operator for report – does
not select for run)
• Tips enabled for test (check boxes for each tip to enable/
disable)
• Comment text box (any additional comments about the
test)
Leaving any of the text boxes blank (except the comment
text box) will produce an error message prompting the operator to enter incomplete information in the specific box(es).
Report Format
A Microsoft Excel file of the raw data and performance
calculations for each tip is automatically displayed following
the completion of the balance test run. Clicking on a function
box labeled “MPII Gravimetric Performance Evaluation
Option” calculates inaccuracy and precision (%CV) for each
tip and across all tips selected for the run, and generates the
final report format.
In addition to the performance results, the report lists all the
information entered in the user-interface screen described
above. A sample report with sample data collected on a
MultiPROBE II is shown below in Figure 4.
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Filenaming Scheme
Running the Balance Test install disk creates a new folder
under Packard\MultiPROBE\bin\Balance. Run reports are
automatically stored in this folder with the filenaming scheme
described below and shown in Figure 5.
The filenaming scheme for Gravimetric Performance Evaluation Option run reports is “BAL-S/N-Vol1-Vol2-Run#”.
• S/N is the serial number of the MultiPROBE II or
MultiPROBE II HT used to run the test.
• Vol1 and Vol2 refer to the first and second volumes the
operator selects in the user interface screen immediately
prior to starting a run.
• “Run#” will automatically continue to increment upwards
for each time a Balance Test is run on the same serial
number MultiPROBE (II or HT). (Using Microsoft Explorer
to display the date of the report will assist with locating
previous reports generated on a specific date).
This filenaming scheme eliminates the possibility a file will
be overwritten since the “Run#” automatically increments
upwards for each repeated run of the same volume combinations. A report file with a unique name is created and
saved after each run automatically.
Conclusion
A Gravimetric Performance Evaluation Option for Packard
Instrument Company’s MultiPROBE II and MultiPROBE II
HT automated performance evaluation applications was
developed to meet user-friendliness and FDA guidelines criteria.
The Gravimetric Option is flexible for use with any combination of tip type(s), performance file(s), and volume(s). It also
allows the use of pure solvents other than water and automatically converts weight data into volume information.
Figure 4.
FDA-compliant report generated post-run from the MultiPROBE II
WinPREP Gravimetric Option
This Gravimetric Option offers ease of installation and foolproof operation on the MultiPROBE II and MultiPROBE II
HT, software user-friendliness, error-prone run information,
report generation and filenaming schemes in accordance
with FDA guidelines. The new accessory is now available
for customers for use in their laboratories.
Figure 5.
Filenaming scheme for Gravimetric Performance Evaluation Option run reports
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Unless otherwise indicated, all trademarks and registered trademarks
are property of Packard BioScience Company or its subsidiaries in the
United States and/or other countries.
M4666 (M4666-00) 7/01 Printed in U.S.A.
 2001 Packard BioScience Company. All rights reserved.