£ rPA United States 0ffice of
\/CrM Environmental Protection Agency Research and Development
The Arizona Border Study
An Extension of the
Arizona National Human Exposure Assessment Survey (NHEXAS)Study
Sponsored by the Environmental Health Workgroup of the Border XXI Program
Quality Systems and Implementation Plan
for Human Exposure Assessment
The University of Arizona
Tucson, Arizona 85721
Cooperative Agreement CR 824719
Standard Operating Procedure SOP-BCO-L-23.0
Title: Calibration, Maintenance, and Operation of Electronic Balances
Source: The University of Arizona
U.S. Environmental Protection Agency
Office of Research and Development
Human Exposure & Atmospheric Sciences Division
Exposure & Dose Research Branch
Notice: The U.S. Environmental Protection Agency (EPA), through its Office of Research and Development (ORD), partially funded
and collaborated in the research described here. This protocol is part of the Quality Systems Implementation Plan (QSIP)
that was reviewed by the EPA and approved for use in this demonstration/scoping study. Mention of trade names or
commercial products does not constitute endorsement or recommendation by EPA for use.
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Title: Calibration, Maintenance, and Operation of Electronic Balances
Document No. BCO-L-23.0
APPROVALS
1 Full SOP 1 Working SOP #pages 6
On Site Principal Investigator:
Issue Date: August 5, 1995
Project QA Director:
Revision No:
Revision Date:
Revision Made:
On Site PI:
Project QA Director:
Independent Reviewer:
Revision No:
Revision Date:
Revision Made:
On Site PI:
Project QA Director:
Independent Reviewer:
Distributed To:
Revision No.
Form TP-2
[12/28/95]
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SOP #BCO-L-23.0
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August 5, 1995
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Calibration, Maintenance, and Operation of Electronic Balances
1.0 Purpose and Applicability
This standard operating procedure (SOP) describes the general procedures to be followed
for the operation, calibration and maintenance of electronic balances.
2.0 Definitions
2.1 Class S weights - a set of NIST-traceable standardized weights used for
calibration. The Battelle Instrument Lab personnel calibrate Class S weights
annually by comparing them with NIST-traceable weights provided by Rice Lake,
an external consultant.
2.2 Weight set ID - the BCO property and serial number, and the date of the last
calibration for the set of Class S weights used for external calibration.
2.3 Balance ID - the BCO property and Mettler serial number of the balance, and the
date the balance was last serviced by a Mettler field technician.
2.4 Laboratory Record Book (LRB) - a bound, uniquely-identified book with
numbered pages in which daily laboratory experiments are recorded.
2.5 Instrument Log Book (ILB) - a bound book dedicated to a single instrument, in
which descriptions of instrument maintenance, repair, and configuration
alterations are recorded.
3.0 References
3.1 "Mettler PC4400," Operator's Manual, Mettler Co.,1981.
3.2 "Mettler AE160," Operator's Manual, Mettler Co.,1983.
3.3 "Mettler AM/PM Balances," Operating Instructions, Mettler-Toledo,1993.
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4.0 Discussion
None
5.0 Responsibilities
5.1 It is the responsibility of the user to ensure that the balance is functioning
properly. This includes performing internal and external calibration procedures.
5.2 The user must record all calibration parameters associated with the preliminary
weighing out of samples in the NHEXAS Sample Preparation LRB.
5.3 The user must discontinue use of a balance that does not meet specifications, and
notify a Project Laboratory Director for further instruction.
5.4 The Project Laboratory Director will determine whether a service call by a
Battelle Instrument Laboratory technician or a Mettler Field Technician is
necessary.
6.0 Materials and Reagents
6.1 Materials
6.1.1 2-place balance - Mettler PC4400, and Mettler PM600
6.1.2 Class S weights, includes weights from 1 mg to 50 g.
6.1.3 4-place balance - Mettler AE160
6.1.4 Kimwipes
6.1.5 Beakers, assorted sizes
6.1.6 Centrifuge tubes, 15 mL
6.1.7 Teflon spatula
6.1.8
Small brush
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6.2 Reagents
Methanol, reagent grade
Procedure
7.1 Operation of 2-Place Balance (Mettler PC4400, PM600)
7.1.1 Wipe the weighing pan with a Kimwipe moistened with methanol. Allow
pan to dry (ca 30 s) before proceeding.
7.1.2 Turn on the balance display, wait approximately 30 s, then zero the
balance by pressing the front control bar.
7.1.3 Check the accuracy of the balance by using at least two different Class S
weights which approximate the material to be weighed.
7.1.4 Record balance ID, the weight set ID, the two weights used, and their
corresponding balance readings in the appropriate LRB.
7.1.5 Check the zero reading after removing the weights, and re-zero if
necessary.
7.1.6 Place the appropriate container on the balance pan.
7.1.7 Tare the balance by pressing the bar, or record the tare weight of the
container if performing percent solids determinations.
7.1.8 Transfer the sample into the container using a clean, Teflon spatula.
7.1.9 Record the weight obtained in the appropriate LRB.
7.1.10 Repeat Steps 7.1.5 - 7.1.9 for multiple samples.
7.1.11 The following samples will be prepared from aliquots weighed out (into
the specified glassware) on the 2-place balance:
7.1.11.1 Soil and dust samples to be analyzed for pesticides (15 mL
centrifuge tube, held upright in a beaker).
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7.1.11.2 Soil and dust samples to be analyzed for metals (appropriately-
sized beaker).
7.1.11.3 Soil and dust samples for the percent solids determination (50
mL beaker).
Operation of 4-Place Balance (Mettler AE160)
7.2.1 Check to see that the balance is level, by verifying that the bubble is inside
the circle of the balancing level, located on the front of the balance. If not,
level the balance by turning the leveling knobs, located on the rear feet of
the balance.
7.2.2 Clean off any apparent residue on the balance pan with a small brush.
Make sure that all the sliding doors to the balance are closed.
7.2.3 Switch the display on, by briefly pressing the single control bar. All
display segments will light up after a few seconds, ("8.8.8.8.8.8.8.8").
Afterwards, the display automatically sets itself to "0.0000".
7.2.4 To perform an internal calibration, press and hold the control bar until
"-CAL-" appears in the display; then release the control bar. The display
changes to "CAL—followed by a blinking "CAL 100".
7.2.5 Move calibration lever, located on the bottom, right of the balance, all the
way to the rear position. Wait for the display to change to ' CAL ,
followed by "100.0000", and finally to a blinking "CAL 0".
7.2.6 Move calibration lever all the way to the front position, and wait for the
display to change from "—", followed by "0.0000".
7.2.7 Record in the appropriate LRB that an internal calibration was performed.
7.2.8 To perform an external calibration, weigh at least two Class S weights that
approximate the anticipated weight of the materials you will be weighing.
Slide open the side glass door to the balance, place weight on the balance
pan, close the door, and record the weight displayed when the green dot at
the left of the display disappears. The green dot is an instability indicator.
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7.2.9 Record the weight set ID, the balance ID, and the two weights used
alongside the reading obtained in the appropriate LRB.
7.2.10 Re-zero the balance, as necessary, after removing any weights from the
balance pan.
7.2.11 To weigh out a sample, place the appropriate container on the balance
pan. To tare the weight of the container, make sure all the sliding doors
to the balance are closed. Press the control bar briefly; the display should
read: "0.0000".
7.2.12 Open any of the sliding doors in order to transfer the sample to the
container. Close all the sliding doors, and record the weight in the
appropriate LRB when the green instability dot disappears from the
display.
7.2.13 The following standards will be prepared from aliquots of neat material
weighed out (into the specified glassware) on the 4-place balance:
Primary standards (4 dram vials).
7.3 Calculations
None.
7.4 Maintenance
7.4.1 If the balance display does not operate, replace the microfuse only after
unplugging the balance.
7.4.2 Any liquid spills must be cleaned up immediately with a Kimwipe.
7.4.3 Any granular spills must be cleaned up immediately with a small brush.
7.5 Quality Control
7.5.1 All Mettler balances within the ASAT, BCO department are serviced and
calibrated annually by Mettler field technicians. A Weight Traceability
Certificate indicating the date of calibration, and NIST Test Weight
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identification numbers is filed in each ILB. A sticker is affixed to the
balance indicating the date the balance was last serviced.
7.5.2 For the 2-place balance, external calibration is performed at least once
with each day's use. Expected precision on the 2-place balance is ±0.02 g.
7.5.3 For the 4-place balance, internal and external calibrations will both be
performed with each day's use. Expected precision on the 4-place balance
is ±0.0002 g.
7.5.4 If the expected precision is not met, the balance is not used, and the
Project Laboratory Director is notified.
Records
8.1 All accuracy checking procedures prior to daily use of a balance, as delineated in
Sections 7.1.3 and 7.1.4, are recorded in ink in the LRB in which the experiments
are being recorded.
8.2 All maintenance, service, and repair activities are recorded in the ILB designated
for a given balance.
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