Using Balances

SOP-L102 Revision 0.3
Author

Marc Los Huertos

EA Program, Pomona College

Published

2026-06-26

1 Purpose

This procedure describes the proper use, zeroing, taring, and routine quality checks for the laboratory balances in the EA Program. Correct weighing technique is fundamental to virtually every quantitative laboratory procedure. For calibration and verification protocols, see SOP-L200 Analytical Balance Calibration.

2 Scope

  • Applies to: All Mettler Toledo balances in the EA Program laboratory, including the basic balances (MS1602TS/00) and the precision balance (XPE205 DeltaRange) (Mettler Toledo, 2015a, 2015b)
  • Does not apply to: Portable field balances or calibration procedures (see SOP-L200)
  • Location: EA Program laboratory, SGM 133

3 Responsibilities

Role Responsibility
Lab PI Approve SOP, ensure training compliance
Trained Personnel Follow this SOP, report malfunctions
New Students Complete training before independent use

4 Definitions

  • Capacity (maximum load): The maximum mass that can be placed on the weighing pan without risking damage to the weighing cell; exceeding the rated capacity will damage the load cell and require expensive repair; the MS1602TS capacity is 1620 g and the XPE205 capacity is 220 g / 81 g (DeltaRange) (Mettler Toledo, 2015a, 2015b).
  • Draft shield: The glass or acrylic enclosure surrounding the weighing pan on the XPE205 precision balance; reduces air current disturbances that cause reading instability; always keep closed except when placing or removing items.
  • Drift: Gradual, directional change in the balance reading under constant load; caused by temperature changes, vibration, or electronic instability; the balance should be allowed to warm up for at least 30 minutes before critical weighing.
  • Linearity: The degree to which balance readings are proportional to applied mass across the full weighing range; verified during calibration per SOP-L200.
  • Net weight: The mass of sample only, after the tare weight of the container has been subtracted; what is displayed after pressing the Tare key with the container on the pan.
  • Readability (resolution): The smallest increment the balance can display; the MS1602TS reads to 0.01 g and the XPE205 reads to 0.1 mg (0.0001 g) (Mettler Toledo, 2015a, 2015b).
  • Repeatability: The standard deviation of repeated measurements of the same weight under identical conditions; a key short-term precision indicator; affected by vibration, draft, and sample placement position.
  • Spirit level (bubble level): A small bubble vial mounted on the balance base; the bubble must be centered in the target circle before weighing; off-level readings can introduce systematic errors.
  • Tare: The function that zeroes the displayed mass when a container is on the pan, so subsequent readings show only the mass of material added (Mettler Toledo, 2023).
  • Weighing cell: The internal transducer (typically an electromagnetic force compensation cell) that converts the mechanical load on the pan to an electrical signal; the most sensitive and expensive component of the balance; protect it from impact, overloading, and corrosive chemicals.
  • Zeroing: Setting the balance display to exactly zero with an empty pan and no load; performed at the start of each session and whenever the balance is moved; distinct from taring, which zeroes the balance with a container already on the pan.

5 Safety and Hazards

WarningHazards
  • Physical: Dropping heavy items onto the balance pan can damage the weighing cell. Handle objects carefully and never exceed the rated capacity.
  • Chemical: Some materials weighed on the balance may be hazardous. Refer to the relevant SOP for the material being weighed. Never place chemicals directly on the weighing pan; always use a sample vessel.

5.1 Required PPE

5.2 Emergency Procedures

If a chemical spill occurs on or near the balance, clean the spill per SOP-L003 Hazardous Materials Handling before resuming use.

6 Equipment and Materials

6.1 EA Program Balances

Balance Model Capacity Readability Location
Precision balance (1) XPE205 220 g / 81 g 0.1 mg SGM 133
Basic balance (1–3) MS1602TS 1620 g 0.01 g SGM 133

(Mettler Toledo, 2015b, 2015a)

6.2 Weighing Supplies

Item Notes
Weighing paper Single use; keeps chemicals off the pan
Sample vessels Weighing boats, crucibles, or tared containers
Forceps or tweezers For handling calibration weights or small containers without contamination
Lint-free wipes (Kimwipes) For cleaning the pan and draft shield
Anti-static brush For removing powder adhering to the draft shield interior

7 Procedure

7.1 Startup and Warm-Up

Allow the balance to warm up for at least 30 minutes before making critical weighings (< 0.001 g significance) (Mettler Toledo, 2015b). This allows the internal components to reach thermal equilibrium.

7.2 Leveling the Balance

  1. Check the spirit level before each use session.
  2. If the bubble is not centered, adjust the leveling feet at the base of the balance.
  3. For the XPE205, use the built-in leveling aid: Balance menu > Leveling aid (Mettler Toledo, 2015b).

7.3 Zeroing

  1. Verify the balance is empty and the draft shield is closed.
  2. Press Zero (or On/Zero). The display should read 0.000 g (for the MS1602TS) or 0.0000 g (for the XPE205).
  3. If the display does not settle, check that the balance is level, no air currents are present, and the pan is clean and dry.

7.4 Taring

  1. Zero the balance (§[sec-zeroing]).
  2. Open the draft shield.
  3. Place the sample vessel on the center of the weighing pan.
  4. Close the draft shield.
  5. Press the Tare key. The display reads zero and the Net indicator appears.

7.5 Performing a Weighing

  1. Open the draft shield (if applicable).
  2. Place the weighing object into the tared sample vessel.
  3. Close the draft shield and wait for the stability indicator.
  4. Record the displayed mass in the lab notebook.
  5. If using the XPE205 electronic results feature, tap Add result to append the value to the results list.

7.6 Completing and Saving Results (XPE205)

  1. Tap Complete to open the task completion dialog.
  2. Select an option to save or print the results list.
  3. Follow the on-screen instructions.
  4. Tap Complete to finalize; the results list is saved or printed and then cleared.

7.7 Shutdown

  1. Remove all samples and vessels from the weighing pan.
  2. Clean the pan and draft shield interior with a lint-free wipe.
  3. Close the draft shield.
  4. To enter standby mode, hold the power/standby key. The display goes dark but the balance remains powered on and thermally stable.
  5. To switch the balance off completely, disconnect from the power supply. Note that the balance will require a full warm-up before its next use.

8 Quality Control and Acceptance Criteria

8.1 Leveling the Balance

Exact horizontal positioning is essential for repeatable and accurate results (Mettler Toledo, 2015b):

  1. Check the spirit level before each use session.
  2. If the message “Balance is out of level” appears, tap Level the balance to open the leveling aid.
  3. Adjust the leveling feet following the on-screen instructions until the bubble is centered.

8.2 Internal Adjustment (XPE205)

  1. Navigate to Methods > Adjustments.
  2. Verify that the adjustment strategy is set to Internal adjustment.
  3. Select the adjustment and tap Start.
  4. Do not touch the balance during the adjustment.
  5. When complete, review the adjustment results.
  6. Tap Print if a record is needed, then tap Finish adjustment (Mettler Toledo, 2015b).

For external calibration verification using traceable reference weights, see SOP-L200.

9 Waste Disposal

No waste is generated by this procedure. Cleaning materials (Kimwipes) can be disposed of in standard trash unless they contacted hazardous chemicals, in which case follow SOP-L003.

10 References

Mettler Toledo. (2015a). MS1602TS basic balance: Operating instructions. https://www.mt.com
Mettler Toledo. (2015b). XPE205 DeltaRange precision balance: Operating instructions. https://www.mt.com
Mettler Toledo. (2023). Good weighing practice: The SOP for balances and scales. https://www.mt.com/us/en/home/library/guides/laboratory-weighing/good-weighing-practice.html

12 Training Record

Before using the laboratory balances independently, personnel must:

  1. Read this SOP in full
  2. Complete SOP-L002 Laboratory Safety training
  3. Demonstrate proper leveling, zeroing, taring, and weighing technique under supervision
  4. For the XPE205 precision balance, also demonstrate use of the draft shield and internal adjustment procedure
  5. Be signed off by the PI or lab manager