BP-A1, Page i

Balance Protocol for Gravimetric Determination of Sample Weight 

Using a Precision Analytical Balance 

BP-A1 

Adoption Date: July 20, 2009 

As Last Amended: January 5, 2010

NOTE: This document, approved by the Air Resources Board at its January 22, 2009 hearing 

for incorporation by reference in California Code of Regulations (CCR), title 17, sections 95360 

through 95370, was originally shown without underline as permitted by California Code of 

Regulations, title 1, section 8. The modifications are indicated in underline to indicate additions 

and in strikeout to indicate deletions.
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Table of Contents 

1. SCOPE AND APPLICATION ............................................................................................................... 1

2. SUMMARY OF METHOD .................................................................................................................... 1

3. DEFINITIONS....................................................................................................................................... 1

4. INTERFERENCES ............................................................................................................................... 1

5. PERSONNEL HEALTH AND SAFETY................................................................................................ 2

6. EQUIPMENT AND SUPPLIES............................................................................................................. 2

7. REAGENTS AND STANDARDS.......................................................................................................... 2

8. SAMPLE COLLECTION, PRESERVATION, AND STORAGE ........................................................... 2

9. QUALITY CONTROL........................................................................................................................... 2

10. CALIBRATION AND STANDARDIZATION..................................................................................... 3

11. PROCEDURE .................................................................................................................................. 3

11.1 OVERVIEW OF WEIGHING SEQUENCE ............................................................................................ 3 

11.2 HANDLING ........................................................................................................................................ 3 

11.3 READING THE BALANCE................................................................................................................... 3 

11.4 INITIAL ADJUSTMENT ....................................................................................................................... 4 

11.5 ZERO CHECK.................................................................................................................................... 4 

11.6 CALIBRATION CHECK....................................................................................................................... 5 

11.7 REPLICATE WEIGHING CHECK ........................................................................................................ 5 

12. DATA ANALYSIS AND CALCULATIONS....................................................................................... 7

13. METHOD PERFORMANCE ............................................................................................................ 8

14. POLLUTION PREVENTION............................................................................................................ 8

15. WASTE MANAGEMENT ................................................................................................................. 8

16. REFERENCES................................................................................................................................. 8
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1. SCOPE AND APPLICATION 

This Protocol summarizes a set of procedures and tolerances for weighing objects in 

the range of 0 to 1,000g with a resolution of 0.001 g. This protocol only addresses 

balance operations, it does not address project requirements for equilibration, sample 

hold time limits, sample collection etc. 

2. SUMMARY OF METHOD 

The balance is zeroed and calibrated using procedures defined herein. Object weight 

determinations are conducted along with control object weight determinations, zero 

checks, calibration checks, sensitivity checks, and replicate weightings in a defined 

sequence designed to control and quantitatively characterize precision and accuracy. 

3. DEFINITIONS 

N/A. 

4. INTERFERENCES 

Object weights can be affected by temperature and relative humidity of their 

environment, air currents, static electricity, gain and loss of water vapor, gain or loss of 

and loss of volatile compounds directly from the sample or from contaminants such as 

finger prints, marker ink, and adhesive tape. 

Contamination, transfer of material to or from the samples, is controlled by conducting 

operations inside a clean area dedicated to the purpose and having a filtered laminar 

air flow where possible; by wearing gloves while handling all samples and related 

balance equipment; by using forceps to handle small objects, and by keeping the 

balance and all related equipment inside the clean area. 

Air currents are controlled by conducting weighing operations inside a closed chamber 

or glove box and by allowing the substrates to reach temperature and relative humidity 

equilibrium. The chamber is maintained at 40% relative humidity and 25 oC by a 

continuous humidity and temperature control system. The temperature and RH 

conditions are recorded at least once per weighing sessions. Equilibration times for 

samples that are particularly sensitive to humidity or to loss of semi-volatiles species 

are specified by project requirements. 

Static electric charges on the walls of the balance and the weighed objects, including 

samples, controls, and calibration weights, can significantly affect balance readings. 

Static is avoided by the operator ground himself and test objects as described in the 

balance manual. 
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5. PERSONNEL HEALTH AND SAFETY 

N/A 

6. EQUIPMENT AND SUPPLIES 

• Filtered, temperature and humidity controlled weighing chamber. 

• Precision Balance 

• Plastic forceps 

• Nylon fabric gloves. 

• Working calibration weights: ANSI Class 2, 1000g and 500 g 

• Working sensitivity weight: 50 mg 

• Reference objects: references are one or more objects that are typical of the 

objects to be weighed during a project, but that are stored permanently inside the 

balance glove box. Reference objects are labeled Test1, Test2, Test3, etc. 

7. REAGENTS AND STANDARDS 

N/A 

8. SAMPLE COLLECTION, PRESERVATION, AND STORAGE 

N/A. See relevant project requirements and SOPs. 

9. QUALITY CONTROL 

Data quality is controlled by specifying frequencies and tolerances for Zero, Calibration, 

Linearity, and Sensitivity checks. If checks do not meet tolerance criteria, then samples 

must be re-weighed. In addition, the procedures specify frequencies for Control Object 

Checks. 

Data quality is quantitatively characterized using Zero Check, Calibration Check, and 

Control Check data. These data are summarized monthly in statistics and QC charts. 

See Section 11 for procedures, frequencies, and tolerances. 
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10. CALIBRATION AND STANDARDIZATION 

The absolute accuracy of the balance is established by calibration against an ANSI 

Class 2, stainless steel working weight: 1000.000 g +/- 0.0025 g. Linearity is 

established checking the midpoint against an ANSI Class 2 stainless steel working 

weight: 500.000 +/- 0.0012 g. Sensitivity is established using and ANSI Class 2 

stainless steel or aluminum working weight: 50 mg. Precision is checked by periodically 

checking zero, calibration, and reference object weights. 

 

See Section 11 for procedure. 

11. PROCEDURE 

11.1 Overview of Weighing Sequence 

Weighing a series of substrates consists of performing the following procedures in 

sequence, while observing the procedures for handling and the procedures for reading 

the balance: 

1. Initial Adjustment 

2. Weigh 8 samples 

3. Zero Check 

4. Weigh 8 samples 

5. Zero Check 

6. Weigh 8 samples 

7. Calibration Check 

8. Return to step 2. 

9. If less than 24 cans are weighed, perform a final Calibration Check at the end of 

weighing. 

This sequence is interrupted and samples are reweighed if QC check tolerances are not 

met. Each of these procedures along with procedures for handling and reading the 

balance are described below. The QC tolerances referred to in these procedures are 

listed in Table 1. The QC codes described in these procedures are summarized in 

Table 2. The data are recorded in the Precision Balance Data Log, a sample is shown 

in Table 3. 

11.2 Handling 

1. Never touch samples, weights, balance pans, etc. with bare hands. Wear powder 

free gloves to handle the weights, controls, and samples. 

11.3 Reading the Balance 

1. Close the door. Wait for the balance stabilization light to come on, and note the 

reading. 
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2. Watch the balance reading for 30 sec (use a clock). If the reading has not 

changed by more than 0.001 g from the reading noted in step 1, then record the 

reading observed at the end of the 30 sec period. 

3. If the reading has drifted more than 0.001 g note the new balance reading and go 

to step 2. 

4. If the balance reading is flickering back and forth between two consecutive values 

choose the value that is displayed more often than the other. 

5. If the balance reading is flickering equally back and forth between two 

consecutive values choose the higher value. 

11.4 Initial Adjustment 

1. Empty the sample pan Close the door. Select Range 1000 g 

2. Wait for a stable reading 

3. Record the reading with QC code IZC (initial zero check) 

4. Press the Tare button 

5. Record the reading in the logbook with QC code IZA (initial zero adjust) 

6. Place the 1,000 g working calibration weight on the balance pan 

7. Wait for a stable reading. 

8. Record the reading with QC code ICC (initial cal check) 

9. Press the Calibrate button 

10. Record the reading with QC code ICA (initial cal adjust) 

11. Remove the calibration weight. 

12. Wait for a stable reading. 

13. Record the reading with QC code IZC. 

14. If the zero reading exceeds +/- 0.002 g, go to step 4. 

15. Place the 500 g calibration weight on the balance pan 

16. After a stable reading, record the reading with QC code C500. Do not adjust the 

balance. 

17. Add the 0.050 g weight to 500 g weight on the balance pan. 

18. After a stable reading, record the reading with QC code C0.05. Do not adjust 

the balance. 

19. Weigh reference object TEST1, record reading with QC code T1. 

20. Weigh the reference object TEST2, TEST3, etc. that is similar in weight to the 

samples that you will be weighing. Record with QC code T2, T3, etc. 

11.5 Zero Check 

1. Empty the sample pan. Close the door. 

2. Wait for a stable reading 

3. Record the reading with QC code ZC 
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4. If the ZC reading is less than or equal to the zero adjustment tolerance shown in 

Table 1, return to weighing and do not adjust the zero. 

 If the ZC reading exceeded the zero adjustment tolerance, proceed with steps 5 

through 7. 

5. Press the Tare button 

6. Record the reading in the logbook with QC code ZA. 

7. If the ZC reading exceeded the zero re-weigh tolerance, change the QC code 

recorded in step 3 from ZC to FZC. Then enter a QC code of FZ into the QC 

code column of all samples weights obtained after the last valid zero check. Reweigh all of those samples, recording new data in new rows of the logbook. 

11.6 Calibration Check 

1. First, follow procedures for Zero Check. If the ZC was within tolerance, tare the 

balance anyway (i.e. follow steps 5 and 6 of the Zero Check method) 

2. Place the 1,000 g working calibration weight on the sample pan, wait for a stable 

reading. 

3. Record the reading with QC code C1000 

4. If the C1000 reading is less than or equal to the calibration adjustment tolerances, 

skip steps 5 through 8 and proceed to step 9. Do not adjust the calibration.

5. If the C100 reading exceeded the calibration adjust tolerance, press the Calibrate 

button. 

6. Record the reading in the logbook with QC code CA 

7. Perform a Zero Check (follow the Zero Check method) 

8. If the C1000 reading exceeded the calibration re-weigh tolerance, change the 

code recorded in step 3 from C1000 to FC1000. Enter FC into the QC column 

for all sample weights obtained after the last valid calibration check. Re-weigh 

all of those samples, recording new data in new rows of the logbook. 

11.7 Replicate Weighing Check 

1. This protocol does not include reweigh samples to obtain replicates. The projects 

for which this protocol is intended already include procedures multiple weightings 

of each sample. 
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Table 1. QC Tolerances and Frequencies for Balance Protocol A1

Reading tolerance: 

 0.001 g, stable for 30 sec 

Adjustment Tolerances: 

 Zero: - 0.003 to +0.003 g. 

 Calibration: 999.997 to 1000.003 g 

 Controls: none 

 Replicates: none 

Re-weigh Tolerances: 

 Zero: - 0.005 to +0.005 g. 

 Calibration: 999.995 to 1000.005 g 

 Controls: none 

 Replicates: none 

Reference Objects: 

 Test 1 – A reference object weighing about 400 g 

 Test 2 – A refernce object weighing about 200 g 

 Test 3 – A reference object weighin about 700 g. 

QC Frequencies: 

 Zero Checks: once per 8 samples 

 Calibration Checks: once per 24 samples 

 Repeat weighings: none (test method includes replicate determinations) 

 Control objects: once per weighing session 

Table 2. QC Codes For Balance Protocol A1

IZC Initial Zero Check 

IZA Initial Zero Adjust 

ICC Initial Calibration Check 

ICA Initial Calibration Adjust 

ZC Zero Check 

ZA Zero Adjust 

CC Calibration Check 

CA Calibration Adjust 

R Replicate Filter Weighing 

FZ Sample Failed Zero Check 

FC Sample Failed Calibration Check 

T1 Test Object 1: empty can of automotive refrigerant 

T2 Test Object 2: 

T3 Test Object 3: 
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12. DATA ANALYSIS AND CALCULATIONS 

For Zero Checks, let Z equal the recorded Zero Check value. For control checks let T1, 

T2, etc. equal the recorded value for control object Test 1, Test 2, etc. For Calibration 

Checks, let C1000 equal C1000 reading minus 1000, M = C500 – 500, S = .C.050 – 

C500 - .050. For Replicate Checks, let D equal the loss that occurred between the first 

and second measurements. In summary: 

 T1 = T1 

 T2 = T2 

 T3 = T3 

 Z = ZC - 0 

 C = C1000 - 1000 

 M = C500 – 500 

 G = C.050 – C500 - .050 

Tabulate the mean and standard deviation for each of the following: Z, C, M, G. T1, T2, 

T3. Depending on the number of operators using the balance and the number of 

protocols in use, analyze the data by subcategories to determine the effects of balance 

operator and protocol. Each of these standard deviations, SZ, SC, etc. is an estimate of 

the precision of single weight measurement. 

For Z, C, M, and G, check the mean value for statistical difference from 0. If the means 

are statistically different than zero, troubleshooting to eliminate bias may be called for. 

For Z, C, M, G, T1, T2, T3, check that the standard deviations are all comparable. If 

there are systematic differences, then troubleshooting to eliminate the problem may be 

called for. 

Note that the precision of a weight gain, involves two weight determinations, and 

therefore is larger than S by a factor of sqrt(2). On the other hand replicates weighings 

improves the precision of the determinations by a factor of sqrt(N). If N= 2, i.e. 

duplicates, then the factors cancel each other. 

To estimate the overall uncertainty in a weight determination, a conservative estimate 

might be to combine the imprecision contributed by the zero with the imprecision 

contributed by the calibration. 

 U. = sqrt( SZ

2

 + SC

2

 ) 

The uncertainty in a weight gain from N replicates is then given by: 

 Ugain. = sqrt(2) * sqrt( SZ

2

 + SC

2

 ) / Sqrt(N) 

But due to the balance adjustment and reweigh tolerances, we expect SZ to 

approximately equal SC, to approximately equal SM, etc. tolerances, so that the 

equation above becomes: 

 Ugain. = 2 * S / Sqrt(N) 
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Where S is any individual standard deviation; or better, a pooled standard deviation. 

13. METHOD PERFORMANCE 

The data necessary to characterize the accuracy and precision of this method are still 

being collected. The method is used primarily to weigh objects before and after a 

period of soaking to determine weight loss by subtraction. Given the reweigh 

tolerances, we expect the that the precision of weight gain determinations will be on the 

order of 0.006 g at the 1-sigma level. Bias in the weight gain determination, due to 

inaccuracy of the calibration weight and to fixed non-linearity of the balance response is 

on the order 0.005% of the gain. 

14. POLLUTION PREVENTION 

When discharging half the can contents during can preparation, do not vent the 

contents to f the small can to the atmosphere. Use an automotive recovery machine to 

transfer small can contest to a recovery cylinder. 

15. WASTE MANAGEMENT 

Return full and half full cans to the place of purchase for a refund of the purchase 

deposit. Dispose of the contents of the recycle cylinder through a service that 

consolidates waste for shipment to EPA certified facilities for reclaiming or destruction. 

16. REFERENCES 

Precision Balance Instruction Manual. Company, City, State 
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Table 3. Precision Balance Data Log 

QC Can Can Recorded

Rec # Date Time Proj. Prot. Tech. Code Type ID# grams Com

123456789

10111213141516171819202122232425