Help and instructions for BufferCapacity3

BufferCapacity3 was developed by USDA Agricultural Research Service scientists at the USDA/ARS laboratory in Raleigh, NC (Food Science Market Quality and Handling Research Unit).

The BufferCapacity3 program processes titrator data to generate buffer models of aqueous food ingredients. Methods for buffer modeling for food ingredients have recently been published (Price et al., 2020; Longtin et al., 2020). The BufferCapacity3 program is currently configured for processing text file output from Hanna Instruments HI900 and HI930 series titrators. An example titration file showing the file format is in Appendix 1. Titrator data files are processed by the readRPT.m algorithm. A matrix consisting of rows with the volume of acid or base (in mL) added at each step of a titration and the resulting pH value is generated. Matrices for acid and base titrations of a food ingredient are then combined and converted into buffer capacity (BC) values, typically over the pH range of pH 2 to 12. It is possible to modify the Matlab readRPT.m algorithm file to accommodate other titrator text output files. A model is then generated from the BC data using a two-step curve fitting algorithm (Price et al., 2020). The output of the program includes a matrix of monoprotic buffers that defines the buffering influencing pH for the food ingredient that was titrated. Output from the program consists of a database file containing the raw data, the buffer model data, parameters used for processing, and other data. Several other files are produced, as described in Appendix 2 of this document.

The file ‘Help and Instructions for BufferCapacity3.pdf’ contains the instructions printed here and is also available for free download.

Installation:
A link for downloading the software and the help file can be found here.

The current software available as a Matlab application or MS Windows executable file which does not require Matlab. For the Matlab version, the Matlab Optimization Toolbox is also required. After downloading the file BufferCapacity3.mlappinstall, simply drag the file into the Matlab command window. The program will install automatically and can be launched from the Matlab Apps tab at the top of the main window. For the MS Windows version, download and run the install program.

References:
Price RE, Longtin M, Conley Payton S, Osborne JA, Johanningsmeier SD, Bitzer D, Breidt F. 2020. Modeling buffer capacity and pH in acid and acidified foods. J Food Sci 85(4):918-925. https://doi.org/10.1111/1750-3841.15091

Longtin M, Price RE, Mishra R, Breidt F. 2020. Modeling the buffer capacity of ingredients in salad dressing products. J Food Sci 85(4):910-917. https://doi.org/10.1111/1750-3841.15018

Steps for processing titrator data files and generating buffer model data:

1) The initial program screen highlights (gold color) the information that should be entered (see Figure 1, below). Item for user input include:
File version 07062022

a. Enter a name for the ingredient to be titrated. It is helpful to use a name with no spaces or characters other than an underscore, as this name will be suggested for use for the program output filenames.
b. Enter a concentration in percent (0 to 100%, for g/100 mL) for the sample being titrated. If the sample consists of a mixture of ingredients, consider using 100% as a concentration representing the mixture.
c. Enter the normality of HCl and NaOH (acid and base) used for the titration. These values should be precisely determined by standardization using end-point titration methods.
d. Enter the initial volume of the solution to be titrated. Typically, 50 mL is used. This should be accurately measured.
e. Enter the NaCl percentage for the solution being titrated. Many acid or acidified foods use 2% NaCl. If other known salts are added the equivalent NaCl concentration can be determined from ionic strength calculations.

Figure 1: The opening screen with gold highlighted entries (default values) for user input.

2) Select Open Acid Titration File and open the appropriate titrator file for the HCl titration. These files may be opened from the menu item, or the buttons as shown in Figure 2. After opening the acid titrations file, select Open Base Titration File, and open the appropriate titrator file for the NaOH titration

Figure 2. Graphs of the acid (red circles) and base (blue circles) titrations should appear in the graph window:

With a successful operation from each button, a green lamp will light

 

3) Select Generate BC curve, A graph of the buffer capacity data with blue circles (datapoints) and black circles (fills) will appear (Figure 3). The dotted line represents the buffer capacity of water, which is shown for reference:

 

Figure 3: BC curve, with fill for data gaps (black circles)

4) The curve may be trimmed if needed. It is important to have roughly equal BC values for the ends of the BC curve to accurately determine the total system buffering. The Trim Beginning or Trim End boxes allow the user to enter the number of points as needed to remove one or the other ends of the curve (Figure 4). Push the OK button when finished. In the example, two data points are removed from the end of the curve:

 

Figure 4: Edited BC curve

Note that Electrode adjustments (plus or minus 0.5 pH units) can be done if the datapoints lie outside of the water curve for low or high pH values. These adjustments are not recommended but can be used if there has been an obvious pH electrode calibration error. If data lies outside the water curve, it is best to recalibrate the titrator electrode and re-do the titration.

 

5) Click on Model BC Curve, a buffer model will be generated (Figure 5). As part of this process pop-up graph will appear (as shown below) with the minimization algorithm function data. The buffer model is shown as the solid line and the shaded area under the curve represents the ‘total buffering’. The vertical lines each represent the individual buffers as represented in the buffer table.

Figure 5. Graph of the buffer model and a table with data for monoprotic buffers that define the pH of the ingredient. A graph of the optimization algorithm output is also shown.

Note that the optimization function output graph may be closed at any time. Because the optimization is a search algorithm, closing the optimization graph window while it is still running will stop the optimization.

6) Data from the program can now be saved by selecting the menu item “Save Data Files”, producing the output described in Appendix 2.

 

Results:

The database file and output information may be useful for determining the total buffering of a food ingredient for comparison with other food ingredients. Total buffering is defined as the area under the curve for the buffer model and is determined by integration of a trigonometric regression model of the BC data (not shown). The value for the definite integral is shown in the Total buffering box at the bottom left of the program screen and is represented graphically as the shaded area under the BC model curve (Figure 5).  

 

Author information:

Fred Breidt, PhD

USDA/ARS Microbiologist

322 Schaub Hall, Box 7624

NC State University

Raleigh, NC 27695-7624

Email: fred.breidt@usda.gov

Web: https://www.ars.usda.gov/southeast-area/raleigh-nc/food-science-research/

 

 

Appendix 1: Example of a titrator data file (TI_00010.RPT). This file is an acid titration file. These files have a .RPT extension and are in a DOS text format.

                        

                         HI902 - Titration Report

 

                Method Name:                1.8 pH Test

                Time & Date:         14:25 Apr 11, 2022

                Titration ID:                  Ti_00010

 

                             Calibration Data

 

                  Buffer    Potential Efficiency Temp.

                                        Time and Date         

                 1.679pH   312.0mV      95.6%   A 20.0§C

                                      13:51 Apr 11, 2022      

                 4.010pH   181.5mV      99.5%   A 18.2§C

                                      13:49 Apr 11, 2022      

                 7.010pH     7.4mV      90.9%   A 18.5§C

                                      13:48 Apr 11, 2022       

                10.010pH  -152.8mV     104.2%   A 19.2§C

                                      13:50 Apr 11, 2022      

                12.450pH  -309.6mV     104.2%   A 18.2§C

                                      13:52 Apr 11, 2022      

 

                          GLP & Meter Information

                Sample Name:                           

                Company Name:                           

                Operator Name:                         

 

                             Method Parameters

                Name:                       1.8 pH Test

                Method Revision:                    1.0

                Titration Type:      Standard Titration

                Stirrer Configuration:        Stirrer 1

                Pump Configuration:

                    Titrant pump:                Pump 2

                Dosing Type:                    Dynamic

                    Min Vol:                   0.015 mL

                    Max Vol:                   0.045 mL

                    delta E:                  12.000 mV

                End Point Mode:          Fixed 1.800 pH

                Pre-Titration Volume:          0.000 mL

                Pre-Titration Stir Time:         30 Sec

                Measurement Mode:       Timed Increment

                    Time interval:               30 Sec

                Electrode Type:                      pH

                Blank Option:                  No Blank

                Calculations:      No Formula (mL only)

                Titrant Name:                  3.0N HCL

                Maximum Titrant Volume:       50.000 mL

                Stirring Speed:                 800 RPM

                Potential Range:   -2000.0 to 2000.0 mV

                Volume/Flow Rate:   25 mL / 50.0 mL/min

                Signal Averaging:            3 Readings

                Significant Figures:                XXX

                Linked To:                      No Link

 

                Final unit is mL.

 

                mL = V * 1000

 

                V = volume dispensed in liters.

 

                  Nr Volume[mL]      mV      pH  Graphic Temp.[C]     Time

                   0      0.000   139.9   4.745      0.0 A   20.4 00:00:00

                   1      0.045   183.6   3.989      4.0 A   20.4 00:01:30

                   2      0.090   216.9   3.389      3.4 A   20.4 00:02:00

                   3      0.105   222.4   3.291      3.3 A   20.3 00:02:30

                   4      0.132   235.1   3.063      3.1 A   20.3 00:03:01

                   5      0.158   244.1   2.900      2.9 A   20.3 00:03:32

                   6      0.194   252.5   2.749      2.7 A   20.3 00:04:03

                   7      0.239   260.2   2.610      2.6 A   20.3 00:04:34

                   8      0.284   266.4   2.500      2.5 A   20.2 00:05:04

                   9      0.329   271.0   2.415      2.4 A   20.2 00:05:35

                  10      0.374   275.1   2.343      2.3 A   20.2 00:06:05

                  11      0.419   278.7   2.278      2.3 A   20.2 00:06:35

                  12      0.464   281.9   2.220      2.2 A   20.2 00:07:05

                  13      0.509   284.9   2.166      2.2 A   20.2 00:07:35

                  14      0.554   287.7   2.115      2.1 A   20.2 00:08:05

                  15      0.599   290.3   2.069      2.1 A   20.2 00:08:35

                  16      0.644   292.5   2.029      2.0 A   20.1 00:09:05

                  17      0.689   294.2   1.997      2.0 A   20.1 00:09:35

                  18      0.734   295.9   1.966      2.0 A   20.1 00:10:05

                  19      0.779   297.6   1.937      1.9 A   20.1 00:10:35

                  20      0.824   299.0   1.911      1.9 A   20.1 00:11:05

                  21      0.869   300.6   1.882      1.9 A   20.1 00:11:35

                  22      0.903   301.8   1.860      1.9 A   20.1 00:12:05

                  23      0.936   303.0   1.839      1.8 A   20.1 00:12:35

                  24      0.957   303.6   1.827      1.8 A   20.1 00:13:05

                  25      0.973   304.1   1.818      1.8 A   20.1 00:13:36

                  26      0.988   304.5   1.811      1.8 A   20.1 00:14:06

                  27      1.003   305.0   1.803      1.8 A   20.0 00:14:36

                  28      1.018   305.4   1.795      1.8 A   20.0 00:15:07

 

                             Titration Results

                Method Name:                1.8 pH Test

                Time & Date:         14:25 Apr 11, 2022

                Analyte Size:                           

                End Point Volume:              1.008 mL

                pH Fixed End Point:               1.800

                Result:                        1.008 mL

                Initial & Final pH:     4.745 to  1.795

                Titration Duration:       15:09 [mm:ss]

                Titration went to Completion

 

                Analyst Signature: ____________________

 

Appendix 2: Titrator data output files. The name “ingredient” is a default name. The program will use automatically use the ingredient name entered by the user for saving these files. The .mat file is a Matlab database file containing most of the information from the titration and processing. Matlab users can open this file and directly access the data fields. The database file is also useful for other programs that process titration data, including IngrendientDB (F. Breidt, unpublished).  

1.) Ingredient.mat: Matlab database file containing one Matlab workspace variable (‘ingredient’) that has multiple fields. This variable represents an ABD class structure with the following fields representing model results and titration data, with notes for each field:

      ingredient =

• buffer_table: [7×3 table] table of buffers (conc, pK)
• name: 'Ingredient' ingredient name
• conc: 100 ingredient concentration
• adjC: -0.0153 the salt of an acid/base or error term
• pH: 5.8870 model pH based on optimized adjC value
• totalBC: 0.0943 area under buffer model curve
• pH_cal: 0 electrode calibration adjustment
• titration: 1 Boolean for titration data (true/false)
• titration_name: "ingredient" ingredient name
• titration_conc: 100 ingredient concentration
• titration_IS: 0.3425 initial ionic strength for the titration
• titration_files: [1×1 struct] titration file names and data
• titration_ModelCurve: [100×2 double] buffer model smooth curve
• titration_BCcurve: [87×2 double] titration BC data
• titration_SCBCcurve: [100×2 double] trigonometric regression curve
• titration_buffertable: [7×4 table] table of buffers from the titration
• titration_SCBC: [1×1 struct] results the regression algorithm
• titration_SPX: [1×1 struct] results from the buffer model algorithm
• titration_SSE: 5.3846e-05 squared error sum for the buffer model
• titration_obspH: 5.8895 initial pH from the titration
• titration_volume: 0.0500 initial titration volume
• titration_HClconc: 2 normality of acid used for titration
• titration_NaOHconc: 2 normality of base used for titration
• parameters: [15×4 table] titration parameter table
• ver: '220701' version of the ADB database class

 

2) Ingredient_BCdatapoints.csv: comma delimited spreadsheet file with buffer capacity data points (i.e. Nx2 array with BC value, pK value).

3) Ingredient_BCmodelcurve.csv: comma delimited spreadsheet file with a smooth curve of buffer capacity data points model (i.e. Nx2 array with BC value, pK value).

4) Ingredient_buffertable.csv: comma delimited spreadsheet file with a table of buffers (i.e. Nx4 array with concentration (M), pK value, a_b letter [a=acid, b=base], and BC value).

5) Ingredient_graph.pdf: pdf file showing the BC graph (BC vs. pH)

6) Ingredient_info.csv: a data table showing data from the titration and processing:

• Ingredient concentration concentration (%) of the ingredient
• NaClpercent NaCl percent equivalent of ionic strength
• InitialVolume initial titration volume (L)
• AcidConc normality of the acid (HCl) used for titration
• BaseConc normality of the base (NaOH) used for titration
• MeasuredpH initial pH of the ingredient solution
• ModelpH model pH with adjC correction
• AdjC adjC value: salt of acid or base

7) Ingredient_paramfile.csv: saved parameters from the titration. This file may be edited and loaded for processing titration data using the “Open Parameter File” menu option. The values in the table represent the default parameter values, which are typically used for most food ingredient titrations:

                               

Value            Parameter          Units     Description (including algorithm used)

0.05                pH                          pH          Data2Beta to generate curve w/o jumps

15                   Order                    Int          SCBCfit number of harmonics

0.001             MinConc              Molar    SCBCfit and SimplexBCPK_DF minimim buffer M/L

2                      NaClpercent       %            SimplexBCPK_DF NaCl percent

7                      NpKs                     Int          SimplexBCPK_DF number of pKs for starting AB matrix

12                   UB                          pH          SimplexBCPK_DF upper pH range for BC curve fit

2                      LB                           pH          SimplexBCPK_DF lower pH range

0.2                  pK_tol                   pH          SimplexBCPK_DF pH range for too-similar pK vals

0                      Trim_beg             Int          DriveFit trim off begining to balance end

0                      Trim_end            Int          DriveFit trim off end to balance begining

0.3                  MinGap                 Float      Minimum gap in pH for not autofilling BC curve

0.1                  Increment           Float      Increment pH value for gap filling of BC curve

2                      HCl                         Normality            Normality of HCl used for titration

2                      NaOH                    Normality            Normalty of NaOH used for titration

0.05                Init_Vol                Liter       Volume (L) of initial titration