Titer Determination: Simultaneous Titration of Duplicates

Synchronous titration of samples that have been duplicated is an appropriate method to increase the sample throughput since it permits a 50% reduction of analysis time. Titration Excellence T9 can carry out the titer determination in two separate beakers simultaneously.

Two methods are synchronized to run the titer standardization at the same time using Tower A and B on the InMotion™ Autosampler with two towers. The analysis of a series sequence comprised of two sample series for the acid content determinations begins using OneClick™.

Using potassium hydrogen phthalate KHP as a primary standard, this text outlines the titer determination of 1 M potassium hydroxide KOH. The titer determination is conducted synchronously at Tower A (M811A) and Tower B (M811B). The titer values acquired can be used for concurrent titration of duplicated resin samples set out in Application M793.

Sample preparation and procedures

Sample handling

Glass titration beakers are used to prevent any issues occurring due to electrostatics, such as the contamination of sample powder onto the sample beaker wall. Weighing 0.8 g of potassium hydrogen phthalate, the sample is then placed in each beaker. Mark each beaker with a pen in line with their position on the sample rack of InMotion Autosampler i.e. B1/A1 for position 1, B2/A2 for position 2.

Deionized water is placed at the position for special beaker 1 and 2 (for InMotion Flex 100 mL: pos. 16 and 15) in two beakers. These beakers are used to clean the sensors and tubes after each sample. Station two empty beakers at the secure conditioning beaker and rinse beaker position (for InMotion Flex 100 mL: pos. 18 and 17). These beakers are utilized for parking the sensors at the end of the titration.

Titer Determination: Simultaneous Titration of Duplicates

Image Credit: Mettler Toledo - Titration

Sample titration

Set down the duplicates on the sample rack:

  • 1st duplicate:   B1   pos. 1
                              A1   pos. 2
  • 2nd duplicate:  B2   pos. 3
                              A2   pos. 4

Pour 80 mL deionized water into each beaker and then simultaneously initiate the two methods on Tower A and B using a series sequence SSQ. The sample series sequence includes a sample series for each tower A and B with a matching number of samples.

Please note: to run in excess of one duplicated sample, it is necessary to define the same number of samples in each of the sample series. For instance, measurement of 7 duplicates -> n=7 in both sample series A and B. For each titrants KOH A and KOH B for both towers A and B, the mean value of titer is saved into the built-in RFID chip of the burettes.

Chemistry

Acid/base neutralization reaction:

C8H5O4K + KOH → C8H4O42- + H2O + 2 K+

Solutions

  • Standard: Potassium hydrogen phthalate (KHP), C8H5O4K, 0.8 g
  • Titrants Tower A and B: Potassium hydroxide in water, KOH, c(KOH) = 1 mol/L
  • Chemicals: Deionized water

Instruments and accessories

  • 1 x Titration Excellence T9 (30252676)
  • 1 x Autosampler InMotion Flex 100 mL (30094120)
  • 1 x additional Analog Board AB (51109818)
  • 1 x Autotitration Kit (51109221)
  • 1 x additional Compact Stirrer for the 2nd tower (51109150)  
  • 1 x DU Dosing Unit (51109030)
  • 1 x Dispensing tube 1.35 m w/tip
  • 1 x additional PowerShower™ 100-250 mL (30094212) 1 x Insert InMotion Head 1/4/4 hole 100 mL (30046200)
  • 1 x additional Tower – InMotion Flex (30094160)
  • 1 x Cover InMotion Flex/Pro 2nd Tower (30094267)
  • 2 x Sb850-S7/120 antimony rod half-cell (59904405)
  • 2 x Burette DV1020 20 mL (51107502)
  • 2 x Y-Cable SYNC 5 pin Titration (30094246)
  • 2 x InLab Reference half-cell (51343190)

Titer Determination: Simultaneous Titration of Duplicates

Image Credit: Mettler Toledo - Titration

  • 2 x 4 mm banana reference cable for InLab Reference (30281922)
  • 4 x NS14.5/15-12 PE sensor adapter (51340024)
  • 1 x additional SC-LEMO cable 160 cm for second electrode (51108034)
  • LabX software
  • Glass titration beakers 100 mL, 20 pcs (00101446)
  • XPR204 Analytical balance (30355419)
  • Spatula

Setup

Electrodes

  • AB1 Sensor 1: Sb850-A                    Tower A
                              InLab Reference A  Tower A
  • AB2 Sensor 1: Sb850-B                    Tower B
                              InLab Reference B  Tower B

Titration stand

Table 1. Source: Mettler Toledo - Titration

Tower Type Name Stirrer Output
A Autostand Autostand 1 MB/Stirrer 1 Sync cable A
InMotion T InMotionT/1A MB/Stirrer 2
B Autostand Autostand 2 AB1/Stirrer Sync cable B
InMotion T InMotionT/1B AB2/Stirrer

 

Overview

Workspaces A and B of Titration Excellence T9 are used to run duplicated samples:

  • Workspace A: Titer determination on Tower A (method M811A) - Client
  • Workspace B: Titer determination on Tower B (method M811B) – Host using the method function SYNC, M811A and M811B are synchronized.

Resources

  • Workspace A: - Sensor: Sb850-A - Titrant: KOH A - Standard: KHP A
  • Workspace B: - Sensor: Sb850-B - Titrant: KOH B - Standard: KHP B

Sample Series

Two sample series with methods M811A and method M811B are generated for the titration of duplicated samples:

1) Sample series ‘Sb850 Titer A7’ (M811A) for titer determination at Tower A:

           a. Input only no. of samples, e.g. n = 7 for 7 duplicated samples

2) Sample series ‘Sb850 Titer B7’ (M811B) for titer determination at Tower B:

           a. Input the no. of samples, e.g. n = 7 for 7 duplicated samples

           b. Start Position - InMotion: 1st MF Titration Stand: InMotion T/1B: 1

                                                            2nd MF Titration Stand: InMotion T/1A: 2

                                                            4th MF Titration Stand: InMotion T/1A: CP+1

                                                            5th MF Titration Stand: InMotion T/1B: CP+1

Series sequence

A sample series sequence ‘Sb850 Titer AB7’ is generated for both methods to begin synchronously with OneClick (choose ‘Immediate start’ when generating the shortcut with ‘Add to Home’):

Titer Determination: Simultaneous Titration of Duplicates

Image Credit: Mettler Toledo - Titration

Method synchronization

Titer Determination: Simultaneous Titration of Duplicates

Image Credit: Mettler Toledo - Titration

Waste disposal and safety measures

  • Use safety goggles, gloves and a lab coat.
  • Neutralize the alkaline solutions prior to final disposal.

Literature

  • Helmuth Galster, ‘pH Measurement: Fundamentals, Methods, Applications, Instrumentation’, Wiley-VCH, 1991, ISBN 978-3527282371.
  • ‘Standardization of Titrants I – Acid-Base, Precipitation, Complexometry’, Titration Applications Brochure No. 8, 09/2012, Product No. 51724650A.

Further information

Results

  • 6 different Sb850-S7/120 antimony rod have been tested:
    • 1. Sensors: Sb850-1 (Tower B) Sb850-2 (Tower A),
    • 2. Sensors: Sb850-3 (Tower B) Sb850-4 (Tower A),
    • 3. Sensors: Sb850-5 (Tower B) Sb850-6 (Tower A).
  • Subsequent to each titer determination (7 duplicates), replacement of the sensors is carried out.

Table 2. Source: Mettler Toledo - Titration

Sensors n Titer Standard
deviation
Relative standard
deviation
Sb850-1 (B)
Sb850-2 (A)
7
7
1.00065
1.00365
0.00108
0.00064
0.108%
0.063%
Sb850-3 (B)
Sb850-4 (A)
7
7
0.99985
1.00289
0.00069
0.00098
0.069%
0.098%
Sb850-5 (B)
Sb850-6 (A)
7
7
0.99970
1.00314
0.00101
0.00067
0.101%
0.066%
  • The results exhibit exceptional repeatability, with comparative standard deviations between 0.06 and 0.1%, therefore extremely similar to those acquired using classical pH glass electrode.
  • The potential change of the entire titration curve lies between approximately -200 down to -650 mV. Even in the acid region the potential measured by the Sb850 antimony rod half-cell is always negative.
  • This can be resolved by considering the fact that the presence of hydroxide ions OH- and not hydrogen ions H+ causes the antimony to react, as in the case of pH sensitive glass membrane. This is because bare antimony rods simply generate a layer of antimony hydroxide when exposed to air and/or sample solution according to:

    4 Sb + 3 O2 + 6 H2O = 4 Sb (OH)3

    The layer sensitive to OH- - presence The hydroxide layer Sb(OH)3 on the surface of the antimony electrode. Therefore, it enables the identification of the pH value based on the ionic product of water, i.e. [H2O] = [H+]*[OH-].
  • The initial derivative peak of the titration curve as illustrated in this text is extremely sharp and can reach up to 2000 mV/mL (see green curve) at the inflection point of the curve. These exceptionally sharp peaks of the first derivative curves enable straightforward evaluation by the control algorithm of the titrator.

Measured values

Titer Determination: Simultaneous Titration of Duplicates

Image Credit: Mettler Toledo - Titration

Table 3. Source: Mettler Toledo - Titration

t
[s]
V
[mL]
E
[mV]
dV
[mL]
T [°C]
[s]
dE
[mV]
dE/dV
[mV/mL]
 
0 0.000 -218.5   25.0      
4 1.143 -260.4 1.143 25.0 -41.9    
7 1.714 -274.2 0.571 25.0 -13.8    
10 2.000 -280.7 0.286 25.0 -6.5    
13 2.200 -284.9 0.200 25.0 -4.2    
22 2.800 -298.8 0.200 25.0 -4.8 -24.86  
26 3.000 -303.8 0.200 25.0 -5.0 -27  
29 3.200 -310.2 0.200 25.0 -6.4 -33.74  
32 3.400 -317.2 0.200 25.0 -7.0 -46.56  
35 3.600 -327.3 0.200 25.0 -10.1 -75.59  
38 3.726 -335.8 0.126 25.0 -8.5 -115.68  
41 3.815 -344.9 0.089 25.0 -9.1 -184.36  
44 3.866 -353.0 0.051 25.0 -8.1 -420.29  
48 3.898 -360.1 0.032 25.0 -7.1 -784.72  
51 3.924 -367.9 0.026 25.0 -7.8 -1005.21  
54 3.944 -377.6 0.020 25.0 -9.7 -1146.8  
57 3.964 -393.2 0.020 25.0 -15.6 -1686.68  
  3.982520 -467.6       -2112.94 EQP
61 3.984 -473.6 0.020 25.0 -80.4 -2112.92  
64 4.004 -534.6 0.020 25.0 -61.0 -1850.48  
67 4.024 -557.2 0.020 25.0 -22.6 -1278.43  
71 4.044 -569.1 0.020 25.0 -11.9 -906.40  
74 4.070 -580.1 0.026 25.0 -11.0 -641.50  
77 4.096 -587.9 0.026 25.0 -7.8    
80 4.134 -596.3 0.038 25.0 -8.4    
84 4.182 -604.5 0.048 25.0 -8.2    
87 4.243 -613.0 0.061 25.0 -8.5    
90 4.313 -620.5 0.070 25.0 -7.5    

 

About Mettler Toledo - Titration

METTLER TOLEDO instruments are used in research, scientific and quality control labs, amongst many others in the pharmaceutical, chemical, food and cosmetics industries. They are a global market leader with the three instrument groups most frequently used in the laboratory, like balances, pipettes, and pH meters, and we are a pioneer in the field of Automated Chemistry.

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Last updated: Dec 22, 2020 at 4:23 AM

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