DEVELOPMENT OF A COULOMETER AT THE NATIONAL METROLOGY INSTITUTE OF COLOMBIA: DETERMINING THE AMOUNT OF SUBSTANCE CONTENT OF POTASSIUM HYDROGEN PHTHALATE

Smith-Osorio, Jessica; Castillo, Andrés; Torres-Quezada, Henry; Sandoval-Rojas, Andrea P.; Ágreda, Jesús

doi:10.21577/0100-4042.20230104

Jessica Smith-Osorio

Departamento de Química, Universidad Nacional de Colombia, 111321 Bogotá, Colombia

https://orcid.org/0000-0001-7124-5935

Andrés Castillo

Subdirección de Metrología Química y Biología, Instituto Nacional de Metrología de Colombia, 111321 Bogotá, Colombia

Henry Torres-Quezada

Subdirección de Metrología Química y Biología, Instituto Nacional de Metrología de Colombia, 111321 Bogotá, Colombia

Andrea P. Sandoval-Rojas

Departamento de Química, Universidad Nacional de Colombia, 111321 Bogotá, Colombia

Jesús Ágreda ^**e-mail: jagreda@unal.edu.co

Departamento de Química, Universidad Nacional de Colombia, 111321 Bogotá, Colombia

https://orcid.org/0000-0002-7371-1749

*e-mail: jagreda@unal.edu.co

Operation	SCPI code	Description
Keithley 2200-60-2 current source
Identify instrument	^*IDN?	Instrument information: serial number and model
Activate output	OUTPUT1	Instrument power on
Output lock	OUTPUT0	Power off
Current configuration	CURR	Current setting in A
Potential configuration	VOLT	Potential configuration in V
Keithley 2002 multimeter
Identify instrument	^*IDN?	Instrument information: serial number and model
Measurement	MEAS?	Start data measurement
Keithley 2700 multimeter
Identify instrument	^*IDN?	Instrument information: serial number and model
Measurement	MEAS?	Start data measurement
Metrohm 781 pH/ion meter^a a The pH meter and the burette work with internal codes from the factory instead of the SCPI code.
Measurement	&Info.Ac.M.PQ	Start data measurement according to specified parameters
SI Analytics titronic 500 burette^a a The pH meter and the burette work with internal codes from the factory instead of the SCPI code.
Dose (volume)	01DA	Dosification of the specified volume in mL
Fill (volume)	01BF	Fill burette
Status	01RS	Burette status
Agilent 53220A frequency counter
Identify instrument	^*IDN?	Instrument information: serial number and model
Total counter cycles	SENSe:TOTalize:DATA?	Total time of counter cycles
Restart	^*RST	Restart the instrument to the initial operating conditions
Counter cycles	TOTalize:CONTinuous	Total cycles according to the input frequency
Start cycle count	INIT	Start the cycle counter at the specified frequency

Navigation tab	Description
Experimental mode	In this panel, the user can configure the current in amperes, the time in milliseconds, and the number of pulses to be applied in the coulometric titration (initial, main, or final titration)
Multi parameters mode	It shows the plot of the pH, current, and potential difference values as a function of time
Multimeter vs. time	It shows the plot of the potential difference values in function of time
pH vs. time	This panel follows the pH measurements as a function of time
Integration mode	Calculates the integral of the applied current pulses in the function of time
Data output	Records the pH values, current and potential difference when current pulses are applied
Configuration	In this panel, the connection between the computer and the instruments is established

Validation parameter	Units	Model
Validation parameter	Units	eWf	TC(NLR)
Amount content mean, -v	mol kg^-1	4.9069	4.8983
SD	mol kg^-1	0.0046	0.0016
RSD	%	0.094	0.033
Bias	%	0.22	0.040

Source	Value	Uncertainty (u_i)	Units	Sensitivity coefficient			Contribution (%)
Source	Value	Uncertainty (u_i)	Units	c_i	Units	u_i × c_i / mol kg^-1	Contribution (%)
E₁	0.0049103	7.6 × 10^-6	V	0.96	mol kg^-1	7.30 × 10^-6	3.16 × 10^-2
R₁	0.99999964	3.5 × 10^-7	Ω	-4.7 × 10^-3	mol kg^-1 Ω-¹1 Shlyamina, O. V.; Ziyatdinova, G. K.; Abdullina, S. G.; Budnikov, G. K.; J. Anal. Chem. 2007, 62, 957. [Crossref] Crossref...	-1.65 × 10^-9	1.61 × 10^-9
t_totalini	100.05497	2.6 × 10^-4	s	1.01 × 10^-4	mol s^-1 kg^-1	1.58 × 10^-8	1.49 × 10^-7
t₁	57.57	0.39	s	-1.01 × 10^-4	mol s^-1 kg^-1	-4.00 × 10^-5	0.95
E_main	0.199486	1.5 × 10^-5	V	24.42	mol kg^-1 V^-1	3.66 × 10^-4	79.58
R_main	0.99999914	3.5 × 10^-7	Ω	-4.87	mol kg^-1 Ω-¹1 Shlyamina, O. V.; Ziyatdinova, G. K.; Abdullina, S. G.; Budnikov, G. K.; J. Anal. Chem. 2007, 62, 957. [Crossref] Crossref...	-1.71 × 10^-6	1.72 × 10^-3
t_main	1182.3816	1.8 × 10^-3	s	4.12 × 10^-3	mol s^-1 kg^-1	7.62 × 10^-6	3.44 × 10^-2
E₂	0.009876	1.5 × 10^-5	V	2.73	mol kg^-1 V^-1	3.66 × 10^-4	0.99
R₂	0.99999914	3.5 × 10^-7	Ω	-2.69 × 10^-2	mol kg^-1 Ω-¹1 Shlyamina, O. V.; Ziyatdinova, G. K.; Abdullina, S. G.; Budnikov, G. K.; J. Anal. Chem. 2007, 62, 957. [Crossref] Crossref...	-9.42 × 10^-9	5.27 × 10^-8
t₂	131.98	0.04	s	2.04× 10^-4	mol s^-1 kg^-1	9.09 × 10^-6	4.90 × 10^-2
m	0.501577	1.8 × 10^-6	g	-9.78	mol g^-1 kg^-1	-1.76 × 10^-4	18.36
h_cor	1.00043050	1.7 × 10^-7	-	-4.90	mol kg^-1	-8.45 × 10^-7	4.24 × 10^-4
			Standard uncertainty ( $u_{v_{e W f}}$ )			0.00041	100%
			Amount of substance content (v_eWf)			4.90338
			Relative uncertainty (%)			0.0084

Source	Value	Uncertainty (u_i)	Units	Sensitivity coefficient			Contribution (%)
Source	Value	Uncertainty (u_i)	Units	c_i	Units	u_i × c_i / mol kg^-1	Contribution (%)
[KHP]₀	0.0092766	1.7 × 10^-6	mol kgsln^-1	528.19	kg_soln kg^-1	8.84 × 10^-4	92.32
m_KCl	0.26419	1.0 × 10^-5	kg	18.48	mol kg_soln^-1 kg^-1	1.85 × 10^-4	4.03
m_HCl	3.5231 × 10^-4	3.0 × 10^-7	kg	18.48	mol kg_soln^-1 kg^-1	5.54 × 10^-6	3.63 × 10^-3
m_KHP	0.501577	18 × 10^-6	g	-9.75	mol kg_soln^-1 g^-1	-1.76 × 10^-4	3.64
h_cor	1.00043050	1.7 × 10^-7	-	-4.90	mol kg^-1	-8.49 × 10^-7	8.51 × 10^-5
			Standard uncertainty ( $u_{v_{T C}}$ )			0.00092	100%
			Amount of substance content (v_TC)			4.89987
			Relative uncertainty (%)			0.018

Instrument	Price (US dollar)
Commercial coulometer
Coulometric equipment	$66,000
Coulometer built-in the INMC
Keithley 2200-60-2 current source	$1,433
Keithley 2002 multimeter	$11,500
Keithley 2700 multimeter	$2,396
MetrOhm 781 pH/ion meter	$2,467
SI analytics titronic 500 burette	$2,655
Agilent 53220A frequency meter	$4,324
Standard resistor SRL-1 IET	$3,000
Total	$27,775

\begin{matrix} H_{2} {C O}_{3 (a q)} + H_{2} O_{(1)} \overset{{K a}_{1 : H_{2} {C O}_{3}}}{⟷} {H C O}_{3 (a q)}^{-} + H_{3} O_{(a q)}^{+} \\ { & {C O}_{2 (a q)} + 2 H_{2} O_{(1)} \overset{{K a p}_{: {C O}_{2}}}{⟷} {H C O}_{3 (a q)}^{-} H_{3} O_{(a q)}^{+} \\ H_{2} {C O}_{3 (a q)} + H_{2} O_{(1)} \overset{{K a}_{1 : H_{2} {C O}_{3}}}{⟷} {H C O}_{3 (a q)}^{-} + H_{3} O_{(a q)}^{+} \end{matrix}

\begin{aligned} [H_{3} O^{+}] + \frac{i \times t}{n \times F \times {k g}_{soln}} = \frac{{K a p}_{: {C O}_{2}} \times {[{C O}_{2}]}_{0}}{[H_{3} O^{+}]} + \\ 2 \times \frac{{K a}_{2 : {C O}_{2}} \times [{H C O}_{3}^{-}]}{[H_{3} O^{+}]} + [H C l]_{0} + \frac{K W}{[H_{3} O^{+}]} \end{aligned}

\begin{aligned} [H_{3} O^{+}] + \frac{i \times t}{n \times F \times {k g}_{soln}} = {[{C O}_{2}]}_{0} \times (\frac{{K a p}_{{C O}_{2}} \times [H_{3 O (m q)}^{+}] + 2 \times {K a p}_{{C O}_{2}} \times {K a}_{2 {O O}_{2}}}{{[H_{3} O_{(a q)}^{+}]}^{2} + {K a p}_{{C O}_{2}} \times [H_{3} O_{(a q)}^{+}] + {K a p}_{{C O}_{2}} \times {K a}_{2 : {C O}_{2}}}) + \\ [K H P]_{0} \times (\frac{{K a}_{1 - H_{2 p}} \times [H_{3} O_{(s q)}^{+}] + 2 \times {K a}_{1 : H_{1 p}} \times {K a}_{2 : H_{2 p}}}{{[H_{3} O_{(m q)}^{+}]}^{2} + {K a}_{1 H_{2 p}} \times [H_{3} O_{(s q)}^{+}] + {K a}_{1 : H_{2 p}} \times {K a}_{2 : H_{27}}}) + [H C l]_{0} + \frac{K W}{[H_{3} O^{+}]} \end{aligned}

\begin{aligned} % {bias}_{e W f} = \frac{(v_{e W f} - v_{R M})}{v_{R M}} \times 100 = 0.22 or \\ % {bias}_{T C (N L R)} = \frac{(v_{T C} - v_{R M})}{v_{R M}} \times 100 = 0.040 \end{aligned}

[1] *e-mail: jagreda@unal.edu.co

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DEVELOPMENT OF A COULOMETER AT THE NATIONAL METROLOGY INSTITUTE OF COLOMBIA: DETERMINING THE AMOUNT OF SUBSTANCE CONTENT OF POTASSIUM HYDROGEN PHTHALATE