An open C4D for capillary electrophoresis

Kelliton José Mendonça Francisco and Claudimir Lucio do Lago

Department of Fundamental Chemistry, Institute of Chemistry, University of São Paulo, Brazil

Email: claudemi@iq.usp.br

Summary

• The capacitively coupled contactless conductivity detection (C4D)

• The openC4D

• Serine Protocol

• openC4D at GitHub

• Perspectives

Conductivity, Admittance, and Impedance

𝑅 =𝑙

𝑎∙1

𝜅

𝑌 =1

𝑍

𝑌 - admittance𝐶- capacitance𝑓- frequency

𝑗 - −1

DC

AC

𝑌 =1

𝑅+ 2𝜋𝑓𝐶𝑗

𝑌 =𝑎

𝑙𝜅 + 2𝜋𝑓𝐶𝑗

𝑅 - resistance 𝜅 - conductivity𝑙 - distance between𝑎 - electrode area𝑍 - impedance

𝑌 =𝑎

𝑙𝜅

2

+ 2𝜋𝑓𝐶 2

magnitude of the admittanceLegend:

𝑓 = 1 𝑘𝐻𝑧

𝑓 > 100 𝑘𝐻𝑧

Make the connections as short as possible.

For a real BGE and frequency < 10 MHz, this capacitor is not important.

For a low output impedance oscillator, this capacitor is not important.

For frequency < 10 MHz and a well-designed ground plane, this capacitor is not important.

∆ 𝑌 ∝ ∆𝜅

Keep everything steady!• Frequency and amplitude• Temperature• Positioning

The admittance detector becomes a conductivity detector.

Anal. Chem. 70 (1998) 4339.

sig

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lta

ge

time

sig

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lta

ge

time

sig

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lta

ge

time

co

nd

uctivity

time

sig

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l vo

lta

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time

∆𝜅

∆ 𝑌

∆ 𝑌 ∝ ∆𝜅

openC4D landmarks

• 1998 – The oscillometric detector

• 2002 – The first revision

• 2005 – The tutorial about C4D

• 2009 – The openC4D is published

• 2010 – openC4D.com is launched

• 2012 – The project is moved to https://sites.google.com/site/openc4d/home

• 2016 – openC4D version 2

• 2018 – The project is moved to https://github.com/claudimirlago/openC4D

C4D: The Second Generation

silica capillary

electrodes18 mm

J. Chromatogr. A 942 (2002) 249.

function generator

power source, baseline compensation, and analog output

Electroanalysis 17 (2005) 1198.

Electroanalysis 17 (2005) 1207.

Which frequency?

Bad contact

Electrodes

What we've learned

The steadiness of the electrode

0.00 0.02 0.04 0.06 0.08 0.10 0.120.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

ca

pa

cita

nce

/

p

F

capillary position / mm

A 360-μm o.d. silica capillary inside a electrode made of a 600-μm i.d. metal needle:

The capacitance is 36% higher!

The electrode should be as tight as possible, and the capillary should not be able to shake.

IC 6

Vref

Vss

+Vin

-Vin

Vdd

SCK

CS

SDOIC 5IC 4 D1

R9

C16R10 R11C11

C20 C21

C12

C18

C19

C17

+5V

+5V

C15

R21

R22

R20

R15 R18 R19

R17

R16

R13

R14

R12

GND

SDO

CS

SCK

C13Electrodes

IC 1-AIC 2

+5V

R5

GND

+9V

IC 1-B

C1

R4C3

C2

R6

R3

R2

R1

+2.5V

+2.5V

IC 3OutIn

GND

+2.5V

C4C5 C6

C8

C9

C10L1

L2

R7

R8

+5V

+5V

+5V

C7 C14

GB PB

Electrophoresis 30 (2009) 3458.

22-bit analog-to-digital

converter

serial

interface

(SPI)

triangular-wave oscillator

low-pass filter

9-V

power

supply

openC4D

sig

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l vo

lta

ge

time

sig

na

l vo

lta

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time

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lta

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time

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lta

ge

time

*

*

* *

* This OpAmp may be different.

polyethylene

insulator

openC4D

copper

ground

plane

generator

boardshield

pickup

boardshieldpolyethylene

insulator

silica capillarypower and

interface cable

openC4D

2 3 4 5 60

1 000 000

2 000 000

3 000 000

4 000 000

time / min

2 3 4 5 6

2 540 000

2 560 000

2 580 000

time / min

2 3 42 578 000

2 579 000

2 580 000

2 581 000

time / min

Sample:

K+, Ba2+, Ca2+, Na+, Mg2+, and Li+

16 µmol/L

2 500 000 3 000 000 3 500 000

0

1

2

3

4

5

100 m

75 m20 m

50 m / m

S c

m-1

ADC reading

0.2 ~ 1.2 mS cm-1

The most common BGEs used in CE

𝜅 𝑟 =𝑟 + 𝑎

𝑏0 + 𝑏1 𝑟 + 𝑎 + 𝑏2 𝑟 + 𝑎 2

𝑎, 𝑏0, 𝑏1, 𝑏2 are obtained by non-linear fitting.

FR04

35 µm copper layer

post-drilled hole

capillary

stainless steel needle

weld

a – the new C4D pickup boardb – the old C4D pickup boardc – silica capillarye – gold-plated viad – stainless steel electrode

gold-plated vias as electrodes

PCB 1.6 mm2.0 mm

Electrophoresis 37 (2016) 1718.

via

A brief history of the openC4D project

C4D• 1998 – The oscillometric detector

• 2002 – The first revision

• 2005 – The tutorial about C4D

• 2009 – The openC4D is published

• 2010 – openC4D.com is launched

• 2012 – The project is moved to https://sites.google.com/site/openc4d/home

• 2016 – openC4D version 2

• 2018 – The project is moved to https://github.com/claudimir-lago/openC4D

CE-C4D instruments

• 1995 – Zé 1

• 1998 – Zé 2

• 2004 – Homer (with 2 C4Ds)

• 2005 – Acquaplay

• 2007 – Sponge Bob (with 8 C4Ds)

• 2009 – Darth Vader (with 2 C4Ds)

Luke, Michael Jackson, Coyote, CEC4D

• 2011 – LOAR3

a b e f c d

g h

j

i

a

b

c

f

g

hh

e

i

jk

d

electrophoresis reservoir electrolysis reservoir

Homer

• Electrolysis separated

• Two C4D

• Double thermal marker

R. M. Saito et al., “Ionic Mobility of the Solvated

Proton and Acid-Base Titration in a Four-Compartment

Capillary Electrophoresis System”, Anal. Methods 2

(2010) 164.

Darth Vader

1st C4D2nd C4D

injection side

LOAR3

Electrophoresis 33 (2012) 2650.

Electrophoresis 37 (2016) 1718.

Talanta 185 (2018) 37.

CE-(C4D)2-ESI-MS/MS

Serine Protocol

• Serine Protocol is a light communication protocol for small microcontrollers

• Communication channels: UART, RS232, I2C, USB, etc.

• Some headlines:– The exchanged messages should be easily and

unequivocally interpreted by a simple microcontroller.

– The messages should resist, as originally generated, to all hardware and software protocols used over the network.

– The messages should be as readable and writable as possible by humans.

• https://github.com/claudimir-lago/Serine-Protocol

Darth Vader

injectordetector

HV power source

thermostat

manager master

virtual device

computer

ATmega328ATmega168

Teensy 2.0

processor

Darth Vader

injectordetector

HV power source

thermostat

manager master

virtual device

computer

ATmega328ATmega168

Teensy 2.0

processor

USBI2C

Darth Vader

injector (i)

detector(d)

HV(h)

thermostat(t)

manager(g)

master(m)

virtual device

processor

USBI2C

dispatcher

Darth Vader

injector (i)

detector(d)

HV(h)

thermostat(t)

manager(g)

master(m)

USBI2C

dmG;

“Detector, Master is requesting an ADC reading.”

Darth Vader

injector (i)

detector(d)

HV(h)

thermostat(t)

manager(g)

master(m)

USBI2C

“Master, Detector says t = 31.063 s, C4D0 = 2,153,383, C4D1 = 2,271,005.”

mdgA003106321533832271005;

https://github.com/claudimir-lago/openC4D

USB and I2C interface

https://github.com/claudimir-lago/openC4D

Firmware

The Java frontend

The Java frontend

Perspectives

• New versions of openC4D– Microchip

– Adjustable frequency

– Even smaller and cheaper

– New electronics

• New software– New stuff in Java and Python

– Coupling to Agilent, Sciex…

– Coupling to OpenChrom

• New version of a CE-C4D– 3D-based version for 2019 (?)

– GitHub

Acknowledgements

Institute of ChemistryUniversity of São Paulo

Carlos A. Neves, Carlos Garcia, Eric T. da Costa, Fernando S. Lopes, Guilherme M. Hotta, Ivano G. R. Gutz, José A. Fracassi da Silva, José G. A. Brito-Neto, Kelliton Francisco, Lucas Blanes, Marcelo F. Barros, Norberto A. Guzman, …

Email: claudemi@iq.usp.br