The instrument is the part of an electrochemistry bench that gets specified. The cell, the reference electrode and the polishing kit are the parts that decide whether the data is worth keeping.
A chemistry department takes delivery of an electrochemical workstation. The box contains the instrument, a power lead, a USB cable and a software disc. Nobody can run an experiment that week, because there is no cell, no electrodes, no reference and nothing to polish a glassy carbon disc with. The instrument was the line item on the purchase order. Everything that actually touches the chemistry was assumed to come with it.
That is the shape of most first electrochemistry purchases in Bangladesh, and it is worth taking seriously, because a potentiostat is a well made piece of electronics that will outlast the people who ordered it, while the electrodes are consumables with a working life measured in months. Getting the split right at the outset is what makes the bench usable.
Nearly every measurement worth making uses three electrodes, and the reason is simple. If current and potential are both carried by the same two electrodes, the potential you read includes the voltage dropped across the solution and across whatever is happening at the counter electrode. Splitting the roles removes that.
In the CH Instruments accessory range those three roles are three separate part numbers. CHI115 is a platinum wire counter electrode. CHI111 is a silver / silver chloride reference with a porous Teflon tip. CHI104 is a 3 mm diameter glassy carbon working electrode, in the same family as the 2 mm gold, platinum and silver discs catalogued as CHI101, CHI102 and CHI103. None of the three arrives with the instrument.
A four electrode arrangement adds a separate sense lead, so the potential is measured at a point in the solution rather than at the current carrying working electrode. That matters for high current work, and it is why the power instruments in the range use it.
CH Instruments split their range by what the electronics has to do, not by price band, and the split maps closely onto research groups.
| Series | What it is | The work that needs it |
|---|---|---|
| 600F | General purpose potentiostat and galvanostat with a fast function generator and dual channel acquisition | Voltammetry, pulse techniques, corrosion, impedance. The default first instrument |
| 700F | Bipotentiostat and galvanostat controlling two working electrodes | Rotating ring disk work and dual channel detection. Behaves as a 600F when used single channel |
| 800D | Electrochemical detector monitoring current through a flow cell | Liquid chromatography and flow injection detection, down to picoamperes |
| 1000D | Eight channel potentiostat | Eight independent cells, or eight working electrodes sharing one reference and counter |
| 1100D | Power potentiostat and galvanostat, four electrode configuration | Battery testing, electrolysis, electroplating, large area corrosion |
| 1200C | Handheld potentiostat and bipotentiostat, USB powered | Teaching laboratories and field work, with no adapter or battery to carry |
| 1400 | Four channel potentiometer combined with a four channel potentiostat | Reading open circuit sensors such as ion selective electrodes at the same time as amperometric ones |
| 920D | Scanning electrochemical microscope, bipotentiostat plus a three dimensional nanopositioner | Mapping chemical reactivity across a surface rather than averaging over one |
Two observations from installing these. First, a group that thinks it wants eight channels usually wants one channel and a working cell design; the Model 1000D Series Multi-potentiostat earns its place where genuinely parallel experiments are being run to a schedule, not where one experiment is being repeated. Second, the Model 1200C Series Handheld Potentiostat/Bipotentiostat is underrated for teaching. It draws power from the host computer's USB port, so a class of students can run voltammetry on laptops without a bench full of mains adapters, and there is no battery to be flat on the morning of the practical.
For battery groups specifically, the Model 1100D Series Power Potentiostat/Galvanostat is the one that matters, because it delivers large current and high compliance voltage while still resolving current down to tens of picoamperes, and the 1140D adds a galvanostat. A general purpose workstation will characterise a coin cell. It will not cycle a pouch cell.
If a laboratory is going to be careless about one component, it will be this one, and every potential it ever reports will be wrong by an unknown offset. The reference is not an accessory. It is the calibration.
Choose it by the electrolyte, not by habit.
Two housekeeping rules decide how long these last. Top the filling solution up when the level falls, and store the electrode standing in the same solution it is filled with rather than dry in a drawer. A reference allowed to dry out at the junction is scrap, and in a Dhaka laboratory that runs warm through the summer it will dry out faster than the manual assumes.
Where the cell is a flow cell rather than a beaker, the reference changes again. CHI134 is built for the CHI130 thin layer flow cell with a polyacetal body and a VYCOR glass frit junction on a 4 mm tip, and CH Instruments state plainly that it suits mild solvents such as acetonitrile and that the plastic does not stand up to strong solvents such as THF. That is the kind of limit worth reading before an order, not after a cell body has softened.
Solid disc electrodes arrive polished and ready to use, and they stop being ready after the first few experiments. Surface renewal is a routine, not a repair, and CHI120 is the kit that makes it one: 1.0, 0.3 and 0.05 micron MicroPolish powders, glass plates for the pads and three grades of 73 mm disc and pad. The published routine works down through the three grades until the surface is mirror shiny, starting at the 1200 grit Carbimet disc if scratches will not lift. A laboratory without a polishing kit is a laboratory whose voltammograms drift week by week for reasons nobody can name.
Microelectrodes behave differently and are worth understanding before buying. CHI105 and CHI106 are gold at 12.5 and 25 micron diameter, CHI107 and CHI108 platinum at 10 and 25 micron. At those dimensions diffusion becomes radial rather than planar, currents fall to the picoampere range, and ohmic drop largely stops mattering, which is what makes work in resistive and non-aqueous media possible. It is also what makes the measurement noise limited rather than instrument limited, and that leads directly to the next section.
Interdigitated arrays sit somewhere between the two. The gold, platinum and carbon IDA electrodes catalogued as 012125, 012126 and 012127 all carry 65 pairs of generator and collector bands, each 10 micron wide and 2 mm long at a 5 micron interval, so a species oxidised at one set of bands is reduced at the other and cycles continuously between them. That redox cycling is what lifts the signal, and dual mode preserves the sample compared with single mode. They are quartz glass, they need the 011066 cable kit to connect, and they break if handled like a metal disc.
For sensor development and for teaching, screen printed strips remove the polishing problem entirely. SE101 is a 3 mm printed carbon working electrode with a published 0.071 cm2 working area, supplied in packs of 40. TE100 puts working, reference and counter on one strip at the same 3 mm working diameter, with 2 mm and 1.5 mm versions catalogued as TE101 and TE102. They are disposable or reusable, need no polishing and can be chemically modified, which is exactly what a sensor group spends its time doing.
The cell decides how repeatable the geometry is between runs. CHI220 is the simple cell stand in stainless steel and Teflon, supplied with four glass cells, and CH Instruments note that it is not remote controllable. Additional or replacement glass cells are CHI222. Two parts carry an explicit warning worth repeating: CHI221, a cell top with a platinum wire counter electrode already fitted, and CHI223, a Teflon cap, are not replacement parts for the CHI220 stand. That single line has caused more wrong orders than any other in this range.
Specialist cells follow the technique. CHI127 is the EQCM cell, completed by the CHI128 reference and CHI129 platinum wire counter, with a CHI125A gold coated quartz crystal as the working surface, and it exists to support the Model 400C Series Time-resolved Electrochemical Quartz Crystal Microbalance (EQCM), where mass change at the electrode is recorded alongside potential, current and charge. CHI130 is the thin layer flow cell, with glassy carbon, gold and platinum working electrodes as CHI131, CHI132 and CHI133 and a 25 mm spacer as CHI135, supplied four to a pack. CHI140A is the spectroelectrochemical cell kit, built around a thin layer quartz cell with a platinum gauze working electrode, and it ships without a reference: 012167 for aqueous work or 012171 for non-aqueous has to be ordered alongside it.
Below about a nanoampere, the room becomes part of the experiment. CHI200(B) combines a picoamp booster with a Faraday cage; the two halves are also catalogued separately as CHI201 and CHI202. The booster places the preamplifier close to the electrode for lower bias current and noise, its sensitivity matching the 1x10^-12 A/V internal range of the 600 series but at a lower bias current, and it switches itself in automatically at sensitivity scales of 1e-8 A/V and below. It stands down for automatic sensitivity switching techniques such as Tafel plots and bulk electrolysis, and for galvanostatic work. On a bipotentiostat it affects the primary channel only. The cage removes line frequency interference, and CH Instruments recommend adding it wherever a cell is picking up noise from its surroundings.
In Bangladesh that recommendation is closer to mandatory than optional. A bench sharing a distribution board with a fume hood motor, a chiller compressor and a corridor of fluorescent fittings will show 50 Hz pickup on any low current trace, and it will get worse when the building is running on generator. The cage is cheaper than the week spent blaming the potentiostat.
At the other end of the current scale, CHI680D extends measurement to 2 A and stacks with the host instrument. Note the two published limits: a Faraday cage may still be needed above 50 mV per second, and the cell control signals for purge, knock and stir are disabled while the booster is connected. Where a sequence of cells has to run unattended, CHI684 is the multiplexer, switching working, sensing, reference and counter lines across up to 64 cells one at a time and saving data to file after each run.
The same catalogue produces very different sensible orders depending on who is buying.
A battery group needs current before it needs anything else. The Model 1100D Series Power Potentiostat/Galvanostat in its four electrode configuration, a cell arrangement matched to the cell format being studied, and reference electrodes chosen for the electrolyte chemistry rather than for convenience. Where the interest is in mass change during deposition or intercalation, the 400C series with a CHI127 cell and CHI125A crystals adds a measurement that no purely electrical instrument can give.
A corrosion group needs a general purpose workstation with impedance, so a Model 600F Series Potentiostat/Galvanostat, plus a cell that presents a defined and repeatable area of the specimen to the electrolyte, and a reference chosen for the test solution. Tafel work and bulk electrolysis both use automatic sensitivity switching, which is precisely when the picoamp booster stands itself down, so budget for the cage rather than the booster if that is the main technique.
A catalysis group is usually asking where on a surface the activity is, not what the average is. That points at the Model 920D Series Scanning Electrochemical Microscope (SECM), whose modes cover SECM imaging, probe scan and approach curves, surface interrogation SECM and surface patterned conditioning. Budget for tips as consumables: CHI116 and CHI117 are the 10 and 25 micron platinum SECM tips, and they are the part that gets crashed into a substrate by a new user.
A sensor group wants throughput and disposability. Screen printed TE100 strips in packs of 40, a 1200C series handheld unit per bench, and the Model 1400 Series 4-Channel Potentiometer/Potentiostat where open circuit and amperometric sensors have to be read at the same time, as they are in electrode array characterisation and real time cell metabolism work.
That list is not long and it is not expensive relative to the instrument. What it does is make the difference between a workstation that produces data in week one and one that sits under a dust cover until the next financial year. The same argument applies to four point probe work, where the geometry and the correction factor matter more than the meter, as set out in where four point probe measurements go wrong.