Spectrophotometer - Determining Copper Concentration

[kadriver]

After allowing the machine to warm up for 45 minutes, I used the 200g/l sample of silver nitrate as the blank and set the transmittence knob to read 100.0 percent.

Then I inserted the cuvette containing the fisrt dilution into the cuvette well of the spectrophotometer and recorded the readings for transmittence and absorbance for this first sample.

I made a mistake with the decimal places on the first two sets of readings on the data sheet - should be 1.075 and 1.025 (not 107.5 and 102.5)

I then did 8 more dilutions and recorded these readings.

Plus, I took a sample of the electrolyte from the silver cell and recorded these readings (labeled "old electrolyte" on the data sheet). I called it "old" because after taking the sample, I disassembled the silver cell and harvested the silver crystals.

Before placing the silver cell back in operation, I took another sample of the electrolyte - this is labeled "new electrolyte" on the data sheet.

Notice that the level of transmittence went up for the "new electrolyte" with a corresponding drop in absorbance. This is because I added 184 grams of fresh clear silver nitrate solution to augment the silver content of the cell's electrolyte before placing it back into operation.

By adding the fresh electrolyte, the copper concentration was reduced, and the spectrophotometer was able to tell the slight difference in the concentration of copper in the cell.

I have not figured out the math yet, but I am way down in the 8/2 range, well below the 60 grams of dissolved copper limit.

I could not tell the difference visually of these samples, but the machine is very sensitive and it can detect slight differences in color that the human eye can't perceive.

kadriver

 

[Woodworker1997]

Hi Kevin,

Is that spectrometer designed to use clynidrical test tubes? In my experience any circular vessel will give wrong data due to refraction. We always used rectangular cuvets for liquids.

If i'm wrong about this please disreguard.

Derek.

 

[kadriver]

Derek,

According to the manual it can use both circular and rectangular. Some of these can only take round, but I looked down in the well and this one has the ability to take both.

The round cuvettes came with the unit. All the video tutorials I have seen use the round cuvettes.

Kadriver

 

[kadriver]

I am thinking I can continue cell operation until I get to these levels from the chart I made:

3/7 (3ml distilled water to 7ml stock solution) Transmittance = 11.2 Absorbance = .945

4/6 (4ml distilled water to 6ml stock solution) Transmittance = 13.6 Absorbance = .865

When a sample drawn from the cell produces readings in this range, then I'll probably replace the electrolyte with freshly made, clear electrolyte.

I used to replace the electrolyte each time I harvested the silver. Now I can use this spectrophotometer to tell me when to replace it.

I guess the next step is to try and determine dissolved palladium content that has accumulated in the cell using the spectronic 20D.

Kadriver

 

[5i1v3r]

I am new to the forum today and joined for silver refining mainly. Stumbling on this I have to be glad I joined. It's almost a coincidence since you just started it up recently. Honestly jealous of your equipment over there. I'm a analytical chem specialist student and will take the time to observe closer your work and respond soon bout my thoughts. Thanks so much.


Why is there such a gap between what we know and what we do.

 

[rickzeien]

I realise this is an old post. I wanted to learn if you found this Electronic 20 useful go PM analysis and if you continued using it for this purpose.

Regards
Rick Zeien

 

[Lou]

It can absolutely be useful. For pure solutions it is very good.

If Kevin willing to follow old school procedures, he can actually spectrophotmetrically determine every precious metal quite reliably. Many of those determinations rely on a very precise balance and chloroform as the solvent for various complexes.

http://www.asianjournalofchemistry.co.in/User/ViewFreeArticle.aspx?ArticleID=22_10_14

 

[4metals]

Kevin's tutorial for a Spec 20 on copper is a valuable tool for an often difficult task of quantifying copper in a cell. I have a few clients who do not have more sophisticated instrumentation, using colorimetry to determine copper.

However for Palladium (as in the PDF posted) it is a lot more work then the selective precipitation of Pd using DMG.

I have yet to see any decent colorimetric methods for Au and Pt. If they were out there I would assume companies like Hach would have methods and powder pillow packaged reagents on the market.

 

[cuchugold]

What was the cost of the Spectrophotometer?. And its precision?. Genuine question. The highest tech device I ever used was a micro-balance, borrowed too. For ICPs I always paid the fees. Not much for me to do these days, except to learn something new.

 

[goldsilverpro]

Since it has the same name, Spectronic 20, as the old B&L, Bausch and Lomb, Spectrophotometer, I assume it's the same unit, with a new company. I haven't used one for probably 50 years. I used it for several different organic brighteners in various plating solutions. I always planned on doing more with it, but it never happened.

 

[James Ball]

I am new to silver refining but found this post recently because I wanted to measure the copper concentration in my silver cell. Turns out Steetips did this awhile ago.

I used the data he generated and to determine a molar absorbtivity coefficient for cupric nitrate at 640 nm. The data shows curvature at high absorbances which is well known especially in the Spec 20 series of spectrometers. This is because so little light makes it through the cell that there is much less to detect. Good spectrometer with sensitive detectors can be linear to an absorbance of 2 which means that 99% of the light has been absorbed by the sample. This is why I used the linear portion of the data to calculate the molar absorbtivity. I wanted to compare these data with known data but I cannot find any data on the web.

The important point is that the data is linear at absorbances less than 0.8. Well done bty,

I used his data to generate some excel plots. Pretty good looking data.

Again, nice work.