Visual evaluation of sample

[Jackus]

Hello everybody

I have a question which is not related with chromatography. I know here is a lot of clever people faced daily with analytical problems so someone can help me.

We perform visual evaluation of our products (solid crystalline powder slightly yellow, green or orange). We describe its colour according to analyst sense but I feel it is not correct method. I think the better way is to buy some certified colour chart and compare colour of sample with colour scale.

Have you been faced with this problem? How did you solved it?

I found Pantone colour charts but I'm not sure if it is what I need. It contains too dark and bright colours. I need nuances of white colour only.


Thank you for comments and ideas. Sorry for my version of english language .

[JGK]

Colour is a very subjective thing and one person's description may differ from another.

I used to get my analysts who were booking in materials to comment as either "Matches Supplied Information" or "Does not match Supplied Information" and go from there. It reduce arguments with QA as to colour interpretation.

[oscarBAL]

Hi Jackus; I do not know what it can work in your case. I remember I used to use Pt/Co scale; is a method for for color in waters approved for the Standat Method for Waters and Waste Water examination.

And I remember to use something similar form ASTM for inspection of solvent; it consist in compare your liquidsample againts std of diferent concentration of a Pt/Co complex.
Probably ASTM has a method for solid sdamples too.

[LC_labrat]

I've used Munsell Color Standards for comparison. It's still subjective but most people are usually within 2 shades of the same color. The criteria was something along the lines of not more than Hue 10RP. They have a nearly neutrals fan deck which is shades of white.

[Jackus]

Hello guys.
Thank you for your comments. I think LC_labrat's contribution is usable for our products. Especially Nearly Neutrals Edition seems to be the best choice.

Thank you again.
Have a nice day.

[Bruce Hamilton]

The issue of reporting of visual examination of chemical solids colour is complex. Most people use a simple progression of 5 - 6 descriptors for general research use of light-coloured chemicals.

If a product is going to fail, the obvious solution is to grind it finer to lighten the colour, or adjust the lighting conditions and background.

A simple standard colour chart can be used - as long as everybody agrees. In general, because it's easy to "adjust" sample and conditions for chemicals, most specifications are "report only", rather than pass/fail.

I'd note that the Pt/Co scale is for transparent liquids, and is unsuitable for solids. It's often used as part of the approval process for industrial solvents and water-based fluids. It's defined for industrial solvents and water in ASTM and AWWA.

I've had a customer specify the Pantone system, but it's actually quite expensive to set up correctly, especially if you plan on using it for accepting/rejecting a product, as the colour patches and the costs of standard viewing conditions aren't cheap.

In general, parties should agree on how pass/fail colour limits will be applied, and what colour descriptors to use, and in those circumstances, simple colour charts can be used.

[AICMM]

jackus,

This may sound odd, and I am sticking my neck out here, non-GC and all, but have you thought about a paint spectrometer? I don't know the exact details about these but I have seen them in use a few times and it seems that this might provide the type of information you need.

For what it is worth.... (You know what they say about free advice...)

Best regards.

[Jackus]

jackus,

This may sound odd, and ...

For what it is worth.... (You know what they say about free advice...)

Best regards.

Hello AICMM.

"...about free advice" Yes I know. It is international truth



Thank you for your comment but visual evaluation is only one of several methods we use for determination of product quality (i.e. HPLC purity and assay, OVI, optical rotation, ...) and we don't suppose to spent too much for supplementary analysis as it is.
I think we order the Munsell Book of Color, Nearly Neutrals Edition for quite big money (approx. $700) and it will be sufficient for now. I hope that this approach will be acceptable for most of regulation authorities.

Thank you guys for your time and usefull help. I'm very glad to have chance to discuss my problem on this excellent board.

[Bruce Hamilton]

I think we order the Munsell Book of Color, Nearly Neutrals Edition for quite big money (approx. $700) and it will be sufficient for now. I hope that this approach will be acceptable for most of regulation authorities.

If you choose to use a colour chart to report chemical descriptions, don't be surprised if an auditor starts to question you about durability and control of the colour charts, standardised lighting conditions, standard colour comparison procedures, and how to show long term consistency in the description.

The reason that vague descriptors are normally used is because "Description" is "report only" in many specifications. For example, pharmacopoeia usually note that " Description " is relatively general in nature, and not part of a chemical's product specification.

If your clients or relevant regulators aren't going to use the same system, an auditor or client may consider the more detailed colour chart description is part of the specification, as it would be for paint or paper, and you may be expected to use an appropriate standard protocol for such colour systems.

[BB65]

When producing a precursor to be used later in a multi-step process, I was told of our company's LPG test as a standard of acceptance.

Of course, I had to ask what LPG stands for...

"Looks Pretty Good"

That was defined (for a liquid) as clear and colorless. Never mind that fact that I've successfully used a cloudy precursor with no adverse effects on the final product.

Bill

[Jackus]

I assume that Munsell Book is standardized material. Then we can set validity of the book for 5, 10 or 15 years (expiration date) and then buy new one.
For our clients purposes we can describe colour of the product verbally (slightly yellowish crystalline substance,...). As supplementary information specify exact hue. It can be good tool how to precisely monitor changes during stability testing too.

If your clients or relevant regulators aren't going to use the same system, an auditor or client may consider the more detailed colour chart description is part of the specification, as it would be for paint or paper, and you may be expected to use an appropriate standard protocol for such colour systems.

Bruce, don't try to terrify me but as I know auditors it may easily happen...

We have to recondsider it again.

[Jackus]

When producing a precursor to be used later in a multi-step process, I was told of our company's LPG test as a standard of acceptance.

Of course, I had to ask what LPG stands for...

"Looks Pretty Good"

That was defined (for a liquid) as clear and colorless. Never mind that fact that I've successfully used a cloudy precursor with no adverse effects on the final product.

Bill

Excellent idea. Now which abbreviations to chose?

AWLI ... As We Like It
LPG
DBS ... Disgusting Brown Substance

[Peter Apps]

GEFN - good enough for now
IWHTD - it will have to do
TATHIS - that's all they had in stock

OK - competition time. For the best acronym denoting a meaningless QC test.

Prize: lunch on me at Hilary's coffee shop, Maun, Botswana. Flights and airport taxes not included. Terms and conditions apply.

Fun

Peter

[Ron]

Just out of curiosity, how do auditors and others react to the use of a visual description of the color? I'm asking because many years ago I was given three samples that were supposed to be the same, two have very similar chromatograms while the third was very different. I was asked what was wrong with the third analysis, and when I replied that I knew the third sample was different because it smelled differently than the other two. (Yes, I'm old enough that I was taught to smell chemicals carefully) I got the strangest look, and was asked "what could that possibly tell you?"

[Bruce Hamilton]

Just out of curiosity, how do auditors and others react to the use of a visual description of the color?... I was asked what was wrong with the third analysis, and when I replied that I knew the third sample was different because it smelled differently than the other two (Yes, I'm old enough that I was taught to smell chemicals carefully) I got the strangest look, and was asked "what could that possibly tell you?"

I once tested strychnine for pharmaceutical use ( added to an aphrodisiac formulation ), and the last pharmacopoeia I found with a suitable monograph had a taste ID test ( two small crystals on the tongue - should be very bitter - it was! ).

We used to put taste, smell, texture tests down as "Organoleptic Evaluation" results. I think the term is still used in the food industry.

In my experience, auditors don't worry too much about "report only" descriptors, provided there is evidence that client and provider have previously agreed. Most regulators have the information present, but make it report only.

The EP 5.0 puts the product visual description and some other properties under a subtitle of "Characters" and then notes " The statements under the heading Characters are not to be interpreted in a strict sense and are not requirements ". USP notes of the Description section " the properties are not in themselves standards or tests for purity even though they may indirectly assist in the preliminary evaluation of an article".

We had one client's auditor suggest that we use the Pantone colour system ( probably because it was used in some downstream product packaging specifications ), however their own R & D staff nixed it because they didn't want the expense and hassle of the charts and lighting systems, especially as the Pantone equipment wasn't designed to view bioactive chemical powders.

We also had one auditor who picked up on national terms, eg dairy cream in NZ is more coloured than cream in the USA, so we were asked not to describe colour as "cream" or use any other terms that may match actual products. That seemed rational to me, so was surprised it came from an auditor.

Please keep having fun,

Bruce Hamilton