Sciencemadness Discussion Board - Which range for a good refractometer?

Which range for a good refractometer?

Keras - 10-10-2021 at 11:08

Hi,

very simple question: what refractive index range should a good refractometer be able to cover? Is 1.3330 to 1.5040 enough, or is it too little?

Thanks!

Mush - 12-10-2021 at 06:28

Quote: Originally posted by Keras

Hi,

very simple question: what refractive index range should a good refractometer be able to cover? Is 1.3330 to 1.5040 enough, or is it too little?

Thanks!

Too little. Go for a std nD1.300 ~ 1.700 one.

Accuracy is more important imo.

Measurement accuracy (nD): ± 0.0002
Refractive index ND Minimum scale value: 0.0005

For hobby purposes I would not spend more than 250-300USD on it.

US $209.38 on Aliexpress
Abbe Refractometer Monochromatic Refractometer Digital Brix Refractometer Laboratory Optical Equipment 2WAJ , fairly good.

Specifications:
Measurement range: nD1.300 ~ 1.700
Measurement accuracy (nD): ± 0.0002
Refractive index ND Minimum scale value: 0.0005
Sugar concentration measurement range: 0 ~ 95%
Sugar concentration Minimum division value: 0.25%
Instrument quality: 2.6kg
Instrument volume: 100 * 200 * 240mm

High end refractometers spec. (price~2000 USD):

SGW®-733

SGW®-731
Measuring range:

Refractive index nD: 1.30000-1.70000
Brix (BX): 0-100%

Refractive index nD: 1.30000-1.70000
Brix (BX): 0-100%
Measuring accuracy:

Refractive index nD: ±0.0002
Dissolved solids Brix: ±0.1%

Refractive index nD: ±0.0002
Dissolved solids Brix: ±0.1%
Measuring resolution:

Refractive index nD: ±0.00001
Dissolved solids Brix: ±0.01%

Refractive index nD: ±0.00001
Dissolved solids Brix: ±0.01%

Temperature
Temperature display range: 0-90℃
Temperature display range: 0-90℃
Thermostatical control range
10-60℃
-----
Temperature control accuracy
±0.1℃
-----
Interface

RS232/USB/U Disk

RS232/USB/U Disk
Display

7 inch color touch screen
7 inch color touch screen
Weight

9kg
9kg
Overall dimensions

500mm×330mm×220mm
500mm×330mm×220mm

This Mettler Toledo RL-2 has a resolution of 0,001 .
It can be read to four decimal places (estimated). Sold for 30 EUR 2nd hand. It does the job rather well to determine the purity of benzyl alcohol.

https://www.youtube.com/watch?v=3CWa7w8zZNM

Using an Abbe Refractometer
https://www.youtube.com/watch?v=nPI-9W9CNGc

$2WAJ Abbe Refractometer index scale.jpg - 71kB$

WYA-2S ABBE refractive index digital refractometer
US $1,100-2,675.40
https://www.aliexpress.com/item/1005003019459423.html?spm=a2...

https://www.youtube.com/watch?v=6II6QChKqOY

Parameters/Model

WYA-2S
Measuring range

Refractive index nD,1.3000-1.7000
Brix,0-100%
Measuring accuracy

Refractive index nD: ±0.0002
Dissolved solids Brix: ±0.1%
Measuring resolution

Refractive index nD: ±0.0001
Dissolved solids Brix: ±0.1%
Temperature

Temperature display range: 0-50℃
Interface

RS232
Display
LCD

Prism
Hard glass

Dimensions/Weight
370x240x470mm/12Kg

[Edited on 12-10-2021 by Mush]

Dr.Bob - 12-10-2021 at 17:19

I think I have a rather nice old one in a box somewhere, if anyone is interested in one in the US. I have not had time to check it out but know that I have one to deal with one day. It is a larger desktop analog type, not a small handheld one. Don;t remember the brand, but it was an older type, likely US or European one.

Keras - 13-10-2021 at 11:18

Quote: Originally posted by Mush

Yuck, Chinese stuff. Shoddy, more likely that not.

Unfortunately I'm in Europe, and Abbe reflectometers seem to cost an arm and a leg, really.

[Edited on 13-10-2021 by Keras]

Mateo_swe - 14-10-2021 at 03:36

I have no experience in D/L or chiral rotation but i have a question.

If i buy an Refractometer, say an 2WAJ Abbe Refractometer 0-95% Brix & 1.300-1.700 ND Lab Monocular.
For example one of these on ebay:
https://www.ebay.com/itm/233440009751?hash=item365a1bde17:g:...

Can i use it to determine the amount of laevorotatory or dextrorotatory of a compound, for example an amino acid?
Lets take an example say Glutamine, it has an Chiral rotation ([α]D) of +6.5º (H2O, c = 2) (wikipedia).
Can i use such refractometer to confirm the actual rotation of a bought glutamine sample?
Or any chemical that have D/L variants?

Dr.Bob - 14-10-2021 at 05:54

No refractometers measure the bending of light, not the rotating of light. You need a polarimeter for that function. They tend to be expensive.

Also, some compounds have a large rotation, so they are easy to determine purity of that way, others have very weak rotations, so it can be very hard to tell their ee from optical rotation. I just made one like that, and the optical rotation is not sufficient to get a real purity determination, although it did confirm the direction (+ or -) of the rotation, and does show a strong enhancement of one isomer, but it is not clear enough to confirm if 99% pure of less. But most compounds are either a 50:50 mixture of isomers or only one isomer.

Mush - 14-10-2021 at 05:59

Quote: Originally posted by Mateo_swe

I have no experience in D/L or chiral rotation but i have a question.

If i buy an Refractometer, say an 2WAJ Abbe Refractometer 0-95% Brix & 1.300-1.700 ND Lab Monocular.
For example one of these on ebay:
https://www.ebay.com/itm/233440009751?hash=item365a1bde17:g:...

Can i use it to determine the amount of laevorotatory or dextrorotatory of a compound, for example an amino acid?
Lets take an example say Glutamine, it has an Chiral rotation ([α]D) of +6.5º (H2O, c = 2) (wikipedia).
Can i use such refractometer to confirm the actual rotation of a bought glutamine sample?
Or any chemical that have D/L variants?

Nope. You need a polarimeter, this:
https://www.aliexpress.com/item/1005001798644891.html?spm=a2...