Ion Exchange Resin Mesh Size Number to Millimeter (mm) Conversion Table

Chromatography Ion Exchange Resins are often sold based on Mesh Size Number. Here is a table showing the conversion to particle size in microns or millimeters.

Mesh Size / Number	Particle Size (mm)
1250	0.010
625	0.020
550	0.025
400	0.037
325	0.044
270	0.053
230	0.063
200	0.075
170	0.090
140	0.106
120	0.125
100	0.150
80	0.180
70	0.212
60	0.250
50	0.300
45	0.355
40	0.425
35	0.500
30	0.600
25	0.710
20	0.850
18	1.000
16	1.180
14	1.400
12	1.700
10	2.000
8	2.360
6	3.350
4	4.750

Typical Commercial Strengths of Common Acids and Bases Used in HPLC

CHEMICAL NAME	MOLECULAR WEIGHT	MOLES / LITER	GRAMS / LITER	PERCENT by WEIGHT	SPECIFIC GRAVITY
Acetic Acid	60.05	6.27	376	36	1.045
Acetic Acid, Glacial	60.05	17.4	1045	99.5	1.05
Formic Acid	46.02	23.4	1080	90	1.21
Hydrochloric Acid	36.5	11.6	424	36	1.18
Nitric Acid	63.02	15.99	1008	71	1.42
Perchloric Acid	100.5	11.65	1172	70	1.67
Phosphoric Acid	98	14.7	1445	85	1.70
Sulfuric Acid	98.1	18.0	1766	96	1.84
Ammonia (in H20)	17.0	14.8	252	28	0.898
Potassium Hydroxide	56.1	13.5	757	50	1.52
Sodium Hydroxide	40.0	19.1	763	50	1.53

Data obtained from The Merck Index, 11^th edition (1989).

Chromophore, Chromophores, UV Absorbing for HPLC Analysis and Detection

A compound's absorption coefficient relates to its "strength". I find it useful to know which compounds can (and cannot) be easily detected by UV/VIS and a quick analysis of their chemical groups can provide an answer. Please note that the actual measured absorbance maximums will vary depending on the solution that the compound is dissolved in. Beta-Carotene is included as a very interesting structural example because it is composed of long chains of conjugated double bonds (isoprene units) which are cyclised at each end. Here are some other popular examples:

KEY CHROMOPHORE        Absorption MAX (nm)  STRENGTH

acetylide                                    177                           medium
aldehyde (2)                                210                           strong
anthracene                                 252 & 375                strong
azido                                          190                           medium
amine                                         195                           weak
benzene                                     184 & 255                strong
β-carotene                                  450                          medium
disulfide                                      194                          medium
ether                                           185                           weak
ethylene                                     190                           medium
ketone (2)                                   190                           weak
naphthalane                              220 & 286                strong
nitrate                                        270                           weak-strong
nitrite                                         225                           weak
nitro                                           210                           strong
oxime                                         190                           medium
thiol                                            195                           weak
thioketone                                  205                           strong
thioether                                     194                           medium
conjugated ring                        varies                          strong

Notes: 

1. Chromophore conjugation is the process that gives rise to multiple spectral peaks (or shoulders) which are very useful in qualitative identification for HPLC (Spectral fingerprinting). For more information on this topic, I recommend a very well written description of UV/VIS spectroscopy fundamentals at this link.
2. Other interesting examples: Carbonyl (aldehyde) as found in Acetaldehyde; 293nm. Carbonyl (ketone) such as found in Acetone; 271nm.

Data supplied from "Instrumental Methods of Analysis"; Willard, Merritt & Dean; D. Van Nostrand Co. Inc., (1965).