Bio-Rad Chelex 100 Resin User Manual

Chelex®100

and Chelex 20

Chelating Ion

Exchange Resin

Instruction Manual

Bio-Rad Laboratories, 2000 Alfred Nobel Dr., Hercules, CA 94547

LIT200 Rev B

Introduction

Chelex chelating ion exchange resin has unusually
high preference for copper, iron, and other heavy met­als over monovalent cations such as sodium and
potassium. Its selectivity for divalent over monovalent
ions is approximately 5,000 to 1, and it has a very
strong attraction for transition metals, even in highly
concentrated salt solution.

Technical Description

Chelating resin is available as Analytical Grade
Chelex 100 resin, Biotechnology Grade Chelex 100
resin, and Technical Grade Chelex 20 resin. The
Analytical Grade Chelex 100 resin has been exhaus­tively sized, purified, and converted to make it suit­able for accurate, reproducible analytical techniques.
Biotechnology Grade Chelex 100 resin is analytical
grade resin which is certified to contain less than 100
micro-organisms per gram of resin. Technical Grade
Chelex 20 resin is coarse mesh resin useful for large

1

scale clean-up, for example metals from waste waters,

CH2COOH CH2COOH CH2COO- CH2COO-

Ø–CH2–NH+Ø–CH2NH+Ø–CH2–NH

+

Ø–CH2–N

CH2COOH

CH2COO- CH2COO- CH2COO-

pH 2.21 pH 3.99 pH 7.41 pH 12.30

where analytical purity is not a major concern.

Chelex 100 resin and Chelex 20 resin are styrene
divinylbenzene copolymers containing paired imin­odiacetate ions which act as chelating groups in bind­ing polyvalent metal ions. Chelex chelating resin is
classed with the weakly acidic cation exchange resins
by virtue of its carboxylic acid groups, but it differs
from ordinary exchangers because of its high selectiv­ity for metal ions and its much higher bond strength.

Chelex chelating resin is efficiently regenerated
in dilute acid and operates in basic, neutral, and
weakly acidic solutions of pH 4 or higher. At very
low pH, the resin acts as an anion exchanger. Figure 1
shows the zwitterionic forms of the Chelex resin as a
function of pH.

Fig. 1. Change in structure of Chelex resin with
increasing pH.

Selectivity for Heavy Metal Ions

The selectivity of Chelex resin for metal cations
corresponds to that of iminodiacetic acid. A list of
selectivity factors for several divalent cations is given
in Table 1. The selectivity factor is a quantitative mea­sure of the affinity that Chelex resin displays for a par­ticular cation compared to its affinity for a reference
cation, in this case Zn

+2

.

2 3

Table 1. Selectivity for Divalent Cations

Hg
Cu
UO
Ni
Pb
Zn
Co
Cd

+2

1060 Fe

+2

126 Mn

+2

+2

+2

+2

+2

+2

5.70 Ba

4.40 Ca

3.88 Sr

1.00 Mg

0.615 Na

0.390

+2

0.130

+2

0.024

+2

0.016

+2

0.013

+2

0.013

+2

0.009

+1

0.0000001

Actual selectivity values for any particular system
depend on the pH, ionic strength, and the presence of
other complex-forming species. Thus Hg

+2

appears
high in the selectivity series in the presence of nitrate
ions, but low in the series in the presence of chloride
ions, with which it forms a complex. The approximate
order of selectivity for cations in nitrate or chloride
solutions is:

+2

Cu

>>Pb+2>Fe+3>Al+3>Cr+3>Ni+2>Zn+2>Ag

>Co+2>Cd+2>Fe+2>Mn+2>Ba+2>Ca+2>>>Na

4 5

+

+

A selectivity series for cations in an acetate buffer

system at pH 5 is:

+2

>Cu+2>>Fe+2>Ni+2>Pb+2>Mn+2>>

Pd

+2

Ca

= Mg+2>>> Na

+

The selectivity for various cations in aqueous

solutions at pH 4 is:

+2

>Cu+2>Pb+2>>>Ni+2>Zn+2>Cd+2>Co+2>Fe+2>

Hg

+2

Mn

>Ca+2>>>Na

+

The selectivity at pH 9 in the presence of 1.5 M

(NH

Co

+2

is:

4)2SO4

>Ni+2>Cd+2>Cu+2>Zn+2>Ca+2>>>Na

+

Instructions for Use

Chelex resins may be used with either a batch

method or a column method.

Batch Method

The batch method is the addition of resin directly

into the sample followed by stirring.

1. Weigh out about 5 grams of resin for every

100 ml of sample. For larger scale applications or
when a more exact amount of resin is needed, use
the capacity guidelines given below to calculate
the resin volume for the specific sample metal
concentration.

2. Add resin to the sample and stir or shake (gently)

for 1 hour.

3. Filter or decant the sample from the resin.

Column Method

The column method involves pouring a column

with the Chelex resin and passing the sample through

6 7

to achieve the separation. Although large mesh mate­rial (50-100 mesh) allows rapid flow rates and the
ability to process large volumes of solution, resolution
may be sacrificed. On the other hand, small mesh
material (200-400 mesh) can achieve very high resolu­tion and analytical results, but will require longer pro­cess time due to the slow flow rate.

1. Calculate the amount of resin required based on
the expected metal concentration. If the metal
concentration is unknown, begin with 5 grams of
resin for 100 ml of sample, and then optimize the
volumes after obtaining the results.

2. Prepare a buffer with a pH and ionic concentration
that will allow the metal to be ion-exchanged easily
onto the column. Use the information from Table 1,
and the selectivity comparisons of different pH
solutions mentioned above, to optimize the buffer.
For unknown solutions, use deionized water.

3. Slurry the resin in the buffer, and pour the col­umn. Allow several bed volumes to pass through
the column to insure a well packed bed.