IgG

IgG - main low molecular weight immunoglobulin present in mammalian serum

Molecular mass ~160 kDa; two light chains: 23-25 kDa each; two heavy chains:~53 kDa each
Isoelectric point 6.1-8.5 (7.3 +/-1.2)
Extinction coefficient at 280 nm is 1.36 (Johnstone and Thorpe 1988)
weight of IgG (or other protein) to molar quantity can be converted here

Molecular weight and isoelectric point of various human immunoglobulins can be found here.

Some interesting features of IgG antibodies:

Activate mammalian complements
Bind to Protein A or Protein G

Chosen examples of techniques where IgG antibodies have been successfully used:

to prepare affinity columns and perform affinity purifications
in Western Blot analysis
in ELISA
biotinylated or labelled with fluorescein or other chromophores
in rocket immunoelectrophoresis
in immunoprecipitation
in immunogold labelling
in immunohistochemistry

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How to store IgG antibodies? General considerations

Antibodies present in serum
This is a very stable format for antibody storage. In -20°C or -70°C serum can be usually stored for years. In some specific cases this time can be shorter for anti-peptide antibodies. For very short time periods serum can be stored at + 4°C. In some cases more careful freezing with a first step at -20°C followed by -70°C can be beneficial.

Total IgG fraction (IgG antibodies purified on Protein G matrix)
Generally antibodies in this format are stable. They can be stored in -20°C or -70°C for years. For short-term use some azide to the final concentration of 0.02 % or other preservative.

Affinity purified antibodies (on a specific matrix allowing protein or peptide coupling)
Used to be the most unstable. Care should be taken when considering storing conditions, which should be checked experimentally for every single antibody. Affinity purified antibodies against different epitopes can vary in stability. Some purified abtibodies can precipitate directly after purification is completed if it is performed in the cold, while the activity may still remain. It is difficult to predict storage conditions for a given antibody in advance - there are some alternatives:

-20°C or -80°C
+ 4°C with preservatives like azide (0.02%) or merthiolate
-20°C with glycerol; Final concentration of glycerol 10 or 50%
-20°C with BSA at final concentration of 0.05-0.5%
lyophilization

General recommendations

Larger volumes of affinity purified antibodies are recommended to be filter-sterilised and aliquoted to avoid multiple freezing and thawing. Some antibodies cope well with thawing some might loose their activity.
Storage at protein concentration around 0.5-1 mg/ml.
Do not purify all serum you have at once. Antibodies in serum can be more stable.

Important note: Sodium azide can inhibit horseradish peroxidase enzyme as well as interfere with some coupling methods and biological assays. However, its amount present in a total, purified chicken antibody (IgY) preparation - 0,02 % will be washed away in ELISA or Western Blot when IgY antibody is used as primary antibody at a dilution of at least 1:2000. Alternative agents for preventing bacterial growth of an antibody solution:

Thimerosal at 0,01%
Gentamicin sulfate at 50 ug/ml

Recommended literature about IgG antibodies:

Using Antibodies: A Laboratory Manual, E.Harlow and D.Lane, 1999,
ISBN: 0879695447; Publisher: Cold Spring Harbor Laboratory Press.
Immunochemistry in Practice, A.Johnstone and R.Thorpe, 1988,
ISBN:0-632-01723-6; Publisher: Blackwell Scientific Publications.

Agrisera secondary antibodies which recognize IgG from various species

Agrisera's Antibody Production Guide

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