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USP GC Column Designations: G-Phase Codes and Cross-Brand Equivalents

9 minutes ago
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A USP G-number names a coating chemistry, not a product. When a United States Pharmacopeia method says "G43", it is telling you to use a column coated with 6% cyanopropylphenyl / 94% dimethylpolysiloxane. Every major manufacturer sells one - they just call it something different. This page turns the codes into real products.

If you are choosing a column from scratch rather than decoding a method, start with our GC column selection guide.

Key Takeaways

  • G-numbers are for GC. L-numbers are for HPLC. Two separate lists. Do not mix them up.

  • A method naming a G-number lets you use any column with that coating, from any supplier.

  • G27 (5% phenyl) and G43 (6% cyanopropylphenyl) cover most pharmacopoeial GC work.

  • The codes match coating chemistry only. Length, diameter and film thickness are still your choice.

  • USP's own Chromatographic Columns database is the official list. Treat this table as a working shortcut.

Can you provide a PDF list of USP GC columns?

USP publishes the official list itself, in its Chromatographic Columns database at usp.org. Several manufacturers publish PDF quick-reference sheets based on it.

The trouble with PDFs is threefold. They go out of date without telling you. They are awkward to read on a phone at the bench. And each vendor's version naturally pushes its own range to the front.

The table below is the same information as a web page. It lists every current G-designation and, where the chemistry has a direct commercial match, the column each major manufacturer sells against it. Check the USP database before you submit anything regulatory - that is the version of record.

The USP G-phase designations

Every G-number in the current GC classification, with the coating it specifies.

USP code

Coating chemistry

Polarity

G1

Dimethylpolysiloxane oil

Non-polar

G2

Dimethylpolysiloxane gum

Non-polar

G3

50% phenyl, 50% methylpolysiloxane

Mid-polar

G5

70% or more 3-cyanopropylpolysiloxane

Very polar

G6

Trifluoropropylmethylpolysiloxane

Mid-polar

G7

50% 3-cyanopropyl, 50% phenylmethylsilicone

Polar

G8

80% bis(3-cyanopropyl), 20% 3-cyanopropylphenylpolysiloxane

Very polar

G9

Methylvinylpolysiloxane

Non-polar

G16

Polyethylene glycol, molecular weight about 15,000

Polar

G17

75% phenyl, 25% methylpolysiloxane

Mid-polar

G19

25% phenyl, 25% cyanopropylmethylsilicone

Mid-polar

G20

Polyethylene glycol, average molecular weight 380-420

Polar

G25

Polyethylene glycol TPA

Polar

G27

5% phenyl, 95% methylpolysiloxane

Non-polar

G28

25% phenyl, 75% methylpolysiloxane

Mid-polar

G32

20% phenyl, 80% methylpolysiloxane

Mid-polar

G35

Polyethylene glycol and diepoxide esterified with nitroterephthalic acid

Polar

G36

1% vinyl, 5% phenylmethylpolysiloxane

Non-polar

G38

Phase G1 plus a tailing inhibitor

Non-polar

G39

Polyethylene glycol, average molecular weight 1,500

Polar

G42

35% phenyl, 65% dimethylvinylsiloxane

Mid-polar

G43

6% cyanopropylphenyl, 94% dimethylpolysiloxane

Mid-polar

G45

Divinylbenzene-ethylene glycol-dimethylacrylate

Porous polymer

G46

14% cyanopropylphenyl, 86% methylpolysiloxane

Mid-polar

G47

Polyethylene glycol, average molecular weight 8,000

Polar

G48

Highly polar, partly cross-linked cyano-polysiloxane

Very polar

G50

Base-deactivated Carbowax

Polar

G52

Polyethylene glycol, average molecular weight above 20,000

Polar

G53

5% polyalkylfluorobenzylsiloxane

Mid-polar

Descriptions follow the USP classification. Confirm against the current USP Chromatographic Columns database before using in a regulatory submission.

Cross-brand equivalents for the common designations

These are the codes that turn up in most pharmacopoeial GC methods, with the matching column from each manufacturer.

USP code

Agilent

Restek

Phenomenex

Supelco

SGE / Trajan

G1 / G2

DB-1, HP-1

Rtx-1

ZB-1

SPB-1

BP-1

G27

DB-5, HP-5

Rtx-5

ZB-5

SPB-5

BPX5

G36

DB-5ms, HP-5ms

Rtx-5ms

ZB-5ms

SLB-5ms

BPX5

G3

DB-17

Rtx-17

ZB-50

SP-2250

BPX50

G42

DB-35

Rtx-35

Not listed

SPB-35

Not listed

G43

DB-624

Rtx-624

ZB-624

VOCOL

BP-624

G46

DB-1701

Rtx-1701

ZB-1701

SPB-1701

BPX10

G16

DB-WAX, HP-INNOWax

Stabilwax

ZB-WAX

Supelcowax-10

BP-20

G35

DB-FFAP

Stabilwax-DA

ZB-FFAP

Nukol

BP-21

G6

DB-210

Rtx-200

Not listed

SP-2401

Not listed

G48

HP-88

Rt-2560

Not listed

SP-2560

BPX70

These match on coating chemistry only. Length, internal diameter and film thickness are separate choices and must match what your method specifies. "Not listed" means that manufacturer does not publish a column against that code - not that no equivalent exists.

Two things catch people out.

Same coating does not guarantee same result. Bonding, deactivation and manufacturing tolerances differ between suppliers. You still have to demonstrate system suitability on the column you actually use.

Some codes overlap. G1, G2, G9 and G38 are all dimethylpolysiloxane variants, separated by physical form or an additive rather than by different chemistry. A single modern bonded column is often accepted against more than one of them. That acceptance is a judgement you document, not an assumption you make quietly.

What is the GC column G43 used for?

G43 is used for residual solvents and volatile organic compounds. Its 6% cyanopropylphenyl / 94% dimethylpolysiloxane coating is mid-polar, which pulls apart the common Class 1, 2 and 3 residual solvents - methanol, acetonitrile, dichloromethane, benzene and the rest. A non-polar column would let several of them come out together.

This is the coating behind the residual solvent methods most pharmaceutical QC labs run daily. It is also used for purge-and-trap volatile organics in water testing.

G43 columns normally come with a thick film - 1.4 um or 1.8 um - because the compounds are so volatile they need extra coating to be held back at all. The matching columns are the DB-624, Rtx-624, ZB-624, VOCOL and BP-624.

What is an L7 column in the USP classification?

L7 is an HPLC packing, not a GC column. It is octylsilane bonded to porous silica - what most people call a C8 column.

L-numbers belong to the USP's liquid chromatography list. G-numbers belong to the gas chromatography list described above. The two lists share nothing except the naming style.

Classification

Technique

Example

What the code specifies

G-numbers

Gas chromatography

G43 = 6% cyanopropylphenyl

The column coating

L-numbers

Liquid chromatography

L7 = octylsilane on silica

The packing material

Put simply: if your method says L-something, you need an HPLC column. If it says G-something, you need a GC column.

How many types of GC columns are there?

There are two physical types - capillary and packed - and three capillary builds within those: WCOT, PLOT and SCOT. Counting by coating instead, the USP list above recognises 29 distinct GC phases, and the market offers well over a hundred named columns across them.

For most labs the working number is far smaller. A 5% phenyl column, a 6% cyanopropylphenyl column and a PEG column between them cover the large majority of routine pharmacopoeial and environmental work.

If the choice between capillary and packed is the live question, our capillary versus packed comparison covers it properly.

A note on availability

LS Scientific does not stock GC capillary columns. That is why this cross-reference carries no prices and recommends no supplier. The manufacturer names above appear because a USP code has to be turned into a real product to be useful - not as an endorsement or an offer.

LS Scientific does supply the instruments these columns run on, including the Thermo Scientific ISQ7610 single quadrupole GC-MS, and the derivatisation reagents used to bring stubborn compounds into GC range.

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