Význam tématu
Derivatizace polárních funkčních skupin prostřednictvím trimethylsilylimidazolu (TMSI) v kombinaci s pyridinem představuje základní postup pro zlepšení volatility, snížení polarity a zvýšení termální stability látek s aktivním vodíkem. Tento přístup je nezbytný pro spolehlivou plynovou chromatografii (GC) širokého spektra biomolekul, organických kyselin a polyhydroxylovaných struktur, jako jsou cukry, steroidy či aminokyseliny.
Cíle a přehled studie / článku
Cílem dokumentu je popsat vlastnosti, aplikační možnosti a doporučený analytický postup pro použití reagensu TMSI+pyridin (1:4) v derivatizačních reakcích. Specifikace zahrnuje:
- reaktivitu vůči hydroxylovým a karboxylovým skupinám,
- manipulaci s vlhkými vzorky,
- multiderivatizační schémata obsahující hydroxyl a aminoskupiny,
- praktické zásady bezpečného zacházení a skladování.
Použitá metodika a instrumentace
Metodika derivatizace TMSI+pyridinem zahrnuje tyto kroky:
- Příprava reagenčního blanku.
- Vážení 1–10 mg vzorku do 5 mL reakční nádobky.
- Přidání nadbytku TMSI+pyridinu (min. 2:1 mol. poměr k aktivnímu vodíku).
- Inkubační doba při pokojové teplotě nebo při zahřátí až na 70 °C dle potřeby.
- Odběry vzorků pro GC analýzu až do stabilizace produktových piků.
Hlavní výsledky a diskuse
V praxi TMSI+pyridin:
- rychle a plynule silyluje jak snadno, tak i stericky chráněné hydroxyly a karboxyly,
- nevyžaduje extrémní sucho – dokonce derivatizuje cukry v přítomnosti malého množství vody,
- umožňuje vícečetné derivatizace funkčních skupin v jednom kroku,
- poskytuje termostabilní deriváty s dobrou separační schopností.
Přínosy a praktické využití metody
Metoda se osvědčila v:
- biochemickém výzkumu cukrů a steroidů,
- kvalitativní a kvantitativní analýze mastných a organických kyselin,
- farmaceutické kontrole kvality derivátů hormonů a aminokyselin,
- potravinářské a environmentální analytice vyžadující odolné a jemně rozlišené deriváty.
Budoucí trendy a možnosti využití
Očekávaný vývoj zahrnuje:
- automatizované on-line derivatizační systémy napojené na GC–MS,
- návrh ekologičtějších silylačních činidel s nižší toxicitou,
- integrované postupy pro vícefázové vzorky (biologické, živné půdy),
- vylepšené kolony s modulárními stacionárními fázemi pro širší škálu analytů.
Závěr
TMSI+pyridin je vysoce účinný nástroj pro silylaci hydroxyfunkcí a karboxylů v rozmanitých materiálech. Díky své schopnosti pracovat s vlhkými vzorky a poskytovat termální stabilitu derivátů zůstává klíčovým reagensem v pokročilé plynové chromatografii.
Reference
- Blau K., Halket J. Handbook of Derivatives for Chromatography, 2nd ed., John Wiley & Sons, New York, 1993.
- Knapp D.R. Handbook of Analytical Derivatization Reactions, John Wiley & Sons, New York, 1979.
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©1997 Sigma-Aldrich Co.
Product Specification
SUPELCO
T496030A
TMSI+Pyridine
796-0260, 0269
TMSI (N-trimethylsilylimidazole) is the strongest reagent for
hydroxyls. It reacts quickly and smoothly with hindered and
unhindered hydroxyl and carboxyl groups. TMSI+Pyridine is useful
for derivatizing wet sugar samples, hindered hydroxyl groups in
steroids and, in conjunction with fluorinated acylation reagents,
amino acids. For moderately hindered or slowly reacting com-
pounds, pyridine is an especially useful solvent for TMSI because
of its ability to act as an HCl acceptor in silylation reactions
involving organochlorosilanes.
Features/Benefits
TMSI is useful for derivatizing alcohols, hormones, fatty and other
organic acids, phenols, prostaglandins, steroids, sulfonic acids,
and thiols. It derivatizes sugars in the presence of small amounts
of water. It also is useful in multiderivatization schemes containing
hydroxyl and amine groups.
TMSI does not react with amines or amides.
TMS derivatives are thermally stable but more susceptible to
hydrolysis than their parent compounds.
Typical Procedure
This procedure is intended to be a guideline and may be adapted
as necessary to meet the needs of a specific application. Always take
proper safety precautions when using a silylating reagent – consult
MSDS for specific handling information. TMSI+pyridine is ex-
tremely sensitive to moisture and should be handled under dry
conditions.
Prepare a reagent blank (all components, solvents, etc., except
sample), following the same procedure as used for the sample.
1. Weigh 1-10mg of sample into a 5mL reaction vessel. If
appropriate, dissolve sample in solvent (see below). If sample
is in aqueous solution, evaporate to dryness, then use neat or
add solvent.
2. Add excess silylating reagent. TMSI+pyridine (1:4) can be
used at full strength or with a solvent.* In most applications
it is advisable to use an excess of the silylating reagent – at least
a 2:1 molar ratio of TMSI+pyridine to active hydrogen.
3. Allow the mixture to stand until silylation is complete. To
determine when derivatization is complete, analyze aliquots
of the sample at selected time intervals until no further
increase in product peak(s) is observed.
Derivatization times vary widely, depending upon the specific
compound(s) being derivatized. Many compounds are com-
pletely derivatized as soon as they dissolve in the reagent.
Compounds with poor solubility may require warming. A few
compounds will require heating at 70°C for 20-30 minutes.
Under extreme conditions compounds may require heating
for up to 16 hours to drive the reaction to completion.
If derivatization is not complete, the addition of a catalyst, use
of an appropriate solvent, higher temperature, longer time
and/or higher reagent concentration should be evaluated.
Use a glass injection port liner or direct on column injection when
working with silylating reagents. Erratic and irreproducible results
are more common when stainless steel injection ports are used.
TMS derivatives and silylating reagents react with and are sensitive
to active hydrogen atoms. Do not analyze TMSI+pyridine deriva-
tives on stationary phases with these functional groups (e.g.,
polyethylene glycol phases). Silicones are the most useful phases
Properties
TMSI Structure:
CAS Number: 18156-74-6
Molecular
Formula:
(CH
3)3SiNCH=NCH=CH
Formula Weight: 140.26
bp: 93-94°/14mm
Flash Point: 42°F (5°C)
d: 0.956
n
D: 1.4750 at 20°C
Appearance:
clear, colorless to light yellow liquid
moisture sensitive
Pyridine Structure:
CAS Number: 110-86-1
Molecular
Formula: C5H5N
Formula Weight: 79.10
bp: 115-117°C
Flash Point: 68°F (20°C)
d: 0.978
n
D: 1.5100 at 20°C
Appearance:
clear, colorless liquid which has an odor
for TMS derivatives – they combine inertness and stability with
excellent separating characteristics for these derivatives. Nonpolar
silicone phases include SPB™-1 and SPB-5. Normal hydrocarbons
(carbon-hydrogen analytes with single bonds) are separated by
these phases. More polar phases, SPB-1701 and SP-2250, separate
carbon-hydrogen analytes that also contain Br, Cl, F, N, O, P, or S
atoms or groups. A highly polar cyanopropylphenylsiloxane phase,
SP-2330, is useful for separating fatty acid methyl esters or aromat-
ics.
*Nonpolar organic solvents such as hexane, ether, benzene, and toluene are excellent
solvents for the reagent and the reaction products; they do not accelerate the rate
of reaction. Polar solvents such as pyridine, dimethylformamide (DMF), dimethylsul-
foxide (DMSO), tetrahydrofuran (THF), and acetonitrile are more often used because
they can facilitate the reaction. Pyridine is an especially useful solvent because it
can act as an HCl acceptor in silylation reactions involving organochlorosilanes.
For more information, or current prices, contact your nearest Supelco subsidiary listed below. To obtain further contact information, visit our website (www.sigma-aldrich.com), see the Supelco catalog, or contact
Supelco, Bellefonte, PA 16823-0048 USA.
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H
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Mechanism (1,2)
Silylation is the most widely used derivatization procedure for GC
analysis. In silylation, an active hydrogen is replaced by an alkylsilyl
group, most often trimethylsilyl (TMS). Compared to their parent
compounds, silyl derivatives generally are more volatile, less polar,
and more thermally stable.
Silyl derivatives are formed by the displacement of the active
proton in –OH, –COOH, =NH, –NH
2, and –SH groups. The general
reaction for the formation of trialkylsilyl derivatives is shown
above.
The reaction is viewed as a nucleophilic attack upon the silicon
atom of the silyl donor, producing a bimolecular transition state.
The silyl compound leaving group (X) must posses low basicity,
the ability to stabilize a negative charge in the transition state, and
little or no tendency for
π (p-d) back bonding between itself and
the silicon atom.
The ideal silyl compound leaving group (X) must be such that it
is readily lost from the transition state during reaction, but pos-
sesses sufficient chemical stability in combination with the alkyl
silyl group to allow long term storage of the derivatizing agent for
use as required. As the formation of the transition state is reversible,
the derivatization will only proceed to completion if the basicity of
the leaving group X exceeds that of the group it replaces. The ease
of derivatization of various functional groups for a given silyating
agent follows this order: alcohol > phenol > carboxylic acid > amine
> amide. Within this sequence reactivity towards a particular
silylating reagent will also be influenced by steric hindrance, hence
the ease of reactivity for alcohols follows the order: primary >
secondary > tertiary, and for amines: primary > secondary.
Toxicity – Hazards – Storage – Stability
TMSI+pyridine is a flammable, moisture-sensitive liquid. It may
irritate eyes, skin, and/or the respiratory system. Store in a brown
bottle or amber ampul at room temperature, in a dry, well venti-
lated area away from ignition sources. Use only in a well ventilated
area and keep away from ignition sources.
Properly stored, this reagent is stable indefinitely. Recommended
storage conditions for the unopened product are stated on the
label. Moisture will decompose both TMS reagents and deriva-
tives. To exclude moisture, Supelco packages this product under
nitrogen. If you store an opened container or transfer the contents
to another container for later reuse, add desiccant. Before reuse,
validate that your storage conditions adequately protected the
reagent.
References
1.
K. Blau and J. Halket
Handbook of Derivatives for Chromatography (2nd
ed.) John Wiley & Sons, New York, 1993.
2.
D.R. Knapp
Handbook of Analytical Derivatization Reactions John Wiley &
Sons, New York, 1979.
Ordering Information
Description
Cat. No.
TMSI+Pyridine, 1:4
20 ampuls x 1mL
33159
25mL
33037
For information about TMSI reagent, refer to Product Specification T496029.
Microreaction Vessels with Hole Caps and Septa
1mL, pk. of 12
33293
3mL, pk. of 12
33297
5mL, pk. of 12
33299
Books
Handbook of Derivatives for Chromatography
K. Blau and J. Halket
Z246220
Handbook of Analytical Derivatization Reactions
D.R. Knapp
23561
Adapted from Knapp (2).
796-0130
For TMSI,
X = NCH=NCH=CH
For Pyridine,
X = C
5H5N
Contact our Technical Service Department (phone 800-359-3041
or 814-359-3041, FAX 800-359-3044 or 814-359-5468)
for expert answers to your questions.
AWR
