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MBTH
 3-Methyl-1,2-benzothiazoline hydrazone
hydrochloride
 Introduced in 1910 by BEST HORN
 Used for estimation of no. of drugs having
1) phenols
2) aromatic amines
3) aldehydes
4) poly hydroxy compounds
5) indoles
6) carbazones
7) pheno thiazines

REACTION WITH PHENOLS
 For the estimation of phenols the MBTH reagent is
oxidised initially with an oxidising agent either FeCl3 or
concentrated ammonium sulphate.
 during oxidation MBTH looses 2 electrons and 1 proton.
 The colours obtained by p- unsubstituted phenol is orange
red where as p-substituted phenol gives violet green.
REACTION WITH AMINES
 MBTH reacts with amines in the similar way as it reacts
with phenols and produces an intense blue colour.

REACTION WITH ALDEHYDES
 MBTH gives azine by reacting with aldehydes
 An intermediate is also obtained when MBTH is oxidised.
 Both the azine and intermediate will react together togive a
complex which is of blue in colour
 For oxidisation of MBTH mainly FeCl3 , CAS are used.
 Other oxidising agents used are
1) sodium meta periodate
2) potassium dichromate
3) potassium bromate
4) ammonium sulphate

The rate of reaction depends upon various factors
 1) nature of oxidising agent
 2) concentration of MBTH reagent
 3) pH of the medium
 4) temperature
 5) order of the addition

Advantage
 The colour produced with MBTH reagent for many of
the drugs is blue colour which is very stable one.
Applications
1) Determination of primaquine:
 MBTH is oxidized with oxidising agent and it forms a
complex with primaquine.
 drug + oxidising agent + MBTH reagent pink
colour
 estimated at 510nm.

2) Determination of adrenergic drugs:
 Drug+ MBTH + CAS pink colour 570nm
3) Determination of ascorbic acid:
 Drug + sodium meta periodate HCHO + MBTH
blue colour
650 nm

4) Determination of menadione:
Drug+ MBTH+ methanol boil 2 minutes + FeCl3 1 min
make up with methanol
blue colour
650nm

FC( Folin- Ciocalteau) REAGENT
About the reagent:
 Ortho phosphoric acid in combination with other
acids like periodic, molybdic, vanidic, tungstic,
molybdo tungstic acids will give a complex mixture
known as hetero poly acid mixtures.
 Treatment of such complexes with a reducing agent
results corresponding product which is blue incolour.
 E.g: phospho tungstate reducing agent tungstic blue

 The hetero poly acid mixture will give blue colour with
a number of reducing agents.
1) stannous chloride
2) 1,2,4-amino napthol
3) sulphuric acid
4) ascorbic acid
5) hydrazine
6) thio sulphate
7) thio urea

Method of preparation:
 Dissolve 10g of sodium tungstate and 2.5 g of sodium
molybdate in 70ml of water.
 Add 5ml of 85% phosphoric acid and 10ml conc. HCl
 Reflux for 10min.
 Add 16 g of lethium sulphate, 5 ml of water, add few
drops of bromine.
 The mixture is boiled for 15 minutes to remove excess
bromine.
 The solution is cooled, and diluted to 100ml and
filtered.

Applications
1)Determination tyrosine:
 Phenolic OH group is responsible for production of
colour.
2) Determination of tryptophan:
 indole group is responsible for production of colour
3) Determination of roxithromycin:
 it reduces FC reagent in the presence of sodium
carbonate to form blue coloured chromogen which can
be measured at 760nm.
4) Determination of lansaprazole:
 Drug + FC reagent blue colour 654nm

PDAB
 Para di methyl amino benzaldehyde(ehrlich reagent)
 This is useful for the determination of amines.
 When the reagent reacts with amines azomethane is
formed.
 The azomethane is also known as schiffs base.
 The reaction takes place in the presence of acids.
 The acids used for the maintenance of acidic
conditions are 1) para toluene sulphonic acid
2) tri chloro acetic acid
3) zinc chloride
4) phosphorous oxy chloride

Applications
1)Determination of chlordiazepoxide:
Drug + dil. acid + PDAB reagent + dilute with water
measure absorbance at 450 nm
2) Determinaion of ethyl morphine HCl:
Drug + dil. H2SO4 + PDAB reagent
keep 1 hr at room temp
Measure absorbance at 450 nm.

3) Determination of paracetamol:
Drug + dil. H2SO4 + PDAB reagent
make up with alcohol
measure absorbance at 440nm
4) Determination of ergotamine tartarate:
Drug + tartaric acid + PDAB reagent
keep aside for 30 min
measure absorbance at 650 nm

2,6- DICHLORO QUINONE CHLORIMIDE
 Gibb’s reagent
 Principle:
 This reagent is capable of reacting with phenols which
are unsubstituted in the para position to the phenolic
hydroxil group to form 2,6-di chloro indo phenol
which s blue in colour.

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MBTH FC-PDAB Reagents

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