Wednesday, 13 July 2011


            MBTH REAGENT



IUPAC Name: 3-methyl-2-benzothiazolinone hydrazone.
SYNONYMS: 3-Methyl-2-Benzothiazolinone hydrazone; Beth hydrochloride dehydrate;
2-hydrazono-3-methylbenzothiazoline hydrochloride
3-methylbenzthiazolinone-2(3H)-hydrazone originally introduced as a reagent for aldehyde. Later its use was extended to a variety of organic compound (example: Phenols, aryl amines and different N- and S- heterocyclic compound). The reagent is used in the form of an aqueous solution and the reaction products can be extracted into chloroform, if desired.
 MBTH reacts with aldehyde first to form an azine. Only if there is remaining MBTH, it is oxidized to another species which combines with the azine to form formazan. However, if there is enough aldehyde, all the MBTH is converted to azine and there is no formation of blue color. Thus, by using the limiting agent MBTH to test the amount of aldehyde around the point of interest, then less aldehyde would produce more blue color and more aldehyde would produce less blue color. The end color may be different depending upon the order of addition of the reactants. For example, if an oxidizing agent and MBTH are mixed before adding the aldehyde, a light green to green/blue color results. This method could be used for solution test or for tests on a solid phase such as on nylon membrane. The latter also could be used for measurements with a device or instrument such as a color reader and used in combination with a second aldehyde tester and a pH tester.

With Phenols under reaction condition MBTH loses two electrons and one proton to form the electrophilic intermediate, which has been identified as the active coupling species that undergoes electrophilic substitution with phenol and other groups  to form the colored product.  
Representative Image:

MBTH for aliphatic aldehyde measurement

 Recommended procedure and calibration curve:

 MBTH (1 ml) was transferred into a series of 10-ml volumetric flasks. Aliquot volumes of acyclovir standard solution was added so that the final concentration was in the range of 20-200 mg/ml, then 1 ml of ferric chloride solution was added. This solution was mixed and allowed to stand for 20 min. The volume was adjusted to the mark with water. The absorbance was measured against a reagent blank (which contains all reagents except acyclovir) at 616 nm. The absorbance versus the final concentration was plotted to get the calibration curve, or to derive the regression equation.

Procedure for the tablets
Ten tablets were weighed and pulverized. A weighed portion of the powder equivalent to 25 mg of acyclovir was transferred into 50-ml standard flask and shaken using a sonicator for 15 min. The volume was adjusted to the mark with water, mixed and filtered and then proceeded as above. The nominal content of the tablets was determined either from the calibration curve or using the regression equation.

Acyclovir.jpg                                                Acyclovir                                                                   Coloured Complex

Standard solutions
A stock solution of ceftazidime (1 mg/mL) in water was kept in dark to avoid drug degradation. The working standard solution of ceftazidime containing 100 mg/mL was prepared by dilution. Aqueous solutions (0.2%) of MBTH was pepared.
 Analytical procedures
Aliquots of the working standard solution of the drug (0.2–1.0 mL) (100 mg ml-1) were transferred into 10-mL calibrated flasks. To each aqueous solution of FeCl3 (1.5 mL, 3*10-2 mol L-1), an aqueous solution of MBTH (1.0 mL, 8.6 * 10-3 mol L-1) was added. The solutions were swirled and allowed to stand for 5 min. Then HCL (1.0 mL, 1*10-2 mol L-1) was added and made up to the mark with water. The absorbance was measured at 628 nm against the corresponding reagent blank and calibration graph was constructed.
CEFTAZIDIME                                                                                COMPLEX
Preparation of Standard:
Accurately weighed 100 mg of Ganciclovir was dissolved in 100 ml of distilled water and further diluted with sufficient quantity of distilled water (i.e.1000 μg/mL).

Preparation of Sample:
For the estimation of Ganciclovir 20 capsule were weighed and triturate to fine powder. Capsule powder equivalent to 100mg of Ganciclovir was weighed, dissolved in 40 ml of distilled water and further diluted with sufficient quantity of distilled ethanol. This was then filtered through whatman filter paper no. 41 to get the stock solution of concentration 100 μg/mL. Further dilution was made with distilled ethanol to get the concentration of 100 μg/mL.

Fresh aliquots of Ganciclovir ranging from 0.5 to 2.5 mL (1 µg/mL-1000μg/mL) were transferred into a series of 10 mL volumetric flasks to provide final concentration range of 50 to 250 μg/mL. To each flask 1ml of aqueous Ferric chloride (1%) solution and 1 ml of MBTH reagent (0.5% in distilled water) were added. The solution in each tube were made upto the mark with distilled water. The absorbance of bluish green colored chromogen was measured at 611.6 nm against the blank. The amount of Ganciclovir present in the sample solution was computed from its calibration curve.


Preparation of Standard:
An accurately weighed amount of CFL was dissolved in water and diluted stepwise to obtain working standard solutions of concentration 100µg/ml.
Tablets and capsules
An accurately weighed quantity of tablet or capsule powder equivalent to 50 mg of active ingredient was extracted with distilled water (2 x 20 ml) and filtered. The volume of the combined extract was brought to 50 ml with water. The filtrate (1 mg/ml) was diluted stepwise with distilled water to give the working ranges 100 µg /ml.
 To a series of 25-ml calibrated flasks, containing aliquots of CFL (0.5-3.0 ml, 50 µg/ml), 2.0 ml portions of MBTH solution were added and kept for 2 min at room temperature. Then 2.0 ml of  Ce(IV) solution was added, kept for 15 min and diluted to the mark  with water. The absorbencies were measured within 45 min at 410 nm against a reagent blank. The CFL concentration was read from a calibration graph prepared under identical conditions. REACTION INVOLVED IN THIS METHOD
  1. This method is applicable to the analysis of drinking surface and saline waters, domestic and industrial wastes.
  2. This method is applicable of measuring phenolic material at the 2 mcg/L level, when the colored end product is extracted and concentrated in a solvent phase using phenol as a standard.
  3. Used for the determination of drugs like acyclovir, ganciclovir, ceftazidime and cefradoxil, nicorandil.
  4. Used in the identification of groups such as
Ø  Aldehydes
Ø   Amines
Ø   Phenols
Ø  Aryl Amines
5.       The MBTH procedure was also adapted for use in seawater samples to measure the formaldehyde given off by the marine methanotroph, Methylomonas pelagic
6.       MBTH used for estimation of samples which contain higher concentrations of aldehydes such as disinfectants


1.        Microchimica Acta Journal
2.       Chemical Book
3.       International Journal of ChemTech Research
4.       Eberhardt et al. (1985) Marine Chemistry vol. 17: 199–212

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