Sounds like weird, right? What is the relationships between AURA, ANTISEPTIC and RED-OX titration???…..he3x….
Actually this story occurred last year when me and my co-workers (Pn. Suryati, lecturer from Padang, Indonesia) did orientation for the new topic of ANALYTICAL-PHARMACEUTICAL CHEMISTRY PRACTICAL (The Most Favorite Subject, isn’t it??? He3x) i.e. RED-OX titration and VISIBLE SPECTROSCOPY. We chosen Determination of Vitamin C using Dichlorophenol Indophenol (DCPIP) method as an experiment for red-ox titration and Determination of Acriflavine using Visible Spectroscopy one as an experiment for spectroscopy.
As we have known that vitamin C (ascorbic acid) is a reducing agent. It is because DIENOL groups will be very easy suffering OXIDATION process, i.e. losing electron (LEO =Losing Electron-à Oxidation) while DCPIP were gaining electron, it undergoes REDUCTION process (GER = Gaining Electron –à Reduction). The dienol groups of vitamin C will be oxidized become diketone by Chlorine (Cl) group of DCPIP via electronic withdrawl effect of Cl. Therefore, the C=N bridge of DCPIP will be hydrogenised (reducing double bond) by vitamin C.
redox reaction of vit.C with DCPIP
In this kind of titration we don’t need an indicator to detect the END POINT of titration since the blue color of DCPIP will play as AUTOINDICATOR. The discoloration of blue DCPIP after wisely dropping of vitamin C will be assigned as the end point of titration. In this titration, the acid pH must be maintained by adding a few drops of strong acid like HCl to avoid the pre-oxidation process by O2 from the air.
dropping vit. c altering the discoloration of blue DCPIP
end point of titration
ACRIFLAVINE is one of drug which is sold as ANTISEPTIC at pharmacy retail. This compound is a reddish brown powder but when it is dissolved in water, it will give yellowish green solution. Later, when I illuminate the acriflavine solution under Na lamp, it produced a green FLUORESCENCE that looks like AURA of sweet angel. Why acriflavine is able producing fluorescent? Please check its molecule structure. Any compounds that is having chromophore (benzene like structure), auxochrome (functional group which is bond to chromophore), and rigid atomic bonding. How can we recognize whether atomic bonding is rigid or not? Rigid character will be occurred when the compound has HETEROCYCLIC RING or non-heterocyclic but having INTRAMOECULAR HYDROGEN BONDING.
dosage form, powder and structure of acriflavine
When the rigid compound being exposed to UV/Visible light, it will absorb energy from there. The Energy absorbed will transfer the electron of compound from the GROUND STATE to the EXCITED state. As we knew that the EXCITED state is unstable condition so the electron tends to turn back to the ground state while emitting the energy absorbed previously. Before grounding back the electrons will get a vibrational relaxation in the lower different step, after that the energy will be emitted as FLUORESCENCE.
energy transition from excited state to the lower level altering the vibration mode & produce fluoresence
After the orientation finished, I still kept in lab while playing around the rest of my reagents. I was just dropping the DCPIP into acriflavine solution, and surprisingly I saw the FLUORESCENCE being disappeared spontaneusly. What an amazing phenomenon I never imagined before. Later, I thought if the fluorescence of acriflavine solution can be LIGHTED OFF by DCPIP, it should be used as internal indicator in Determination of Vitamin C using IODIMETRIC method. The C=N of acriflavine who is responsible to its fluorescence character will be oxidized by I2 after all molecule of vitamin C completely consumed by these oxidizing agent.
vit. C & iodine solution before titration
vit.c added by acriflavine (look at the yellow fluorescence) & iodine solution before titration
acriflavine solution, used as indicator in determination of vit. C using iodimetric method
vit. c after end poit, look at the dissappearing of yellow fluorescence
Iodimetric titration is a redox titration in which analyte will be titrated using Iodine solution (I2) as an oxidizing agent (titrant). So far, starch 10% has been commonly used as indicator in this kind of titration by producing blue color at the end point of titration. Next, I made my own trial and error experiment using acriflavine solution as indicator in determination of vitamin C using Iodimetric method. And DONE!!! The yellow fluorescence of analyte solution suddenly disappeared at the volume of standard solution as exact as THE TRUE VALUE. I made 3 replications (TRIPLO) and gave the sharp Standard Deviation statistically.
I compared the titration using starch 10% as indicator
blue complex of iod-amylum after end point of titration, right side: acriflavine solution
So, what can be learned from that??? Even though Titration is the oldest method of drug determination but it still important to study as the basic concept of analytical chemistry. Nowadays, HPLC has been favorable to be applied in drug determination but without studying TITRATION, it is difficult to understand the sophisticated one. So, this experiment will enrich us about the availability of redox indicators.
I remembered that in my country INDONESIA, one of ACRIFLAVINE derivate, i.e. ETHACRIDINE LACTATE (Popular as RIVANOL solution) also free sold in Pharmacy Retail (APOTEK) as external ANTISEPTIC. So, hey INDONESIAN!! Why don’t you try to explore more about THE AURA of that such ANTISEPTIC (Rivanol) in RED-OX TITRATION????
Rivanol, antiseptic freely sold in Indonesia