CHAPTER ONE
INTRODUCTION
1.1 ASCORBIC ACID
Vitamin C otherwise known as ascorbic
acid is a water soluble vitamin that is naturally present in some foods, added
to others and taken as a dietary supplement. Though it is derived from glucose,
humans and some other primates like guinea pigs, teleost, fishes, bats and
birds cannot synthesize it invivo due to the genetic mutation that prevents
them from synthesizing L-gluconolactone oxidase enzyme, which converts glucose
to ascorbic acid. Vitamin C can be synthesized by some other animals like dogs,
goats, sheep, etc. (Storn, 1972). Vitamin C is an important component of a
healthy diet. Its history revolves around that of the human scurvy disease; a
severe form of vitamin C deficiency, probably the first human sickness to be
recognized as a deficiency disease. Its symptoms includes exhaustion, massive
haemorrhaging of flesh and gums, general weakness and diarrhoea. Presently, it
is rare to be seriously deficient of vitamin C, although evidence suggests that
many people may have low levels of Vitamin C. Smoking cigarettes lowers the
amount of vitamin C in the body. Smokers are therefore at a higher risk of its
deficiency. (retrievded from national institute of health, United States).
Vitamin C is needed for the growth and repair of tissues in all parts of the
body. It helps the body make collagen; an important protein used to make skin,
cartilage, tendons, ligaments and blood vessels. It is also needed for healing
of wounds and maintenance of bones and teeth.(Briggs, 1981).
In recent years, the determination of
ascorbic acid has become an important subject. This is because of the important
role it plays in maintaining human health. (Chen and Sato, 1995).
One of the most intensely studied
areas of vitamin C benefits is in the area of cardiovascular health. Researchers
are finding that vitamin C impacts several aspects of cardiac health, ranging
from blood pressure to endothelia health. As the relationship between oxidative
damage, inflammation and atherosclerosis becomes increasingly investigated by
science, vitamin C is seen as a key protective element against the aspects of
cardiovascular disease. (Forther et al, 2000). Laboratory studies have
confirmed that high dosing with vitamin C is cytotoxic to wide range of cancer
cell lines and that it boots the anti-cancer activities of several common
chemotherapy drugs. In animal models (rats), intra-venous vitamin C has been
shown to significantly decrease growth rates of liver, ovarian, pancreatic and
globlastoma tumors with dosages easily achievable in humans.(Riordan et al,
2005). Vitamin C has also been shown to have an effect against the HIV virus. A
study carried out by Linus Pauling in 1990 clearly showed that the vitamin is
very effective in killing HIV virus by inhibiting its replication invitro.
(Jeffery, 1995). Also in a report published by Harakeh and Jariwalla in
December, 1991, calcium ascorbate and two thiol based reducing agents
(glutathione and N-acetyl-L-cysteine) has the ability of reducing extracellular
HIV reverse transcriptase an vitamin C does. Mega dosing with vitamin C is
known to be able to strengthen the immune system, reduce anxiety and oxidative
stress, it is also important for treating opportunistic infections like viral
pneumonia and candidiasis. (Cathcart, 1981)
For ascorbic acid tablets to be
effective, it must contain active ingredient in conformity to the
specifications in official compendia. There has been a lot of report on fake
drugs worldwide. (WHO, 1999). Drugs play an important role in improving human
health and promoting well-being, however, to produce the desired effect, they
have to be safe, efficacious and of acceptable quality. The use of ineffective
and poor quality drugs will not only endanger therapeutic treatment but also
erode public confidence in a country‘s health program. (WHO,1999). In the past
few decades, many pharmaceutical industries and distribution channels have
flourished throughout the world leading to an increase in the number of
products circulating in national and international markets. At the same time,
the presence of counterfeit and substandard drugs in those markets has
increased substantially as a result of ineffective regulation of the
manufacturing and trading of pharmaceutical products by both exporting and
importing countries. (WHO 1999). Though in pharmacovigilance, it is often
assumed that drug quality and efficacy are assured therefore safety monitoring
does not take into consideration the quality of drugs being monitored. For many
countries where counterfeit drugs have been reported, it is no longer safe to
make this assumption while monitoring safety of medicines, (Akunyili, 2005).
Also, empirical observations have shown in Nigeria that there may be more fake
than genuine drugs in circulation (Osibo, 1998). According to Adenika, (1998)
vitamins are among the most used drugs in Nigeria that have been found to have
70% less of the active ingredient, hence the need for the quantitative
evaluation of drugs, particularly vitamins to ascertain their authenticity.
Due to the importance of ascorbic acid
in humans, qualitative and quantitative evaluation of ascorbic acid has gained
a significant increase in several areas of analytical chemistry such as
pharmaceutical analysis. Several analytical methods have been developed. Most
of these methods are laborious and some require much reagents that may be
either not readily available or are expensive. In a report by Pourmorad et al,
(2003), some of the common methods for ascorbic acid analysis have some
failures regarding manipulative steps, therefore the need to develop a simple,
sensitive, reliable and accurate UV spectrophotometric method for the estimation
of ascorbic acid in tablet dosage forms that is comparable with existing
official method.
1.2. STATEMENT OF RESEARCH PROBLEM. Several methods for ascorbic acid
analysis have been developed, most of these methods are laborious and some
require much reagents that may be either not readily available or are
expensive. In a report by Pourmorad et al, (2003), some of the common
methods for ascorbic acid analysis have some failures regarding manipulative
steps; therefore the neeed to develop a simple sensitive and accurate UV
spectrophotometric method for the estimation of ascorbic acid in tablet dosage
forms that is comparable with existing official method.
1.3 JUSTIFICATION OF THE STUDY Vitamins are among the most used
drugs in Nigeria (Adenika, 1998). Vitamin C has been reported to be of great
value in tackling global health issues of HIV/AIDS and cancer (Cathcart,1981).
In view of the widespread use of vitamin C, several methods were developed for
the determination of vitamin C in pharmaceutical preparation. According to a
report by Pourmorad et al (2003) titrimetric and colorimetric methods
commonly used to assay ascorbic acid have some failures regarding manipulative
steps.
1.4 RESEARCH HYPOTHESIS 1.4.1 Null Mineral
ascorbates and ascorbic acid tablets marketed in Zaria conform to
specifications in official compendia
1.4.2 Alternative hypothesis Mineral ascorbates and ascorbic acid
tablets marketed in Zaria do not conform to specifications in official
compendia
1.5 AIMS AND OBJECTIVES. 1.5.1 Aim To evaluate the ascorbic acid content
of mineral ascorbate and six brands of ascorbic acid tablets
1.5.2 Specific objectives
To develop a new
spectrophotometric method for determination of ascorbic acid
To apply the developed
method along with official methods in the determination of percentage content
of ascorbic acid in mineral ascorbate and six brands of tablet.
To compare the values obtained from
the different methods.