Ultraviolet-Visible Spectrophotometry in Pharmaceutical Analysis

S. Gorog

• Publisher: CRC Press
• Year: 2018
• ISBN:
  9781351094320
• Edition: 1
• Topic: Physical Sciences
• Subtopic: Chemistry
• Index: Chemistry

This book provides an overview of the state of the art in pharmaceutical applications of UV-VIS spectroscopy. This book presents the fundamentals for the beginner and, for the expert, discusses both qualitative and quantitative analysis problems. Several chapters focus on the determination of drugs in various matrices, the coupling of chromatographic and spectrophotometric methods, and the problems associated with the use of chemical reactions prior to spectrophotometric measurements. The final chapter provides a survey of the spectrophotometric determination of the main families of drugs, emphasizing the achievements of the last decade.

Chapter 10

SPECTROPHOTOMETRIC ANALYSIS OF SOME IMPORTANT GROUPS OF DRUG COMPOUNDS

A. INTRODUCTION

In this chapter the practical aspects of the spectrophotometric analysis of drug compounds are briefly summarized based on the general aspects described in Chapters 1, 2, 3, 4, 5, 6, 7, 8, 9. Subjectivity could not be entirely excluded when the material of the chapter was arranged under 16 subtitles. In general it was our aim to bring together those compounds in one subchapter the chemistry of which can be treated in a uniform way; in some cases, however, exceptions had to be made (e.g., in the case of vitamins, antibiotics). In these instances the pharmacological effect of the drug substances was the basis of the classification. It has to be stressed that the character of this book, its scope and limitations precluded an exhaustive survey: several minor groups of drugs have been omitted and even inside a given group, no attempt has been made to discuss the spectrophotometric analysis of all drug substances belonging to the group.

The above-mentioned scope and limitation have forced us to make serious omissions in discussing the spectrophotometric analysis of a given group of drug substances, not only from the point of view of the discussed compounds but also regarding the methods used for the analysis, too.

The References of the 16 sections of Chapter 10 include about 1500 literature data. This figure represents a small portion only of the overall number of publications published on the spectrophotometric analysis of drugs from the beginning up to the present time. The modest aim in selecting the above mentioned 1500 papers for review was to give an overview to the reader about the possibilities of spectrophotometry in the analysis of the given drug compounds emphasizing those possibilities which can be regarded as more or less up-to-date even at the present time. Excellent monographs are available containing thorough summaries of the old literature of the spectrophotometric analysis of drugs (e.g., the books of Kakac and Vejdelek, Pesez and Bartos, Snell and Snell, and others which can be found in the References section at the end of Chapter 1 (11, 12, 17, 22, 28)). The spectrophotometric chapters of other, general books on drug analysis also contain useful information on the possibilities of spectrophotometry. Although the majority of the methods described there can be regarded as being obsolete, in some cases good ideas can be obtained from these sources to solve current problems. Because of the above reasons, references are only seldom made in this book to the literature covered by the above listed books: the majority of the references here are from the last 15–20 years, primarily from the last few years. This selflimitation, however, brought about various problems. Namely, in the last twenty years the publication of papers dealing with the spectrophotometric analysis of drugs has shifted from the developed countries to the least developed ones. This means that the majority of such papers are nowadays published in less accessible East European, Indian, Chinese, etc., journals. In order to facilitate the readers’ orientation, the accessibility of the cited literature was considered as an important factor in the selection of the references. However, the proportion of the papers published in not widely known languages and in less widespread journals is rather high in the literature of the recent years and hence despite all efforts, many of such papers are referred to in the subsequent subchapters.

Another problem is that studying the old literature reveals that even the majority of the methods described in the past 15–20 years have their ancestors, and the differences between the “old” and “new” versions of the methods are often not too great. Since the above discussed limitations of this book precluded the presentation of the history of the development of even the most important methods, the reader can get a full picture about the possibilities and limitations of the described methods if the above listed monographs and the literature cited therein are also studied.

An important factor in the selection of the methods presented in this book i.e., the judgment whether a method can be considered to be up-to-date was that the methods which are official in the present pharmacopoeias (especially in the British and U.S. Pharmacopoeias) have been emphasized.

Even with these limitations the selection of the papers referred to in this book was made difficult as a consequence of the “confusion of abundance.” For this reason further limitations have to be applied:

1. With some exceptions only methods for which the chemical background is known have been selected for presentation, i.e., which are based either on natural absorption or on well defined, stoichiometric chemical reactions.

2. Only quantitative analytical methods are discussed: color reactions serving primarily for the identification of drug substances are not discussed.

3. Although the scope of this book includes the determination of drugs in human, animal and plant samples (see 9.H and 9.1 chapters), the main emphasis is still the investigation of bulk drugs and pharmaceutical formulations, and for this reason the proportion of the methods for the analysis of biological samples is less than it is in the literature itself.

4. The spectrophotometric methods associated with chromatographic separation have been discussed in Chapter 5. For this reason thin-layer densitometric methods are not mentioned in this chapter at all and spectrophotometric methods after column or thin-layer chromatographic separation are only included if the spectrophotometric method has interesting features.

5. No attempts have been made, even in the case of the most important methods, to present detailed procedures: for this, the reader is referred to the original publications cited.

The treatment of the spectrophotometric analysis of the individual groups of drugs ...