By S. Banjeree - A rapid method for estimating moisture in opium samples

Determination of loss on drying or consistency of opium samples using microwave ovens

S. BANERJEE
Manager Research and Development, Government Opium & Alkaloid Works, Neemuch (M.P.), India

A. AGNIHOTRI,
Research Officer

G. DAS,
Research Officer

R. S. CHOUHAN,
Chemist Quality Control

V. HARIT,
Production Manager

Abstract
Introduction
Materials
Methods
Results
Discussion
Conclusion
Acknowledgements
Reference material

ABSTRACT

A rapid method for estimating moisture in opium samples was being looked for to enable rapid payment to Indian opium cultivators. Efforts were made to replace the traditional “hand parakh” system and conventional oven method with a method that would provide rapid, simple, precise and reproducible results. A large number of techniques commonly used for the estimation of moisture in agricultural produce were tried, such as near infra-red spectrometry, low resolution pulsed nuclear magnetic resonance spectrometry, dielectric constant, time domain reflectometry and even instruments based on density measurements. Infra-red moisture balances were also tried. None of these techniques, however, yielded satisfactory results in regard to opium. Finally, the estimation of loss on drying was resorted to through the use of a microwave oven with a turntable facility. Results obtained with the microwave oven were within the acceptable limit, with a maximum standard deviation of only ±0.28, compared with the standard electric oven method.

Introduction

Opium is a cash crop for Indian cultivators. Its collection from the cultivators, its transportation to weigh-in centres and the way in which its value is assessed are being done in the very traditional and age-old manner which has hardly changed since the imperial era. Payment to the cultivators for their opium is made not for the alkaloid content but for the total (unadulterated) solid content. The officer from the Government of India, who is deputed to make the assessment, uses his hand to assess the purity and consistency of the opium. The District Opium Officer, as he is known, dips his hand in the opium brought in containers by the cultivators and “senses” its purity and moisture content. The officer grades the opium on the basis of this assessment. The practice of testing opium by hand is popularly known as the “hand parakh” method.

Based on this assessment and gradation, a 90 per cent payment is made to the cultivator on the spot. The opium is then sent for detailed analysis to the laboratories at the Government Opium and Alkaloid Works. Final payment, made for the consistency of the product, is based on the laboratory results. The drawback in the hand parakh method is that the result will depend solely upon the skill and experience of the officer, with no actual scientific measurement being made. Given the number of cultivators at each weigh-in centre, which ranges between 300 and 400 each day, there has so far been no other way of rapidly determining moisture content. The drawback in determining consistency at the laboratory is the slow speed of disposal of the sample, thereby delaying the final disposal of the cases. In the laboratory, the loss on drying, or determination of consistency, is done in conventional electric ovens. The process adopted in the laboratory for this purpose is tedious, labour-intensive and time-consuming.
For the past two years, an intensive search has been conducted to identify suitable equipment for estimating loss on drying, or consistency of opium samples. During that time, a large number of alternatives have been tried but none met the requirements of rapidity, reproducibility, precision and simplicity. The reason for this was not the lack of availability of methods to the scientific world or consumer market but the inherent nature of opium which did not respond to the tests.

Materials

The materials used were:

(a)Microslides, porcelain plates 25 cm in diameter, rectangular glass plate and spatulae;

(b)BPL microwave oven, model 900-T, with turntable facility and microwave frequency of 2450 MHZ;

(c)Conventional electric oven and opium samples received from the Government Opium and Alkaloid Works, Neemuch.

Methods

Determination of loss on drying (% moisture ) or consistency (% solid content) using a BPL microwave oven

Calibration

The microwave oven used in the present study was calibrated against opium samples of known consistency using the standard electric oven method for optimization of time at the highest energy level. Studies have revealed that keeping the samples for a period of 10 minutes at the “High” or “10” level of energy in the microwave oven, followed by a standing or cooling time in the oven of 10 minutes, gave results comparable to the standard oven method. In the case of the BPL microwave oven where a turntable facility was available, the heating was uniform throughout the surface except in the central portion. Thus a measurement can be made at any point except for that particular area (see table 1).

Determination of consistency of opium samples using a BPL microwave oven

Loss on drying or the consistency of opium samples was determined on 75 mm x 25 mm glass microslides. Washed and cleaned microslides were dried at the High level for a period of three minutes in the BPL microwave oven until constant weight was reached. About 0.2 to 1.0 grams of thoroughly mixed opium sample was weighed accurately on tared microslides in triplicate. The slides were carefully kept on the round turntable of a BPL microwave oven. The space available on the turntable is adequate for 24 slides. Thus eight different samples can be tested in triplicate in one microwave oven at the same time.
Determination of loss on drying was carried out at oven level “High” or “10” for 10 minutes. A further 10 minutes were allowed as standing or cooling time, during which the plates or slides remained in the oven. The microslides were then transferred to a desiccator and weighed on a digital balance. The percentage of loss on drying or of consistency was calculated through the data of weights of the opium sample before and after drying (see table 2).

Conventional method of determining the percentage of loss on drying using an electric oven

One hundred grains (6.47989 grams) of a very accurately weighed opium sample were dried on porcelain plates at 100° C (±5° C) for 5 hours, or until constant weight was reached, in an electric oven. During the process, the mass is intermittently turned to make a free-flowing powder. The samples were done in triplicate.

Use of the “hand parakh” method at field weigh-in centres

In India, the opium produced during each crop season is collected and stored by the cultivators at their homes prior to rendering it to the Government. The Narcotics Control Bureau sets up temporary weigh-in centres at the end of the lancing season in each of the three opium growing states, namely, Madhya Pradesh, Rajasthan and Uttar Pradesh. The number of weigh-in centres varies from state to state depending upon the area of cultivation. At each weigh-in centre, the number of cultivators who submit their produce ranges between 300 and 400 each day. The District Opium Officer appointed by the Government of India makes a provisional assessment of the product by dipping his hand in the opium of each individual cultivator, sensing its consistency and feeling for foreign particles, adulteration etc. Separate laboratory tests for purity are carried out simultaneously in the temporary laboratory set up at the centre. Based on the sensing test, the opium of each individual cultivator is categorized into different classes. Opium of the same class is mixed together and transferred in high density polyethylene (HDPE) containers of 35 kilograms capacity. A maximum of 100 such containers constitute one challan. The challans are sent to the opium factories where the opium is sampled by the laboratory for the final estimation, which is the basis for the final payment to the cultivators. In general, 10 to 16 samples are drawn from each challan. The samples are used for various tests, including the estimation of percentage of solid content or of consistency.

Results

Discussion

Table 3 above shows the results obtained through grading solid content at the weigh-in centres by the hand parakh method, compared with results achieved in the laboratory. Grading by the hand parakh method is classified into eight categories; each grade, class or category has a range of three degrees. Opium with a solid content of less than 58 per cent is termed a “water mix”. Categories start in the ascending order from there. The classification is represented below:

Careful study of table 3 discloses the inherent fault in the existing practice of field determination of moisture. Since the hand parakh method is not a scientific means of estimation, there is a range of variation between the hand parakh mode of measurement and the two oven methods. The table lists samples for which there is no variation between the two measurements and samples which vary as high as five grades. There seems to be no pattern in the variation between the two results, thereby confirming the arbitrariness of the method of field estimation. In general, however, the results of the field assessment are found to be on the higher side and, con-sequently, recoveries must be made from the cultivators. Since estimation by means of electric oven is a very time- consuming process, the final payment to cultivators may not be made for a considerably long time. The reduction in the final stock of opium from the initial assessment may be anywhere between 5 and 35 per cent, and any delay in the final assessment affects the functioning of the opium industry.

Given all the demerits in the existing system, a need to overhaul the system has been strongly felt for some time. Many modern instrumental techniques are being used for the rapid and precise determination of various parameters of commercial importance in grains, wood, cereals, pulses, oil seeds, rubber latex etc. These parameters, which determine the quality and hence commercial value of agricultural produce, are oil content, fat content and moisture. The principles used in these determinations include:

(a)Near infra-red spectrometry [1-3];

(b)Density;

(c)Dielectric constant [4-6];

(d)Low resolution nuclear magnetic spectrometry [7].

Apart from these instrumental techniques, titrimetric methods, such as Karl Fischer, or a distillation method, such as Dean and Stark, are also available for moisture determination. Infra-red moisture balances are also quite popular methods.

Use of these techniques in regard to opium has been tried for the estimation of loss on drying. However, none of the techniques have been found to yield satisfactory results. The reason for such a lack of response to these techniques seems to lie in the very nature of opium.

Opium, a dark viscous latex, forms a surface crust or scum upon exposure to air. This phenomenon brings about a variation in consistency at different points on the surface area and in different layers of the sample. Use of the near infra-red (NIR) technique in such a situation gives a constantly changing loss on drying value which does not stabilize or show any reproducibility or repeatability owing to variation in constant composition.

Use of density as loss on drying parameter does not yield satisfactory results owing to the development of air pockets, temperature sensitivity and a calibration problem arising from variations in the composition of samples.

Use of a simple instrument for the measurement of dielectric constant followed by its correlation to loss on drying again does not work because of similar problems. On the other hand, measurement of dielectric constant through the principle of time domain reflectometry showed slight improvisation. A great deal of research, however, needs to be undertaken before this technique can be adopted.

Preliminary work on the estimation of moisture in opium was carried out using low resolution pulsed nuclear magnetic resonance (NMR). This technique was not pursued further since, besides the exorbitant cost of the instrument, the operation of NMR, which requires a stabilized magnetic field, cannot be accomplished at a weigh-in centre. The supply of electricity is also quite erratic in summer, the opium harvest season. Thus, since estimation by NMR cannot be adopted for field tests, this technique loses its applicability.

The Karl Fischer method [8-9] cannot be applied because of the higher moisture content of opium, whereas the Dean and Stark method [10] is time-consuming and does not fulfil the objectives of this search. Similarly, use of an infra-red moisture analyser has a restricted application since only one sample can be run at one time.

The advantages of using a microwave oven are as follows: rapidity of estimation and economy of time, manpower, energy and money. The time required for drying and cooling in a microwave oven is 20 minutes as opposed to 5 hours in a con-ventional electric oven. The quantity of the sample required is small (02-1.0 grams), compared to the large and specific quantum (100 grains, i.e., 6.47988 grams) required for the conventional method using an electric oven. The energy requirement is also very nominal. For one set of eight samples run in triplicate, 0.2 kilowatts energy is consumed in a microwave oven, compared with a requirement of 8 kilowatts for the same set in an electric oven. Microwave ovens are very cheap in comparison with the other, more sophisticated instruments and are easily affordable at a large number of opium weigh-in centres during the season. The instruments used in NIR and NMR techniques, or the instrument based on time domain reflectometry, cost not less than US$ 28,000 per set in India, whereas the cost of one microwave oven is about US$ 690, comparable to the cost of one electric oven which is about US$ 418. The operation of the microwave oven is simple and does not require highly skilled staff. In the laboratory, this can easily substitute for the electric oven method in the measurement of consistency since the results are reproducible.
The authors trained the staff of the Government Opium and Alkaloid Works, Ghazipur, Uttar Pradesh, India, to utilize the microwave ovens in determining the consistency of opium so that a simultaneous changeover may be brought about throughout the country.

Conclusion

Based on the simplicity, reproducibility and rapidity of the consistency results, the microwave ovens may be successfully used to replace the hand parakh method adopted in the field, as well as the electric ovens used in the laboratories.
Switching over from the hand parakh method to the use of microwave ovens would assist rapid payment to the Indian opium cultivators, who have had to depend on arbitrary measurement through the age-old hand parakh system, and the pro-posed switch over in the laboratories would save a lot of energy, time and manpower.

Acknowledgements

The authors wish to place on record their sincere thanks to Mr. M. Sivaraman, then Revenue Secretary, Ministry of Finance, Government of India, for his encouragement and keen interest in this work. The authors also wish to thank Mr. S. C. Mathur, Chief Controller of Factories and Mr. H. K. Chaturvedi, General Manager, Government Opium and Alkaloid Works, Neemuch, Madhya Pradesh, India, for extensive help in the completion of this project.

Reference material

1. D. A. Keyworth, “Determination of water by near infra-red spectrophotometry”, Talanta, vol. 8 (1961), p. 461.
2. Owen H. Wheeler, “Near infra-red spectra of organic compounds”, Chemical Review, vol. 59 (1959), p. 629.
3. K. Bulis and C.J.H. Schutte, “An infra-red study of the hydrates of sodium carbonate”, Spectrochimica Acta, vol. 17 (1961), p. 917.
4. F. A. Keidel, “Determination of water by direct amperometric measurement”, Analytica Chimica, vol. 31 (1959), p. 2043.
5. Winthrop C. Wolfe, “Differential dielectric apparatus for determining water added to solvent”, Analytica Chimica, vol. 35 (1963), p. 1884.
6. H. W. Van Der Marel, “Rapid determination of soil water by dielectric measurement of dioxane extract”, Soil Science, vol. 87 (1959), p. 105.
7. P. N. Gambhir, D. K. Joshi, P. N. Tiwari and J. Mani, “Quick determination of dry rubber content in natural rubber latex by low resolution pulsed NMR techniques”, J. Natural Rubber Research, vol. 8, No. 3 (1993), p. 208.
8. Frank J. Welcher, Standard Methods of Chemical Analysis (New York, Robert E. Krieger, 1975), vol. 3, part B, p. 1159.
9. R. F. Swensen and D. A. Keyworth, “Determination of water below 10 p.p.m. in benzene and related solvents using colorimetrically generated iodine”, Analytica Chimica, vol. 35 (1963), p. 863.
10. D. Snell Foster and M. Biffen Frank, “Commercial methods of analysis”, New York edition (1972 ), p. 41.