7 Release Rates of Pheromones from Hollow Fibers J. W E A T H E R S T O N and M . A . G O L U B Albany International, Controlled Release Division, Needham Heights, MA 02194
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M. H. BENN University of Calgary, Department of Chemistry, Calgary, Alberta, T 2 N 1N4, Canada
Following a review of methods used to measure the r e l e a s e r a t e of pheromones from hollow f i b e r formulations two newly designed pieces o f appa ratus are d e s c r i b e d . Results o f r e l e a s e r a t e s t u d i e s obtained w i t h the new apparatus are d i s cussed. The increased use o f pheromones t o monitor and/or c o n t r o l i n s e c t pests i s d i r e c t l y r e l a t e d t o the development o f e f f i c a cious c o n t r o l l e d r e l e a s e f o r m u l a t i o n s . In order f o r such f o r mulations t o be e f f e c t i v e i t i s necessary t o know the r a t e o f r e l e a s e o f the pheromone and the l o n g e v i t y o f the f o r m u l a t i o n . I t has been noted (!_, 2) t h a t the r e l e a s e r a t e o f v o l a t i l e mater i a l s appears t o be r e l a t e d t o the method used i n the measurement hence s t u d i e s were undertaken t o improve the methodology by which r e l e a s e r a t e s are measured. Release Rate Methodology Although a more d e t a i l e d overview o f r e l e a s e r a t e methodology has already been presented {3) a b r i e f o u t l i n e o f the methods c u r r e n t l y being used i n t h i s l a b o r a t o r y i s i n order here. Release r a t e methodology can g e n e r a l l y be d i v i d e d i n t o two categ o r i e s : those methods which measure the amount o f m a t e r i a l r e maining i n the r e l e a s e d e v i c e , c a l l e d r e s i d u e a n a l y s i s methods, and those methods which measure the amount o f m a t e r i a l being r e l e a s e d , c a l l e d e f f l u e n t a n a l y s i s methods. 9
Residue A n a l y s i s Methods. Among the methods r o u t i n e l y used f o r residue a n a l y s i s are determination o f weight l o s s , e x t r a c t i o n o f the residue and q u a n t i t a t i o n o f the e x t r a c t by e i t h e r gas chromatography o r l i q u i d s c i n t i l l a t i o n c o u n t i n g , and measurement o f the increase i n v o i d space w i t h i n a f i b e r with time, o r meniscus r e g r e s s i o n method.
0097-6156/ 82/0190-0145$06.00/ 0 © 1982 American Chemical Society
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
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INSECT P H E R O M O N E
TECHNOLOGY
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While each o f these methods has i t s own advantages and d i s advantages a l l o f the r e s i d u e a n a l y s i s methods are more r a p i d than e f f l u e n t a n a l y s i s methods. Weight Loss. Of a l l the methods the weight l o s s method i s the most simple, r e q u i r i n g o n l y the c a l c u l a t i o n o f the d i f f e r e n c e i n weight as a f u n c t i o n o f time. However, the method a l s o has some s e r i o u s disadvantages, the major one being that no q u a l i t a t i v e information can be obtained about the a c t i v e i n g r e d i e n t . For example, changes i n the composition o f the a c t i v e i n g r e d i e n t caused e i t h e r by degradation o f the pheromone or a change i n the r a t i o o f components o f a multicomponent f o r m u l a t i o n would not be detected by t h i s method. In p r a c t i c e , two other disadvantages have a l s o been observed. For very slow r e l e a s i n g components i t has been found t h a t the decrease i n weight over a reasonable time period can be too small to detect on the balance required to accommodate the weight o f the r e l e a s e device i t s e l f . Secondly, adsorption or absorption o f m a t e r i a l s from the atmosphere by the r e l e a s e device i t s e l f can sometimes a c t u a l l y r e s u l t i n a weight gain with time. Meniscus Regression. The meniscus r e g r e s s i o n method i s comparable to the weight l o s s method i n i t s s i m p l i c i t y and r a p i d i t y . The increase i n the l e n g t h o f the void space between the open end o f the hollow f i b e r and the meniscus o f the column o f l i q u i d i s measured p e r i o d i c a l l y using a Wilder Varibeam™ o p t i c a l comparator which has been described by Weatherston e t . al_. (3). Since t h i s instrument can a l s o be used to measure tïïê i n t e r n F l diameter o f the f i b e r , the volume and t h e r e f o r e the weight o f material l o s t can be c a l c u l a t e d as a f u n c t i o n o f time. This method can more e a s i l y be used to detect the v a p o r i z a t i o n o f very slow r e l e a s i n g pheromones than the weight l o s s method s i n c e the o p t i c a l comparator can detect changes i n length o f +0.002 mm which represents l e s s than 0.1 yg f o r most pheromones and f i b e r s . The method i s , however, l i m i t e d to transparent r e l e a s e devices i n which the r e l e a s e o f pheromone can be d i r e c t l y r e l a t e d to a change i n the l e n g t h or width o f the space occupied by the pheromone, and l i k e the weight l o s s method, o f f e r s no q u a l i t a t i v e information concerning the a c t i v e i n g r e d i e n t . E x t r a c t i o n and Q u a n t i f i c a t i o n o f the Residue. When gas chromatography i s used as the method o f q u a n t i f i c a t i o n , e x t r a c t i o n provides the most i n f o r m a t i o n o f any o f the r e s i d u e a n a l y s i s methods s i n c e both q u a l i t a t i v e and q u a n t i t a t i v e i n f o r m a t i o n can be obtained. In t h i s way any changes i n r a t i o s or the presence of degradation products i n the residue can a l s o be detected. This method i s , however, the most time consuming o f the r e s idue a n a l y s i s methods. Other disadvantages are t h a t the method i s d e s t r u c t i v e as once the pheromone has been extracted from the dev i c e , i t i s u s e l e s s . Since examination o f the r e s i d u e at various time periods i s necessary to e s t a b l i s h a r e l e a s e r a t e t h i s necess i t a t e s a l a r g e sample s i z e .
In Insect Pheromone Technology: Chemistry and Applications; Leonhardt, B., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1982.
7.
WEATHERSTON E T A L .
Release Rates of
Pheromones
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Some o f the disadvantages o f each method s e p a r a t e l y can be p a r t i a l l y overcome by employing a combination o f methods. One such combination which has been used t o good advantage i n t h i s l a b o r a t o r y has been t h a t o f meniscus r e g r e s s i o n t o e s t a b l i s h a r e lease r a t e over a s p e c i f i e d period i n combination with e x t r a c t i o n at more widely spaced i n t e r v a l s t o determine the composition o f the r e s i d u e . Major Pisadvantages o f Residue A n a l y s i s. In the foregoing d i s c u s s i o n several advantages and disadvantages o f the various methods have been d i s c u s s e d , but the most severe l i m i t a t i o n o f the r e s i d u e a n a l y s i s methods has not been touched upon. That d i s advantage i s that none o f these methods provide any d i r e c t i n f o r mation about e i t h e r the q u a l i t y o r q u a n t i t y o f the m a t e r i a l a c t u a l l y r e l e a s e d . I f v o l a t i l e degradation products are produced, t h i s information would not be detected nor would the r a t i o o f components a c t u a l l y released be d i r e c t l y measurable. Since the m a t e r i a l released i s the a c t i v e i n g r e d i e n t o f any c o n t r o l l e d r e lease system, t h i s l a c k o f information i s a s e r i o u s drawback t o dependence on residue a n a l y s i s f o r r e l e a s e r a t e determinations. E f f l u e n t A n a l y s i s Methods The e f f l u e n t a n a l y s i s methods commonly employed may be c a t e gorized i n terms o f a i r flow. One method measures the r e l e a s e o f pheromone i n a c l o s e d apparatus i n which e s s e n t i a l l y no a i r move ment occurs w h i l e the second
