A Portable Precision Salinometer for Use with Small Samples

Abstract

ABSTUCT A p o r t a b l e s a l i n o m e t e r f o r u s e w i t h small b o t t l e samples i s described. I t i s based on the continuous flow principle used in our precision laboratory salinometer. Bowever, (I) i t i s not thermostatted, i n s t e a d i t has two c e l l s i n t h e same bath and Greasures t h e c o n d u c t i v i t y r a t i o of sample t o s t a n d a r d s e a w a t e r a t t h e same temperature; (2) t h e water is drawn from t h e s a m p l e b o t t l e by s u c t i o n i n s t e a d of d r i v e n by pressure; ( 3 ) t h e r e q u i r e d sample i s l e s s t h a n 1 / 1 0 t h a t of t h e l a b o r a t o r y model so that standard water can be used continuo u s i y a s r e f e r e n c e ; ( 4 ) t h e r e is no contamination of the rest of the sample, alnost the whole of which i s a v a i l a b l e f o r o t h e r m a s u r e s e n t s . The r e a d i n g c i r c u i t o p e r a t e s on 100-200 Hz square wave current and determines the ratio of conductivi t y of t h e measured sample t o s t a n d a r d s e a w a t e r a t t h e same temperature directly. Appropriate trims are provided to compensate fgr cell constant d i f f e r e n c e s and d e v i a t i o n of the standard seawater from exactly 35 O / o o S. IKTRODUCTION The l a b o r a t o r y s a l i n o a t e r i s t h e m a i n s t a y of a great mny ocean systems, either as a c a l i b r a t i o n device or for checking the performance of t h e CTD being used. Also i n many surveys large numbers of b o t t l e s a n p l e s a r e o b t a i n e d and t h e s a l i n i t y n e e d s t o be correlated with other measurements being c a r r i e d o u t on t h e same s a n y l e s . Most e a r l i e r s a l i n o m e t e r s s u f f e r e d from one o r more d e f i c i e n c i e s s u c h as: requirement for a l a r g e b o t t l e s a m p l e , p a r t i c u l a r l y i f t h e l a s t s a m p l e had r a d i c a l l y d i f f e r e n t s a l i n i t y ; r a p i d d r i f t of s t a n d a r d i z a t i o n r e q u i r i n g f r e q u e n t u s e of s t a n d a r d or substandard seawater reference; many and inconv e n i e n t c o r r e c t i o n s ; e r r o r s c a u s e d by bubble f o r m a t i o n , p a r t i c u l a r l y i f t h e s a m p l e w a t e r was c o l d ; r e l a t i v e l y s l o w o p e r a t i o n p a r t i c u l a r l y i f data processing time was included; and inaccurate compensation for temperature. Several years ago a p r e c i s i o n l a b o r a t o r y s a l i n ometer was developed a t NRC[ 11 i n which the use of d i s c r e t e s a s p l e s w i t h r e p e t i t i v e f l u s h i n g was replaced by a continuous flow systen with a h e a t exchanger and masuring cell i n s e r i e s and mounted i n a p r e c i s e l y t h e r m o s t a t t e d s t i r r e d b a t h . T h i s instrument is now commercially available* and has become t h e s t a n d a r d i n s t r u m e n t i n many l a b o r a t o r i e s a l l over the world. I t s chief advantages were a reduced number of c o r r e c t i o n s , e a ...

Automated oxygen titration and salinity determination

“…The Autosal uses a four cell electrode (Dauphinee, 1975) to measure the conductivity ratio of seawater to a known standard within a range of .005 to 42 Practical Salinity units (PSU). The manufacturer claims an accuracy of r 0.003 PSU and a resolution of 0.0002 at 35 PSU.…”