Journal of Hospital Infection
(1985), 6, 3 1 4 0A c o m p a r i s o n of s o d i u m hypochlorite and s o d i u m dichloroisocyanurate products
D. C o a t e s
Public Health Laboratory, Preston Infirmary, M e a d o w Street, Preston, Lancashire P R 1 6 P S
Accepted for publication 15 M a y 1984
Summary: A comparison of commercial sodium hypochlorite (NaOCl) and sodium dichloroisocyanurate (NaDCC) products was made. Solutions of NaOCI and NaDCC containing the same levels of available chlorine (av.C1) exhibited very similar bactericidal activities, despite significant differences in pH. A level of 12-5 ppm av.C1 achieved a > 5 log~0 reduction of
Staphylococ- cus aureus
in 2 rain. A level of 5 ppm av.Cl achieved a > 5 log10 reduction ofPseudomonas aeruginosa
in 2min whilst approximately 100ppm av.C1 achieved the same reduction in the presence of 1% horse serum, and approximately 200 ppm av.Cl in the presence of 2% horse serum, indicating inactivation levels of around 95 and 97.5% respectively. Tablets of NaDCC were stable but solutions were unstable and decomposed much faster than NaOC1 solutions of the same strength. Batch-to-batch variability of different NaOC1 and NaDCC products was investigated; whilst NaDCC products always contained the minimum level of av.C1 specified, concentrated NaOC1 products sometimes did not due to inherent instability.Introduction
H y p o c h l o r i t e s h a v e b e e n u s e d for a l m o s t 200 years. P o t a s s i u m h y p o c h l o r i t e ( E a u de Javelle) was p r e p a r e d b y B e r t h o l l e t in 1789, a n d s o d i u m h y p o c h l o r i t e ( E a u de L a b b a r a q u e ) was u s e d as a d i s i n f e c t a n t in 1820.
' E u s o l ' a n d D a k i n ' s s o l u t i o n w e r e i n t r o d u c e d early this c e n t u r y , a n d ' M i l t o n ' ( R i c h a r d s o n - V i c k s L t d ) was first m a r k e t e d in 1916. I n c o n t r a s t , s o d i u m d i c h l o r o i s o c y a n u r a t e ( N a D C C ) f o r m u l a t i o n s w e r e i n t r o d u c e d r e l a t i v e l y r e c e n t l y . ' K i r b y c h l o r ' ( K i r b y - W a r r i c k P h a r m a c e u t i c a l s L t d ) e f f e r v e s c e n t d i s i n f e c t a n t tablets w e r e i n t r o d u c e d in 1971, a n d s i m i l a r p r o d u c t s in t h e last year.
N a D C C t a b l e t s p o s s e s s s o m e definite a d v a n t a g e s o v e r s o d i u m h y p o c h l o r i t e ( N a O C 1 ) , as well as s o m e t h e o r e t i c a l a d v a n t a g e s a w a i t i n g e x p e r i m e n t a l i n v e s t i g a t i o n . N a D C C t a b l e t s are c o m p a c t a n d stable ( H o f f m a n , D e a t h & C o a t e s , 1981) a n d u s e - d i l u t i o n s c a n be p r e p a r e d safely a n d a c c u r a t e l y . T h e m i c r o b i c i d a l a c t i v i t y o f s o l u t i o n s p r e p a r e d f r o m N a D C C t a b l e t s p o s s i b l y m a y be g r e a t e r t h a n t h a t o f N a O C 1 s o l u t i o n s c o n t a i n i n g t h e s a m e total available c h l o r i n e (av.C1) f o r t w o r e a s o n s . F i r s t , t h e p H o f s o l u t i o n s p r e p a r e d f r o m N a D C C t a b l e t s is m u c h l o w e r t h a n t h a t o f N a O C 1 s o l u t i o n s , a n d a c t i v i t y i n c r e a s e s w i t h acidity. I n s o l u t i o n free av.C1 is p r e s e n t e i t h e r as h y p o c h l o r o u s acid or h y p o c h l o r i t e ion, d e p e n d i n g
0195 6701/85/011)(131 + 10 $/)3.00/0 ~) 1985 'l'he Hc~spital lnfectioi~ Society
31
32 D. Coates
on p H , and it has been postulated (Ortenzio & Stuart, 1959; T r u e m a n , 1971) that h y p o c h l o r o u s acid is the p r e d o m i n a n t l y active species whilst hypochlorite ion has little activity due to its negative charge i m p e d i n g penetration of the microbial cell wall and m e m b r a n e . T h e ratio of h y p o c h l o r o u s acid to hypochlorite ion increases with acidity. T h e author's study ( D e a t h & Coates, 1979) of b u f f e r e d s o d i u m h y p o c h l o r i t e solutions d e m o n s t r a t e d the m a r k e d effect of p H on the activity against Bacillus subtilis spores. Secondly, in N a D C C solutions only a p r o p o r t i o n of the total av.C1 is free whilst the rest is c o m b i n e d ; as free av.Cl is used up so the latter is released. T h i s m e c h a n i s m m a y serve to increase the microbicidal capacity of N a D C C solutions as f o u n d by Bloomfield (1973) and Bloomfield & Miles (1979), and possibly m a y also make t h e m less corrosive, less toxic and less prone to inactivation by organic matter than NaOC1 solutions of the same total av.C1.
T h e p u r p o s e of the present study was to c o m p a r e s o m e well-established N a O C I p r o d u c t s with the n e w e r N a D C C products. T h e parameters investigated were bactericidal activity in the absence and presence of serum, stability of p r o d u c t s and use-dilutions, and b a t c h - t o - b a t c h variability.
M a t e r i a l s a n d m e t h o d s
Disinfectants
T h e disinfectants tested were ' M i l t o n ' which contains 1% NaOC1 and 16"5% NaC1 ( R i c h a r d s o n - V i c k s Ltd), 'Chloros' which contains 10%
NaOC1 (Imperial Chemical Industries Ltd), ' K i r b y c h l o r ' 2 5 r a m , 5 g effervescent disinfectant tablets containing 2"5g of N a D C C ( K i r b y - Warrick Pharmaceuticals Ltd), 'Presept' 25 m m , 5 g disinfectant tablets containing 2"5 g of N a D C C (Surgicos Ltd), and 'Sanichlor' 20 ram, 3"2 g sanitizing tablets containing 55% N a D C C (G. H. W o o d Ltd).
Test organisms
T h e test organisms used were Staphylococcus aureus N C T C 4163 and Pseudomonas aeruginosa N C T C 6749 which were c u l t u r e d overnight at 37~
on C o l u m b i a blood agar plates. S t a n d a r d i z e d suspensions in normal saline containing a p p r o x i m a t e l y 4 • cells per ml were prepared s p e c t r o p h o t o m e t r i c a l l y using a P e r k i n - E l m e r m o d e l 6/20 set at a wavelength of ~. = 450.
Available chlorine assays
Assays of av.C1 in disinfectant solutions were m a d e using a s o d i u m arsenite titration m e t h o d (Coates, 1977).
p H measurements
p H m e a s u r e m e n t s were m a d e using either a D i g i - S e n s e digital p H m e t e r
C o m p a r i s o n of hypochlorite and d i c h l o r o i s o c y a n u r a t e 33 ( C o l e - P a r m e r I n s t r u m e n t C o m p a n y L t d ) or a P W 9409 digital p H m e t e r (Philips Ltd).
Bactericidal studies
E x p e r i m e n t s were carried out in an agitating water bath t h e r m o s t a t i c a l l y controlled at 25~176 F o r each e x p e r i m e n t a stock solution of disinfectant in sterile distilled water containing exactly 1000 p p m av.Cl was prepared and assayed, from which test dilutions were prepared. F o r experiments with serum, inactivated horse serum 5 (Wellcome L t d ) was diluted in saline. A standardized suspension of test o r g a n i s m s was prepared as previously described. Reagents were pipetted into universal bottles and placed in the w a t e r - b a t h to equilibrate. S u b s e q u e n t l y , test m i x t u r e s containing 5 ml of disinfectant, 2 ml of saline, 1 ml of s e r u m or saline and 2 ml of test-organism suspension were prepared and vortex stirred. F o r experiments with s e r u m the test-organisms were added exactly 1 m i n after adding serum to the disinfectant. T w o rnl samples were taken after intervals of 2, 10 and 3 0 m i n and added to 8 m l of p r e - w a r m e d 0"6% s o d i u m thiosulphate inactivator broth. F o u r serial deci-dilutions in saline were prepared 0"1 ml samples into 0.9 ml of saline in 3 x 0"5 inch tubes). Seven drops f r o m each dilution and the inactivator b r o t h were pipetted on to well- dried C o l u m b i a blood agar plates using 50-dropper pipettes. T h e plates were incubated at 37~ for 24 48 h and colony counts made. C o m p a r i s o n of average drop counts obtained in the presence of disinfectant with control counts (saline s u b s t i t u t e d for disinfectant) enabled log10 reductions in c o u n t to be calculated.
Stability testing of N a D C C tablets
' K i r b y c h l o r ' tablets in their plastic containers were placed in a refrigerator m a i n t a i n e d at 6~ and incubators at 28 and 42~ At m o n t h l y intervals tablets were r e m o v e d a n d dissolved in 500 ml of deionized water. T h e av.C1 content of solutions was assayed and the p H measured.
Stability testing of solutions of N a O C l and N a D C C
One litre volumes of solutions were prepared and placed in plastic sterile water for irrigation ( T r a v e n o l L a b o r a t o r i e s L t d ) bottles which were incubated in a w a t e r - b a t h thermostatically controlled at 25~176 At regular intervals samples were taken and the av.C1 assayed and the p H measured.
Testing the variability of different N a O C l batches and N a D C C tablets
T h e variability of different batches of ' M i l t o n ' and ' C h l o r o s ' was tested by sampling new deliveries of these p r o d u c t s into the hospital and assaying the av.C1 c o n t e n t and m e a s u r i n g the p H . T h e variability of different batches of ' K i r b y c h l o r ' , 'Presept' and 'Sanichlor' was tested by r a n d o m l y selecting34 D . C o a t e s
several t a b l e t s f r o m a c o n t a i n e r , d i s s o l v i n g e a c h o f t h e m in 5 0 0 m l o f d e i o n i z e d w a t e r , a n d a s s a y i n g t h e av.C1 c o n t e n t a n d m e a s u r i n g t h e p H o f the s o l u t i o n s .
R e s u l t s
B a c t e r i c i d a l studies
T h e a c t i v i t y o f d i l u t e s o l u t i o n s o f ' C h l o r o s ' , ' M i l t o n ' a n d ' K i r b y c h l o r ' a g a i n s t S t a p h . aureus is s h o w n in T a b l e I. T h e t h r e e p r o d u c t s w e r e c o m p a r a b l e in so far as a c o n c e n t r a t i o n o f 1-0 p p m av.C1 e x h i b i t e d n e g l i g i b l e a c t i v i t y a f t e r 30 r a i n w h i l s t 12.5 p p m av.C1 a c h i e v e d a > 5 log10 r e d u c t i o n in 2 rain. A t i n t e r m e d i a t e c o n c e n t r a t i o n s ' M i l t o n ' a c h i e v e d t h e b e s t results, f o l l o w e d b y ' C h l o r o s ' a n d t h e n ' K i r b y c h l o r ' . T h e p H of r e a c t i o n m i x t u r e s was h i g h e s t f o r ' M i l t o n ' , i n t e r m e d i a t e f o r ' C h l o r o s ' a n d l o w e s t f o r ' K i r b y c h l o r ' . T h u s t h e r e s u l t s w e r e in r e v e r s e o r d e r o f t h a t e x p e c t e d f r o m the h y p o t h e s i s t h a t a c t i v i t y is p r i m a r i l y d u e to the c o n c e n t r a t i o n o f h y p o c h l o r o u s a c i d p r e s e n t .
T h e a c t i v i t y o f d i l u t e s o l u t i o n s o f ' C h l o r o s ' , ' M i l t o n ' , ' K i r b y c h l o r ' , ' P r e s e p t ' a n d ' S a n i c h l o r ' a g a i n s t Ps. aeruginosa is s h o w n in T a b l e I I . C o m p a r i s o n w i t h T a b l e I s h o w s t h a t Ps. aeruginosa N C T C 6749 was m o r e sensitive to h y p o c h l o r i t e t h a n S t a p h . aureus N C T C 4163. T h e five p r o d u c t s w e r e c o m p a r a b l e in so far as a c o n c e n t r a t i o n o f 1"0 p p m av.C1 e x h i b i t e d n o a c t i v i t y a f t e r 30 r a i n w h i l s t 5-0 p p m av.C1 a c h i e v e d a > 5 log10 r e d u c t i o n in 2 rain. A t 2"5 p p m av.C1, t h e o v e r a l l r e s u l t s o b t a i n e d for N a O C 1 p r o d u c t s
Table I. Bactericidal activity of aqueous solutions of 'Chloros', 'Milton' and 'Kirbychlor"
against Stapb. aureus N C T C 4163 at 25~
Log,, reductions in:
Disinfectant pH av.Cl (ppm) 2 min 10 min 30 rain
7.1 1.0 0 0 < I
7.5 2.5 <1 <1 <1
'Chloros' 7"9 5"0 < 1 1 2-3
7'9 7"5 3 4 5 >5
7"9 10'0 3-4 >5 >5
8'0 12.5 >5 >5 >5
8'0 1 "0 0 0 0
8"0 2'5 <1 <1 <1
'Milton' 8.0 5"0 2-3 5 > 5
8' 1 7-5 4-5 5 > 5
8"1 10.0 >5 >5 >5
8'1 12.5 >5 >5 >5
6"7 1 '0 0 0 < 1
6'6 2.5 0 <1 <1
'Kirbychlor' 6.5 5"0 < 1 < 1 < 1
6.4 7-5 2-3 3-4 4-5
6"2 10.0 3-4 > 5 > 5
6"1 12.5 >5 >5 >5
Comparison of hypochlorite and diehloroisocyanurate 35 Table I I. Bactericidal activity of aqueous solutions of'Chloros', ' Milton', 'Kirbychlor', 'Presept'
and 'Sanichlor' against Ps. aeruginosa N C T C 6749 at 25~
Log10 reductions in:
Disinfectant pH av.Cl (ppm) 2 min 10 rain 30 rain
7.2 1"0 0 0 0
'Chloros' 7-5 2'5 3 4 > 5 > 5
7.9 5"0 >5 >5 >5
7.1 1'0 0 0 0
'Milton' 7.3 2"5 0 0 0
7.8 5"0 >5 >5 >5
6"5 1 "0 0 0 0
'Kirbychlor' 6"3 2"5 0 0 0
6.1 5-0 >5 >5 >5
6.6 1 "0 0 0 0
'Presept' 6.6 2.5 3-4 4-5 > 5
6.6 5.0 >5 >5 >5
6.2 1-0 0 0 0
'Sanichlor' 6.3 2.5 > 5 > 5 > 5
6.3 5.0 >5 >5 >5
w e r e c o m p a r a b l e to t h o s e f o r N a D C C p r o d u c t s , d e s p i t e t h e l o w e r p H o f r e a c t i o n m i x t u r e s o f t h e latter.
T h e a c t i v i t y of m o r e c o n c e n t r a t e d s o l u t i o n s o f ' M i l t o n ' a n d ' P r e s e p t ' a g a i n s t Ps. aeruginosa in t h e p r e s e n c e o f h o r s e s e r u m is s h o w n in T a b l e I I I.
I n the p r e s e n c e o f 1 % s e r u m , s o l u t i o n s o f ' M i l t o n ' c o n t a i n i n g 1 0 0 p p m av.C1 a n d ' P r e s e p t ' c o n t a i n i n g 90 p p m av.C1 a c h i e v e d > 5 log10 r e d u c t i o n s o f Ps. aeruginosa in 2 rain. T h u s ' P r e s e p t ' was f o u n d to be s l i g h t l y m o r e active. H o w e v e r , in the p r e s e n c e o f 2 % s e r u m , s o l u t i o n s o f ' M i l t o n ' c o n t a i n i n g 180 p p m av.C1 a n d ' P r e s e p t ' c o n t a i n i n g 200 p p m av.C1 a c h i e v e d
> 5 log10 r e d u c t i o n s in 2 m i n . T h u s ' M i l t o n ' was f o u n d to be s l i g h t l y m o r e active. O n b a l a n c e , it a p p e a r s t h a t t h e a c t i v i t y of t h e t w o d i f f e r e n t d i s i n f e c t a n t s was similar, d e s p i t e t h e s i g n i f i c a n t d i f f e r e n c e s in p H o f t h e i r r e a c t i o n m i x t u r e s . C o m p a r i s o n o f T a b l e I I a n d I I I s h o w s t h a t a level o f 5 p p m av.C1 in t h e a b s e n c e of s e r u m is e q u i v a l e n t to a level of a r o u n d 100 p p m av.C1 in t h e p r e s e n c e o f 1% s e r u m , a n d a r o u n d 200 p p m av.C1 in t h e p r e s e n c e o f 2 % s e r u m . T h i s data i n d i c a t e s t h a t in t h e p r e s e n c e o f 1 % s e r u m a r o u n d 9 5 % o f av.C1 is i n a c t i v a t e d , a n d in t h e p r e s e n c e o f 2 % s e r u m a r o u n d 97"5% of av.C1 is i n a c t i v a t e d .
S t a b i l i t y of N a D C C tablets
' K i r b y c h l o r ' t a b l e t s s t o r e d f o r 9 m o n t h s at 6~ 28~ a n d 42~ e x h i b i t e d n o visible c h a n g e s . T h e av.C1 c o n t e n t o f 30 s o l u t i o n s p r e p a r e d f r o m t a b l e t s o v e r this p e r i o d r a n g e d f r o m 3 0 4 0 - 3 5 4 0 p p m av.C1 w i t h a m e a n o f 3258 p p m av.C1. T h e p H o f all t h e s o l u t i o n s w a s p H 5-5. C o m p a r i s o n w i t h
36 D . C o a t e s
Table III. Bactericidal activity of aqueous solutions of 'Milton" and 'Presept' against Ps.
aeruginosa N C T C 6749 in the presence of horse serum, at 25~
Serum log10 reductions in:
Disinfectant concentration pH av.C1 (ppm) 2 min 10 min 30 min
9-0 60 0 0 0
1% 9.1 75 0 0 <1
9"2 90 3 4--5 4-5
'Milton' 8.9 100 > 5 > 5 > 5
8-9 120 0 0 0
9.0 135 < 1 1-2 4-5
2% 9.0 150 4--5 5 > 5
9.2 165 4-5 5 > 5
9.4 180 > 5 > 5 > 5
6.8 50 0 0 < 1
1% 6.7 60 0 0 < 1
6.6 75 < 1 4-5 > 5
'Presept' 6.7 90 > 5 > 5 > 5
6"5 135 0 0 1 2
6"5 150 0 0 2
2% 6.4 165 1 4 >5
6.4 180 4 >5 >5
6'3 200 > 5 > 5 > 5
t h e d a t a s h o w n in T a b l e V I I s h o w s t h a t n o d e t e c t a b l e d e c o m p o s i t i o n o f t a b l e t s o c c u r r e d o v e r t h e s t o r a g e p e r i o d .
S t a b i l i t y o f N a O C l a n d N a D C C solutions
T h e relative s t a b i l i t y o f s o l u t i o n s o f ' M i l t o n ' , ' C h l o r o s ' a n d ' K i r b y c h l o r ' all c o n t a i n i n g initially a r o u n d 11,000 p p m av.C1 is s h o w n in F i g u r e 1. It is a p p a r e n t t h a t ' M i l t o n ' is m u c h m o r e stable t h a n ' C h l o r o s ' w h i c h in t u r n is v e r y m u c h m o r e stable t h a n ' K i r b y c h l o r ' . ' M i l t o n ' still c o n t a i n e d 6720 p p m av.C1 a f t e r a y e a r w h i l s t ' C h l o r o s ' c o n t a i n e d 1980 p p m av.C1 a f t e r a year;
' K i r b y c h l o r ' lost all its av.C1 in 12 weeks. T h e t i m e t a k e n for s o l u t i o n s to lose 5 0 % o f t h e initial av.C1 was a p p r o x i m a t e l y 78 weeks f o r ' M i l t o n ' ( T a b l e IV), 16 w e e k s f o r ' C h l o r o s ' , a n d j u s t 2 - 3 w e e k s for ' K i r b y c h l o r ' . T h e p H o f all t h r e e p r o d u c t s d r o p p e d d u r i n g s t o r a g e . T h a t o f ' M i l t o n ' d r o p p e d f r o m p H 11"7 to 11"4 o v e r 78 weeks, t h a t o f ' C h l o r o s ' f r o m p i l l 1"7 to 10"4 o v e r 52 weeks, a n d t h a t o f ' K i r b y c h l o r ' f r o m p H 5"5 to 4"9 o v e r 12 weeks.
T h e s t a b i l i t y o f n e a t ' M i l t o n ' a n d t w o d i l u t i o n s is s h o w n in T a b l e I V . A 1 in 20 d i l u t i o n ( a p p r o x i m a t e l y 500 p p m av.C1) is i s o t o n i c w i t h b o d y fluids a n d is t h e u s u a l d i l u t i o n f o r t o p i c a l a n t i s e p t i c p u r p o s e s . A 1 in 80 d i l u t i o n is t h a t r e c o m m e n d e d f o r i m m e r s i o n o f b a b i e s ' b o t t l e s a n d teats. I t c a n be seen t h a t a l t h o u g h n e a t ' M i l t o n ' was r e l a t i v e l y stable, the t w o d i l u t i o n s w e r e m u c h less stable, a n d d e c o m p o s i t i o n was a c c o m p a n i e d b y a d e c r e a s e in p H .
T h e s t a b i l i t y o f s o l u t i o n s o f d i f f e r e n t N a D C C p r o d u c t s is s h o w n in T a b l e s V a n d V I . T h r e e d i l u t i o n s o f ' K i r b y c h l o r ' w e r e t e s t e d ( T a b l e V). All p r o v e d to be v e r y u n s t a b l e , a n d d e c o m p o s i t i o n was a c c o m p a n i e d b y a
C o m p a r i s o n o f hypochlorite and d i c h l o r o i s o c y a n u r a t e 37 12
9
•
8
O .
7 "
o 6
Jzz o
2 2 4
5 2
8 16 24 32 4 0 4 8
Storage time (weeks)
Figure 1. Loss of available chlorine from 'Milton' and aqueous solutions of 'Chloros' and 'Kirbychlor' stored in a water-bath at 25~ A, 'Milton'; I , 'Chloros'; O, 'Kirbychlor'.
Table IV. S t a b i l i t y o f aqueous solutions o f " M i l t o n ' in a w a t e r - b a t h at 2 5 ~
Weeks
Dilution
Neat 1 in 20 1 in 80
av.C1 (ppm) pH av.C1 (ppm) pH av.C1 (ppm) pH
0 11,500 11.7 580 10"6 160 9.8
2 11,140 11-7 480 10.4 160 9.4
4 10,880 11.6 480 10.4 120 9,2
6 10,780 11.6 420 10.2 120 8'8
11 10,460 11.6 420 10.2 120 8"7
16 10,120 11.6 400 9"8 120 8.5
22 9820 11-6 310 9.8 120 8-4
32 9200 11 "6 200 9"6 80 8'0
42 7900 11.6 120 9"2 ~< 40 7.8
52 6720 11.6 ~<40 8.6
78 5620 11.4
d e c r e a s e in p H . T h e relative stability o f ' P r e s e p t ' a n d ' S a n i c h l o r ' s o l u t i o n s c o n t a i n i n g initially a r o u n d 10,000 p p m av.C1 is s h o w n in T a b l e V I . T h e r e s u l t s o b t a i n e d f o r ' P r e s e p t ' are s i m i l a r to t h o s e o b t a i n e d f o r ' K i r b y c h l o r ' ( F i g u r e 1), b u t differ f r o m t h o s e f o r ' S a n i c h l o r ' in t w o r e s p e c t s . F i r s t , t h e rate o f d e c o m p o s i t i o n o f t h e ' S a n i c h l o r ' s o l u t i o n was m u c h faster t h a n t h a t o f t h e ' P r e s e p t ' s o l u t i o n d u r i n g t h e first w e e k after p r e p a r a t i o n , b u t t h e n s l o w e d d o w n c o n s i d e r a b l y so t h a t available c h l o r i n e was still p r e s e n t in t h e
38 D. C o a t e s
Table V. Stability of aqueous solutions of 'Kirbychlor" in a water-bath at 25~
One tablet dissolved in:
0"5 1 2.5 1 10'0 l
Weeks av.C1 (pprn) pH av.C1 (ppm) pH av.Cl (ppm) pH
0 3100 5"5 580 5"6 160 5"9
1 2540 5.5 580 5"6 160 5'9
2 1920 5.4 440 5"4 120 5"9
3 1560 5-3 360 5"4 120 5"7
4 1180 5.3 300 5"4 80 5"6
6 740 5.2 200 5'3 80 5.4
8 400 5.1 120 5"3 ~<40 5.4
11 180 5.1 80 5"2
13 120 5.0 80 5" 2
16 ~<40 5.0 ~<40 5"2
Table VI. Stability of aqueous solutions of 'Presept" and 'Sanichlor' in a water-bath at 25~
'Presept' 'Sanichlor'
Weeks av.Cl (ppm) pH av.Cl (ppm) pH
0 10,640 5.9 10,320 6.3
1 8140 5.7 4400 6.5
2 6720 5.6 3520 6.6
4 4100 5.4 2200 6.8
6 2240 5.4 1540 6.8
8 1100 5.3 1060 6.9
10 380 5.1 720 7.0
12 100 5.0 500 6.8
14 0 4-9 340 6.8
18 160 6.8
22 ~<40 6.8
' S a n i c h l o r ' s o l u t i o n 8 w e e k s a f t e r d e p l e t i o n o f t h e ' P r e s e p t ' s o l u t i o n . S e c o n d l y , d e c o m p o s i t i o n o f ' S a n i c h l o r ' s o l u t i o n w a s a c c o m p a n i e d b y an i n c r e a s e in p H .
V a r i a b i l i t y o f N a O C l b a t c h e s a n d N a D C C t a b l e t s
T h e v a r i a b i l i t y o f av.C1 c o n t e n t a n d p H o f d i f f e r e n t b a t c h e s o f ' M i l t o n ' a n d ' C h l o r o s ' , a n d d i f f e r e n t t a b l e t s o f ' K i r b y c h l o r ' , ' P r e s e p t ' a n d ' S a n i c h l o r ' is s h o w n in T a b l e V I I . R e g a r d i n g N a O C 1 p r o d u c t s , it c a n b e s e e n t h a t ' M i l t o n ' is m u c h less v a r i a b l e t h a n ' C h l o r o s ' . O n e b a t c h o f u n o p e n e d ' C h l o r o s ' t e s t e d s e v e r a l m o n t h s a f t e r d e l i v e r y i n t o t h e h o s p i t a l ( a n d n o t , t h e r e f o r e , i n c l u d e d in t h e d a t a f o r T a b l e V I I ) c o n t a i n e d o n l y 6 6 , 0 0 0 p p m av.C1, a n d h a d a p H o f 12"0, d e m o n s t r a t i n g t h a t this p r o d u c t c a n d e c o m p o s e r a p i d l y d u r i n g s t o r a g e . R e g a r d i n g N a D C C p r o d u c t s , it c a n b e s e e n t h a t ' K i r b y c h l o r ' , ' P r e s e p t ' a n d ' S a n i c h l o r ' w e r e c o m p a r a b l e in so f a r as s o l u t i o n s p r o d u c e d f r o m t a b l e t s v a r i e d s l i g h t l y o r m o d e r a t e l y in av.C1
C o m p a r i s o n of hypochlorite and d i e h l o r o i s o e y a n u r a t e 39
Table V I I.
Variability of available chlorine content and p H of different batches of 'Milton" and'Chloros', and different tablets of 'Kirbychlor', "Presept' and 'Sanichlor"
N u m b e r of tests av.C1 ( p p m ) p H
P r o d u c t B a t c h e s T a b l e t s R a n g e M e a n R a n g e M e a n
' M i l t o n ' 6 1 0 , 4 0 0 - 1 1 , 4 0 0 10,900 11"5 11"7 11.6
' C h l o r o s ' 6 9 4 , 0 0 0 - 1 2 0 , 0 0 0 109,000 11.6 12.3 11.9
' K i r b y c h l o r ' * 1 10 3 0 4 0 - 3 5 2 0 3180 5"5 5-5
' P r e s e p t ' * 1 10 2 9 2 0 - 3 2 0 0 3070 5"7 5"7
' S a n i c h l o r ' * 1 6 2 1 0 0 - 2 2 0 0 2160 6"2 6"2
* One tablet dissolved in 500 ml of deionized water.
content, b u t s h o w e d no variation in p H . T h e tablets of all three p r o d u c t s dissolved quickly in water leaving a few particles which could be dissolved by crushing and stirring.
D i s c u s s i o n
W h e n this s t u d y was started, it was anticipated that N a D C C solutions would prove to be m o r e bactericidal than NaOC1 solutions of the same strength due to their lower p H . T h e p r o p o r t i o n s of undissociated h y p o c h l o r o u s acid present at different p H s are 97"3% at p H 6"0, 78"1% at p H 7"0, 50% at p H 7"55, 26"3% at p H 8"0, and 3"45% at p H 9"0. In the present s t u d y ( T a b l e I I I ) the p H of reaction mixtures containing ' M i l t o n ' and horse s e r u m varied from p H 8"9 to p H 9.4 whilst that of reaction mixtures containing 'Presept' and s e r u m varied from p H 6"3 to p H 6"8.
Despite this, the reaction mixtures p r o v e d to be similar in bactericidal activity, which d e m o n s t r a t e s that factors other than p H are involved.
Investigations b y Bloomfield (1973), and Bloomfield & Miles (1979) using capacity test m e t h o d o l o g y s h o w e d that N a D C C solutions possessed significantly higher bactericidal capacity than NaOC1 solutions of the same total available chlorine. T h e i r results also indicated that differences in activity b e t w e e n N a D C C and NaOC1 formulations are not entirely d u e to p H effects and that f u n d a m e n t a l differences exist b e t w e e n the p r o p e r t i e s and m o d e of action of the two systems. As in the present study, analysis of their data indicated no simple relationship b e t w e e n bactericidal activity and h y p o c h l o r o u s acid concentration. It has been firmly established, e.g. by D e a t h & Coates (1979), that the sporicidal activity of NaOC1 solutions (which are alkaline) increases m a r k e d l y as the p H is lowered. T h e effect of p H on the sporicidal activity of N a D C C solutions (which are acidic) remains to be established.
One of the p r o b l e m s of concentrated NaOC1 p r o d u c t s is their instability,
especially at elevated t e m p e r a t u r e s ( H o f f m a n , D e a t h & Coates, 1981). In
the present study, the rates of d e c o m p o s i t i o n of ' M i l t o n ' and ' C h l o r o s ' at
25~ were c o m p a r e d , and it was d e m o n s t r a t e d that ' M i l t o n ' is relatively
40 D. Coates
m u c h m o r e s t a b l e t h a n ' C h l o r o s ' . I n p r a c t i c e , t h e s e p r o d u c t s s h o u l d b e m o r e s t a b l e t h a n t h e r e s u l t s s u g g e s t as t h e y w e r e i n c u b a t e d in p l a s t i c s t e r i l e w a t e r f o r i r r i g a t i o n b o t t l e s r a t h e r t h a n in t h e i r p r o p e r c o n t a i n e r s . T o p r e v e n t h y p o c h l o r i t e d e c o m p o s i t i o n a c o n t a i n e r is r e q u i r e d w h i c h c u t s o f f light b e l o w 475 n m a n d t r a n s m i t s less t h a n 2 % at 5 0 0 n m ( t e c h n i c a l i n f o r m a t i o n o f R i c h a r d s o n - V i c k s L t d ) . I n c o n t r a s t , t a b l e t s o f N a D C C p r o v e d to b e v e r y s t a b l e ; s o l u t i o n s p r e p a r e d f r o m t a b l e t s s t o r e d f o r 9 m o n t h s at 42~ c o n t a i n e d j u s t as m u c h a v a i l a b l e c h l o r i n e as s o l u t i o n s p r e p a r e d f r o m n e w t a b l e t s . H o w e v e r , s o l u t i o n s o f N a D C C w e r e v e r y m u c h less s t a b l e t h a n N a O C 1 s o l u t i o n s . H e n c e , if N a D C C t a b l e t s a r e to b e u s e d in h o s p i t a l s it is i m p o r t a n t t h a t s o l u t i o n s are p r e p a r e d f r e s h l y w h e n r e q u i r e d , a n d a r e n o t p r e p a r e d in b u l k f o r d i s t r i b u t i o n to s t a t i o n s w h e r e t h e y m a y b e s t o r e d .
P r e p a r a t i o n o f u s e - d i l u t i o n s o f N a O C 1 d i s i n f e c t a n t s is o f t e n d o n e b y a d d i n g an a p p r o x i m a t e m e a s u r e o f t h e n e a t p r o d u c t into a c o n t a i n e r , a n d t h e n filling u p w i t h w a t e r f r o m a t a p . S p l a s h e s m a r k c l o t h e s a n d t h e av.C1 c o n t e n t o f t h e u s e - d i l u t i o n s c a n v a r y c o n s i d e r a b l y . I n a s t u d y o f t h e av.C1 c o n t e n t o f 15 d i s c a r d j a r s in a v i r o l o g y l a b o r a t o r y t h e a u t h o r f o u n d a v . C ] levels r a n g i n g f r o m 5200 to 16,200 p p m av.C1 w i t h a m e a n o f 10,100 p p m av.C1. T h e i n t e n d e d c o n c e n t r a t i o n w a s 2500 p p m av.C1. N a D C C t a b l e t s a r e easier a n d s a f e r to h a n d l e t h a n c o n c e n t r a t e d N a O C 1 s o l u t i o n s , a n d a c c u r a t e u s e - d i l u t i o n s c a n b e p r e p a r e d easily.
I n c o n c l u s i o n it c a n b e said t h a t the m a i n d i s a d v a n t a g e o f N a D C C p r o d u c t s is t h a t c u r r e n t l y , in t e r m s o f av.C1 c o n t e n t , t h e y c o s t m u c h m o r e t h a n N a O C 1 p r o d u c t s . H o w e v e r , t h e y h a v e s e v e r a l a d v a n t a g e s o v e r N a O C 1 p r o d u c t s : t h e t a b l e t s are s t a b l e a n d c o m p a c t , a n d u s e - d i l u t i o n s c a n b e p r e p a r e d s i m p l y , s a f e l y a n d a c c u r a t e l y , w h e n a n d w h e r e r e q u i r e d .
R e f e r e n c e s
Bloomfield, S. F. (1973). The bactericidal capacity of sodium dichloroisocyanurate formulations used for the sterilisation of infant feeding bottles and teats. Laboratory Practice 22, 672-673.
Bloomfield, S. F. & Miles, G. A. (1979). The antibacterial properties of sodium dichloroisocyanurate and sodium hypochlorite formulations. Journal of Applied Bacteriology 46, 65-73.
Coates, D. (1977). Kelsey-Sykes capacity test: origin, evolution and current status. The Pharmaceutical Journal 219, 402-403.
Death, J. E. & Coates, D. (1979). Effect of pH on sporicidal and microbicidal activity of buffered mixtures of alcohol and sodium hypochlorite. Journal of Clinical Pathology 32, 148 153.
Hoffmann, P. N., Death, J. E. & Coates, D. (1981). The stability of sodium hypochlorite solutions. In Disinfectants: Their Use and Evaluation of Effectiveness (Collins, C. H., Allwood, M. C., Bloomfield, S. F. & Fox, A., Eds), pp. 77 83. Academic Press, London.
Ortenzio, L. F. & Stuart, L. S. (1959). Behaviour of chlorine bearing organic compounds in the A.O.A.C. available chlorine germicidal equivalent concentration test. Journal of the Association of Official Agricultural Chemists 42, 630-633.
Trueman, J. R. (1971). The halogens. In Inhibition and Destruction of the Microbial Cell (Hugo, W. B., Ed.), pp. 137-183. Academic Press, London.
