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Relative stability of sodium hypochlorite liquids and sodium dichloroisocyanurate effervescent disinfectant tablets
96
Letters
to the Editor
potential risk of infection to the patient, and their use should be restricted the purpose for which they were developed and marketed.
to
Dept. of Microbiology Newcastle General Hospital Newcastle NE4 6BE
M. S. Sprott A. M. Kearns D. Keenlyside References Leigh,
D. A. & Petch,
V. J. (1987).
Sterility
of incontinence
pads and sheets. Journal
of
Hospital Infection 9, 91-93.
Sir, Relative stability of sodium hypochlorite liquids dichloroisocyanurate effervescent disinfectant
and sodium tablets
One of the main problems of sodium hypochlorite formations is their lack of stability (Hoffman, Death & Coates, 1981). Decomposition of hypochlorites is catalysed by light, organic matter and heavy metal ions, and increases with ambient temperature. Hence, containers of strong sodium hypochlorite solution must be fitted with an effective pressure release closure, and must be stored in a cool place (15518°C) not exposed to direct sunlight (Department of Health and Social Security, 1978). Another consequence is that the available chlorine content of stored stock solutions is unknown. One batch of unopened ‘Chloros’ (ICI, Macclesfield) assayed several months after delivery into our hospital contained 6.6% available chlorine instead of the 10% present at manufacture (Coates, 1985). Accurate use-dilutions can only be prepared if the available chlorine content of the stock solution is known, which necessitates titration with sodium thiosulphate or sodium arsenite (Ayliffe, Coates & Hoffman, 1984). One way of avoiding the above problems is to use sodium dichloroisocyanurate (NaDCC) effervescent disinfectant tablets which dissolve in water releasing available chlorine. The first tablets marketed in 25 mm, 5 g tablets containing 50% UK hospitals were ‘Kirbychlor’ NaDCC (Kirby-Warwick Pharmaceuticals Ltd), followed by ‘Presept’ 25 mm, 5 g tablets containing 50% NaDCC (Surgikos Ltd) and ‘Sanichlor’ 20 mm, 3.2 g tablets containing 55% NaDCC (G. H. Wood Ltd). In order to determine the stability of such tablets I kept containers (plastic tub with press down lid) of ‘Kirbychlor’ tablets in a refrigerator at 6°C in laboratory incubators at 28°C (high humidity) and at 42°C for 40 months. Periodically, tablets were removed, dissolved in water and the available chlorine content and pH of the solutions determined. The results obtained are given in Table I. The manufacturers claim that one tablet dissolved in 10 1 of water will give at least 140 ppm available chlorine, so one tablet in 500 ml of water should give at least 2800 ppm available chlorine. The results show that the
Letters Table
I. Stability
of ‘Kirbychlor’
tablets at dzserent
of storage
0 i 9 18 :i 36 40 * One tablet dissolved
temperatures 42°C
28°C
6°C Months
97
to the Editor
ppm av. Cl*
pH
ppm av. Cl
pH
ppm av. Cl
3100 3220 3280 3300 3220 3140 2980 2920 3260
5.5
3200 3200 3300 3360 3100 3020 2900 2660 1980
5.5 5.5 5.5 5.5
3200 3340 3340 3200 3120 3000 2840 2960 2840
5.5 5.5 5.5 5.5 5.4 5.5 5.4 5.4
in 500ml deionized
5.5 5.4 5.5 5.5 5.4
pH
::: 5.5 5.5 5.5 5.4 5.4 5.3 5.3
water. Ppm available chlorine.
tablets stored at 6°C and 42°C which looked normal after 40 months, still contained the specified level of available chlorine. However, the tablets stored at 28°C in a humid atmosphere began to decompose after 30 months presumably due to moisture penetration. After 40 months the tablets had swollen markedly, were very brittle, and had lost 38% of their available chlorine. This demonstrates thle importance of storing NaDCC tablets in a dry environment. The conclusion is that whereas sodium hypochlorite formulations are intrinsically unstable, NaDCC tablets are stable so long as they are kept dry. D. Coates
Public Health Laboratory Preston Infirmary Meadow Street Preston PRl 6PS
References Ayliffe, G. A. J., Coates, D. & Hoffman, P. N. (1984). CI zemical Disinfection in Hospitals. Public Health Laboratory Service, London. Coates, D. (1985). A comparison of sodium hypochlorite and sodium dichloroisocyanurate products. Journal of Hospital Infection 6, 3140. Department of Health and Social Security (1978). Possible explosion hazard: pressure build up in containers of strong sodium hypochlorite solution supplied by BDH Chemicals Ltd. Health Notice (Hazard) 43. 31 October. Hoffman, 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.
Letters
to the Editor
potential risk of infection to the patient, and their use should be restricted the purpose for which they were developed and marketed.
to
Dept. of Microbiology Newcastle General Hospital Newcastle NE4 6BE
M. S. Sprott A. M. Kearns D. Keenlyside References Leigh,
D. A. & Petch,
V. J. (1987).
Sterility
of incontinence
pads and sheets. Journal
of
Hospital Infection 9, 91-93.
Sir, Relative stability of sodium hypochlorite liquids dichloroisocyanurate effervescent disinfectant
and sodium tablets
One of the main problems of sodium hypochlorite formations is their lack of stability (Hoffman, Death & Coates, 1981). Decomposition of hypochlorites is catalysed by light, organic matter and heavy metal ions, and increases with ambient temperature. Hence, containers of strong sodium hypochlorite solution must be fitted with an effective pressure release closure, and must be stored in a cool place (15518°C) not exposed to direct sunlight (Department of Health and Social Security, 1978). Another consequence is that the available chlorine content of stored stock solutions is unknown. One batch of unopened ‘Chloros’ (ICI, Macclesfield) assayed several months after delivery into our hospital contained 6.6% available chlorine instead of the 10% present at manufacture (Coates, 1985). Accurate use-dilutions can only be prepared if the available chlorine content of the stock solution is known, which necessitates titration with sodium thiosulphate or sodium arsenite (Ayliffe, Coates & Hoffman, 1984). One way of avoiding the above problems is to use sodium dichloroisocyanurate (NaDCC) effervescent disinfectant tablets which dissolve in water releasing available chlorine. The first tablets marketed in 25 mm, 5 g tablets containing 50% UK hospitals were ‘Kirbychlor’ NaDCC (Kirby-Warwick Pharmaceuticals Ltd), followed by ‘Presept’ 25 mm, 5 g tablets containing 50% NaDCC (Surgikos Ltd) and ‘Sanichlor’ 20 mm, 3.2 g tablets containing 55% NaDCC (G. H. Wood Ltd). In order to determine the stability of such tablets I kept containers (plastic tub with press down lid) of ‘Kirbychlor’ tablets in a refrigerator at 6°C in laboratory incubators at 28°C (high humidity) and at 42°C for 40 months. Periodically, tablets were removed, dissolved in water and the available chlorine content and pH of the solutions determined. The results obtained are given in Table I. The manufacturers claim that one tablet dissolved in 10 1 of water will give at least 140 ppm available chlorine, so one tablet in 500 ml of water should give at least 2800 ppm available chlorine. The results show that the
Letters Table
I. Stability
of ‘Kirbychlor’
tablets at dzserent
of storage
0 i 9 18 :i 36 40 * One tablet dissolved
temperatures 42°C
28°C
6°C Months
97
to the Editor
ppm av. Cl*
pH
ppm av. Cl
pH
ppm av. Cl
3100 3220 3280 3300 3220 3140 2980 2920 3260
5.5
3200 3200 3300 3360 3100 3020 2900 2660 1980
5.5 5.5 5.5 5.5
3200 3340 3340 3200 3120 3000 2840 2960 2840
5.5 5.5 5.5 5.5 5.4 5.5 5.4 5.4
in 500ml deionized
5.5 5.4 5.5 5.5 5.4
pH
::: 5.5 5.5 5.5 5.4 5.4 5.3 5.3
water. Ppm available chlorine.
tablets stored at 6°C and 42°C which looked normal after 40 months, still contained the specified level of available chlorine. However, the tablets stored at 28°C in a humid atmosphere began to decompose after 30 months presumably due to moisture penetration. After 40 months the tablets had swollen markedly, were very brittle, and had lost 38% of their available chlorine. This demonstrates thle importance of storing NaDCC tablets in a dry environment. The conclusion is that whereas sodium hypochlorite formulations are intrinsically unstable, NaDCC tablets are stable so long as they are kept dry. D. Coates
Public Health Laboratory Preston Infirmary Meadow Street Preston PRl 6PS
References Ayliffe, G. A. J., Coates, D. & Hoffman, P. N. (1984). CI zemical Disinfection in Hospitals. Public Health Laboratory Service, London. Coates, D. (1985). A comparison of sodium hypochlorite and sodium dichloroisocyanurate products. Journal of Hospital Infection 6, 3140. Department of Health and Social Security (1978). Possible explosion hazard: pressure build up in containers of strong sodium hypochlorite solution supplied by BDH Chemicals Ltd. Health Notice (Hazard) 43. 31 October. Hoffman, 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.