Reagent preservation

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Although many chemical compounds and elements can be stored indefinitely (ex: sodium chloride, barium sulfate, titanium dioxide, oxalic acid, carbon, gold, etc.) in most if not all storage conditions, there are many reagents that tend to undergo chemical changes, regardless of the storage. Even in the best storage conditions, they will degrade over long periods of time. To maintain their long shelf life, preservatives as well as other additives are added.

General

Many chemicals, such as ethers or secondary alcohols, tend to undergo autoxidation when in contact with air. Halogenated carbons will too suffer similar effects. Alkaline metals like potassium also build up dangerous peroxides in contact with oxygen.

Other compounds, such as sugar or citric acid will serve as nourishment for mold or other biological organisms. Alcohols, like ethanol, will not turn into their respective carboxylic acids (like acetic acid) if they're concentrated enough.

Some elements like silver will darken in prolonged contact with polluted air, even though silver resists atmospheric oxidation. Many other metals suffer similar effects. Some metals, like magnesium, zinc or lanthanides are relative stable in dry air, but will quickly tarnish if moisture is present.

Note that preservatives have poor efficiency if you do not store your reagents properly.

Reagents and preservatives used

Compound Preservative Notes
1-Methyl-1,4-cyclohexadiene Butylated hydroxytoluene (BHT) 50-500 ppm[1]
1-Vinyl-2-pyrrolidone N,N'-di-sec-butyl-1,4-phenylenediamine [2]
1,3-Diiodopropane Copper [3]
1,4-Butanediol vinyl ether Potassium hydroxide 0.01% potassium hydroxide[4]
1,4-Dioxane Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone 0.0015-0.003 % w/w[5]
1,8-Diiodooctane Copper [6]
2-Ethylhexyl acrylate Mequinol (MEHQ) 1-3%[7]
2-Iodoxybenzoic acid Benzoic acid, isophthalic acid ~25%[8]
2-Vinylpyridine 4-tert-Butylcatechol 0.1 wt. %[9]
3-(Trimethoxysilyl)propyl methacrylate Butylated hydroxytoluene (BHT) [10]
3-Chlorostyrene 3,5-Di-tert-butylcatechol 0.1% 3,5-di-tert-butylcatechol[11]
3-Phenylpropionaldehyde Citric acid, α-tocopherol Small amounts[12]
6-Methoxy-2,6-dimethylheptanal α-Tocopherol Small amounts[13]
10-Undecen-1-ol α-Tocopherol Small amounts[14]
Acetaldehyde Niacinamide Minute amounts[15]
Acrolein Hydroquinone Does not always work, possibly due to impurities[16]
Allyl bromide Propylene oxide ≤1000 ppm[17]
Aluminium powder Charcoal Aluminium powder is grounded together with less than 10% charcoal
Barium ferrate Potassium hydroxide, sodium hydroxide
Benzyl chloride Propylene oxide Concentration 0.25-1%
Bromodichloromethane Potassium carbonate [18]
Buffer solutions for HPLC (e.g. phosphate, acetate, formate, etc.) Sodium azide Less than 0.1% as a biostat. Safer biocides cannot generally be used for HPLC as these would interfere with the chromatography by introducing ghost peaks.
Chloroacetone Calcium carbonate Aprox. 1%
Chloroform Ethanol, methanol, pentene (amylene) Accepted values of 1% for ethanol; 100 ppm for amylene[19]
Citric acid Biocides, like benzalkonium chloride Aqueous solutions and wet citric acid are prone to mold; solid or anhydrous citric acid less so
Cyanide solutions Potassium hydroxide, sodium hydroxide Usually <1%
Cyclohexene Butylated hydroxytoluene (BHT) 100 ppm[20]
Dichloromethane Ethanol, methanol, cyclohexane, cyclohexene, amylene Accepted values of 100 ppm for amylene, cyclohexane, cyclohexene[21]
Dicyclopediene Butylated hydroxytoluene (BHT) 0.05 % [22]
Diethyl ether Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, ethanol, hydroquinone Accepted values 1-2% for ethanol[23]
Diisopropyl ether Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone The amount of preservative added must be greater compared to other ethers
Ethyl 2-trans-4-cis-decadienoate α-Tocopherol Small amounts[24]
Formaldehyde Methanol For aqueous formaldehyde (Formalin) the concentration is 10-20%; Inhibits oxidation and polymerization[25]
Hexadecanolide Butylated hydroxytoluene (BHT) [26]
Hydrogen peroxide Acetanilide, phosphoric acid, EDTA, tripotassium phosphate, sodium stannate, sodium pyrophosphate (tetrasodium diphosphate), various organophosphates Conc. for sodium pyrophosphate: 25 - 250 mg/L[27]
Hydroiodic acid Hypophosphorous acid <1.5%[28]
Isopropanol Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone Only required if kept for more than 1-2 years in contact with air
Lead(II) azide Dextrin Generally used in Pb(N3)2 aqueous solutions and during production to inhibit the growth of large crystals
Lead(IV) acetate Anhydrous (glacial) acetic acid, acetic anhydride
Metaphosphoric acid Sodium phosphite 57.0-63.0%[29]
Methyl cellosolve Butylated hydroxytoluene (BHT) 50 ppm[30]
Methyl iodide Copper or silver wire/powder Small amounts[31]
Methyl methacrylate Hydroquinone, quinol, topanol, MEHQ <0.1-1% hydroquinone[32], quinol[33], topanol[34]; ≤30 ppm MEHQ[35]
Methyl vinyl ketone Hydroquinone 0.3-1.0% hydroquinone[36]
Natural rubber latex Ammonia 0.2 % m/m (short term storage) to 0.7 % m/m (long term storage)[37]
Pentaerythritol tetranitrate Urea
Phenol Hypophosphorous acid 0.15%[38]
Poloxamer 188 EMPROVE® EXPERT Butylated hydroxytoluene (BHT) 70 ppm[39]
Potassium ferrate Potassium hydroxide
Schweizer's reagent Excess ammonia
sec-Butanol Butylated hydroxytoluene (BHT), butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone Only required if kept for more than 1-2 years in contact with air
Smokeless powder Diphenylamine
Sodium bisulfite Sulfur dioxide
Sodium ferrate Sodium hydroxide
Styrene 4-tert-Butylcatechol 30-50 ppm[40]
Sulfur trioxide Antimony pentafluoride, antimony pentachloride Concentration 0.5-1%; antimony pentafluoride gives a better performance than the pentachloride[41]
Tetraamine copper(II) complex Excess ammonia
Tetraaminecopper(II) persulphate Excess ammonia
Tetrahydrofuran Butylated hydroxytoluene (BHT), Butylated hydroxyanisole (BHA), fresh copper, diphenylamine, hydroquinone Accepted values of 100-300 ppm for BHT[42]
Tributyltin hydride Butylated hydroxytoluene (BHT) 0.05%[43]
Trichloroethylene Diisopropylamine 40 ppm diisopropylamine[44]

Storage atmosphere

Some materials that react with air are best or can only be safely stored under air-free atmosphere. While noble gasses like argon are commonly used, being relative cheap, other gasses like nitrogen, sulfur hexafluoride, most saturated perfluorocarbons can also be used. Carbon dioxide or gaseous saturated hydrocarbons (methane, ethane, propane, butane) can also be used in some cases. Some compounds like sulfur dioxide or ammonia are being used as preservatives themselves.

Compound Noble gasses Nitrogen Sulfur hexafluoride Perfluorocarbons Carbon dioxide Hydrocarbons Notes
Alkali metals Compatible Compatible, save for lithium Compatible Incompatible Incompatible Compatible Lithium is incompatible with SF6 at high temperatures
Alkaline metal hydroxides Compatible Compatible Compatible Compatible Incompatible Compatible
Alkaline earth metals Compatible Compatible Compatible Compatible Incompatible Compatible Calcium and strontium slowly react with nitrogen
Alkali earth metal hydroxides Compatible Compatible Compatible Compatible Incompatible Compatible
Bisulfites Compatible Compatible Compatible Compatible Compatible Compatible Only compatible with carbon dioxide in dry conditions
Chlorocarbons Compatible Compatible Compatible Compatible Compatible Compatible
Ethers Compatible Compatible Compatible Compatible Compatible Compatible
Sulfites Compatible Compatible Compatible Compatible Compatible Compatible

Safety

Reagents treated with preservatives must be inspected periodically for any signs of degradation, in the event said preservatives failed to do their job.

See also

References

  1. https://www.sigmaaldrich.com/catalog/product/aldrich/w508101
  2. www.merckmillipore.com/EN/en/product/1-Vinyl-2-pyrrolidone,MDA_CHEM-808518
  3. https://www.sigmaaldrich.com/catalog/product/aldrich/238414
  4. https://www.sigmaaldrich.com/catalog/product/aldrich/406198
  5. http://shop.biosolve-chemicals.eu/detail.php?id=1592
  6. https://www.sigmaaldrich.com/catalog/product/aldrich/250295
  7. https://ie.vwr.com/store/product/7450415/2-ethylhexyl-acrylate-stabilized
  8. https://www.sigmaaldrich.com/catalog/product/aldrich/661384
  9. https://www.sigmaaldrich.com/catalog/product/aldrich/132292
  10. https://www.tcichemicals.com/eshop/en/us/commodity/M0725/
  11. https://www.sigmaaldrich.com/catalog/product/aldrich/c71009
  12. https://www.sigmaaldrich.com/catalog/product/aldrich/w288705
  13. https://www.sigmaaldrich.com/catalog/product/aldrich/w474505
  14. https://www.sigmaaldrich.com/catalog/product/sial/w562125
  15. https://www.sigmaaldrich.com/catalog/product/sial/w200320
  16. https://www.youtube.com/watch?v=7oAcT4Duun4
  17. https://www.sigmaaldrich.com/catalog/product/aldrich/a29585?lang=en
  18. https://www.sigmaaldrich.com/catalog/product/aldrich/139181
  19. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  20. https://www.sigmaaldrich.com/catalog/product/sial/29240
  21. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  22. https://www.sigmaaldrich.com/catalog/product/aldrich/454338
  23. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  24. https://www.sigmaaldrich.com/catalog/product/sial/w314820
  25. https://www.sigmaaldrich.com/catalog/product/mm/104002
  26. https://www.sigmaaldrich.com/catalog/product/sial/w800002
  27. http://www.h2o2.com/faqs/FaqDetail.aspx?fId=11
  28. https://www.sigmaaldrich.com/catalog/product/sigald/210021
  29. https://www.sigmaaldrich.com/catalog/product/sigald/239275
  30. https://www.sigmaaldrich.com/catalog/product/sigald/360503
  31. https://www.sigmaaldrich.com/catalog/product/sial/289566
  32. https://www.fishersci.com/shop/products/methyl-methacrylate-stabilized-hydroquinone-baker-j-t-baker/02003484
  33. https://www.limac.lv/catalog/params/category/93695/item/427086/
  34. https://www.fishersci.se/shop/products/methyl-methacrylate-extra-pure-slr-stabilised-quinol-2/p-7073315
  35. https://www.sigmaaldrich.com/catalog/product/aldrich/m55909
  36. https://www.sigmaaldrich.com/catalog/product/aldrich/m87509
  37. Polymer Latices: Science and technology Volume 2: Types of latices, D.C. Blackley, p. 28
  38. https://www.sigmaaldrich.com/catalog/product/sial/242322?lang=en&region=EN
  39. https://www.sigmaaldrich.com/catalog/product/mm/137112
  40. https://www.sigmaaldrich.com/catalog/product/sial/s4972
  41. https://www.google.com/patents/US2511072
  42. http://www.sigmaaldrich.com/chemistry/solvents/learning-center/stabilizer-systems.html
  43. https://www.sigmaaldrich.com/catalog/product/aldrich/234788
  44. https://www.sigmaaldrich.com/catalog/product/sial/372145

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