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Thursday, July 23, 2009

Spots on Glassware

I have an under the counter glassware washer and I keep finding spots on the glassware after each cleaning. I am fairly certain that the detergent is responsible. At this point I want to replace the detergent but I don’t know what product would work better. What is the difference between an acidic and alkali detergent? Is a neutralizer necessary? What does having an ionic and anionic detergent do for you?

The three most common causes of spots on glassware are: heavy metal hydroxide/oxide deposits; water spots from hard tap water rinsing; and water spots from improper glassware loading with wash water holding cups such as the upturned bottoms of large graduated cylinders that are not loaded at an angle to allow proper drainage.

If you have any glassware residues of heavy metals that form insoluble hydroxides/oxides at alkaline pH, then you need an acid rinse to remove these. Citrajet is the recommended product. Hopefully your washer has some provisions for dosing a liquid acid rinse during a rinse cycle.

If you have hard tap water that is being used to rinse with, then you need to take precautions to assure that this tap water does not dry on to your glassware and leave mineral deposits. This can be achieved by putting in deionized water rinsing, eliminating the heated drying cycle and manually rinsing in deionized water, skipping the heated evaporating drying cycle and doing some kind of manual water removing drying process (wiping, blowing, or isopropanol dipping off the tap water and not allowing it to evaporate and form spots),

You can open the machine during a wash cycle and inspect the glassware to see if there is any significant volume of wash water that is trapped due to the way it is loaded in the racks. Change the angle at which you load problem glassware to allow drainage, or wash the problematic glassware by hand to avoid this problem.

If you suspect that the residues are simply dried on detergent due to incomplete rinsing, you could confirm this by doing a quick cursory water rinse of the problem glassware. If the residue comes off quickly and easily in water, then you may well have simple detergent residue. This would indicate something wrong with the rinsing. Check the programming to make sure multiple rinse cycles are running. Open and inspect the washer during rinse cycles to make sure water is actually getting in to rinse with. Consider running any empty cycle with Citrajet acid rinse (just dump a few ounces in to the bottom of the chamber at the start of a wash cycle if there is no way to dose in an acid rinse - this will unclog any clogged up spray jets inside the washer. Note this type of failure is fairly unusual, but I wanted to address it because you indicate that this is what you think is happening.

Neutralizers or acid rinses are required when any metal residue is present that can cause the formation of an insoluble metal hydroxide or oxide. As a generalization, you should use nonionic detergents. You need to use low or non foaming detergents in a washer. The most common low or non foaming detergents are nonionic.

Alconox, Inc manufactures several brands of detergents for under the counter machine washers, our customer recommendations for "">Laboratory.

Alconox cleaners are available globally with consistent formulations and are GMP compliant. Downloadable certificates of analysis, technical bulletins, MSDS, trace analysis, and inhibitory residue testing are available from the Alconox website at

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