Although the sink and the dishwasher may be right next to each other in the kitchen, detergents for cleaning dishes are very specific for one method vs. the other.
For people who have a cramped kitchen, it might seem unnecessary to have one detergent for washing dishes in the sink and one for washing dishes in the dishwasher, but these products are definitely not interchangeable.
Because many people do not wear gloves when washing dishes in the sink, dish soap not only must get dishes clean, it must also be gentle on hands. It should also be stable over time, have a pleasant smell, and produce a lot of long-lasting suds. Dish soap is specifically formulated to meet these goals.
The first ingredient in dish soap is the surfactant. The surfactant, or surface active agent, encapsulates grease and allows it to dissolve in the water. It is also the chemical that creates the suds and keeps food and dirt particles suspended in water. Additional ingredients keep the dish soap from separating over time, make it easy to squirt, prevent the growth of microorganisms, and add aesthetic qualities such as color, fragrance, and moisturizer. Many dish soaps also include antibacterial agents to prevent bacteria from contaminating the user’s hands.
Dishwasher detergent, by contrast, uses far less surfactant since it cleans under harsher conditions of higher pH, higher temperature, and strong agitation. Suds are undesirable. Phosphates were once used widely in dishwasher detergent as they were for laundry detergents since they are excellent at removing minerals from hard water that can smear and stain dishes, at buffering the pH, and at preventing loosened soil and food from redepositing on dishes. Phosphates have been replaced by other chemical compounds because their presence in waste water often created excessive algae growth in ponds and lakes. Dishwasher detergents now generally contain a small amount of nonionic surfactant combined with some combination of a bleaching agent, enzymes, and an anti-corrosion agent.
Both kinds of dish detergents – for handwashing and for the dishwasher – have been optimized for their specific purposes, so you still need both products for all your dishwashing needs.
More information on this topic may be found at http://www.healthycleaning101.org/english/SDAC_handdish.html and http://www.post-gazette.com/pg/11013/1117540-28.stm