Should All Drops Be the Same Size?

[HouTex]

Last year when I ran out of R-0009 I bought a .75 oz. size bottle at Leslie's to resupply my TFP-100 kit for that one reagent. I'm still using the 1.0 oz. R-0007 and R-0008 bottles that came with my refill set from the TFP website.

I notice that the drops from the 1.0 oz. bottles of R-0007 and R-0008 seem much larger than the drops from the .75 oz. bottle of R-0009 from the pool store. Yes, I'm wiping the tip of the bottle and they still seem smaller. So I'm wondering if my TA is reading a little high.

Should the drops be the same size from the different bottles? Has anyone heard of a defective bottle tip that produces smaller drops than normal?

 

[Hawk]

Why would you compare the drop size of different reagents?

 

[HouTex]

I'm wondering if my TA is reading higher than it is and if this is the reason. In the past I've noticed that my TA reading will go up or down by 10-20 whenever I open a new bottle of R-0009. Perhaps this is within the margin of error of the test.

Based on your reply, do you believe the different reagent bottles have their own unique drop size? The 1 oz. reagent bottles (the bottles seem identical) for R-0007 and R-0008 seem to produce the same size of drop as far as I can tell.

 

[JasonLion]

The drops of different reagents of the same brand are generally supposed to be the same size. But different brands sometimes use different drop sizes.

The TA test tends to have static electricity issues. Sometimes you need to wipe the tip with a damp tissues at regular intervals to insure consistent drop size.

 

[duraleigh]

Houtex,

Yes, the drop size matters....you are being very observant and that's a good thing!

Here's the deal (and this ONLY applies to R-0009....none of the other reagents)......

When you buy very fresh R-0009, it is often possible for a static charge to develop between the liquid and the dropper tip.

When this occurs, the drop (instead of falling off the dropper tip from gravity) actually "jumps" off the tip before it is fully formed and the subsequent drops size is smaller than a normal drop.

The end result is your TA test will read high.

Wiping the tip with a damp cloth or paper towel in between drops always eliminates this issue so I cannot understand why that didn't correct your problem.

The issue always goes away after just a few weeks at most so it only occurs when your R-0009 is very new and fresh.

 

[JesseWV]

I noticed the drop size for R-0011L (Calcium Indicator) is very small. It seems very "sticky." This is normal, yes?

 

[chem geek]

The drop size in the Taylor kits (including the TFTestkits based on Taylor) should be 24 drops +/- 1 per milliliter. That's 120 drops in 5 ml or 240 drops in 10 ml.

 

[Hawk]

I noticed the drop size for R-0011L (Calcium Indicator) is very small. It seems very "sticky." This is normal, yes?

Mine is the same way. That's why I originally answered that I wouldn't expect a drop from one reagent to another to be the same size.

 

[chem geek]

Fortunately, the relatively viscous R-0011L drop size is not critical. The number of drops for indicator dyes is not that important. You need enough so that the color transition is easily seen but an excess of dye is not usually a problem and for the pH test I sometimes use less than 5 drops to better match the color comparator. Where the drop size really matters most is for the titration reagents where you are counting the drops.

 

[HouTex]

Thanks for the replies. Very helpful.