Question about photometer 93713

[jlinzmaier]

Hello.

I have this photometer (93713)

http://www.marinedepot.com/Hanna_Instruments_Phosphate_(LR)_Photometer_with_890_nm_LED_Single_Item_Monitors_Controllers_for_Sal twater_Aquariums-Hanna_Instruments-HN1191-FITEMOID-vi.html

I have relatively low phosphate in my aquarium - always less than 0.06 mg/L.

I notice that when I mix in the reagent powder there is always some that gets stuck to the side and some that simply stays in suspension. The stuff that stays on the side is tough to get off becuase is seems to almost stick with ionic pull (like static electricity). To mix the reagent in the vial I simply invert the vial a half dozen times and never shake it so I don't create a large amount of agitation (which then causes microbubbles to form). After a little bit of mixing I'm able to get most reagent off the sides but never all of it.

I tried a bit of a test this morning. In my first test I only used 1/4th of the total reagent from the packet. With less total reagent I had little to no reagent sticking on the side and nothing that I could see in suspension. There was still some visible at the bottom that didn't dissolve. When doing this test I got a reading of 0.00 mg/L. I then repeated the test with a full packet of reagent and got a reading of 0.03 mg/L. I'm assuming the reagent sticking to the side and sitting in suspension is interfering with the reading and falsly reading high as the reagent occludes some light as it would if the water was less clear (like from the reagent reacting with po4 and turning the water darker).

Sorry for the long story but I just wanted to paint a clear picture of what I'm seeing. My question is: If I add some, but not all of the reagent, will I still get an accurate reading?? I'm assuming there is enough reagent in the packet to dissolve when there is upwards of 2.5 mg/L of phosphate present but when there is little to no po4 (like my tank) much less reagent is necessary. I'm assuming that as long as there is undissolved reagent in the bottom of the vial then there has been sufficient reagent added to react with the amount of phosphate present. If it would all become dissolved then there is potential for more to dissolve as it reacts with po4 therefore it could give a false low reading due to insufficient reagent. Are my assumptions correct??

The reason I ask is because the difference between an accurate reading of 0.00mg/L and 0.03mg/L (or higher) would be the difference between me adding more GFO or not.

Thanks.

Jeremy

[xp964]

The amount of reagent in the packets is weighed out precisely, and you should use all of it (or as much as you can get out) to get the correct reading.

The more phosphate is present in your sample, the more reagent is needed to react to it.

I haven't heard of the powder sticking to the sides of the cuvet before. Are you adding it before or after you put the water sample in the cuvet? You may want to speak to our Tech Support team, you can contact them at [email protected], or 1-800-426-6287.

Thanks
Jessica

[jlinzmaier]

The amount of reagent in the packets is weighed out precisely, and you should use all of it (or as much as you can get out) to get the correct reading.

The more phosphate is present in your sample, the more reagent is needed to react to it.

I haven't heard of the powder sticking to the sides of the cuvet before. Are you adding it before or after you put the water sample in the cuvet? You may want to speak to our Tech Support team, you can contact them at [email protected], or 1-800-426-6287.

Thanks
Jessica


Thanks Jessica. Not sure why I see some powder sticking to the sides lately. I always add the water ,wipe the cuvette clean, zero the machine, add the reagent, wipe again, and perform the test. The reagent on the side of the cuvette isn't something I've noticed before. Maybe just something I've overlooked previously.

I'm guily of waiting for your response before I let you in on my experiment. I used distilled water and even with the reagent sticking to the side (full packet added), it read at 0.00 (did this test several times) so the reagent sticking to the side doesn't seem to interfere.

Appreciate your response!

Jeremy

[xp964]

Thanks Jeremy! I'm glad it didn't seem to interfere. Can you tell me the lot number of the reagent? I'll have Chemistry double check on that lot, just to be sure that isn't the issue.

[jlinzmaier]

Lot # H 060 expiration 5/11

Very much appreciate you checking with chemistry on this one. I'd send you a pic of the reagent sticking to the glass but right now I don't have access to a camera with a good enough macro setting to display it properly.

Thanks.

Jeremy

[xp964]

Jeremy,

I talked to the chemist and she doesn't think its the reagent that is causing it to stick. She believes your cuvette is dirty and need some cleaning solution. The part number is (HI 93703-50) After you clean your cuvettes, try to test again and let me know how you make out. It should not stick on a clean cuvette

Here’s a tip for opening your reagent packets to make sure all of the reagent comes out. Shake reagent to one corner. Cut (with scissors) the two opposing top sides of the packet. Pull the packet apart and form crease at opposing corner. Pour powder directly into center of the cuvette by pouring on the crease. Tighten cap.

Then shake vigorously! Hope this helps!

[jlinzmaier]

Jeremy,

I talked to the chemist and she doesn't think its the reagent that is causing it to stick. She believes your cuvette is dirty and need some cleaning solution. The part number is (HI 93703-50) After you clean your cuvettes, try to test again and let me know how you make out. It should not stick on a clean cuvette

Here’s a tip for opening your reagent packets to make sure all of the reagent comes out. Shake reagent to one corner. Cut (with scissors) the two opposing top sides of the packet. Pull the packet apart and form crease at opposing corner. Pour powder directly into center of the cuvette by pouring on the crease. Tighten cap.

Then shake vigorously! Hope this helps!

The instructions say not to shake vigorously because that causes the formation of microbubbles?????

FWIW. I've tested hundreds of times and I know how to open the reagent packet and pour it into the cuvette. Thanks for the tips though.

What would make my cuvette dirty?? If there is microscopic abiotic precipitation that the reagent molecules are sticking on, then vinegar is far more realistic for me to use than buying a special "cleaning agent" (which is likely a diluted vinegar solution).

Jeremy

[mrvicz]

JThen shake vigorously! Hope this helps!

just wanted to tag along for the reply on this matter. Do we have to shake vigorously or gently? Says in the instruction not to create too much agitation.

TIA

[jlinzmaier]

I first cleaned the cuvettes with some vinegar and still saw the reagent sticking to the side of the vial. I gave in a spent the $20 on the cleaning solution and what a waste of money. The reagent still sticks to the cuvette!! Should have just used the money to buy new cuvettes!! What a waste.

Any comment on your indication to shake vigorously when the instructions clearly say not to shake vigorously?? Either way it doesn't make a difference in the amount of reagent that will dissolve nor does it make a difference in the amount of reagent that sticks to the inside of the cuvette.

Jeremy