NanoDrop Spectrophotometry

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Tony Rook
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NanoDrop Spectrophotometry

Has anybody used the NanoDrop Spectrophotometry technology? Instead of using a 1 to 2 mL cuvette for samples, the user can place as little as 1 to 2 uL of sample on a light source (no cuvettes necessary). I am looking into the possiblity of purchasing a system and would like to know how well it works? If anyone has any experience please post your reactions and commments. Thanks!

bobk
bobk's picture
I have not used this product

I have not used this product myself, although several groups I am aware of have. Their general comments are favourable, with repeatability being the main concern. An alternative solution might be to use a microvoluve cuvette adapter in your existing instrument.

microvolume cuvettertrook wrote:

Has anybody used the NanoDrop Spectrophotometry technology? Instead of using a 1 to 2 mL cuvette for samples, the user can place as little as 1 to 2 uL of sample on a light source (no cuvettes necessary). I am looking into the possiblity of purchasing a system and would like to know how well it works? If anyone has any experience please post your reactions and commments. Thanks!
samm
samm's picture
The device does not use any

The device does not use any cuvettes at all. You just wipe down a slide like platform, place a single drop (~2-5 ul, appropriate dilution) on it, lower the head, and you have your absorbance! Its a great machine - still very new here, so i really don't know about the possible reliability issues mentioned in the previous post. Have mostly used it for DNA quant so far - (where it works great - going by parallel densitometric and spectro comparisons on the same sample when the machine was being evaluated), but it is capable of more applications.
If you need to use cuvettes, or envisage very high sensitivity applications, and more flexiblity, Perkin Elmer makes systems that hold 400 ul micro-cuvettes - you can get by with ~200 ul of sample.

bobk
bobk's picture
I just checked the date for

I just checked the date for this original enquiry, it was ages ago so the author has probably already found a solution. Further to my earlier post, and following a little further research, you will find that the Nanodrop is fine for scanning and quantitation readings on fairly highly absorbing samples The pathlength is fixed at 1mm (somebody told me it also had a 0.2 mm option?) which means an undiluted sample with a nominal 0.5 Abs in 1cm would only have 0.05 Abs in this device, probably not enough for great precision. However a sample you would have to dilute 10X (or more) to read in a normal spectro would be fine here. Starna and Hellma make microvolume cuvettes down to 2.5ul for normal spectros and there is a special cell (Traycell) from Hellma that works very well down to about 5ul in some spectrophotometers, which is also 'cuvette free' as you just apply a drop of sample to the top, like the Nanodrop. I guess the jury is out as to whether a micro device like the Nanodrop can compete on precision with a full size spectrophotometer with a microvolume accessory, Intuition says you can't build a high precision spectro in a tiny box and there must be compromises, even with CCD or DAD detection, but then you also have compromises if you are only using a small part of the beam in a larger device. Maybe a focussed beam spectrophotometer and microcell is the best solution of all?

samm wrote:

The device does not use any cuvettes at all. You just wipe down a slide like platform, place a single drop (~2-5 ul, appropriate dilution) on it, lower the head, and you have your absorbance! Its a great machine - still very new here, so i really don't know about the possible reliability issues mentioned in the previous post. Have mostly used it for DNA quant so far - (where it works great - going by parallel densitometric and spectro comparisons on the same sample when the machine was being evaluated), but it is capable of more applications.
If you need to use cuvettes, or envisage very high sensitivity applications, and more flexiblity, Perkin Elmer makes systems that hold 400 ul micro-cuvettes - you can get by with ~200 ul of sample.
Tony Rook
Tony Rook's picture
bobk:

bobk:

Thankyou for your response regarding the nanodrop device. Fortunately, we have not yet made a decision on purchasing this system. Your reference for micro-cuvette was very helpful! Also, in regards to precision, this is something that our application cannot afford to lose. Therefore, I think what we will do is continue using our standard spectrophotometers, while keeping on eye on the nanodrop market.

bobk
bobk's picture
Hi Again,

Hi Again,

This is turning into a hot topic, and we have done some work to try to find out which solution works best with small volumes. Working with porphyrins and light harvesting complexes needs a precise solution. The TrayCell was tried in two of the Sheffield University research grade spectrophotometers ( A Cary 50 and a Cary 500)
In the smaller Cary 50 the results were very precise and reproducible, probably due to the beam being very small and getting most of the energy into the device. A variance of about 0.002 Abs between readings meant that it was possible to work with confidence down to about 0.005 Abs (equivalent to 0.05 Abs in 1cm) and up to about 2.5 Abs (25 Abs)
The Cary 500, a big and powerful UV/Vis/NIR spectrophotometer made 3ul seem like 3ml. The baseline flatness was better than 0.00015 Abs, and scans of a light absorbing complex which had a peak absorbance of 1.6 Abs and minor peaks of 0.006 Abs looked as if they had been scanned in 3 ml. The 500 beam is not highly focussed, and the blank transmission of the traycell was only 10% so this result was quite a surprise.
If you have access to a research grade spectrophotometer, see if you can try the TrayCell!
I don't know if I can post the results on this forum?

Fraser Moss
Fraser Moss's picture
I know the main complaint

I know the main complaint about the nanodrop is reproducibility between readings.

I have found in my short experience with the device that repeated readings from the same sample show a creeping increase of about 0.1-0.2 Abs units per measurement.

My theory is that there is some evaporation issue when working with such a small volume.

When I have put on a fresh drop of the same sample the readings are usually +/- 1% of the original reading of the first sample.

Oh my samples are usually cDNA by the way

Tony Rook
Tony Rook's picture
Thanks to everybody who has

Thanks to everybody who has shown interest in this topic. Just as an update, I received some marketing information today from Nanodrop regarding their new ND-3300 Flourospectrometer.

Here are the system specifications:

Excitation sources:
▪UV LED (excitation center point 365 nm)
▪Blue LED (excitation center point 470 nm)
▪White LED (500-650 excitation)
1-2 ulsample volume
2048-element linear silicon CCD array detector
Measurement range: 400-750 nm
Wavelength accuracy: 1 nm
Wavelength resolution: 8 nm (FWHM at Hg 546nm)
Fluorescence precision: < 5% CV @ 1 nM Fluorescein)
Fluorescence range: up to 5 orders of magnitude (Fluorescein)
Detection limit: ~0.1 nM Fluorescein
Maximum concentration: ~10 uM Fluorescein
Measurement cycle: 10-15 seconds
Dimensions: 20 cm x 15 cm x 12 cm

I suspect this system is going to run into tho the same sort of reproducibility issues. I would think to get around the evaporation issue, one could simply pull samples for every read (at 1-2 uL per sample that should work for most applications). Anyway I just thought the forum may be interested in this new flourometer.

bobk
bobk's picture
Hi Again,

Hi Again,

The issue you mention with evaporation might be the explanation for variability of results with the NanoDrop. Repeat scans with the Traycell were within 0.1% ( with 1 nm bandwidth and 1nm resolution) in a Cary 500, repeated over about ten minutes, so evaporation is probably far less of an issue with the closed cap design of the traycell.

The microvolume fluorimeter seems like a nice idea. I think we would have to look at it's 'real world' performance before making further comment.

I guess that there are more solutions out there for you to take your choice from. For precision and sensitivity, opt for the Traycell in a decent spectrophotometer for UV and a microcell (40ul) in a full-spec fluorimeter. If the requirement is for higher throughput with a reasonable tolerance of errors in precision and reproducibility, then I guess the NanoDrop family is a good option. I'm sure the fluorimeter is a lot less expensive than a true research grade instrument.

Tony Rook
Tony Rook's picture
I certainly see the benefit

I certainly see the benefit of using a Nanodrop family device for large sample throughput applications such as in quality assurance / quality control laboratories. However, for a high throughout research application a 96 well plate fluorometer with UV capabilities seems to be a better option. Any opinion?

aaronharmon
aaronharmon's picture
Hey,

Hey,
We purchased a nanodrop for our lab last fall. It pretty good, but we found that 2ul samples are more reproducible than using 1ul samples. I also had problems with accuracy in samples that had less than 10ng/uL DNA. I haven't heard how it performs with protein though.

Tony Rook
Tony Rook's picture
aaronharmon wrote:Hey,

aaronharmon wrote:

Hey,
We purchased a nanodrop for our lab last fall. It pretty good, but we found that 2ul samples are more reproducible than using 1ul samples. I also had problems with accuracy in samples that had less than 10ng/uL DNA. I haven't heard how it performs with protein though.

aaronharmon:

Have you also used traycells or microCuvettes? How do these compare with the Nanodrop?

samm
samm's picture
Evaporation is very likely

Evaporation is very likely the culprit behind the variability in readings - the same sample over a 8-min period, with readings evry 20 sec initially to 1 min after 2 mins fluctuated quite a lot - though of the 13 readings, 12 tended up. However, 10 mins after start, following a wipe, the same sample gave readings 0.4% off, 15 mins later, 0.3% off - so I guess the system is fine - just put in a fresh sample every time - no "direct" kinetics!

aaronharmon
aaronharmon's picture
Have you also used traycells

Have you also used traycells or microCuvettes? How do these compare with the Nanodrop?

I've used the cuvettes before we got the nanodrop, but i never compared the two. It would be nice to do though. Thanks for bringing that up.

Tony Rook
Tony Rook's picture
aaronharmon wrote:Have you

aaronharmon wrote:

Have you also used traycells or microCuvettes? How do these compare with the Nanodrop?

I've used the cuvettes before we got the nanodrop, but i never compared the two. It would be nice to do though. Thanks for bringing that up.

aaronharmon:

If you do decide to compare the two, can you please post your results and/or opinion? That would be most helpful. Thanks.

mol
mol's picture
samm wrote:Evaporation is

samm wrote:

Evaporation is very likely the culprit behind the variability in readings - the same sample over a 8-min period, with readings evry 20 sec initially to 1 min after 2 mins fluctuated quite a lot - though of the 13 readings, 12 tended up. However, 10 mins after start, following a wipe, the same sample gave readings 0.4% off, 15 mins later, 0.3% off - so I guess the system is fine - just put in a fresh sample every time - no "direct" kinetics!

In my experience when you do proper replicates (replacing the sample before each reading) we get variation of less than 0.5% (DNA and RNA). I therefore no longer bother doing replicates. I always use 1.5ul and am very surprised people question reproducibility. It was bought for my lab almost a year ago and everyone uses it without complaint.

I agree it isn't designed for kinetics unless you place a fresh aliquot on for each reading.

Tony Rook
Tony Rook's picture
mol wrote:

mol wrote:

In my experience when you do proper replicates (replacing the sample before each reading) we get variation of less than 0.5% (DNA and RNA). I therefore no longer bother doing replicates. I always use 1.5ul and am very surprised people question reproducibility. It was bought for my lab almost a year ago and everyone uses it without complaint.

I agree it isn't designed for kinetics unless you place a fresh aliquot on for each reading.

mol:

What assay are you using the nanodrop with? Do you have to be concerned with degradation of your sample? If so, I would be curious to know how you deal with a rapidly degrading sample.

Thanks for you input to this topic,

mol
mol's picture
Hi Trook,

Hi Trook,
My applications are mainly for genomics (microarray and genotyping) - DNA, RNA cDNA quantification. I know there are people using it for proteins here too but i don't really have any feedback on that.
Degradation of the sample isn't an issue - if our RNA degrades on the pedestal it doesn't matter as it all absorbs at 260nm (an advantage and drawback of absorbance). We don't retrieve the sample (although i am told some of the protein crystallography group do).
What sort of assay are you looking at performing?

Tony Rook
Tony Rook's picture
We have a generational

We have a generational oxidative chemistry used for disinfection and/or sterilization of medical devices. Unfortunately, the active proprietary chemistry rapidly degrades as the reaction proceeds. Therefore, characterization of the kinetics is extremely important to understand the disinfection properties of this chemistry. We currently use a Spec 20 for our analysis and I was interested to find out of the nanodrop system woudl be helpful.

mol
mol's picture
trook wrote:We have a

trook wrote:

We have a generational oxidative chemistry used for disinfection and/or sterilization of medical devices. Unfortunately, the active proprietary chemistry rapidly degrades as the reaction proceeds. Therefore, characterization of the kinetics is extremely important to understand the disinfection properties of this chemistry. We currently use a Spec 20 for our analysis and I was interested to find out of the nanodrop system woudl be helpful.

NanoDrop may be too slow for your application then. Measurement takes about 10seconds and with cleaning and reloading you can probably do a reading every 20 seconds or so.
It is great for us as we don't have to clean cuvettes etc but all our stuff is end point / quantification

Tony Rook
Tony Rook's picture
mol:

mol:

I didn't realize that a measurement took so long using the nanodrop. You are correct to assume that this would become a real problem for my application. Thank you very much for you input, it has been more than helpful.

mol
mol's picture
trook wrote:mol:

trook wrote:

mol:

I didn't realize that a measurement took so long using the nanodrop. You are correct to assume that this would become a real problem for my application. Thank you very much for you input, it has been more than helpful.

Yep, it does a full spectral scan on each sample (220 - 750nm). For us this is a bonus as we use the spectrum as a rough guide to sample purity, but it means that it takes a little longer and sounds like it counts your application out. It is a shame you can't just select one wavelength (in case anyone from nanodrop is listening!) In our lab it is still a lot quicker than our previous spec (GeneQuant) as we never have to dilute the samples or clean cuvettes.

mol
mol's picture
I've just tried the Traycell

I've just tried the Traycell cuvettes after using the nanodrop for 2 years. They are incredibly fiddly to use and clean and i'm highly suspicious of the design being able to maintain the pathlength. Thanks, but i'm done with cuvettes and i'm sticking with my nanodrop

trook wrote:

aaronharmon wrote:
Have you also used traycells or microCuvettes? How do these compare with the Nanodrop?

I've used the cuvettes before we got the nanodrop, but i never compared the two. It would be nice to do though. Thanks for bringing that up.

aaronharmon:

If you do decide to compare the two, can you please post your results and/or opinion? That would be most helpful. Thanks.

Jon Moulton
Jon Moulton's picture
It would be interesting to

It would be interesting to run a nanodrop rig in a warm closet with a humidifier. Perhaps that would solve the reproducibility issue, at least until the grad student in the closet keels over and starts to mildew.

- Jon

beanoic
beanoic's picture
Hi all,

Hi all,
I'm a student currently doing a marketing survey on small volume spectrophotometer- nanodrop & Nanophotometer. I would appreciate that you can actively participate in the survey. The feedbacks will be read by the company. This is the time to air any comments or feedback if you want. =)

Thank you for taking your time in doing the survey.

Survey link

amalr
amalr's picture
Yes I am using this

Yes I am using this wonderfull thing,, it is very easy to use and you can print the results

Amal

Tony Rook
Tony Rook's picture
beanoic:

beanoic:

Would you be willing to share the results of your marketing survey with the rest of the board? If possible, could you post a link to the survey results? I know that I would be interested to see what you find out.

sampope
sampope's picture
trook wrote:Has anybody used

trook wrote:

Has anybody used the NanoDrop Spectrophotometry technology? Instead of using a 1 to 2 mL cuvette for samples, the user can place as little as 1 to 2 uL of sample on a light source (no cuvettes necessary). I am looking into the possiblity of purchasing a system and would like to know how well it works? If anyone has any experience please post your reactions and commments. Thanks!

YES! I have used a nanodrop and love it for both DNA and RNA quantitation. The only thing that seemed negative was that it showed a low wavelength absorbance if my trizol RNA purification was not done well. I guess it was picking up excess phenol, but the 260 absorbance did not seem to be affected. The scale shown on the readout was "rescaled" because of the higher low wave length absorbance. I hope this made sense.

samm
samm's picture
trook wrote:mol:

trook wrote:

mol:

I didn't realize that a measurement took so long using the nanodrop. You are correct to assume that this would become a real problem for my application. Thank you very much for you input, it has been more than helpful.

Hi Tony! There is now an eight-channel version of this, with the same 2 ul sample volume - measurement time remains at ~10 secs if you want to do the full dual path read. I'm still sticking to single measurements though - no kinetic measurements on the Nanodrop.
Btw, Tecan now has a plate reader capable of 2 ul sample volumes (16 at a time, Nanoquant, from a variety of plates) - have no idea how the device actually works.
-sam

mbicking
mbicking's picture
Greetings from the Analytical

Greetings from the Analytical Chemistry section, and kind regards from us HPLC-ophiles.

It occurred to me while reading this interesting series of posts that there is another way to do analysis of small volumes. It's an old-fashioned concept called flow injection analysis, using a "new-fashioned" HPLC.

A good quality diode array detector (cf. Agilent 1100 or 1200) will have baseline noise of less than 0.0001 AU (<0.1 mAU) under fairly typical conditions. The standard flow cell has a volume of 8 uL and a path length of 10 mm. Semi-micro and micro flow cells have even smaller volumes, but maintain a fairly long path length (> 3 mm). Plus, you can get an entire absorbance spectrum several times a second.

Simply couple the detector with a pump and autosampler and you are ready to go (just bypass the column if you have an existing unit). In-line/integrated autosamplers can inject variable volumes of sample (< 1 uL to 100 uL) with no waste. Simply pump a matching solvent through the system and you should have an anwer in a few seconds. You can vary flow rate and injection volume as needed. Yes, there would be some dilution of sample, but not much if your tubing is short.

Of course, cost may be an issue. I don't know how much these nano spectrophotometers cost, but if you already have an HPLC, or want more justification to purchase one, this is something to consider.

Let me know if you have additional interest.

Regards,
Merlin K. L. Bicking, Ph.D.
Moderator, Analytical Chemistry

Tirumal Rao
Tirumal Rao's picture
hi,

hi,
This very good instrument for quantification of protein ,DNA,RNA samples.very pricise mesurment .cutties are very sensitive.its more cost.this ver advance technology for molecular level analysis.
Thanks,
Tirumal

Biju
Biju's picture
wrote:

wrote:

Hi
I have use it for DNA and RNA quantification with great savings of DNA as well as time to measure.
I will recommend buying it is not a bad idea

shareef
shareef's picture
The Nanodrop works great, it

The Nanodrop works great, it saves a lot of time and reagents.  I use it for DNA/RNA as well as reading protein concentrations. 

Ivan Delgado
Ivan Delgado's picture
I add my vote to all those

I add my vote to all those that have experience using the NanoDrop and find it to be one of the best spectrophotometers out there. At its price point (~$8,000) and ease of use (no consumables), there is nothing out there that compares.  
If you haven't seen this video about the NanoDrop, check it out:
http://www.youtube.com/watch?v=aUZD8sj5c4w

Ivan Delgado
Ivan Delgado's picture
Has anyone had any experience

Has anyone had any experience with the new NanoDrop? I recently came across their website (http://www.nanodrop.com/) and saw that they had updated the instrument (now the 2000c model). It also seems to be slightly taller yet also thinner. 
Just curious.

g a
g a's picture
Have you all come across with

Have you all come across with the picodrop? check the following link. http://www.picodrop.com/ 
using the picodrop one can even recover the volume of sample used for quantitation.
However, the question of reproducibility is always there and we prefer using the BIOANALYZER which isnt the only quantitation instruments but at the same time gives you the electropherograms, chromatograms and at the same time highly reproducible results. One can analyse DNA, RNA, proteins as well as conduct flow cytometry on this instrument too.
Cost could be a factor.... but for high precision experiments involving siRNA, Microarrays, proteomic screening etc. it gives more relaible results.
 

Wigan
Wigan's picture
I think before you use any

I think before you use any instrument you should check the performance for accuracy and reproducibility. The nanodrop does show evaporation and drift so regualr servicing is a must.
The NanoPhotometer seems to give the best overall performance and is always in calibration. 

ama
ama's picture
I am interested in accurate

I am interested in accurate small volume measurements of proteins.  Can anyone comment on reproducibility and accuracy of nanodrop?  What about other instruments?  How low can your protein concentration be? 

Wigan
Wigan's picture
The Nanodrop struggles with

The Nanodrop struggles with proteins due to solvent effects and again evaporation - check out the nanophotometer as this has a better design for more difficult samples

ama
ama's picture
Thanks for replying. O.K.

Thanks for replying. O.K. the nanophotometer is better. Have you heard anything good/bad about the BioPhotometer plus from Eppendorf (used with a Hellma TrayCell)? I believe it is 1/3 the cost of the nanophotometer.

PhilM
PhilM's picture
Has anyone tried the BioSpec

Has anyone tried the BioSpec-nano from Shimadzu and how does it compare with the nanophotometer or the nanodrop?

Does anyone know the price differences without going through a rep?

mol
mol's picture
All these instruments would

All these instruments would be fantastic if the nanodrop didn't exist, but it does and anyone who uses it loves it. Only reason not to go for nanodrop is if you don't have the budget. And in my opinion, you'd be better off looking for the $$$

Wigan
Wigan's picture
PhilM - The Shimadzu is a

PhilM - The Shimadzu is a neat design and it even wipes the sample head automatically although you have to change the wipe after only 50 shots or so and it is not easy.  there is a question mark over its performance and few people seem to have gone this way - it is also more expensive that the other options by 10%  over the nanodrop and 25% more than the nanophotometer plus it requires servicing so you have the running costs to consider

mol -people love the NanoDrop becasue it is easy to use however it also is easy to get the wrong answers which people are now becoming aware of. It goes out of calibration and drifts plus it needs frequent reconditioning which nobody seems to do - check out the nanodrop web site for the details. 

[NB Moderator added link to the maintenance web site here  - www.nanodrop.com/Support.aspx]
For some reason good science seems to go out of the window with these low volume techniques 

mol
mol's picture
 Wigan - it isn't good or bad

 Wigan - it isn't good or bad science, it's good or bad scientists. In my previous lab in UK Pharma my boss thought it was reasonable to dilute 1ul in 999ul in a cuvette and expect a reliable answer! Not uncommon at the time! 

Get it checked every 12 months - part of our service plan - surely good practice for an important piece of kit. 
Never had to recondition - i guess they do this at service but never asked. 

If it helps, when i have new students i tell them to use 1.5 ul or 2ul for protein and don't be afraid to clean it properly - it doesn't scratch when you rub it with a tissue!! 

I check it with a DNA standard every month or so rather than their calibration fluid and i've seen no drift in the results to date.

Wigan
Wigan's picture
very true - some scientists

very true - some scientists are too trusting
Apparently the recomendation is to have it serviced every 6 months and the reconditioning should be at least every month depending on work load. Solvents kill the drop shape so worth keeping a check on this. For proteins 3ul may be better and use reverse pipetting to avoid bubbles.  Worth also checking the same sample over a period of a minute to see if that changes as sometimes you can see variations.
 

Wigan
Wigan's picture
Hi Ama

Hi Ama
Sorry I did not get notification of this and it is probably far too late.
 The eppendorf is much cheaper than the nanophotometer however it is very limited as it has a very old xenon source which is noisy and not optimised for the Traycell so you will have poor reproducibility and limited working range. You also cannot see the scan of the uv region so you cannot tell if you have any contamination.  It is the same if you try to fit a Traycell into a standard spectrophotometer as the optics are not optimised to work with it.  You need a properly optimised system to get the best performance
The eppendorf is ok for teaching principles (although these days you should see the scan of the peaks)  but probably not ideal for serious quantification

mol
mol's picture
I was intrigued by the

I was intrigued by the conditioning as i've never seen a problem. It seems that another group here that has a couple of nanodrops use one exclusively for proteins - this one has needed reconditioning twice in 18 months - some sort of cream they add to the pedestal? They aren't over concerned by it as it is pretty quick. DNA and RNA seem to be no problem so i guess it is something in the buffers (any thoughts?). They always use 2ul. No problems but i guess if you're using stuff that severely affect surface tension you could increase it without any issues?

Why would you check the concentration over a minute? it takes about 10 seconds to measure. Your sample would never be on there for a minute.  Leaving a sample on there and pressing measure isn't a replicate as this is not how the instrument is used. This is an important point to remember when new people come in to the lab to use it. Samples evaporate over time, of course they do. The nanodrop is good but as far as i'm aware it doesn't change the laws of physics. What it does, is measure in a timeframe where evaporation doesn't have a measurable effect. Need a replicate - do a proper one. Add another aliquot of sample. This is the argument that one of the reps for either picodrop or nanophotometer used and it annoyed the hell out of me. Might as well of just called me an idiot (not that i want to start a Rep-bashing thread on here)   

Wigan
Wigan's picture
the reconditioning I think is

the reconditioning I think is an acid wash and probably only needed in a lab which shares resources as you never know what people leave on the window. Nuclic acid s should be Ok it is the solvents in proteins which can cause the problems.  To check the same sample a couple of times gives an indication of the noise in the system - evaporation I would have thought shouldn't be a problem over a minute although the sample does have a large surface area for the volume.  The nanophotometer lid system does limit evaporation as it encloses the sample so it becomes a non arguement.
Interesting stuff and good luck with the teaching

mol
mol's picture
 I was always way more

 I was always way more concerned what people were leaving in the cuvettes than on the pedestal! 
Instrument noise is interesting - out of interest, if you do an experiment where you replace the sample on the pedestal to get replicate measurements  and get within say 1% routinely, but if you leave the sample on you see a drift upwards over say 5 mins do you think this represents instrument noise? 
For me this demonstrates low instrument noise but an evaporation effect over a period well outside the measurement window - this was the fact that the rep couldn't grasp. 

 I think take home message is that you should always get the usual suspects in to demo and make sure the comparison makes sense. In my humble opinion Wigan, testing as you suggested seems like a smoke screen used by desperate sales reps trying to sell inferior instruments rather than a genuine comparison of performance (sorry, my distaste for some reps may of surfaced again there). 

M

The FFM
The FFM's picture
 So Wigan, you seem to be

 So Wigan, you seem to be somewhat of an authority on these devices.  How many different types have you actually used / trialed and have you actually had the chance to do a genuine side-by-side comparison of each device with the same samples?

bobk
bobk's picture
Hi all,

Hi all,

I've used several of the devices under discussion here, and spend most of my time concerned with spectrophotometry in various forms.  The achilles heel of the NanoDrop is evaporation, and generally limited high bandwidth optics.  Place a TrayCell in most spectrophotometers and you will get fairly mediocre performance, because the machines are designed to work with a beam image which is a lot bigger than the window on the TrayCell.  Much of the beam is therefore lost, usually up to about 90%, and this shifts an instrument which would have been comfortable 0-1 Abs into a region where the stray light and signal to noise performance are simply not a match for even the humble NanorDrop.   Place the same TrayCell in a spectrophotometer that can easily handle a 90% loss of beam image, and you will get far better results than a NanoDrop, the same is true if you use the device in a spectrophotometer with a focussed beam such as the Beckman or Varian.     In my experience the nanoDrop is fine for quick and approximate quantitation. Anything more involved  or requiring repeatability and the TrayCell wins easily, in a powerful spectrophotometer it becomes an excellent high precision research grade tool.

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