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Gerard's Content

There have been 41 items by Gerard (Search limited from 20-April 20)

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#99768 Absorbance microplate reader

Posted by Gerard on 06 February 2011 - 09:50 AM in Lab Equipments

If you don't know wich filter you need, don't buy it because you don't need it. Save your money until you know wich filter you need.

#98947 hedon-fleig's saline

Posted by Gerard on 29 January 2011 - 05:50 AM in General Lab Techniques

Lockwood A P M 1961 Ringer solutions and some notes on the physiological basis of their ionic composition; Comp. Biochem. Physiol 2 241-289

#98944 ELISA reader theory

Posted by Gerard on 29 January 2011 - 05:39 AM in ELISA and Immunoassay

Thanks for that info, so it works because the chromogenic Substrates used have a high molar absorption?

Do you have a link or book reference for that? just to be able to make my point.

Yes that's right and no I don't have a link or a book because it is simple reasoning.

What I didn't mention is the origin from the statement that the absorbance should be read between 0.200 en 1.000, this comes from the earlier photometers these were equiped with a analog logaritmic scale and tube amplifier. The ampliflier had a significant noise in the lower region and therefor the reading was less reliable in the lowerpart of the scale and a analog logaritmic scale is hard to read accurate above the 1.000

#98910 ELISA reader theory

Posted by Gerard on 28 January 2011 - 02:02 PM in ELISA and Immunoassay

The statement that the Beer-Lambert law states a reading only in the linear range of an absorbance reading between 0.2 and 0.8 OD is correct isn't right, it states that in very diluted samples the concentration is linear to the absorbance.
This means that the range in with you can use the law depends on the molar absorbtion from the solution, with a high molar absorbtion the maximal absorbance of a solution can be much higher then in a solution with a low molar absorbtion.

#95457 sample pool

Posted by Gerard on 20 December 2010 - 02:25 AM in General Lab Techniques

It's possible to tell if the two samples are statistically different from each other if the the specs ( as VC at the same level) from the method are known.
We had a simular problem and after consulting our biostatistic department we could tell if the groups where different or not.
As I remember one of the big issues was the presence of very abnormal values in 1 one of the samples and the confidence of the test depended strongly of the number of samples in the pool.

#95113 Why store pipette in upright position?

Posted by Gerard on 16 December 2010 - 07:08 AM in General Biology Discussion

I don't think that there is a specific reason, I've never seen a publication with this topic.
A reason to do so maybe that when someone has got fluid in the pipet it will drip out and not contaminate the plunger.

#86036 Absorbance reading does not match spectra

Posted by Gerard on 06 September 2010 - 11:54 AM in General Lab Techniques

You have to give more details, what you're writing looks impossible.
The readings from your sample looks as the didn't react, a other possibility is that the reactionproduct breaks down. I,m just guessing by lack of information.

#84329 Potency, Free Base and Lot Purity

Posted by Gerard on 22 August 2010 - 01:26 AM in General Lab Techniques

Look into this PDF

#84328 How to accurately pipet blood?

Posted by Gerard on 22 August 2010 - 01:14 AM in Hematology

I use two methods for accurately pipet blood.
With a tip
First pipette the blood very slowly. When taking blood in let the piston come up slowly and wait for 20-30 seconds so you're sure the blood is in.
Then slowly push the piston down and watch very carefully if all the blood from the wall of the tip is coming down, if not you're pushing to fast. It,s a very slow proces it can take minutes.
(With a glass pipet it works the same)

Much faster is using a positive displacement pipette as mentioned before.

Weight is not a solution because the specific weight of blood is not known therfor you can't calculate the volume.

#82056 Ponceau Red Staining Problem

Posted by Gerard on 31 July 2010 - 06:51 AM in SDS-PAGE and Western Blotting

Itīs normal, Ponceau red washes away.

#79065 measurement units of DNA

Posted by Gerard on 12 July 2010 - 03:44 AM in General Lab Techniques

Google: mCi unit
Hit 1: http://en.wikipedia.org/wiki/MCI

can do it for all :rolleyes:

#78099 help me

Posted by Gerard on 04 July 2010 - 09:00 AM in General Lab Techniques

wrong reading.

#77912 No SDS in gels

Posted by Gerard on 02 July 2010 - 09:59 AM in SDS-PAGE and Western Blotting

I've never seen this kind of crackling as in the picture thus i'm guessing.
I,m not sure but looking at the picture i have the feeling that the problem originates from the gel casting or the imager. I don't think the blotting or the probing caused this problem.

#76514 low dead volume

Posted by Gerard on 22 June 2010 - 07:29 AM in Biochemistry

Assuming that the system is provided with a liquid detection system put a known volume (500 ul) in a sampletube and let the system sample a small volume (25 ul) into another tube and count the cycles it can do before the detecting system tells there is not enough sample anymore. Than the remaining sample is easy calculated.

#76150 IgG SDS-PAGE

Posted by Gerard on 19 June 2010 - 11:57 PM in SDS-PAGE and Western Blotting

Maybe this can help.


#75647 Bromophenol blue turns yellow

Posted by Gerard on 16 June 2010 - 10:06 AM in Molecular Biology

It's a problem in your buffer

Bromophenol blue is an acid-base indicator its useful range lies between pH 3.0 and 4.6. It changes from yellow at pH 3.0 to purple at pH 4.6; this reaction is reversible. Bromophenol blue is structurally related to phenolphthalein-a popular indicator.


#75352 BSA Standard Curve Dilution (BCA Kit)

Posted by Gerard on 14 June 2010 - 11:52 AM in Protein and Proteomics

I mean just NaCL 9g/l but PBS will do to.

#75324 Reducing Pipetting Error?

Posted by Gerard on 14 June 2010 - 09:43 AM in General Lab Techniques

If there are outliers once and a while you have to practice again and again, you have seen your skills improve over the last 2 years and it will get better intime although it will go slower and slower.
Be concentrated and let nothing distract you when you're pipetting. Try to get in a constant flow to get every thing as stable as possible as the speed of pressing the plunjer, the waiting time for the liquid to flow downwards before you press the plunjer completely down etc.

#75133 BSA Standard Curve Dilution (BCA Kit)

Posted by Gerard on 12 June 2010 - 06:24 AM in Protein and Proteomics

I dilute the standard with Saline 0.9% and have no concern about the matrix of my samples because I assume the the fact that in the samples a mix of protein are present and not only albumin as in the standard this will have more influence on my results.

#75130 well washer

Posted by Gerard on 12 June 2010 - 06:14 AM in Immunology

Take care that no wash solution stays put in the plate otherwise you get problems.
Hit the platea few times on a papertowel on the bench.

#74994 Springerlink--Zymography

Posted by Gerard on 11 June 2010 - 02:36 AM in SDS-PAGE and Western Blotting

Google helps:

#74660 pH hepes

Posted by Gerard on 09 June 2010 - 11:45 AM in General Lab Techniques

With a pKa = 7,55 (20 °C) the buffer has a good buffering capacity therefore adding NaCl and CaCl2 will have almost no effect on the pH.

#74223 Hemocytometer

Posted by Gerard on 06 June 2010 - 12:56 PM in Tissue and Cell Culture

WIKI can:

#74185 How to prepare ascorbic acids

Posted by Gerard on 06 June 2010 - 08:02 AM in General Lab Techniques

It's my my field of work but if i'm correct DMEM is a water based solution then dissolve the ascorbic acid directly into the medium.

#74179 Shelf life of self prepared solvents

Posted by Gerard on 06 June 2010 - 05:17 AM in General Lab Techniques

Quality systems often demands a expiry date but I find it hard to do so because to be sure it's valid you have to test it for a long period and big number of solutions at every test it's used in.
If you pick a date of wich you want to be certain it's ok then you will have to dispose a lot of perfect working solutions and make a lot of not nessecary costs.
Take for instance the NaOH 1M solution and it's used for correcting a buffer used in a test that is not influenzed by carbonate(CO2 from the air) it will be useable for indefined time.

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