Frequently asked questions
Here you might find answers for some typical questions. For any further questions please contact us.
1. How can I place an order?
Orders may be placed via website (www.micromod.de), e-mail (email@example.com) or fax (+49 381 54345620). Please have shipping and billing information available. European customers have to provide their VAT number.
2. What methods of payment are accepted?
Orders may be placed using a purchase order or credit card. We accept Visa and MasterCard.
3. How will the shipment be arranged?
All shipments will be arranged with United Parcel Service (UPS), freight and insurance charges are prepaid and added to the invoice (DAP destination). The standard shipment fee is 25 EUR to Europe, 60 USD to USA, 70 EUR (100 USD) to Japan and other countries. Some countries imposes Entry customs clearance / Entry Taxation fees for import, these are not included.
If you wish to use an own courier account, please specify the courier and account number at the time of ordering.
4. Do you have any distributors in other countries?
Customers from Asian countries can place their orders via local traders:
Corefront Corporation (www.corefront.com
Funakoshi Corporation (www.funakoshi.co.jp
Nacalai Tesque Inc. (www.nacalai.com
Hannotech Co. Ltd. (www.hannotech.com.cn
Shanghai Biochemical Co. Ltd. (www.shbcbio.com
KYS Technology Co., Ltd. (www.kyst.com.tw.com
JYSCO Ltd. (www.jysco.com
Scientific Procurement (S) Pte Ltd. (www.scientificprocurement.com
5. How can I get a copy of your print catalog?
You can download a pdf-Version of our print catalog from the print catalog link on our website.
6. How is the relation between nominal and measured mean particle diameter?
All particle diameters that are given in our product descriptions and technical data sheets are nominal values which may deviate from the measured mean particle diameter. The size of particles with diameter < 2 µm is measured by Dynamic Light Scattering (DLS) with the Zetasizer Nano ZS 90 (Malvern Instr. Ltd.). DLS is also known as Photon Correlation Spectroscopy (PCS). The size of particles ≥ 2 µm is measured with the Coulter® Multisizer III. The specification for the particle diameter and the size distribution of each particle type is available on request.
7. How do you measure the size of your microparticles?
The size of particles with diameter ≥ 2 µm is measured with the COULTER® Multisizer II. This is a multichannel particle size analyzer, which employs the electrical impedance method to provide a particle size distribution analysis. The method is based on the change of the impedance, when a particle passes the measurement zone. This change is proportional to the particle volume.
8. What is the “Coefficient of Variation (% CV)”?
The coefficient of variation (CV) typically refers to the size variation of a bead population. The CV relates the measure of dispersion to the average about which it is measured in percentage. The CV is obtained by dividing the standard deviation by the mean particle diameter, i.e.: % CV = 100 % x Standard deviation / Mean diameter.
Our micromer® particles with diameters between 2 and 10 µm have CV values ≤ 5%.
9. How do you measure the size of your nanoparticles?
In general the size of particles with diameters < 2 µm is measured by Dynamic Light Scattering (DLS) with the Zetasizer Nano ZS 90 (Malvern Instr. Ltd.). DLS is also known as Photon Correlation Spectroscopy (PCS).
The Zetasizer determines the size by first measuring the Brownian motion of the particles in a sample using Dynamic Light Scattering (DLS) and then interpreting a size from this using established theories.
There are four different types of data analysis of the PCS measurement:
- the cumulants analysis
- the multi exponential analysis,
- the CONTIN analysis and
- the non negative least squares analysis.
The Z-average Size is the most important and stable number produced by the technique. This is the size to use if a number is required for quality control purposes.
The Z-average Size is obtained by the cumulants analysis. This analysis gives only two values, a mean value for the size and a width parameter known as Polydispersity Index (PDI). This mean size is an intensity mean and directly calculated from the signal intensity.
According to our experiences we use different types of analysis for the evaluation of our nanoparticles. Especially the different scattering properties of fluorescent or magnetic nanoparticles require on optimal adjustment of the analytical methods.
10. What is the Polydispersity Index (PDI)?
The size distribution of our nanoparticles is measured by photon correlation spectroscopy (PCS). The quality of size distribution is given by the polydispersity index (PDI). This value is calculated as deviation between the measured autocorrelation function and the mathematically adapted correlation function. This value is below 0.2 for nanoparticles with a small size distribution and between 0.2 and 0.5 for broad size distributions. PDI values higher than 0.5 show that the measurement can not be analyzed.
11. How do you measure the surface charge of your particles?
We measure the Zeta Potential of our particles with the Zetasizer Nano ZS 90 (Malvern Instr. Ltd.). The Zeta Potential is measured using a combination of the measurement techniques: Electrophoresis and Laser Doppler Velocimetry, sometimes called Laser Doppler Electrophoresis. This method measures how fast a particle moves in a liquid when an electrical field is applied – i.e. its velocity.
12. Which magnetic separation device do you recommend for larger volumes of magnetic particle suspensions?
We recommend the SEPMAG Q1L (www.sepmag.eu)
for volumes up to 1L. For example, our nanomag-D, 500 nm particles (V = 600 ml, c = 10 mg/ml, product code: 09-00-502) were separated with the SEPMAG Q1L within ~ 30 min.
13. Why is the zeta potential of silica particles with amino groups on the surface negative?
The amino functionalization of silica particles is performed by polycondensation of the Si-OH groups on the surface of plain silica particles with 3-(aminopropyl)triethoxysilane. Beside the NH2 groups there are numerous acidic Si-OH groups on the particle surface available that are responsible for the overall negative zeta potential of the amino-functionalized silica particles. The comparison of the zeta potential-pH functions of plain and amino functionalized silica particles with a diameter of 1 µm demonstrates the shift of the zeta potential of plain silica particles into positive direction for amino functionalized silica particles. The amino functionalized silica particles have a positive zeta potential at pH < 4 and a negative zeta potential at pH > 4.
Comparison of the zeta potential-pH functions of plain and amino functionalized silica particles (diameter: 1 µm)