13 nov. 2017

Bandwidth in the NIR Spectral Region

A question from Gabriela (thanks for your nice words about the blog) about the importance of the  resolution and bandwidth in the NIR instruments, takes me to see the paper from Karl Norris: "Limitations of Instrument Resolution and Noise on Quantitative analysis of Constituents with very Narrow Bandwidth in the NIR Spectral Region".
In this paper Karl Norris conclude that instruments with 10nm bandpass and a good signal to noise level ratio can measure constituents having a bandpass as narrow as 2 nm. It is not necessary to increase the resolution to detect them in case we increase the noise because the quantitative analysis become less accurate.
The experiment has been done with talc (2 nm bandwidth) in Avicel.

2 nov. 2017

Waiting for the instrument to be warming up to calibrate (DS2500)

Before to proceed to the instrument calibration in a DS2500 it is important to check that the instrument is stabilized fine. It is not enough to see that the instrument has pass the diagnostics, yo have to run several times the diagnostics and see that the "deltas" (difference between the nominal and founded values) for the wavelengths checked is stable and it finish drifting due to the warm up of the instrument.
In case that the deltas are close to cero for all wavelengths it is not necessary the calibration with the ERC, but if there is an slope in the values or a systematic difference it is better to calibrate to came with the values close to cero for all the wavelengths.
We don´t want to see drifts in the deltas as the instrument is warming up, and the ideal is to see random differences in the deltas for the several repetitions of the wavelength checks:

At this point we can continue with the calibration of the instrument (video).

23 oct. 2017

Enable Auto Archiving - ISIscan™

Testing the PC Standardization (Part 1)

PCA standardization is part of the types of standardization algorithms used in Win ISI. We start with a REP file with a certain scan spectra from two different instruments (same samples scanned on both instruments and giving the same name to them). When we select PCA standardization we go to the option "Create a Score file from a spectra file", and we see that the option to create a PCS file is activated, so when we do it, apart from to get a PCS file we get also a PCA file.

This PCS file is used after to reduce our CAL file ( the one  we use to develop the calibration). When we use "Reduce", we see how we can use a PCS file as optional:
We will use the reduced output file to develop the calibration.

9 oct. 2017

How many samples are needed for a calibration?

One of the questions normally asked is: how many samples are needed for a calibration?, for how long I have to add samples to a calibration.

Of course what is necessary is calibration data from different years. At the beginning we can have a nice SEC but not so nice SECV or SEP, but as soon as we have more data from next years we will see how the SEC is increasing and the SECV and SEP are decreasing and are becoming closer to the SEC and the continue to become similar, but not bellow.
The idea is to continue adding samples and variability while SECV is significantly different than the SEC and while the SEP is significantly different than the SECV.

23 sept. 2017

Draft of Win ISI diagram

Working on the main diagram of Win ISI for a presentation. This is a draft and I have to add more tools from new versions.

18 sept. 2017

Diagnostics : Peak to Peak (P2P)

Is the way we can see if we have extreme peaks on the noise spectra (like in this case due to encoder noise).
It is the absolute value between the absorbance in the highest peak and the absorbance in the lowest peak.
The manufacturers fix this value according to the  quality of the instrument components.

7 sept. 2017

PUZZLE: Spectra Reconstruction

I use to explain the concept of the spectra reconstruction as trying to fix a puzzle. We have the pieces ( loadings) which once are multiplied by the scores have difference sizes, but the same pattern.

We fit all the pieces, but it can be that the puzzle does not fit correctly, that we have some gaps or spaces not filled,...., etc. is the concept of spectra reconstruction whe we have a error matrix which is the part of the puzzle not completed. It can be small, large,...

One application of this concept is used to define if the spectra belongs to a certain category.

In this blog you will find post about the spectra reconstruction.

6 sept. 2017

Sub-sample and sub-scan concept

When we analyzed heterogeneous samples, it is normal to use large cups. The cups rotate and stops in certain places called sub-samples (suppose eight). At each sub-sample several sub-scans (normally  four) are acquired.
So we have eight sub-samples spectra composed of the average of four sub-scans each. In total we have thirty two scans.
We can get a prediction of each of the sub-samples to get the eight predictions and calculate the standard deviation for every constituent in order to see the heterogeneity of the sample composition.
We can export the average spectrum of all the sub-samples,  the eight spectra of the eight sub-samples or the thirty two total sub-scans for further study.

5 sept. 2017

Thanks a lot (more than 250.000 visits to this blog)

Thanks to all of you who read and follow this blog. We have pass the 250.000 visits in this Blog Life and I really happy about that.
Of course these are the main countries who visit the Blog, but I appreciate visits from many other places.

                  thanks so much