Thursday, May 2, 2019

The Multiple Benefits of Cold EI – Leading the Way to the Future of GC-MS

Aviv Amirav, Alexander B. Fialkov and Tal Alon, Tel Aviv University and Aviv Analytical. 


GC-MS is characterized by many performance aspects and most of them are not mentioned or discussed by the GC-MS vendors and/or by any user's paper. The purpose of this paper is to list 72 such performance parameters and discuss how Cold EI improves the vast majority of them. GC-MS with Cold EI is based on a GC and MS interface with a Supersonic Molecular Beam (SMB) and on electron ionization of sample compounds while they are vibrationally cold in the SMB (thus named Cold EI) in a contact-free fly-through ion source.

Cold EI Improves all the central GC-MS performance aspects, including: identification, mass spectral information, range of compounds that are amenable for analysis, sensitivity (detection limits), speed of analysis, and response uniformity.

Eight categories of GC-MS performances are listed below and in each of them we have several sub categories (given in the number in bracket):    
  1. Improved sample identification (13).
  2. Extending the range of compounds amenable for GC-MS analysis (3).
  3. Speed – faster GC-MS analysis (9).
  4. Sensitivity (12).
  5. Uniform, compound independent ion source response, quantitation and reproducibility (4).
  6. Improved compatibility with GC-MS enhancement technologies (11).
  7. Improved GC-MS maintenance, flexibility, ease of use and price (15).
  8. Improved utilization of mass analyzer specifications (5).  
Quoting Aristotle "The whole is greater than the sum of its parts", this combination of so many improvements (>60) creates a new and qualitatively superior technology that actually improves every type of analysis. While GC-MS with Cold EI enables new type of analyses and significantly improves challenging analyses, it does not impede on any simple method of analysis (compared with standard EI). Consequently, GC-MS with Cold EI is leading the way to the future of GC-MS. 

Tuesday, January 1, 2019

GC-MS with Cold-EI Demonstration Video



Aviv Amirav, Tal Alon and Alexander B. Fialkov, Tel Aviv University and Aviv Analytical 

In this video we demonstrate a live analysis of a test mixture, showing how the Cold EI technology improves all the central performance aspects of GC-MS. The test mixture includes 1 ng on-column each n-C16H34, methylstearate, cholesterol and n-C32H66 plus 10 pg OFN, and via its analysis we demonstrate twelve unique benefits of GC-MS with Cold EI.

Have a happy new year

Monday, December 24, 2018

Classical EI-SMB Ion Source and its Comparison with Classical EI with High Efficiency Source



Aviv Amirav, Tel Aviv University and Aviv Analytical Ltd.

Executive Summary

GC-MS with Cold EI includes, among its several benefits, a classical EI mode of operation. Mode changing is uniquely achieved in a few seconds via a click of the mouse method change that involves the reduction of the helium make-up cooling gas flow rate without touching any hardware. Classical EI with the Cold EI contact-free fly-through ion source (named Classical EI-SMB) provides classical EI mass spectra with high NIST library matching factors and identification probabilities. Furthermore, in comparison with the various other standard EI ion sources, Classical EI-SMB excels in having a contact-free fly-through ion source structure and as a result: a) It exhibits uniform compound independent response; b) It has no ion source peak tailing thus preserves the chromatographic separation; c) It is an inherently inert ion source thus it extends the range of compounds amenable for analysis via the analysis of polar and labile compounds such as free fatty acids and/or amides without derivatization; d) It has much lower noise and thus exhibits very high total ion count mass chromatograms signal to noise ratio. Classical EI-SMB is compared in this article with the Agilent 5977B with high efficiency ion source (HES) and all the above written benefits are demonstrated.   

Monday, December 17, 2018

Achieving the Lowest Limits of Identification – GC-MS with Cold EI versus Standard EI with High Efficiency Source


Aviv Amirav, Tel Aviv University and Aviv Analytical Ltd.

Executive Summary  

GC-MS sensitivities are specified with octafluoronaphthalene (OFN). However, for many GC-MS users the most important operational parameter is the sample limits of identification. We compared the Aviv Analytical GC-MS with Cold EI with the Agilent 5977B GC-MS with high efficiency ion source (HES) in sample identification. We found that Cold EI far outperforms the 5977B-HES in both detection and identification limits. Cold EI detected and identified thirteen impurity compounds in a given test mixture while the HES standard EI failed to detect most of these impurities and failed to identify any of them. In this article we demonstrate and discuss several Cold EI benefits of superior sensitivity, better identification capability, greater range of compounds amenable for analysis and faster speed of analysis. The graphical abstract figure above demonstrates the absence of impurity peaks in the TIC with HES versus at least thirteen detected peaks in Cold EI in which each peak exhibits a molecular ion and is amenable for trustworthy identification.   

Thursday, October 11, 2018

Permethrin Drug Impurity Analysis with GC-MS with Cold EI and the Road to Failure in Such Analysis by GC-MS with Standard EI


























Aviv Amirav, Tel Aviv University and Aviv Analytical

Abstract

A Permethrin impurity was successfully analyzed by GC-MS with Cold EI after it failed to be analyzed by GC-MS with standard EI. In this application note we demonstrate and discuss the ways GC-MS with standard EI analysis of relatively large compounds gradually becomes more difficult as the sample compound size is increased due to reduced total ion count signal, reduced molecular ion relative abundance and increased noise. Accordingly, as the analyzed sample compound becomes larger its GC-MS analysis becomes harder in a gradual fashion until it fails. In contrast, GC-MS with Cold EI can analyze twice larger compounds and thus significantly extends the range of compounds amenable for GC-MS analysis.    

Thursday, June 14, 2018

Cold EI Versus Low Electron Energy EI





Aviv Amirav, Tel Aviv University and Aviv Analytical

Executive Summary
Recently, the use of low electron energy electron ionization is claimed to serve as a soft ionization method and it is sometimes referred to as "Soft EI". In this application note, we show and discuss that low-eV EI is not a universal soft ionization method, its applicability is limited to small molecules that exhibit molecular ions in 70 eV EI, and its enhancement of molecular ion abundances is small or non-existent for many compounds. Furthermore, the addition of a 2nd analysis and loss of signal with low eV EI rarely justify its use in real-world applications.

In contrast, Cold EI (electron ionization of cold molecules in supersonic molecular beams) is a far superior "Soft EI" ion source with close to universal applicability. We demonstrate that for squalane (C30H62), the molecular ion is the base peak in the 70 eV Cold EI mass spectrum, which is 10,000-fold higher than its 0.01% relative ion abundance in 14 eV low electron energy EI. Furthermore, Cold EI is the best ion source in all other main performance aspects, and most importantly, it significantly increases the range of compounds and applications amenable for analysis. Thus, Cold EI bridges the GC-MS gap with LC-MS and can increase the total GC-MS market.


Tuesday, June 12, 2018

Lipids in Human Serum Analysis by the 5975-SMB GC-MS with Cold EI



Aviv Amirav and Svetlana Tsizin, Tel Aviv University and Aviv Analytical, Tel Aviv Israel. 
Gabi Shefer, Ichilov hospital Tel Aviv Israel 

Introduction 
Cholesterol and triglycerides analysis in human blood is among the most widely used chemical medical diagnostics tests. Some estimate the number of such analysis at 1 Billion/year with cost of about $30 for each analysis (three analyses of cholesterol LDL, HDL and triglycerides at $10 each). Thus, the total lipids in blood analysis market is about $30 Billion/year. However, current analysis brings limited information and mass spectrometry can provide far better and more detailed lipids in blood information if an appropriate instrument for such analysis will be available. We used our GC-MS with Cold EI and demonstrated as below the analysis of large range of lipids in blood. Each analysis provided information on the amount of several free fatty acids, cholestadiene, cholesterol, vitamins E and 25 Hydroxy vitamin D3 and many diglycerides, cholesteryl esters and triglycerides. Notably, we can clearly distinguish differences among samples from different people. Each analysis took only 10 min via the use of column flow programing. Our results yielded extensive lipidomics information that may include new diagnostic tools. We feel that this new and advantageous assay for lipids profiling in blood is worthy of further investigation and evaluation.  

Tuesday, June 5, 2018

Impurities Analysis in Active Pharmaceutical Ingredients Comparison of Cold EI with Standard EI


Aviv Amirav, Tel Aviv University and Aviv Analytical, Tel Aviv Israel.

Introduction

Active pharmaceutical ingredients (APIs) in drug formulations need to have impurity levels < 0.1% according to the FDA or else the impurities need to be characterized via lengthy and expensive clinical toxicology procedures. Current impurities in APIs are typically analyzed by LC-MS. However, such LC-MS analysis is confronted by ion suppression effects for impurities that elute near the API, non-polar impurities are not ionized, those impurities that are discovered exhibit mostly protonated molecular ions without structural information and since Electrospray LC-MS has highly non-uniform ionization yields there is no information on the concentration of the discovered impurities. Thus, those API impurities that are observed need to be fully identified, synthesized and follow compound specific concentration calibration.

GC-MS with Cold EI is ideal for analysis of API impurities because:
  • It has uniform compound independent response, thus detected impurity concentrations can be assessed, and those below 0.1% can be neglected 
  • It often provides EI-based library identification, which is usually improved by the presence of an enhanced molecular in Cold EI plus structural information from the full display of fragment ions 
  • Cold EI ionizes non-polar as well as polar analytes 
  • It does not suffer from any ion suppression effects 
  • Total ion mass chromatograms in Cold EI often provides greater sensitivity than ESI-LC-MS 
  • Cold EI has much greater range of compounds amenable for analysis than any other GC-MS. 
Thus, Cold EI seems ideal for API impurities analysis.

Monday, November 7, 2016

Triglycerides in Oils Analysis by the 5975-SMB GC-MS with Cold EI


Aviv Amirav, Tel Aviv University and Aviv Analytical, Tel Aviv Israel.
Hans-Gerd Janssen, Unilever R&D Vlaardingen and University of Amsterdam, Amsterdam The Netherland

Introduction 

Triglycerides analysis is challenging since these large compounds do not elute from standard GC columns under the conditions used in GC-MS and furthermore their standard EI mass spectra do not exhibit any molecular ion, as shown in the NIST library. In addition, their analysis by LC-MS is also challenging in view of their poor proton affinity. Thus, and in view of the importance of triglycerides analysis we decided to analyze three oil samples that were previously analyzed by GC-FID in order to evaluate these oils analysis by GC-MS with Cold EI. The challenge was to properly elute these large compounds and demonstrate the availability of abundant molecular ions plus useful and informative high mass fragments. Triglycerides analysis is very important for the food industry and such analysis can also be potentially important for human medical diagnostics in the form of cholesterol and triglycerides analysis in blood. Currently triglycerides are hydrolyzed and methylated to form FAMEs (fatty acid methyl esters) that are analyzed by GC-MS. However, in such analysis vital information is lost on the actual structure and concentration of the various parent triglycerides and GC-MS with Cold EI is challenged to exhibit such information.     

Wednesday, May 27, 2015

How Enhanced Molecular Ions in Cold EI Improves Sample Identification by the NIST Library


Tal Alon (1,2)  and Aviv Amirav (1,2)

1. School of Chemistry, Tel Aviv University, Tel Aviv 69978 Israel.
2. Aviv Analytical LTD, 3 Haarad Street, Tel Aviv 69107 Israel.

Abstract

Library based compound identification with electron ionization (EI) mass spectrometry (MS) is a well-established identification method which provides sample compounds names and structures up to the isomer level. The library (such as NIST) search algorithm compares different EI mass spectra in the library's database with the measured EI mass spectrum, assigning each of them a similarity score called 'Match' and an overall identification probability.

Cold EI is electron ionization of vibrationally cold molecules in supersonic molecular beams. Cold EI provides mass spectra with all the standard EI fragment ions combined with enhanced Molecular Ions (MI) and high mass fragments. As a result, Cold EI mass spectra differ from those provided by standard EI and tend to yield lower matching scores. However, in most cases library identification actually improves with Cold EI, as library identification probabilities for the correct library mass spectra are increased, despite the lower matching factors.

This research examines the way enhanced molecular ion abundances affect library identification probability and the way Cold-EI mass spectra, which include enhanced molecular ions and high mass fragments, typically improve library identification results. It describes the results of several computer simulations, which incrementally modified the relative abundance of the various ions and analyzed the resulting mass spectra. The simulation results support previous measurements, showing that while enhanced molecular ion and high mass fragments lower the matching factor of the correct library compound, the matching factors of the incorrect library candidates are lowered even more, resulting in a rise of the identification probability for the correct compound. This behavior which was previously demonstrated by analyzing Cold-EI mass spectra occurs because high mass ions, and especially the molecular ion, characterize a compound more than low mass ions and therefore carry more weight in library search identification algorithms. 

Keep reading to find out how the Aviv Analytical 5975-SMB GC-MS with Cold EI uniquely enables the combination of enhanced molecular ion and improved NIST library based sample identification.