Analytical Methods Blog

Test for methylarginines in newborn infants

Developing an analytical technique for use in the field of neo-natal intensive care presents a significant challenge to researchers. Newborn infants who are very premature and unwell can’t safely provide large blood samples for analysis, and a fast turn-around of lab results is crucial for a life-saving diagnosis.

Methylarginines (MAs) are nitric oxide synthase inhibitors which have been linked to respiratory problems in newborns. Researchers led by Susan Lunte at the University of Kansas, USA, report the use of capillary electrophoresis (CE) to measure and track methylarginine concentrations in infant blood plasma for the first time. Their newly developed sample preparation and separation methods are specifically designed to cope with low volume plasma samples, and the results confirm that infants in neo-natal intensive care units (NICUs) have extremely high MA levels.

Click the link below to read more… This article will be free to access until June 7^th.

Determination of methylarginines in infant plasma by CE-LIF
Thomas H. Linz and Susan M. Lunte
Anal. Methods, 2014, Advance Article
DOI: 10.1039/C4AY00340C

GC-MS/MS in residual pesticide analysis

The laws surrounding trace amounts of pesticide found in food and the environment are designed to protect consumers and ensure that agricultural practises do not have a detrimental effect on the natural world. Even after being washed and prepared, crops can carry residual pesticides into processed products. These compounds must be both identified and quantified at very low concentration, presenting a particular challenge to analytical chemists.

In this critical review, Felíx Hernández and researchers at the University Jaume I, Spain, examine the use of gas chromatography coupled to tandem mass spectrometry (GC-MS/MS) with a triple quadrupole (QqQ) analyzer for the identification and quantification of pesticide compounds. This technique has emerged as a reliable, highly sensitive and selective tool for pesticide analysis in a complex matrix.

The authors have identified and explored a range of instances where GC-MS/MS has been successfully employed in this way. They make comparisons in a number of areas, including sample preparation, type of analyte, and mode of analysis. The food matrices being tested range from fruit and vegetables to milk, meat, ginseng and olive oil.

To read the full article, please access the link below. This paper will be free to read until October 18th.

The role of GC-MS/MS with triple quadrupole in pesticide residue analysis in food and the environment
F. Hernández, M. I. Cervera, T. Portolés, J. Beltrán and E. Pitarch
Anal. Methods, 2013, Advance Article
DOI: 10.1039/C3AY41104D

Mass spectral analysis of blood samples

Analysing blood samples for the presence of legal and illegal drugs can present a challenge to forensic scientists; blood is a complex matrix which requires cleaning up before analysis, and the standard tests tend to be specific to a single drug or drug class.

Lambert Sørensen and Jørgen Hasselstrøm from the Department of Forensic Medicine at Aarhus University, Denmark, have developed a rapid method for quantification of around 50 drugs and metabolites in whole blood samples. The process uses ultra-high-performance liquid chromatography tandem mass spectrometry (UPLC-ESI-MS/MS) and shows low limits of detection even with post-mortem blood samples, which are more difficult to analyse due to varying degrees of putrefaction.

The simple sample preparation procedure involves deproteinisation by methanol/acetonitrile and ultrafiltration of the extract, and the researchers used a 96-well format to obtain high sample throughput.

To know more, access the link below. This paper will be free to read for the next 10 days.

A high-throughput multi-class liquid chromatography tandem mass spectrometry method for quantitative determination of licit and illicit drugs in whole blood
Lambert K. Sørensen* and   Jørgen B. Hasselstrøm
Anal. Methods, 2013,5, 3185-3193
DOI: 10.1039/C3AY40443A

Lipid bilayer structure of the liposome

The small size and lipid bilayer structure of liposomes make them an excellent carrier for use in drug delivery and gene therapy. Determining the chemical and physical properties of a liposome is key to evaluating its potential for different applications.

A range of techniques have been used to measure factors such as size, surface charge and encapsulation efficiency of these spherical structures. In this minireview, Xiaomei Yan and colleagues at Xiamen University, China, explore recent advances in techniques for single-liposome characterization. They evaluate the latest adaptations of traditional microscopy techniques and investigate the advantages and limitations of using flow cytometry for characterisation. Recently developed commercial techniques such as scanning ion occlusion sensing (SIOS) and nanoparticle tracking analysis (NTA) also offer more advanced methods of single-liposome analysis.

To access the full article, please click on the link below. This paper will be free to read until May 14th.

Analytical techniques for single-liposome characterization
Chaoxiang Chen, Shaobin Zhu, Tianxun Huang, Shuo Wanga and   Xiaomei Yan  
Anal. Methods, 2013,5, 2150-2157
DOI: 10.1039/C3AY40219C

Synthesis of gold-antibody nanocomposite and AFP immunoassay

The construction of successful biosensors is often hampered by the difficulty of immobilising biomolecules onto the desired surface in an orderly fashion. As a support medium, nanoparticles display a particularly large surface-to-volume ratio and their physical properties can be adjusted to match requirements.

Researchers led by Zhihui Dai from the Nanjing Normal University, China, have used a liquid-liquid interface technique to immobilise Ab₁ antibodies onto gold nanoparticles, characterising the material using energy dispersive spectroscopy (EDS).

Detection of abnormal levels of alpha-fetoprotein (AFP) can indicate the presence of cancerous cells. In this work, a sandwich immunoassay was used to test the sensitivity of the Au-Ab₁ nanocomposite towards AFP, demonstrating good selectivity, stability and reproducibility of the sensor. In clinical samples, the gold-based sensor performed well against the current enzyme-linked immunosorbant assay (ELISA) method of testing.

Do you want to know more about this research? Click on the link below, this article will be free to read until April 19th:

Gold–antibody nanocomposite thin film fabricated by a liquid–liquid interface technique and its application for the sensitive immunoassay of alpha-fetoprotein
Kun Wang ,  Tianxiang Wei ,  Wenwen Tu ,  Min Han and Zhihui Dai
Anal. Methods, 2013,5, 1909-1914
DOI: 10.1039/C3AY26541B

A non-enzymatic glucose sensor

Detecting glucose is not only important in the diagnosis and monitoring of diabetes; it has also wide applications in food analysis and waste water treatment. Traditional glucose sensors are based on an enzymatic method, employing glucose oxidase. Although this makes for a highly selective electrode, enzymes are easily affected by environmental factors such as temperature, humidity and pH.

Researchers led by Yongqing Zhao and Cailing Xu at Lanzhou University, China, have designed and created a new glucose sensor which is non-enzymatic and uses a 3D electrode architecture to increase the surface area in contact with the electrolyte. The porous nickel foam scaffold is loaded with nickel oxide, which has fast redox kinetics and better stability towards air and water than nickel metal.

The sensor has been evaluated against traditional methods by measuring glucose levels in blood serum samples and was found to perform well, with excellent response times, high selectivity, a low detection limit and good electrocatalytic activity.

To know more about this research, please access the link below. This paper will be free to read until April 2^nd.

Non-enzymatic glucose sensor based on three dimensional nickel oxide for enhanced sensitivity
Chunyan Guo,  Yinmei Wang,  Yongqing Zhao and Cailing Xu
Anal. Methods, 2013, Advance Article
DOI: 10.1039/C3AY00067B

Analysis of gas and liquid phase photoreduction products

Carbon dioxide produced by combustion of fossil fuels can potentially be removed from the atmosphere using an abundant carbon-neutral form of energy: sunlight. Photocatalytic reduction is a promising strategy for CO₂ conversion, but controlling the reaction pathways can be difficult. Identification and isolation of the range of reduction products provides a way of evaluating the efficiency of different photocatalysts.

In this minireview, Rong Xu and researchers at the Nanyang Technological University examine different analytical methods for these conversion products.  They compare a range of GC, HPLC and other chromatographic systems for separation of compounds including alcohols, aldehydes, carboxylic acids and small hydrocarbons. Moreover, they apply their findings to a new set of techniques for accurate detection of CO₂ reduction products with low detection limits, employing a combination of GC and HPLC.

In a useful addition to the study, the authors also investigated the effects of organic additives such as solvents and photosensitisers on these analytical methods.

Photocatalytic reduction of CO₂: a brief review on product analysis and systematic methods
Jindui Hong, Wei Zhang, Jia Ren and Rong Xu
Anal. Methods, 2013,5, 1086-1097
DOI: 10.1039/C2AY26270C

Mandel's test for goodness of fit

The economic and time constraints that limit the collection of calibration data mean that analytical chemists rely on robust statistical tests for linearity to support the accuracy of their findings. Mandel’s test was first proposed in 1964 and despite being simplified and suggested by IUPAC in 1998, has not been used broadly. Recently the Mandel’s test enjoyed an increase in popularity, possibly because non-linear data points are now more straightforward to plot using spreadsheets (linear model).

In this Analytical Methods paper, José M. Andrade and María P. Gómez-Carracedo at the University of A Coruna examined the validity of the definition of the test provided by IUPAC. They compared this approach to Mandel’s original definition, presenting ten different scenarios from simulated data. These simulations vary by number of data points and magnitude of the variances of the linear (IUPAC) or non-linear (Mandel’s) models. Surprisingly, the authors concluded that the 1998 IUPAC interpretation of this test does not strictly adhere to the definition published by Mandel, and is only valid within certain key limitations. The authors provide useful recommendations to analytical chemists intending to use Mandel’s test in their calibration calculations.

Notes on the use of Mandel’s test to check for nonlinearity in laboratory calibrations
J. M. Andrade and M. P. Gómez-Carracedo
Anal. Methods, 2013, Advance Article
DOI: 10.1039/C2AY26400E