Direct analysis of volatile organic compounds in foods by headspace extraction atmospheric pressure chemical ionisation mass spectrometry

Abstract

RationaleThe rapid screening of volatile organic compounds (VOCs) by direct analysis has potential applications in the areas of food and flavour science. Currently, the technique of choice for VOC analysis is gas chromatography/mass spectrometry (GC/MS). However, the long chromatographic run times and elaborate sample preparation associated with this technique have led a movement towards direct analysis techniques, such as selected ion flow tube mass spectrometry (SIFT‐MS), proton transfer reaction mass spectrometry (PTR‐MS) and electronic noses. The work presented here describes the design and construction of a Venturi jet‐pump‐based modification for a compact mass spectrometer which enables the direct introduction of volatiles for qualitative and quantitative analysis.MethodsVolatile organic compounds were extracted from the headspace of heated vials into the atmospheric pressure chemical ionization source of a quadrupole mass spectrometer using a Venturi pump. Samples were analysed directly with no prior sample preparation. Principal component analysis (PCA) was used to differentiate between different classes of samples.ResultsThe interface is shown to be able to routinely detect problem analytes such as fatty acids and biogenic amines without the requirement of a derivatisation step, and is shown to be able to discriminate between four different varieties of cheese with good intra and inter‐day reproducibility using an unsupervised PCA model. Quantitative analysis is demonstrated using indole standards with limits of detection and quantification of 0.395 μg/mL and 1.316 μg/mL, respectively.ConclusionsThe described methodology can routinely detect highly reactive analytes such as volatile fatty acids and diamines without the need for a derivatisation step or lengthy chromatographic separations. The capability of the system was demonstrated by discriminating between different varieties of cheese and monitoring the spoilage of meats.

Volatile compounds profiling by using proton transfer reaction‐time of flight‐mass spectrometry (PTR‐ToF‐MS). The case study of dark chocolates organoleptic differences

“…[49][50][51] Portable APCI instruments were developed, [52][53][54][55] and such a compact mass spectrometer has been recently used efficiently for discriminating between different varieties of cheese and monitoring the spoilage of meats. 56 As APCI accomplishes the whole process of reagent ions formation and proton transfer to the analytes in a small source region, it suffers from problems of suppression of ionization and relatively low ionization efficiency. Even if in some cases carefully controlled conditions can afford quantitative data for a limited number of analytes in a run, 50,51 these controlled conditions (based on ion-entrance cone voltage adjustments of the spectrometer) are not accessible on every instrument and are not applicable for monitoring a large number of VOCs as necessary in profiling experiments.…”

“…For years, APCI‐MS has been the reference technique for in vitro and in vivo monitoring of flavour compounds, and the method with its advantages and drawbacks were reviewed in detail elsewhere . Portable APCI instruments were developed, and such a compact mass spectrometer has been recently used efficiently for discriminating between different varieties of cheese and monitoring the spoilage of meats . As APCI accomplishes the whole process of reagent ions formation and proton transfer to the analytes in a small source region, it suffers from problems of suppression of ionization and relatively low ionization efficiency.…”

Novel ionization reagent for the measurement of gas‐phase ammonia and amines using a stand‐alone atmospheric pressure gas chromatography (APGC) source

“…Several commercial APCI sources have been modified to allow direct air sampling for the analysis of various amines including pyridine 37 and diamines from food via headspace extraction of the amines and direct injection into the APCI source. 38 Finally, particle-bound amines (aminium and ammonium ions) have been detected using thermal desorption chemical ionization mass spectrometry (TDCIMS), where the particles are collected onto the tip of a platinum wire followed by subsequent thermal desorption and ionization using water clusters formed using a 210 Po radioactive source. 12,39,40 Ambient ionization mass spectrometry methods have been exponentially growing over the past ten years due to their versatility, ease of use, reduced fragmentation due to 'soft' ionization mechanisms, and minimal sample preparation.…”

Rapid and non‐invasive multivariate approach for the quality control of raw milk from mountain areas based on proton transfer reaction mass spectrometry data

“…Briefly, PTRMS uses a mass spectrometer to provide non‐destructive headspace analysis of volatiles and it can perform an analysis of one sample in a very short time. In recent years, PTRMS has been more commonly applied for volatile fingerprinting of food and dairy products . Previous researchers have established that PTRMS can be successfully used to identify the authenticity of butter and cheese, the quality control of lamb meat, saffron, powder milk and retail milk …”

“…In recent years, PTRMS has been more commonly applied for volatile fingerprinting of food and dairy products. 10,11 Previous researchers have established that PTRMS can be successfully used to identify the authenticity of butter 12,13 and cheese, 14 the quality control of lamb meat, 15 saffron, 16 powder milk 17 and retail milk. 18 However, there is a lack of evidence on the capacity of PTRMS to analyse the volatile organic compounds (VOCs) profile of raw milk and eventually to correlate the samples with their geographical origin.…”