Assessment of an electron‐impact GC‐MS method for organic acids and glycine conjugates in amniotic fluid

Abstract

We assessed the reliability of a method designed for common electron-impact GC-MS systems to determine in a single run most organic acids and glycine conjugates of clinical interest in amniotic fluid. Suitable sensitivity was achieved by dividing the selected-ion chromatogram into 12 time segments during which the monitoring dwelt on specific ions. Twelve metabolites were simultaneously quantified in amniotic fluid, with performances ranging from very good to clinically acceptable. The total coefficient of variation was 2.5-14.1% and the detection limit was well below the lower value of the physiological range. For five other metabolites, the precision was lower and/or the detection limit was near the physiological range. The method was clinically assessed by the prenatal detection of three cases of tyrosinaemia type I and one case of propionic acidaemia. Analytical and clinical evaluation of the method showed that GC-MS with electron-impact fragmentation can be an informative analytical approach for low-level organic acids in physiological fluids. Apart from the case of glycine conjugates, the method shows a fair reliability for amniotic fluid analysis, which might warrant its use for prenatal diagnosis of organic acidurias. However, this method cannot replace procedures using isotopic internal standards, nor GC-MS based on chemical ionization fragmentation, which remain confirmatory analytical methods of choice.

Gestational age‐related reference values for amniotic fluid organic acids

“…In AF, methylcitric acid is reliably increased in association with the disease (e.g. Buchanan et al, 1980;Kumps et al, 2004;Perez-Cerda et al, 2004;Hasegawa et al, 2005;Inoue et al, 2008).…”

Prenatal diagnosis of propionic acidemia by measuring methylcitric acid in dried amniotic fluid on filter paper using GC/MS

“…This method has been applied to many inborn errors of metabolism (IEMs) [5][6][7][8] and offers the considerable advantages of a repeatable, rapid, and early diagnosis.…”

A GC/MS validated method for the nanomolar range determination of succinylacetone in amniotic fluid and plasma: An analytical tool for tyrosinemia type I

“…Moreover, no intramolecular reaction can occur during oximation, in contrast to a likelihood of it occurring if hydroxylamine is used [10]. Very few methods have been used to extract SA from biological fluids prior to GC/MS analysis: one method requires a relatively long time span, while necessitating lyophilization and a liquid partition chromatography technique [13], whereas the others are based on liquid-liquid extraction [12,23,25]. Solvent extraction, on the other hand, is simple and we were able to confirm the efficiency of this known method [10,26] by comparing, in a triplicate assay, the peak areas of SA standards obtained after solvent extraction with those obtained after evaporation of pure oximated standards prepared in methanol (unextracted standards).…”

“…Some well-established methods are used to diagnose the disease, most of which rely either on GC/MS, GC/MS/MS, capillary electrophoresis (CE) or tandem mass spectrometry (MS/MS) for direct quantification of SA [10][11][12][13][14][15][16][17] or are based on inhibition of ␦-aminolevulinc acid dehydratase [18]. However, NTBC administration treatment reduces the levels of SA to near the normal range after only a few weeks, hence, the majority of current, published methods do not offer sufficient sensitivity or have not been designed for measuring SA levels in healthy individuals or at the basal range.…”