The occurrence of 2-furaldehyde (F) and 5-hydroxymethyl-2-furaldehyde (HMF) in processed citrus juices is an indication of quality deterioration. A close relationship between flavor changes and F content exists, while HMF can give rise to browning reactions. Both F and HMF are formed during heat processing or storage at improper temperatures. The detection of these compounds becomes more and more important as aseptic processing and packaging of citrus juices are becoming widespread. Aseptic packaging allows higher temperatures during distribution and storage to be employed without microbial spoilage, but off-flavors develop as citrus products are exposed to these conditions. In this paper a method of determination by high performance liquid chromatography (HPLC) is described. The method is based on the formation of the 2,4-dinitrophenylhydrazones of carbonyl compounds and subsequent reversed-phase separation of these derivatives. Derivatization is carried out by utilizing an acidic solution of 2,4-dinitrophenylhydrazine in acetonitrile. Precipitation of the derivatives of carbonyl compounds is thus avoided, and direct injection of the sample into the HPLC system is allowed. The determination- offers a high specificity and a detection limit of the order of 10⁻⁸ mol/1 for both analytes. Recoveries from an orange juice spiked at different levels are quantitative. Reproducibility data are presented.

The preparation and characterization of several nitrosyl complexes of nickel with ditertiary phosphines (L–L) are reported. With the ligand Ph₂PCH₂PPh₂(dppm) the mononuclear complex [Ni(NO)(dppm)₂]BPh₄ is obtained, in which one diphosphine acts as unidentate and one as a chelating ligand. With R₂P(CH₂)_nPR₂(R = Ph or Me, n= 2 or 3) binuclear compounds [Ni₂(NO)₂(L–L)₃]Y₂(Y = BF₄ or BPh₄) are formed, in which one diphosphine bridges two Ni(NO)(L–L) moieties. I.r., u.v.–visible, and ³¹P n.m.r. data suggest a pseudo-tetrahedral co-ordination for the nickel atom with linear Ni–NO groups for both mono- and bi-nuclear species. Binuclear complexes containing phenyl-substituted diphosphines show an unusual low-temperature ³¹P n.m.r. behaviour which is interpreted in terms of slow Ni–P bond rotation. A series of complexes [Ni(NO)L(L–L)]Y [L = PHR₂, PR₃, or P(OR)₃; Y = BPh₄ or BF₄] has been prepared, and their low-temperature ³¹P n.m.r. behaviour compared with that of the binuclear species. The structure of [Ni₂(NO)₂(dppe)₃][BF₄]₂(dppe = Ph₂PCH₂CH₂PPh₂) has been determined by X-ray methods. Crystals are monoclinic, space group C2/c with Z= 4 in a unit cell of dimensions a= 35.073(8), b= 14.012(4), c= 17.351 (5)Å, and β= 112.24(2)°. The structure has been solved by Patterson and Fourier methods and refined by full-matrix least squares to R= 0.0878 for 2 029 observed reflections. In the cation one dppe ligand acts as a bridge between the two nickel atoms, while the other two chelate the two metals. One nitrogen atom from a terminal nitrosyl ligand completes the distorted tetrahedral co-ordination around each Ni atom. The Ni–N bond distance and the Ni–N–O bond angle are 1.67(2)Å and 168.2(14)°, respectively.