The effective peroxidase-like activity of chitosan-functionalized CoFe2O4 nanoparticles for chemiluminescence sensing of hydrogen peroxide and glucose

Here, we report a highly simple and general protocol for functionalization of the CoFe(2)O(4) NPs with chitosan polymers in order to make CoFe(2)O(4) NPs disperse and stable in solution. The functionalized CoFe(2)O(4) NPs (denoted as CF-CoFe(2)O(4) NPs) were characterized by scanning electron microscope (SEM), thermogravimetric (TG), X-ray diffraction (XRD) and FT-IR spectra. It was found that the CoFe(2)O(4) NPs were successfully decorated and uniformly dispersed on the surface of chitosan without agglomeration. The CF-CoFe(2)O(4) NPs were found to increase greatly the radiation emitted during the CL oxidation of luminol by hydrogen peroxide. Results of ESR spin-trapping experiments demonstrated that the CF-CoFe(2)O(4) NPs showed catalytic ability to H(2)O(2) decomposition into ˙OH radicals. On this basis, a highly sensitive and rapid chemiluminescent method was developed for hydrogen peroxide in water samples and glucose in blood samples. Under optimum conditions, the proposed method allowed the detection of H(2)O(2) in the range of 1.0 × 10(-9) to 4.0 × 10(-6) M and glucose in the range of 5.0 × 10(-8) to 1.0 × 10(-5) M with detectable H(2)O(2) as low as 500 pM and glucose as low as 10 nM, respectively. This proposed method has been successfully applied to detect H(2)O(2) in environmental water samples and glucose in serum samples with good accuracy and precision.     

Spectrofluorimetric determination of benzoimidazolic pesticides: effect of p-sulfonatocalix[6]arene and cyclodextrins

The effect of the addition of a macrocyclic host (H) such as p-sulfonatocalix[6]arene (C6S), native and modified cyclodextrins (CDs), on the fluorescence of benzoimidazolic fungicides (P), like Benomyl (BY) and Carbendazim (CZ), has been studied. The fluorescence of BY in water at pH 1.000 and 25.0 degrees C was increased in the presence of C6S, alphaCD and hydroxypropyl-beta-CD (HPCD). The association constants determined by fluorescence enhancement showed weak interactions (K(A) approximately 10(1) to 10(2) M(-1)) between the fungicide with both CDs, whereas they were stronger with C6S (K(A) approximately 10(5) M(-1)). Molecular recognition of BY for C6S was mainly attributed to electrostatic interactions, and for CDs to the hydrophobic effect and hydrogen bond formation. On the other hand, the fluorescent behaviour of CZ in the presence of C6S at pH 6.994 was interpreted as the formation of two complexes with 1:1 (P:H) and 1:2 (P:H(2)) stoichiometry, the latter being less fluorescent than the free analyte. Relative fluorescence quantum yield ratios between the complexed and free BY (phi(P:H)/phi(P)) were 2.00+/-0.05, 1.40+/-0.03 and 2.8+/-0.4 for C6S, alphaCD and HPCD, respectively. The analytical parameters improved in the presence of C6S and CDs. The best limit of detection (L(D), ng mL(-1)) was 17.4+/-0.8 with HPCD. The proposed method with C6S and HPCD was successfully applied to fortified samples of tap water and orange flesh extract with good recoveries (91-106%) and R.S.D. (< or = 2%) by triplicate analysis. The method is rapid, direct and simple and needs no previous degradation or derivatization reaction.     

Determination of iodide in samples with complex matrices by hyphenation of capillary isotachophoresis and zone electrophoresis

A method has been developed for the determination of iodide in mineral water, seawater, cooking salt, serum, and urine based on hyphenation of capillary ITP and zone electrophoresis. A commercially available instrumentation for capillary ITP with column-switching system was used. ITP served for removal of chloride present in the analyzed samples in a ratio of 10(6)-10(7):1 to iodide, zone electrophoresis was used for evaluation. Isotachophoretic separation proceeded in a capillary made of fluorinated ethylene-propylene copolymer of 0.8 mm id and 90 mm total length to the bifurcation point filled with a leading electrolyte (LE) composed of 8 mM HCl + 16 mM beta-alanine (beta-Ala) + 10% PVP + 2.86 mM N(2)H(4)x2HCl, pH 3.2; and a terminating electrolyte composed of 8 mM H(3)PO(4) + 16 mM beta-Ala + 10% PVP + 5 mM N(2)H(4), pH 3.85 for all the matrices except seawater. For ITP of seawater the LE consisted of 50 mM HCl + 100 mM beta-Ala + 10% PVP + 2.86 mM N(2)H(4)x2HCl, pH 3.52. Distance of conductivity detector from the injection point and bifurcation point was 52 and 38 mm, respectively. Zone electrophoresis was performed in a capillary made of fused silica of 0.3 mm id and 160 mm total length filled with LE from isotachophoretic step. LODs reached for all matrices were 2-3x10(-8) M concentration (2.5-4 microg/L) enabled monitoring of iodide in all analyzed samples with RSD 0.4-9.3%. Estimated concentrations of iodide in individual matrices were 10(-6)-10(-8) M.     

Detection of hydrogen peroxide in rainwater based on Mg-Al-carbonate layered double hydroxides-catalyzed luminol chemiluminescence

Using a green catalyst of luminol chemiluminescence (CL), Mg-Al-carbonate layered double hydroxides (denoted as Mg-Al-CO(3) LDHs), a novel, sensitive and rapid CL method was developed for the determination of hydrogen peroxide (H(2)O(2)). The corresponding linear regression equation was established in the range of 0.05-10 μM for H(2)O(2). The detection limit (S/N = 3) is 0.02 μM and the relative standard deviation (RSD) for nine repeated measurements of 1.0 μM H(2)O(2) was 2.9%. This proposed method has been successfully applied to detect H(2)O(2) in rainwater samples with good accuracy and precision. The novel methodology is expected to provide a general protocol for the determination of H(2)O(2) as well as for numerous other oxidase-based reactions giving H(2)O(2) as a product (e.g., glucose).     

Catalytic stripping analysis: sensitivity enhancement for reciprocal derivative constant-current stripping determination of palladium in the presence of tin(II) during stripping

The reciprocal derivative constant-current stripping signal of palladium at a mercury film electrode is increased, as in anodic stripping voltammetry (ASV), by a factor of ca. 80 if a certain amount of tin(II) is present in the stripping solution. This catalytic stripping phenomenon has been successfully used as a means of sensitivity enhancement in constant-current stripping determination of trace palladium. The limit of detection is 4 x 10(-10)M at S/N = 3, which is about two decades lower than that obtained without tin(II) present. Linear response was observed over the range 10(-10)-10(-7)M. This method has been applied to determine palladium in waste water and mineral samples. The experimental results support the postulated mechanism of signal enhancement, namely a chemical redeposition reaction occurring during the stripping, giving a cycle of stripping and deposition and thus increasing the stripping signal.     

Flow-injection analysis method for the determination of nitrite and nitrate in natural water samples using a chemiluminescence NOx monitor.

A flow-injection analysis method for the determination of nitrite and nitrate in natural water samples has been developed that consists of two systems based on their reduction to NO with hydrazine and/or ascorbic acid, followed by chemiluminescence detection. The procedure of sweeping the generated NO into an NOx monitor, by means of a gas-liquid separating coil consisting of microporous polytetrafluoroethylene (PTFE) tubing, offers practical advantages. The adjustment of the carrier gas-flow rates could yield the same calibration graphs for the two measurement systems, and the accumulation sweeping mode provides a higher sensitivity. Chemiluminescence detection allows a wide linear calibration range of 5 x 10(-8) to 5 x 10(-5) M. The detection limits for nitrate and nitrite, defined as three-times the standard deviation of measurement blanks, are 2 x 10(-8) M and 1 x 10(-8) M, respectively, and the average precision was 3.2% at ambient natural concentration levels. Recovery tests were between 94% and 106% for a variety of natural water samples. The method is relatively free from interferences from the substances normally found in natural water, and only ferric ion has an effect for the nitrite determination.     

Ultrasound-enhanced flow injection chemiluminescence for determination of hydrogen peroxide

A novel ultrasonic flow injection chemiluminescence (FI-CL) manifold for determining hydrogen peroxide (H2O2) has been designed and evaluated. Chemiluminescence obtained from the luminol-H2O2-cobalt(II) reaction was enhanced by applying 120 W of ultrasound for a period of 4 s to the reaction coil in the FI-CL system and this enhancement was verified by comparison with an identical manifold without ultrasound. The system was developed for determining ultra-trace levels of H2O2 and a calibration curve was obtained with a linear portion over the range of 10-200 nmol L(-1) H2O2 (correlation coefficient 0.9945). The detection limit (3sigma) and the quantification limit (LOQ) were found to be 1 x 10(-9) and 3.3 x 10(-9) mol L(-1) respectively and the relative standard deviation was 1.37% for 2 x 10(-7) mol L(-1) H2O2 (n = 10). The method was applied to the determination of trace amounts of H2O2 in purified water and natural water samples without any special pre-treatments.     

Trace analysis of aluminum in natural waters with rubeanic acid by adsorption chronopotentiometry

The determination of trace levels of aluminum in natural waters with rubeanic acid (RA) by adsorption chronopotentiometry is developed in this paper. Optimum experimental conditions include an accumulation potential of -0.40 V, accumulation time of 60 s, and a RA concentration of 6x10(-6) M in 0.2 M NaAc-HAc buffer solution (pH 4.6). The response is linear over the 1x10(-8) approximately 4x10(-7) M concentration range. The detection limit is 5.6x10(-9) M and the relative S.D. (at the 3x10(-7) M level) is 2.6%. Possible interferences are evaluated. The method has been applied to the determination of trace levels of Al in various real samples. Direct determination of toxic forms of Al in surface waters by this technique is also explored.     

Rapid spectrophotometric method (aqueous and extractive) for the determination of titanium in silicate rocks

A sensitive and highly selective aqueous as well as extractive spectrophotometric method has been developed for the determination of titanium(IV) using 2,3-dihydroxynaphthalene (H(2)ND) as a chromogenic agent. The reagent (H(2)ND) forms a 1:3 (TiOH(3+):ligand) complex at pH 4-9. The molar absorptivity and Sandell's sensitivity are 3.2 x 10(4) l . mol(-1)mol . cm(-1) and 0.001 microg/cm(2), respectively at lambda(max) 375 nm. The method has been found highly selective for Ti(IV) determination in rock samples. Solvent extraction of Ti(IV) in ethylacetate greatly improves the detection limit of the method. The method has been successfully applied to diverse silicate rock samples and results obtained are favourably comparable with those obtained from the tiron method. The reagent (H(2)ND) used in the present investigation is a much better variant than tiron for titanium(IV) determination in silicate rock samples in terms of sensitivity, selectivity, operational simplicity and economy.     

测定超痕量铁的高灵敏指示反应

在稀 H2 SO4 介质中 ,1 ,1 0 -邻菲 口罗啉存在下基于 Fe( )催化过氧化氢氧化棉红的新指示反应建立了测定超痕量铁的一个新方法。方法检出限 1 .0× 1 0 - 11g/m L ,线性范围 0 .0 0～ 1 .2 ng/m L。用于井水、一次蒸馏水、黄豆、芹菜中痕量及超痕量铁的测定获得满意结果     

Liquid chromatography--multiple tandem mass spectrometry for the determination of ten azaspiracids, including hydroxyl analogues in shellfish

Azaspiracids (AZAs) are a group of polyether toxins that cause food poisoning in humans. These toxins, produced by marine dinoflagellates, accumulate in filter-feeding shellfish, especially mussels. Sensitive liquid chromatography-electrospray ionisation mass spectrometry (LC-ESI-MS(n)) methods have been developed for the determination of the major AZAs and their hydroxyl analogues. These methods, utilising both chromatographic and mass resolution, were applied for the determination of 10 AZAs in mussels (Mytilus edulis). An optimised isocratic reversed phase method (3 microm Luna-2 C18 column) separated 10 azaspiracids using acetonitrile/water (46:54, v/v) containing 0.05% trifluoroacetic acid (TFA) and 0.004% ammonium acetate in 55 min. Analyte determination using MS3 involved trapping and fragmentation of the [M + H]+ and [M + H - H2O]+ ions with detection of the [M + H - 2H2O]+ ion for each AZA. Linear calibrations were obtained for AZA1, using spiked shellfish extracts, in the range 0.05-1.00 microg/ml (r2 = 0.997) with a detection limit of 5 pg (signal : noise = 3). The major fragmentation pathways in hydroxylated azaspiracids were elucidated using hydrogen/deuterium (H/D) exchange experiments. An LC-MS3 method was developed using unique parent ions and product ions, [M + H - H2O - CgH10O2R1R3]+, that involved fragmentation of the A-ring. This facilitated the discrimination between 10 azapiracids, AZA1-10. Thus, this rapid LC-MS3 method did not require complete chromatographic resolution and the run-time of 7 min had detection limits better than 20 pg for each toxin.     

Determination of aluminium in tree samples by cathodic adsorptive stripping voltammetry

This paper presents a method of determination of aluminium in tree samples (wood, leaves, roots) based on the cathodic adsorptive stripping voltammetry. Al(III) complexed with alizarin S was determined by ASV method using a hanging mercury drop electrode. Optimal conditions were found to be: accumulation time 30-90 s, accumulation potential - 0.70 V versus SCE, supporting electrolyte 0.1 M ammonia-ammonium chloride buffer at pH 8.2 and concentration of alizarin 1 x 10(-5) M. The response of the system, a linear current-concentration relationship was observed up to 8 x 10(-6) M. The developed method has been tested by analysing international reference materials (BCR 62 Olive leaves and BCR 101 spruce needles).     

Determination of azaspiracids in shellfish using liquid chromatography/tandem electrospray mass spectrometry.

Azaspiracid (AZA1), a recently discovered marine toxin, is responsible for the new human toxic syndrome, azaspiracid poisoning (AZP), which is caused by the consumption of contaminated shellfish. A new, sensitive liquid chromatography/mass spectrometry (LC/MS) method has been developed for the determination of AZA1 and its analogues, 8-methylazaspiracid (AZA2) and 22-demethylazaspiracid (AZA3). Separation of these toxins was achieved using reversed-phase LC and coupled, via an electrospray ionisation (ESI) source, to an ion-trap mass spectrometer. Spectra showed the protonated molecules, [M + H]+, and their major product ions, due to the sequential loss of two water molecules, [M + H - H2O]+, [M + H - 2H2O]+, in addition to fragment ions that are characteristic of these cyclic polyethers. A highly specific and sensitive LC/MS(3) analytical method was developed and, using shellfish extracts containing AZA1, the detection limit (S/N = 3) was 4 pg on-column, corresponding to 0.8 ng/mL. Using the protocol presented here, this is equivalent to 0.37 ng/g shellfish tissue and good linear calibrations were obtained for AZA1 in shellfish extracts (average r2 = 0.9988). Good reproducibility was achieved with % RSD values (N = 5) ranging from 1.5% (0.75 microg/mL) to 4.2% (0.05 microg/mL). An efficient procedure for the extraction of toxins from shellfish aided the development of a rapid protocol for the determination of the three predominant azaspiracids.     

Unusual syntheses, structures, and electronic properties of compounds containing ternary, T3-type supertetrahedral M/Sn/S anions [M5Sn(mu3-S)4(SnS4)4](10- (M = Zn, Co)

A recently discovered series of quaternary compounds of the general type [K(m)(ROH)(n)()][M(x)Sn(y)()Se(z)] (R = H, Me), containing ternary anions with [SnSe(4)](4-)-coordinated transition metal centers (M = Co, Mn, Zn, Cd, Hg) has now been extended by the synthesis and characterization of the two ortho-thiostannate-coordinated species, [Na(10)(H(2)O)(32)][M(5)Sn(mu(3)-S)(4)(SnS(4))(4)].2H(2)O (M = Zn (1), Co (2)). The central structural motifs of compounds 1 and 2 are highly charged [M(5)Sn(mu(3)-S)(4)(SnS(4))(4)](10-) anions, being the first T3-type supertetrahedral ternary anions reported to date. The exposure of single crystals of 2 to a dynamic vacuum for several hours resulted in the reversible formation of a partially dehydrated, but still monocrystalline material of the composition [Na(10)(H(2)O)(6)][Co(5)Sn(mu(3)-S)(4)(SnS(4))(4)] (3). The loss of 28 of the 34 water molecules only slightly affects the internal structure of the ternary anion in 3 and leads to a significant compacting of the crystal structure with closer linkage of the [Co(5)Sn(5)S(20)](10-) cluster units via the Na(+) cations. Magnetic measurements on 3 show that the ground state of the Co/Sn/S cluster is S = 1/2, indicating a significant antiferromagnetic coupling between the Co centers, which has also been rationalized by DFT investigations of the electronic situation in the ternary subunits of 1-3.     

Synthesis of a novel chemiluminescent reagent for the determination of hydrogen peroxide in snow waters

7-(4,6-Dichloro-1,3,5-triazinylamino)-4-methylcoumarin (DTMC) was synthesized as a completely new chemiluminescent reagent, and with it a novel chemiluminescence method was developed for the determination of hydrogen peroxide in the absence of any added catalyst or co-oxidant. The chemiluminescence intensity of the DTMC-H(2)O(2) system could be enhanced by the addition of cation surfactants. The chemiluminescence intensity was directly proportional to the concentration of H(2)O(2) in the range 1.0 x 10(-7)-4.0x10(-4) mol l(-1), and the detection limit was 4.0 x 10(-8) mol l(-1). The relative S.D. was 4.9% for 1.0 x 10(-6) mol l(-1) of H(2)O(2) (n=10). The selectivity of this method was high, and most of the transition metal ions have no effect on the determination. The proposed method has been applied to the determination of trace amounts of hydrogen peroxide in snow water. A possible mechanism of the chemiluminescence reaction is also discussed.     

Interactions of Pb2+ with fulvic acid by electrophoretically mediated on-capillary microanalysis

Studies of yessotoxin involving confirmation of fragmentation processes using a high-resolution orthogonal hybrid quadrupole time-of-flight (QqTOF) mass spectrometer and nanoLC hybrid quadrupole TOF MS have been undertaken. The fragmentation of YTX was studied in negative mode using nano electrospray (nanoESI) QqTOF mass spectrometry. Three major molecule-related ions were observed, [M - 2Na + H]-, [M - Na]- and [M - 2Na]2-, and fragmentation of the latter was studied in detail. This showed that product ions were formed as a consequence of charge-remote fragmentation processes that included a strong directional cleavage of the polyether rings of YTX. NanoLC coupled with QqTOF MS was used to determine YTX in small samples of the phytoplankton, Protoceratium reticulatum, by monitoring the [M - 2Na]2- ion at m/z 570. A PepMap C18 nanoLC column (75 microm x 10 cm, 100 A, 3 microm, LC Packings) was used and the solvent was acetonitrile/water (90:10 (v/v)) containing 1 mM ammonium acetate, at a flow rate of 400 nl/min, for 30 min. Calibrations obtained with YTX standard solutions were linear over four orders of magnitude, 0.75-250 ng/ml; r2 = 0.9947-0.9998. Phytoplankton cells (ca. 100-300) were picked, extracted with methanol/water (40:60), and the YTX concentration was determined over the range 0.011-0.020 ng/cell. The detection limit (3 x S/N) of this method was ca. 0.5 pg YTX on-column.     

Spectrophotometric determination of aluminium by morin

A direct spectrophotometric method for the determination of aluminium with morin has been developed. Morin reacts in slightly acidic 50% ethanolic media (0.0001-0.0015 M H(2)SO(4)) with Al to give a deep-yellow chelate which has an absorption maximum at 421 nm. The average molar absorptivity and Sandell's sensitivity were found to be 5.3 x 10(3) l mol(-1) cm(-1) and 5 ng of Al cm(-2), respectively. The reaction is instantaneous and absorbance remains stable for 48 h. The colour system obeys Beer's law from 10 ng ml(-1) to 5.0 mug ml(-1) of Al; the stoichiometric composition of the chelate is 2:3 (Al:morin). The interference from over 50 cations, anions and complexing agents has been studied at 0.1 mug ml(-1) of Al. The method was applied successfully to some certified reference material samples (alloys and steels), environmental waters (inland and surface), biological samples (human blood, urine and gallstone), soils and complex synthetic mixtures.     

Determination of agmatine in biological samples by capillary electrophoresis with optical fiber light-emitting-diode-induced fluorescence detection

A capillary electrophoresis (CE)/optical fiber light-emitting diode (LED)-induced fluorescence detection method is developed for the determination of agmatine in biological samples. The agmatine was precolumn-derivatized with fluorescence tagging reagent, fluorescein isothiocyanate (FITC). Optimal separation and determination for agmatine were obtained with an electrophoretic buffer of 20 mM sodium borate (pH 9.2). Under the optimal conditions, the determination of agmatine was achieved in less than 4 min, and the detection limit was 4.1x10(-9) M (S/N = 3). The relative standard deviation (RSD) for 11 parallel determination of agmatine was less than 3.0%. The present CE-LED induced fluorescence detection method has been applied to detect agmatine in rat brain tissue, rat stomach tissue, human serum, and human urine. The level of agmatine in human urine was quantified by CE for the first time and found to be in the range 2.5-4.1x10(-7) M.     

Spectrophotometric flow injection determination of formetanate and m-aminophenol in water after reaction with p-aminophenol

An automated procedure has been developed for the determination of formetanate and its metabolite m-aminophenol (MAP) in water samples. MAP can be selectively determined in the presence of formetanate by direct on-line reaction with p-aminophenol and spectrophotometric measurement of the absorbance at 576 nm in the presence of KIO(4), as oxidizing agent. The method has a limit of detection of 5 x 10(-7)M, it provides a recovery percentage from 95 to 104% and permits one to carry out 120 measurements/hr. The spectrophotometric determination of formetanate must be carried out after a previous hydrolysis to MAP. To determine formetanate in the presence of MAP, two steps are necessary. Firstly, the MAP content is selectively determined as has been mentioned above. After that, the sample is treated with 0.05M NaOH at 90' degrees C, to hydrolyze the formetanate to MAP, and then the sum of both is determined spectrophotometrically. The difference between the results obtained in each step gives the formetanate concentration. The developed procedure for the determination of formetanate provides a sensitivity of 1070 absorbance units mol(-1) l and a limit of detection of 1.9 x 10(-7)M, which corresponds to 50 mug/l of formetanate hydrochloride. The method has been applied to the analysis of natural water samples fortified with formetanate and MAP, and formetanate has also been quantitatively recovered in irrigation waters at a concentration level of 1.9 x 10(-6)M which corresponds to 500 mug/l. On the other hand, working in the stopped-flow mode, for a reaction time of 100 sec, the sensitivity of the formetanate determination can be increased to 4642 absorbance units mol(-1) l but the limit of detection remains of the order of 44 mug/l.     

Differentiation of Boc- alpha,beta- and beta,alpha-peptides and a pair of diastereomeric beta,alpha-dipeptides by positive and negative ion electrospray tandem mass spectrometry (ESI-MS/MS)

Positive and negative ion electrospray ionization (ESI) tandem mass spectral study of a new series of hybrid peptides, viz, BocN-alpha,beta-peptides and BocN-beta,alpha-peptides, synthesized from C-linked carbo-beta3-amino acids [Caa (S)] and L-Ala has been carried out. The alpha,beta-peptides have been differentiated from beta,alpha-peptides by the collision-induced dissociation (CID) of [M + H]+ and [M - H]- ions in positive and negative ion ESI-MS respectively. The fragment ion [M + H - C(CH3)3 + H]+ formed from [M + H]+ ions by the loss of 2-methyl-prop-2-ene in alpha,beta-peptides with L-Ala at the N-terminus is insignificant or totally absent for beta,alpha-peptides which have the Caa (S) at N-terminus. The fragment ion [M - H-C(CH3)3OH - HNCO]- formed from [M - H]- of beta,alpha-peptide acids is totally absent for alpha,beta-peptide acids. This has been attributed to the absence of the beta-methylene group in alpha,beta-peptides, and the participation of the beta-methylene group in the loss of HNCO in beta,alpha-peptide acids is confirmed by the deuteration experiments. The CID of [M + H-Boc + H]+ ions of these peptides also produce characteristic fragmentation. In the CID spectra of alpha,beta-peptides, the b(n)+ ions and the resulting y(n)+ ions occur at a mass difference of 243 and 71 Da corresponding to the successive losses of Caa and L-Ala, whereas a mass difference of 71 and 243 Da is observed for beta,alpha-peptides. In contrast to the CID of protonated peptides, the CID of [M - H]- ions of the alpha,beta- and beta,alpha-peptide acids do not give b(n)- ions and show abundant z(n) (-) ions. Further, a pair of diastereomeric dipeptide esters and acids have been distinguished by the CID of [M + H]+ ions. The loss of 2-methyl-prop-2-ene is more pronounced for Boc-NH-Caa(R)-D-Ala-OCH3 (21) and Boc-NH-Caa(R)-D-Ala-OH (23) with Caa (R) at the N-terminus, whereas it is totally absent for Boc-NH-Caa (S)-D-Ala-OCH3 (22) and Boc-NH-Caa(S)-D-Ala-OH (24) peptides, which have Caa (S) at the N-terminus. Thus, on the basis of our previous and present studies, we propose that the CID of [M + H]+ ions provides a simple and useful method for distinguishing the configuration of Caa (S or R) at the N-terminus of BocN-carbo beta,alpha- and beta,beta-dipeptides.