Molecularly imprinted probe for solid‐phase extraction of hippuric and 4‐methylhippuric acids directly from human urine samples followed by MEKC analysis

Abstract

Hippuric acid (HA) and 4-methylhippuric acid (4-MHA) are metabolites as well as biological indicators for toluene and xylenes, respectively, and their determination in urine samples is very important, in order to monitor the occupational exposition to these solvents, ensuring a safe working environment. Thus, this paper describes the synthesis and characterization of a probe impregnated with molecularly imprinted polymers (MIPs) for the solid-phase extraction of HA and 4-MHA directly from untreated urine samples followed by micellar electrokinetic chromatography (MEKC) analyses. The MIP probe selectivity was compared to the non-imprinted polymer probe. The MEKC separations were carried out in 50 mmol/L sodium tetraborate pH 10.0/0.5 mmol/L cetyltrimethylammonium bromide aqueous solution, with a constant voltage of -15 kV. The system variables were optimized to provide ideal conditions for the extraction and desorption of the analytes, as well as for the MEKC analyses. The method was linear from 0.5 to 5.0 g/L for both analytes, with correlation coefficients > 0.994. Precisions and accuracies, expressed as relative standard deviation and relative error, were < 20.0 and within -15.4 to 16.6%, respectively, in accordance with the United States Food and Drug Administration recommendation. The MIP probe has proven to be simple, cheap, resistant, and synthetically reproducible, being successfully used to analyze both HA and 4-MHA from real samples.

Online fully automated SPE‐HPLC‐MS/MS determination of ceftiofur in bovine milk samples employing a silica‐anchored ionic liquid as sorbent

“…The analyte to be quantified being present in a complex matrix must be extracted from it. For this purpose there are several extraction techniques such as liquid‐liquid extraction (LLE), solid phase extraction (SPE), pressurized fluid extraction (PFE) and supercritical fluid extraction (SFE) , among which SPE has received special attention because this technique can be coupled online with HPLC‐MS/MS systems . The on‐line SPE is an efficient fully automatic sample preparation that has several advantages such as: reduced errors and analysis time; smaller amount of samples and organic solvents is necessary; reduced the contact to hazardous reagents and infectious materials; lower detection limits; improve method sensitivity and robustness when compared to off‐line SPE sample preparation .…”

A Molecularly Imprinted Polymer for Selective Extraction of Phenolic Acids from Human Urine

“…The absence of characteristic bands for template also indicates a successful extraction process [15,16]. Some authors are associated other characteristic MIP and NIP bands to crosslinker or the existence of poly(EGDMA) [14,22]. MIP and NIP present similar spectra, except for the intensity of the C=O stretching vibration band (1724 cm −1 ).…”

“…Some authors suggested that the best recognition ability depended on the pKa relationship between monomer and template. The basic character of 4-Vpy (pKa = 5.4) makes it a good candidate for phenolic acid templates [10,18,22]. Sun et al also related the rigid structure of templates to the recognition ability of synthesized MIP [19].…”

“…4-methylhippuric acid has been used as a template for the synthesis of an MIP for the extraction of hippuric and 4-methylhippuric acids for the assessment exposure of toluene and xylenes [22]. Main functional monomers used in these molecular imprinting procedures were 4-Vpy, acrylamide, and methacrylic acid [10,[13][14][15][16][17][18][19][20][21][22]. To our knowledge, only one work reported the application of MIP for the phenolic acid analysis in urine, but with a different purpose, the assessment exposure of toluene and xylenes [22].…”

Benzene, toluene, ethylbenzene, and xylene: Current analytical techniques and approaches for biological monitoring

“…In addition, the "dilute-and-shoot" approach without need for a sample preparation step is used [97,98,100,102]. Recently, a method has been developed to direct extraction of HA and MHA from untreated urine samples using a probe impregnated with molecularly imprinted polymers (MIPs) and subsequent analysis by micellar electrokinetic chromatography [116].…”