Blank chromatogram

A blank or nearly blank chromatogram can be the result of several situations. The concentration in the headspace may be too low for detection by GC, even with the concentrating... 

Figure 9-8. (A) Signal noise from blank chromatogram. (B) Peak height measurement for calcnlation of LOQ.

Tenax trap) have also been optimized in order i) to obtain a total desorption of volatiles trapped on the auxiliary tube (confirmed by a blank chromatogram for a second heat desorption), ii) to avoid losses of volatiles during the adsorption phase (sensorially verified at the odor port). 

HPLC profiles that resulted from the in gel tryptic digest of 34 pmol (2.1 pg) of a 62 kD protein are shown in Fig. 1. At this low level there are at least 5-6 peaks present in the blank chromatogram that are similar in size to peaks... 

Run a procedure blank to ensure that the blank chromatogram does not contain any interfering peaks (see Figure 5.13 for comparison between a good and a bad blank chromatogram in gradient HPLC). 

Figure 5.13. A good vs. a bad blank chromatogram from a gradient trace analysis for impurity testing of pharmaceuticals. The ghost peaks from the blank injection are derived mostly from the trace contaminants in the weaker mobile phase, which are concentrated during column equilibration. Reprint with permission from reference 16.

The purity of mobile phase A (MPA, the weaker initial mobile phase) is critical since several milliliters of MPA are used to equilibrate the column and any trace contaminants in MPA are concentrated and elute as ghost peaks in the blank chromatogram. One successful strategy is to use high-purity buffer (>99.995%) and to eliminate the buffer filtration step to minimize potential for contamination. 

Table 10-5 gives the equipment parameters used for the practical determination of VOCs. A blank chromatogram of an untreated blood sample is shown in Fig. 10-7. 

The carryover test checks for residual memory effects. Basically, it measures the residual peak area of the target compound in the chromatogram of a blank sample injected immediately after injection of a concentrated solution of the compound (e.g., 1000 mg/L). The carryover effect is evaluated as the percentage of the residual peak area in the blank chromatogram with respect to the peak area of the analyte after the injection of the concentrated solution. Limits of 0.1-0.2% could be considered as acceptable. 

A typical chromatogram of the laminated foil extract is presented in Figure 1 showing two major extractable compounds, identified as peaks 1 and 2, with the corresponding UV spectra (insert). The blank chromatogram (not shown) showed no peaks in the HPLC beside the solvent front. The retention times for triplicate analysis of the foil extract were 8.4 (0.4% R.S.D) and 10.2 (0.3% R.S.D) minutes, respectively, for peaks 1 and 2, and the resolution (Rs) between the two peaks was 4.6. The limits of detection and quantitation were determined to be 0.02 ppm and 0.06 ppm (1.4% RSD, n=3), respectively, with the corresponding signal-to-noise ratios of approximately 3-8 and 9-9 [15]. Under the described HPLC conditions, several fractions of the extractable peaks 1 and 2 were collected and prepared for structural elucidation. 

Fig. 1 Fluorescence plot of a blank (A) and a chromatogram track of a diabetic chocolate extract (B). Circa 50 ng lactose and fructose were applied. Start (1), lactose (2), fructose (3).

Fig. t Fluorescence plot of a blank track (A) and of a cholesterol standard with 200 ng substance per chromatogram zone (B). 

Fig. 1 Reflectance curve of a blank track (A) and a chromatogram (B) with 80 ng prostaglandin El (1), -front (2).

Fig. 1 Absorption scan of a chromatogram track (A) of a gentamycin standard (600 ng gentamycin C complex) and of an accompanying blank (B). Start (1), gentamycin Ci (2), gentamycin C2 and 2. (3), gentamycin Ci, (4), solvent front (5).

Rg. 1 Fluorescence scan of (A) a blank and (B) a carbamazepine standard with 200 ng per chromatogram zone. Start (1), carbamazepine (2), solvent front (3). 

Figure 11.16 Chromatograms of plasma samples obtained by using SPE-SFC with super-aitical desorption of the SPE cartridge (a) blank plasma (20 p.1), UV detection at 215 nm (b) blank plasma (20 p.1), UV detection at 360 nm (c) plasma (1 ml) containing 20 ng mitomycin C (MMC), UV detection at 360 nm. Reprinted from Journal of Chromatography, 454, W. M. A. Niessen et al., Phase-system switching as an on-line sample pretreatment in the bioanalysis of mitomycin C using supercritical fluid cliromatography, pp. 243-251, copyright 1988, with permission from Elsevier Science.

Figure 13.10 LC-LC chromatogram of a surface water sample spiked at 2 p.g 1 with ati azine, and its metabolites (registered at 220 nm). Conditions volume of sample injected, 2 ml clean-up time, 2.60 min ti ansfer time, 4.2 min The blank was subtracted. Peak identification is as follows 1, DIA 2, HA 3, DEA 4, atrazine. Reprinted from Journal of Chromatography, A 778, F. Hernandez et al, New method for the rapid detemiination of triazine herbicides and some of thek main metabolites in water by using coupled-column liquid cliromatography and large volume injection , pp. 171-181, copyright 1997, with permission from Elsevier Science.

Figure 13.15 Chromatograms obtained by on-line ti ace enrichment of 50 ml of Ebro river water with and without the addition of different volumes of 10% Na2S03 solution for every 100 ml of sample (a) blank with the addition of 1000 p.1 of sulfite (b) spiked with 4 p.g 1 of the analytes and 1000 p.1 of sulfite (c) spiked with 4 p.g 1 of the analytes and 500 p.1 of sulfite (d) spiked with 4 p.g 1 of the analytes without sulfite. Peak identification is as follows 1, oxamyl 2, methomyl 3, phenol 4, 4-niti ophenol 5, 2,4-dinitrophenol 6, 2-chlorophenol 7, bentazone 8, simazine 9, MCPA 10, atrazine. Reprinted from Journal of Chromatography, A 803, N. Masque et ai, New chemically modified polymeric resin for solid-phase extraction of pesticides and phenolic compounds from water , pp. 147-155, copyright 1998, with permission from Elsevier Science.

Figure 13.20 GC-FID chromatograms of an exuact obtained by (a) SPE and, (b) lASPE of 10 ml of municipal waste water, spiked with 1 p.g 1 of seven s-triazines (c) represents a blank mn from lASPE-GC-NPD of 10 ml of EIPLC water. Peak identification is as follows 1, ati azine 2, terbuthylazine 3, sebuthylazine 4, simetiyn 5, prometiyn 6, terbutiyn 7, dipropetiyn. Reprinted from Journal of Chromatography, A 830, J. Dalliige et al, On-line coupling of immunoaffinity-based solid-phase exUaction and gas chi-omatography for the determination of 5-triazines in aqueous samples , pp. 377-386, copyright 1999, with permission from Elsevier Science.

Figure 5.67 Reconstructed ion chromatograms for Idoxifene and internal standard (ds-Idoxifene using LC-ToF-MS for (a) double-blank human plasma extract, (b) extract of blank human plasma containing internal standard (IS), and (c) control-blank human plasma spiked with Idoxifene at 5 gml , the LOQ of the method. Reprinted from 7. Chromatogr., B, 757, Comparison between liquid chromatography-time-of-flight mass spectrometry and selected-reaction monitoring liquid chromatography-mass spectrometry for quantitative determination of Idoxifene in human plasma , Zhang, H. and Henion, J., 151-159, Copyright (2001), with permission from Elsevier Science.

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