Sulfur compounds detection methods

Corrosive sulfnr componnds can be detected by their effect on copper and the form in which the general copper strip corrosion test (ASTM D1838) for petrolenm prodncts is applied to liqnefied petrolenm gas. Hydrogen sulfide can be detected by its action on moist lead acetate paper, and a procedure is also used as a measure of sulfur compounds. The method follows the principle of the standard Doctor test. 

Table 4 summarises the p>arameters obtained from the calibration graphs for all of the reductive sulfur analytes, along with the method detection and quantification limits for each compoimd. Linear regression analysis revealed that very good linearities (R > 0.992) were obtained in the calibration graphs for all of the reductive sulfur compounds. The method provided very good detection limits, which were well below the sensory thresholds (See Table 1) of the analysed sulfur compounds. 

The System described in the previous section has been extended with a sulfur chemiluminescence detector (SCO) for the detection of Sulfur compounds (32). The separated fractions were thiols + sulfides + thiophenes (as one group), benzothio-phenes, dibenzothiophenes and benzonaphtho-thiophenes. These four groups have been subsequently injected on-line into and separated by the GC unit. Again, no overlap between these groups has been detected, as can be seen from Figure 14.20, in which the total sulfur compounds are shown and from Figure 14.21 in which the separated dibenzothiophenes fraction is presented. The lower limit of detection of this method proved to be 1 ppm (mg kg ) sulfur per compound. 

Thus, XANES spectroscopy of elemental sulfur has mainly be used to detect the particular sulfur species in samples not accessible to other spectroscopic methods, e.g., in cultures of sulfur bacteria [215, 221, 222, 224]. However, the main application is in the area of sulfur compounds with other elements. For a recent review, see [226]. 

As a more sensitive detection method, MS can be very useful in amino acid determinations. For example, S-carboxymethyl-(R) cysteine or SCMC, is a mucolytic agent used in the treatment of respiratory diseases. The development of a method utilizing high performance IEC and atmospheric pressure ionization (API) mass spectrometry to quantify SCMC in plasma has been described.66 This method is simple (no derivatization needed), rapid (inn time 16 min.), sensitive (limit of quantification 200 ng/mL in human plasma), and has an overall throughput of more than 60 analyses per day. API-MS was used successfully with IEC to determine other sulfur-containing amino acids and their cyclic compounds in human urine.67 IEC has also been used as a cleanup step for amino acids prior to their derivatization and analysis by gas chromatography (GC), either alone or in conjunction with MS.68 69... 

Puacz et al. (1995) developed a catalytic method, based on the iodine-azide reaction, for the determination of hydrogen sulfide in human whole blood. The method involves the generation of hydrogen sulfide in an evolution-absorption apparatus. In addition, the method allows for the determination of sulfide in blood without interference from other sulfur compounds in blood. A detection limit of 4 g/dm3 and a percent recovery of 98-102% were achieved. Although the accuracy and precision of the catalytic method are comparable to those of the ion-selective electrode method, the catalytic method is simpler, faster, and would be advantageous in serial analysis. 

Where the target analyte contains heteroatoms such as nitrogen, phosphorus and sulfur, atom-selective detectors can provide an ideal detection method. A number of examples appear in the literature of the use of a detector called a thermal energy analyser (TEA) for the measurement of A-nitroso compounds [14-17] and aromatic nitro compounds [18]. This has also been used as an HPLC detector [19, 20], and a modified TEA has been reported to be useful for analysis of amines and other nitrogen-containing compounds [17]. Unfortunately, this technique appears not to have gained in popularity, since no reports have appeared in the literature for over two decades. 

The lifetime of the RSSR radical anions is usually very short on the microsecond timescale in water. However, they have been detected and characterized by time-resolved optical methods. In one early study, y irradiation of matrices containing alkyl and aryl disulfides provided spectroscopic evidence for the formation of the corresponding radical anions. Subsequently, the formation of RSSR radical anions has been well documented, particularly by EPR, flash photolysis, and pulse radiolysis. In fact, 2a/ a three-electron bonded radical anion species, particularly from sulfur compounds, constitute significant and interesting intermediates. The RSSR radical anions may be obtained from different approaches. One is by one-electron reduction of disulfides (equation 75), such as by pulse radiolysis. However, the most common approach is by association of RS and RS (equation 79). ... 

The OPA method is based on the formation of a highly fluorescent isoindole derivative by reaction with o-phthalaldehyde and 2-aminoethanol in mildly basic aqueous solution (331. The advantage of this technique is that a large variety of thiols and other reduced sulfur compounds can be detected at subnanomolar to nanomolar concentrations. Its disadvantage is that the fluorescent derivative, which preserves the thiol in its reduced stage, is unstable and must be formed just prior to injection. These characteristics preclude the delayed analysis (e.g., in the laboratoiy) of large numbers of samples collected in the field. 

A DTNP method for HPLC has recently been reported (34). The sulfur compounds are stable after derivatization and the detection limits are quite low. The major disadvantages are that the derivatized thiols are detected by absorbance, and sediment porewaters and biological samples often contain large numbers of absorbing compounds which interfere with authentic thiols. In addition, sulfide is not detected. 

Making some assumptions on the chemical filiation between some organo-sulfur compounds, it was possible to establish the mathematical variation law for the concentration ratio of the various detected species and consequently to deduce the depletion rate constant of these compounds. From the measurements at the "Pointe de Penmarc h" in September 1983, the DMS lifetime estimations obtained are reported in Table I. This method for determining chemical lifetimes can only be applied for local and intensive sources. The most critical point concerns the chemical relation between the various sulfur compounds which should be verified in order to validate these estimations. However, the other assumptions do not seem to have a significant influence on the lifetime estimation within an order of magnitude. 

Chemiluminescence methods are known for their high sensitivities. Typical detection limits range from parts per million to parts per billion or lower. Applications include the determination of gases, such as oxides of nitrogen, ozone, and sulfur compounds, determination of inorganic species such as hydrogen peroxide and some metal ions, immunoassay techniques, DNA probe assays, and polymerase chain reacrion methods.- ... 

Neither pure methane nor hydrogen has an odor. To increase safety, a trace of a substance with a powerful distinctive odor is added to natural gas. This provides a characteristic odor, allowing people to detect leakage by smell. This same precaution can be applied with hydrogen. The shortcoming of the current method is the odorous substance most used contains sulfur compounds. These bum to sulfur dioxide and contribute to air pollution. 

In addition to this comprehensive scheme, other determinations may be carried out by utilizing specific properties of the sulfur compound types (54, 72). Sulfur may be determined by removal with elemental mercury 51, 70), or by reaction with a mercaptan. In the latter case the sulfur determination is made by measurement of the excess mercaptan after the sample has been treated with litharge, sodium hydroxide, and a known excess of butyl mercaptan 78,81). A qualitative method of detecting elemental sulfur in gasoline is by the addition of sodium hydroxide to a pyridine solution of the gasoline which turns blue if sulfur is present 67). Free sulfur can also be determined polarographically 60). 

Identified in roasted coffee by Sullivan et al. (1959), Heins et al. (1966), and Stoffelsma et al. (1968). Merritt et al. (1970) characterized it in roasted but not in green coffee. It is present in the headspace of roasted coffee (Cros et al., 1980 Wang et al., 1983 ), in the headspace of a brew (Shimoda and Shibamoto, 1990a) where it represents 0.67% (GC). Silwar et al. (1986) found concentrations of 0.01 ppm in arabicas and 0.10-0.12 in robustas after simultaneous distillation/extraction, capillary GC using simultaneously flame ionization or flame photometric (for sulfur-selective analysis) detectors (FID/ FPD). With a similar detection method in the GC analysis of the headspace compounds, Guyot and Vincent (1990) found 0.04-0.05 ppm in a roasted healthy arabica and 0.3-0.4 in the stinking quality (see Q.4). Procida et al. (1997) identified dimethyl disulfide in a roasted arabica but in none of the green coffees examined, contrary to their result for dimethyl sulfide (Q.ll). 

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